Symposium Organizers
Kornelius Nielsch Max-Planck-Institute of Microstructure Physics
Oliver Hayden IBM Research GmbH
Hirotaka Ihara Kumamoto University
Deli Wang University of California-San Diego
U1: Inorganic Nanotubes I
Session Chairs
Joerg Appenzeller
Kornelius Nielsch
Tuesday PM, April 18, 2006
Room 2002 (Moscone West)
9:30 AM - U1.1
Fabrication of Inorganic Tubular Structures Using Lipid Nanotube as a Template in Aqueous Solution.
Ji Qingmin 1 , Iwaura Rika 1 , Kogiso Masaki 1 , Jung Jong Hwa 2 , Shimizu Toshimi 1 2
1 Nanoarchitectonics Research Center (NARC), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan, 2 CREST, Japan Science and Technology Agency (JST), Tsukuba, Ibaraki, Japan
Show AbstractThe use of organic materials for the generation of inorganic materials with well-defined structures has received increasing attention over the last decade. Especially, the fabrication of tubular architectures with a nanometer-sized hollow cylinder is challenging from the viewpoint of their potential applications in natural science and materials science fields. Surfactant-mediated or organogel-templated fabrication provides a typical method as a wet process to form isolated tubular structures. However, surfactant-mediated fabrication always produces silica structures. Organogel-templated fabrication always occurs in organic solvents in the presence of only a small amount of water. Here we describe the aqueous sol-gel transcription from a lipid nanotube template into different inorganic nanotubes of silica, titania, tantalum oxide and vanadium oxide, which proceeds in water containing no solution catalysts. A secondary ammonium hydrochloride of a peptidic lipid proved to form nanotube structures by self-assembly in water. Using the self-assembled nanotube as a template, we carried out the sol-gel transcription to silica in the aqueous dispersion in the absence of solution catalysts. The gradual solidification to a gel phase, after adding TEOS, evidenced the occurrence of the sol-gel transcription. Transmission electron microscopy (TEM) image clearly indicated that the gel is composed of abundant nanotube assemblies with uniform size, i.e., 20-nm wall thickness, 200-nm inner diameters, and 10-30-μm tube lengths. After removal of the organic template by calcination, we obtained a replicated silica tube with a uniform shape and dimensions of 200-nm diameters and 8-nm wall thickness. Compared with silica precursors, titania, tantalum and vanadium precursors have higher reactivity to water or moisture. Therefore, the fabrication of well-defined transition metal oxide structures is generally carried out in organic solvents. However, by freezing the aqueous dispersion to form an iced lipid nanotube template, we succeeded in the sol-gel transcription to transition metal oxide nanotubes from the aqueous dispersion. We found that in this frozen state, the sol-gel reaction of the inorganic precursors has proceeded gradually. Scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray (EDX) analysis proved that the obtained nanotubes are composed of titania, tantalum oxide, or vanadium oxide respectively. Reference1.Q. Ji, R. Iwaura, M. Kogiso, J. H. Jung, K. Yoshida and T. Shimizu, Chem. Mater., 2004, 16, 250.2.Q. Ji and T. Shimizu, Chem. Commun., 2005, 4411.
9:45 AM - U1.2
Layer-by-layer Assembled Magnetic Polyelectrolyte Hollow Tubes.
Daeyeon Lee 1 , Robert Cohen 1 , Michael Rubner 2
1 Chemical Engineering Department, MIT, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractMagnetic polyelectrolyte hollow tubes are prepared based on layer-by-layer (LbL) assembly of polyelectrolytes and iron oxide (Fe3O4) nanoparticles. Track-etched polycarbonate membranes were used as templates to assemble hollow tubes with poly(allylamine hydrochloride) (PAH) and sodium (polystyrene sulfonate) (PSS). Additional layers of PAH and 8 nm citrate-coated Fe3O4 nanoparticles were assembled in the interior of these tubes and then the membrane templates were dissolve to produce nanocomposite hollow tubes. The polyelectrolyte multilayers comprised of PAH and SPS were assembled at a high pH condition which allows a high concentration of free amine groups to be available after the assembly. This approach overcomes the problem of irreversible aggregation in creating colloidal hollow structures via LbL assembly which is often observed during LbL deposition of partially charged weak polyelectrolytes onto spherical particles. Scanning electron microscopy and transmission electron microscopy confirmed that nanocomposite hollow tubes were created successfully. Magnetic properties of the magnetic polyelectrolyte tubes were characterized by SQUID magnetometer, and the tubes retained the superparamagnetic properties of Fe3O4 nanoparticles. It is demonstrated that these nanocomposite hollow tubes can be utilized to separate and release anionic dye molecules triggered by changes in the pH condition of solutions. Also the availability of free amine groups within the tube walls allows for further chemistry such as metallization of hollow tubes via electroless plating.
10:00 AM - **U1.3
Metallic Nanorods and Their Use as Templates for Hollow Nanotubes.
Catherine Murphy 1
1 Dept. of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina, United States
Show AbstractGold and silver nanorods can be made with controllable aspect ratios, by a seed-mediated growth procedure in water, at room temperature. The presence of a directing surfactant is critical for the production of anisotropic nanoparticles. The directing surfactant exists as a bilayer on the metal nanorod long faces. This can be displaced by polymerization reactions that yield soft shells, or hard shells (silica) around the nanorods. Subsequent dissolution of the inner metal core yields hollow nanotubes. Partial dissolution of the inner metal core yields "peas in a pod" structures which have potentially interesting optical properties.
10:30 AM - **U1.4
Molecular Design and Assembly of Mono- and Multicomponent Nanotubes and Tube-Encapsulated Nanowire Devices
Nina Kovtyukhova 1 , Tom Mallouk 1
1 Chemistry, Penn State University, University Park, Pennsylvania, United States
Show AbstractThis presentation summarizes our progress in the synthesis and characterization of inorganic and composite inorganic/organic nanotubes and wire-in-tube nanostructures, and considers perspectives of their application as building blocks for self-assembling logic and memory circuits. Our strategy is based on shaping established thin-film devices, such as p-n heterojunction and Schottky diodes, insulating layers, and thin film transistors, into tube-encapsulated nanowire structures. This has been achieved by combining template electrochemical synthesis with wet adsorption methods for making thin-film devices. We have recently demonstrated the applicability of two layer-by-layer assembly techniques to template membranes with cylindrical pores and to metal nanowire substrates [1-4]. A variety of building blocks, such as semiconductor particles, short individual single-walled carbon nanotubes, polymers, and molecular precursors, can be alternately adsorbed one-layer-at-a-time inside the membrane pores and/or around metal wires. Important advantages of this strategy are (i) the possibility of organizing chemically and geometrically different blocks within a single nanostructure, (ii) technologically simple, inexpensive and scaleable synthesis of relatively uniform nanowire devices with excellent control over their length and diameter, (iii) precise control over thickness of the electroactive tube-shell, which is easy achievable by varying the number of adsorption cycles and by washing between adsorption steps in order to remove weakly bound particles or molecules. Importantly, the electrical characteristics of the tube-encapsulated nanowire devices are similar to those of large area planar thin film devices. This means that molecular organic and nanoparticle components can be introduced into the wire-in-tube structures without qualitative changes in their electrical, and most probably, chemical properties. References1. N. I. Kovtyukhova et al. J. Phys. Chem. B, 2001, 105, 8762-8769.2. N. I. Kovtyukhova, T. E. Mallouk, T. S. Mayer, Adv.Mater. 2003, 15, No 10, 780-785.3. N.I. Kovtyukhova, B.K. Kelley, T.E. Mallouk, J. Am. Chem. Soc., 2004, 126, 12738-12739.4. N.I. Kovtyukhova, T.E. Mallouk, Adv. Mater. 2005, 17, 187-192.
11:30 AM - U1.5
Electrical Conductance of Stand-Alone Metal Oxide Nanotubes
Jiyoung Kim 1 , Bongki Lee 1 , Dongkyu Cha 1 , Moon Kim 1 , Sanghee Won 2 , HyunJung Shin 2 , Jaegab Lee 2 , MyungMo Sung 3
1 Electrical Engineering, The Univ. of Texas at Dallas, Richardson, Texas, United States, 2 Advanced Materials Engineeering, Kookmin University, Seoul Korea (the Republic of), 3 Dept. of Chemistry, Kookmin University, Seoul Korea (the Republic of)
Show AbstractLow dimensional inorganic nanostructure materials, such as TiO2 tubes, have been attracted lots of attentions for a wide range of potential applications including nano-sensors and integrated systems. Unfortunately, there are only a few papers regarding the electrical conduction mechanism of the metal oxide nanotubes. In particular, it is expected to be observed unique quantum size effects in the oxide nanotubes because electrons should be confined in ultra-thin tube-wall. Localized electron status in the oxide tubes, which is an important factor to decide electronic conduction of the oxide, would be significantly different due to severe deformation of the lattice resulting from extremely large curvature of the tube. We, therefore, need to precisely control the geometrics of the nanotubes, such as wall-thickness, diameter and stacking layers. It has been successfully demonstrated that with atomic level accuracy metal oxide nanotubes have been made by a use of atomic layer deposition (ALD) on nano-templates with self-assembled monolayer (SAM) treatments. In addition, this vapor phase approach enhances uniformity, repeatability and variety of stacking materials and sequences of the tube-walls. Various metal oxide (TiO2, ZrO2 etc) nanotubes will be prepared with 20 – 200 nm of diameter and 5 – 20nm of wall-thickness. In this study, we fabricate devices of stand-alone nanotubes by direct patterning the probing pads inside of vacuum chamber of focused ion beam (FIB) system. We observe that TiO2 nanotubes with diameter of 200nm show Ohmic contacts with the Pt pads. I-V measurement shows that the current linearly increases as the voltage increases from 0 to 3.2 V. However, the TiO2 nanotubes show failure at 5.2 V and then completely break down at 6.2 V. It is confirmed by SEM that hard-breakdown occurs. The resistivity of TiO2 tube is roughly 1 ohm/cm which is much higher than that of stoichiometric TiO2 bulk. It is possibly due to reduction of oxide tube surface by electron and ion beams. Pt interconnections as well as pads are formed between the tube and e-beam patterned probing pad. The reduced oxide surface is expected to be activated to adsorb detecting chemical and biological species and to enhance modulating the conductance. The relation between tube materials and sensing species will be also evaluated in this project. In addition, metal-insulator transition (MIT) phenomena of TiOx nanotubes will be investigated related with their geometric factors (diameter and wall-thickness) which may affect significantly on interaction of electron and phonon due to non-uniform stress distribution in the tubes. We will comparatively study characteristics of the nano-devices fabricated by conventional E-beam lithography method. This research was supported by a grant (code #: M105KO010026-05K1501-02611) from 'Center for Nanostructured Materials Technology' under '21st Century Frontier R&D Programs' of the Ministry of Science and Technology, Korea
11:45 AM - U1.6
Synthesis and Electrochemical Properties of InVO4 Nanotube Arrays
Ying Wang 1 , Guozhong Cao 1
1 Materials Science and Engineering, University of Washington, Seattle, Washington, United States
Show AbstractInVO4 belongs to the family of orthovanadates with attractive properties as Li intercalation electrodes, and thus has potential applications in lithium secondary batteries and electrochromic windows. A capillary-enforced template-based method is described for the preparation of InVO4 nanotube arrays. InVO4 sol was synthesized using the sol-gel route from vanadium oxoisopropoxide and indium nitrate with ethanol as the solvent. Nanotube arrays of InVO4 were prepared by filling the sol into pores of polycarbonate membranes and sintering at high temperatures. Nanotube arrays annealed at 500°C consist of mixed monoclinic (InVO4-I) and orthorhombic (InVO4-III) phases, while InVO4 nanotube arrays of pure orthorhombic phase are obtained by annealing at 600°C. The third type of InVO4 nanotube arrays (InVO4/acac) are obtained from the sol with the addition of acetylene acetone (acac) followed by sintering at 500°C. Scanning electron microscopy (SEM) characterizations indicate that the nanotubes are well-aligned, perpendicular to substrate surface, of 10 micron long and 200 nm in diameter. For comparison purposes, InVO4 films were prepared by drop casting from the same sol. Electrochemical measurements were carried out in a standard three-electrode cell with 1M-LiClO4/propylene carbonate as electrolyte and the samples were cycled between 0.4 and -2.8 V versus Ag/Ag+. Chronopotentiometry results reveal that InVO4 film electrode delivers a capacity around 560 mAh/g at the specific current of 100 mA/g, while all three types of nanotube arrays demonstrate higher capacity than the film does. Specifically, at the specific current of 100 mA/g, InVO4 nanotube arrays of pure orthorhombic phase and nanotube arrays of mixed monoclinic and orthorhombic phases have similar capacities around 610 mAh/g, and InVO4/acac nanotube arrays deliver the capacity of 725 mAh/g, the highest among the three, due to the amorphization in the crystalline structure. This difference of capacities between nanotube arrays and films is more pronounced at higher discharge rate, e.g. nanotube arrays can achieve five times higher capacity than films do at a specific current of 500 mA/g. Such enhanced lithium-ion intercalation properties are ascribed to the large surface area and short diffusion distance offered by nanostructures. In addition, nanotubes can operate as electrolyte-filled channels for faster transport of the ions to the intercalation sites. Therefore, InVO4 nanotube arrays are the promising candidates for the electrode materials in lithium batteries with high power density and charge/discharge rates, and in electrochromic window with fast switching rate.
12:00 PM - U1.7
Synthesis and Characterization of Ceria Oxide Nanotubes.
Wei-Qiang Han 1 , Lijun Wu 1 , Xianqin Wang 2 , Yimei Zhu 1 , Jose Rodriguez 2
1 Center for Functional Nanomaterials, Brookhaven National Lab, Upton, New York, United States, 2 Department of Chemistry, Brookhaven National Laboratory, Upton, New York, United States
Show Abstract12:15 PM - U1.8
Metal Dichalcogenide Nanotubes from Single Source Precursors.
Bruce Parkinson 1 , Manashi Nath 1 , Anna Chick 1 , Shannon Riha 1 , David Seley 1
1 Department of Chemistry, Colorado State University, Fort Collins, Colorado, United States
Show AbstractThe formation of nanotubules and other nano-structures from layered metal dichalcogenides has been beautifully demonstrated by Tenne and other researchers [1]. Most of the synthesis methods produce nanotubules in conjunction with other nano-structures such as fullerenes, nanoparticles, nanowires etc. Since one-dimensional nanostructures of these materials have a wide range of possible applications, it would be interesting to design synthesis methods that produce nanotubules or nanowires as the sole or major product. The use of a template-assisted synthesis along with a single source precursor seems to be a suitable choice for achieving this goal. We have successfully synthesized a variety of dichalcogenide nanotubules (MS2, M=Mo, W and Re) from single source precursors, such as the ammonium thiometallate, or molybdenum diethyldithiocarbamate complexes, decomposed inside the pores of an anodic aluminium oxide membrane. Since many diethyldithiocarbamate complexes vaporize or sublime at fairly low temperatures, this opens up a wide range of possible reaction schemes which can be designed to grow nanotubes by chemical vapor deposition (CVD) on substrates prepatterned with gold or other meal nanoparticles. The attachment of the metal tip to the semiconductor nano-stucture also provides new functionalities such as the formation of natural anchor points for forming designed architectures by self-assembly on suitable substrates or for wiring them into functional circuitry. Hence, we decomposed a molybdenum diethyldithiocarbamate complex inside the pores of an alumina membrane with or without previously coating with gold. The precursor was deposited inside the pores of the membrane by sublimation. High yield of nanotubes and nanowires were obtained by this method. The nanotubes obtained from bare alumina membranes were mostly open at one end, thin-walled and grew out in oriented clusters. The nanotubes and nanowires obtained from the Au-coated alumina membrane were uniformly tipped with the Au cluster at one end. The Au clusters were mostly spherical with diameters in the range of 70-100 nm while that of the MoS2 nanostructures were in the range of 40-80nm with lengths of few micrometers. Decomposition of the ammonium thiometallates inside the pores of bare alumina membrane yielded nanotubules with diameters in the range of 50-200nm. In some cases holey tubes were obtained where the nanotube walls contained several regularly spaced holes along the length of the tube. We are presently directing our efforts towards carrying out measurement of the electrical properties of individual nanotubes. References:1. R. Tenne, L. Margulis, M. Genut, G. Hodes,. Nature, 360, 1992, 444; R. Tenne, Angewandte Chem. Intl. Ed., 42, 2003, 5124.
12:30 PM - U1.9
Growth of Vertically Aligned Boron Nitride Nanotubes on Substrates.
Jiesheng Wang 1 , Ming Xie 1 , Vijaya Kayastha 1 , Yoke Khin Yap 1 , Zhiyong Fan 2 , Jia Lu 2 , Zhengwei Pan 3 , David Geohegan 3
1 , Michigan Technological University, Houghton, Michigan, United States, 2 , University of California-Irvine, Irvine, California, United States, 3 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractHigh growth temperatures (>1100 °C), low production yield, and impurities have prevented research progress and applications of boron nitride nanotubes (BNNTs) in the past ten years. Here, we show that BNNTs can be grown on substrates at 600 °C [1]. These BNNTs are vertically aligned on the substrate surface, constructed of high-order tubular structures, and can be used without purification. BNNTs are structurally similar to carbon nanotubes (CNTs) and exhibit extraordinary mechanical properties. BNNTs possess uniform electronic properties that are insensitive to their diameters and chiralities. Theoretically, their band gaps (~5eV) are tuneable and can even be eliminated by transverse electric fields through the giant dc Stark effect. In addition, BNNTs demonstrate high oxidation resistance up to 800 °C, excellent piezoelectricity, and present potential material for room temperature hydrogen storage. However, growing BNNTs is challenging. In the last ten years, BNNTs were grown by arc discharge, laser ablation, substitution reactions from carbon nanotubes, ball-milling, and chemical vapor deposition (CVD), at temperatures from 1100 to 3000 °C. These BNNTs were dominated by impurities including amorphous boron nitride (a-BN) powders and other solid-state by-products. It is impossible to use these techniques to directly grow BNNTs on substrates for device fabrication. We grow BNNTs directly on substrates at 600 °C by a plasma-enhanced pulsed-laser deposition (PE-PLD) technique. Scanning electron microscopy (SEM) indicates that multiple BNNTs grown from adjacent Fe catalyst particles tend to form vertical bundles. Long and straight tubular structures were detected by transmission electron microscopy (TEM). These BNNTs are found to have square-like cross-section caps, which are typical for high-quality BNNTs. Tunneling spectroscopy indicates that their band gap ranges from 4.4 to 4.9 eV. Details of these results and a phase selective growth mechanism will be discussed in the meeting.Y.K.Y acknowledges supports from the Michigan Tech Research Excellence Fund, Army Research Office (W911NF-04-1-0029), CNMS at ORNL, and NSF CAREER Award (0447555).[1]. Yap et al., Bulletin of the American Physical Society Vol 50, No. 1, Part 2 (March 2005) page 1346-1347 paper W25 3.
U2: Inorganic Nanotubes II
Session Chairs
Ulrich Goesele
Nina Kovtyukhova
Tuesday PM, April 18, 2006
Room 2002 (Moscone West)
2:30 PM - **U2.1
Synthesis and Transport Studies of Transition Metal Oxide Core-Shell Nanowires and Nanotubes.
Chongwu Zhou 1
1 , University of Southern California, Los Angeles, California, United States
Show AbstractWe will present a generic nonequilibrium synthesis technique to produce novel transition metal oxide (TMO) core-shell nanowires and nanotubes, including YBa2Cu3O6.66, La0.67Ca0.33MnO3, PbZr0.58Ti0.42O3 and Fe3O4. Key to our success is the growth of vertically aligned single-crystalline MgO nanowires, which worked as excellent templates for epitaxial deposition of the desired transition metal oxides and led to high-quality core-shell nanowires. Transport studies on ultrafine La0.67Ca0.33MnO3 nanowires have revealed the remarkable persistence of metal-insulator transition and magnetoresistance down to nanometer scale. In addition, we have also demonstrated a wet etching technique to selectively remove the inner cores of the core-shell nanowires and leave behind clean single crystalline Fe3O4 nanotubes. Intriguing magnetoresistance has been observed with these nanotubes at low and elevated temperatures. Our technique will enable various in-depth studies such as phase transition in nanoscale oxides and may pave the way for novel applications of these fascinating materials.
3:00 PM - **U2.2
Iridium Oxide Nanotubes as High Sensitivity Chemo/Biosensors ,
Fengyan Zhang 1 , Shaidi Dayeh 2 , Robert Barrowcliff 1 , Sheng-Teng Hsu 1 , Deli Wang 2
1 PTL, sharp labs of america, Camas, Washington, United States, 2 Department of electrical and computer engineering, university of california at san diego, San Diego, California, United States
Show Abstract1D semiconductor nanowires and nanotubes have been extensively studied as very attractive and versatile building blocks for the ‘bottom-up’ assembly of electronic and photonic systems, a wide range of nanostructures, including group IV, III-V, and II-VI materials have been demonstrated reproducible fabrication of a number of nanodevices including field effect transistors, photodetectors, light-emitting-diodes, and sensors. Metallic nanowires could play a very important role as nanoscale interconnects but have been less studied. Herein we report the synthesis of Iridium oxide (IrO2) nanotubes MOCVD with (methycycpentadienyl-1,5-cyclooctadiene) iridium as the precursor. It was found that the IrO2 nanowires growth is self-mediated that have diameters of 150-180 nm and length of 2 microns. The diameter of nanotube and wall thickness are very uniform along the axial growth direction from SEM and LRTEM studies. HRTEM image and electron diffraction pattern reveal single crystal IrO2 nanotubes have rutile structure with the growth direction along <001>. The IrO2 nanotubes are metallic conductive with measured resistivity around 300 - 400 microohm-cm. The IrO2 nanotubes are biocompatible and the usage as pH sensor and biosensor will be discussed.
3:30 PM - **U2.3
VLS Nanowire Growth Dynamics and Vertical Nanowire Devices.
Erik Bakkers 1 , M. Borgstrom 1 , O. Wunnicke 1 , A. Helman 1 , W. van den Einden 1 , M. A. Verheijen 1
1 Electronic Materials and Devices, Philips Research Laboratories, Eindhoven Netherlands
Show AbstractSemiconducting nanowires are one of the most promising materials for the monolithic integration of high-performance semiconductors with silicon technology. For the fabrication of optical or electrical devices, local variations in the electronic structure of the wire, such as hetero junctions, are required. Ultimate control over the growth rates of segmented nanowires is desired since the opto-electronic properties of the sections critically depend on their dimensions in the nanometer regime. We have studied the Vapor-Liquid-Solid (VLS) growth dynamics of GaP and GaAs in heterostructured GaP-GaAs nanowires. The wires containing multiple GaP-GaAs junctions were grown by the use of metal-organic vapor-phase-epitaxy (MOVPE) and the lengths of the individual sections were obtained from transmission electron microscopy (TEM). The wires have been grown on ‘inert’ SiO2 surfaces, such that material deposition at the substrate surface is suppressed. This enables to study the catalytic action of the metal particle. The growth kinetics have been studied as a function of temperature and the partial pressures of the precursors. We have also studied the competitive reaction, i.e. growth of a thin film on the sidewalls of the nanowires, which occurs at elevated temperatures and results in tapered nanowires. We were able to study this reaction in detail since the hetero structures offer a precise internal ‘time reference’, such that exposure times at specific positions on the wires could be accurately determined afterwards with TEM. In addition, we have grown III-V nanowires epitaxially on silicon substrates and fabricated basic vertical nanowire devices. Some first preliminary electrical characteristics of vertical gate-around field-effect transistors will be shown.
4:15 PM - U2.4
Coaxial ALD of High-κ Dielectrics and Metals on Functionalized SWNTs.
Damon Farmer 1 , Roy Gordon 2
1 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Dept. of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States
Show AbstractInherent deposition properties such as low temperature processing and sub-nanometer thickness precision makes atomic layer deposition (ALD) an ideal method for nondestructively covering single-walled carbon nanotubes (SWNTs) with very thin, uniform high-κ dielectrics and/or metals. The problem in using ALD for this purpose is that the SWNT surface is chemically inert to ALD precursor molecules, which eliminates the possibility of radially isotropic, coaxial deposition. Here, a gas-phase, physical functionalization technique has been used to make the SWNT surface chemically susceptible to ALD precursors. SWNTs are exposed to 50 alternating pulses of nitrogen dioxide (NO2) gas and trimethylaluminum (TMA) vapor. Electrically probing SWNTs during the functionalization procedure reveals that the desorption of NO2 from the SWNT surface is hindered by the presence of TMA. The result is that the nanotube surface is covered with a uniform monolayer that is stable at room temperature. The thickness of this coating appears to be self-limiting at a monolayer for up to 200 cycles. The stability of this monolayer is then reinforced by 0.5 nm of ALD Al2O3 deposited at 25°C, resulting in a uniform coating of aluminum oxide less than 1 nm thick. The resulting coated tube remains intact after heating to higher temperatures (200–300°C), at which temperatures it can be further coated with a variety of materials, including high-κ dielectrics (such as Al2O3, HfO2, or LaAlO3), and/or metals (such as WN, Ru, or Cu). The diameters of the resulting nanowires are highly uniform, and can be controlled to any predetermined thickness.
4:30 PM - U2.5
Atomic Layer Deposition of Ruthenium in Nanoporous Templates.
Mihaela Daub 1 , Mato Knez 1 , Kornelius Nielsch 1 , Ulrich Goesele 1
1 , Max-Planck-Institute for Microstructure Physics, Halle Germany
Show AbstractNoble metals are often desirable in integrated circuits or in various microelectronic applications, like capacitor electrodes in random access memories or gate metal in future MOSFETs. In this context, atomic layer deposition is offering perfect control of the growth using self-limiting surface reactions, with precise film thickness and excellent conformability on high aspect ratio structures. Thin films of noble metals (e.g. Ru, Pd, Pt) deposited by atomic layer deposition (ALD) have already been produced in the past. However, in these cases, oxygen was used as the second precursor in the deposition process. We present highly conformal and uniform Ru nanotubes obtained from RuCp2 (Ruthenocene) and hydrogen as ALD precursors. The Ru deposition was performed onto the pore walls of self ordered or perfectly ordered porous alumina membranes with pore diameters ranging from 40 to 180 nm. The aspect ratio (pore length/diameter: 10-1000) and the physical properties of the tubes as a function of the deposition temperature and other parameters were investigated by means of SEM and TEM. Ru nanotubes were also obtained with ruthenocene and air as ALD precursors and their properties compared with the properties of Ru nanotubes using the metal precursor with hydrogen.Acknowledgement: This work was supported by the German Federal Ministry for Education and Research (BMBF), project number 03N8701.
4:45 PM - U2.6
Enhanced Field Emission and Morphology of Atomic Layer Deposition ZnO Coated Carbon Nanotubes.
Joshua Green 1 , Lifeng Dong 1 , Timothy Gutu 1 , John Conley 2 , Jun Jiao 1 , Yoshi Ono 2
1 Department of Physics, Portland State University, Portland, Oregon, United States, 2 IC Process Technology Group, Sharp Labs of America, Camas, Washington, United States
Show AbstractDue to purge separation of precursor pulses and self limiting surface reactions, atomic layer deposition (ALD) offers highly conformal deposition, creating the potential for many interesting nanostructure coating applications. In this work, ALD was used to coat multiwall carbon nanotubes (CNTs) with a thin conformal layer of ZnO. Although scanning and transmission electron microscopy revealed no significant changes in the internal structure of the CNTs, annealing of the ZnO coated CNTs resulted in the agglomeration of ZnO into ball-shaped single crystalline nanoparticles attached to the sidewalls of the CNTs. CNTs are well known to be excellent field emitters. It was found that the electron field emission properties of these ZnO coated nanotubes are much improved over uncoated CNTs and over ZnO nanowires. The diameter of the ZnO nanoparticles is approximately equal to the diameter of the multiwall CNTs. It is proposed that the ZnO nanoparticles serve as additional emission sites, resulting in an effective geometric enhancement of the field emission properties and demonstrating how ALD can be used to engineer the surface properties of nanostructures.
5:00 PM - U2.7
Synthesis, Characterization and Physical Properties of Transition Metal Silicide Nanowires.
Song Jin 1 , Andrew Schmitt 1 , Lei Zhu 1 , Yipu Song 1 , Jeannine Szczech 1
1 , University of Wisconsin-Madison, Madison, Wisconsin, United States
Show Abstract5:15 PM - U2.8
Molybdenum Sulfide as Electrochemical Ultracapacitors
Jia Mei Soon 1 , Kian Ping Loh 1
1 Department of Chemistry, National University of Singapore, Singapore Singapore
Show AbstractConcerns over global warming issues and natural resources depletion have fueled current research in the direction of renewable energy sources over the last decade. Electrochemical ultracapacitors [1],[2] ,[3] are ideal candidates for energy storage devices in high-power applications for storing electricity when it is available and retrieving when it is needed. Using the single source precursor Mo(IV)-tetrakis(diethylaminodithiocarbomate)[4] we deposited nanoporous thin films and nanotubules of MoS2 via chemical vapor deposition. Portions of each specimen were fluorinated at room temperature using XeF2 to form a MoFx-MoS2 composite. The four samples, MoFx-MoS2 and MoS2 thin film; as well as MoFx-MoS2 and MoS2 nanotubules, were tested for their electrochemical ultracapacitance properties. The as-deposited MoS2 thin film exhibited good ultracapacitance properties of 8.0F/g. In spite of the larger surface area of the MoS2 nanotubules compared to the thin films, it is interesting to note that the ultracapacitance of the thin film is twice that of the nanotubules due to the large number of reactive basal edges on the nanoporous thin films. Fluorination significantly reduces the ultracapacitance of both nanoporous thin film and nanotubular MoS2 by two orders of magnitudes due to enhanced hydrophobicity of the surface after fluorination, as analyzed by rheology study. Deposition of RuO2 nanoparticles onto the non-fluorinated MoS2 thin film improves its ultracapacitance by more than two times while retaining the original morphology of the nanoporous MoS2 thin film.*author to whom correspondence should be addressed:
[email protected][1] M. Nakayama, A. Tanaka, Y. Sato et al.; Langmuir 21, 5907 (2005)[2] T-C Liu, W. G. Pell, B. E. Conway; J. Electrochem. Soc. 6, 1882 (1998)[3] S. L. Roberson, D. Finello, R. F. Davis; J. Appl. Electrochem. 29, 75 (1999)[4] H. Zhang, K. P. Loh, C. H. Sow et al.; Langmiur 20 (16), 6914 (2004)
5:30 PM - U2.9
Nanotubes in Low Temperature Spray Deposited Nanocrystalline HgSe: I thin films.
Ranga Rao Arnepalli 1 , Viresh Dutta 1
1 Centre for Energy Studies, Indian Institute of Technology, Delhi, New Delhi, New Delhi, India
Show Abstract5:45 PM - U2.10
Modifying Magnetic Properties of Nanotubes by Doping with Magnetic and Nonmagnetic Elements.
Yuan Ping Feng 1 , Rongqin Wu 1 , Hui Pan 1 , Guowen Peng 1 , Jianyi Lin 1 , Alfred Huan 2
1 Physics, National University of Singapore, Singapore Singapore, 2 , Nayang Technological University, Singapore Singapore
Show AbstractCarbon and other types of nanotubes have attracted much attention because of their potential applications. Physical properties of nanotubes, as well as other nanostructures, can be further modified by chemical binding of atoms, molecules or molecular groups. Our recent work on first principles studies of magnetic properties of functionalized carbon and other types of nanotubes will be presented. Effects of carbon doping of BN nanotubes, OH functionalization of carbon nanotube, and Mn-doping of B2O nanotubes on the magnetic properties of the nanotubes will be discussed. Carbon substitution for either boron or nitrogen in BN nanotubes was found to induce magnetization. Band structure calculation revealed a spin polarized, dispersionless band near the Fermi energy. The magnetization can be attributed to the carbon 2p electron. Magnetism was also found in OH-functionalized single-wall carbon nanotube, when two functional OH groups are close to each other. The magnetic moment increases with decreasing tube-tube distance. A possible mechanism for the magnetism of OH-functionalized SWCNT is the electron-electron interaction induced by the flat bands near the Fermi level. Manganese doping of single-wall B2O nanotube was also investigated. It was found that the bridge site above the axial B-B bond is the most energetically favorable site when the Mn atom is adsorbed outside the (3,0) B2O nanotube. The magnetic moment of the Mn-doped nanotube is similar to that of the free Mn atom. The atop oxygen site, however, is the most stable site if the Mn atom is inside the tube. In this case, the Mn atom is seven-coordinated and the nanotube is significantly distorted, leading to the largest binding energy among all adsorption sites and a smaller magnetic moment.
Symposium Organizers
Kornelius Nielsch Max-Planck-Institute of Microstructure Physics
Oliver Hayden IBM Research GmbH
Hirotaka Ihara Kumamoto University
Deli Wang University of California-San Diego
U3: Fluidic Transport Through Tubes
Session Chairs
Wednesday AM, April 19, 2006
Room 2002 (Moscone West)
9:00 AM - U3.1
Gated Chemical Transport and Enhance Flow through Carbon Nanotube Membranes
Bruce Hinds 1 , Mainnak Majumder 1 , Nitin Chopra 1
1 Chemical and Materials Engineering, Univ. of Kentucky, Lexington, Kentucky, United States
Show AbstractA promising architecture for ion-channel mimetics is a composite membrane structure containing vertically aligned carbon nanotubes, with inner core diameters of 7 nm, passing across a polystyrene matrix film. Plasma oxidation during the fabrication process introduces carboxylic acid groups on the CNT tips that are modified using carbodiimide mediated coupling between carboxylic acid on the CNTs and accessible amine groups of the functional molecule. The entrances to CNT’s cores were thus functionalized with aliphatic amines of different lengths, charged dye molecule and an aliphatic amine elongated by spacers containing poly-peptides. The transport through the membrane of two differently sized but equally charged molecules, ruthenium bi-pyridine [Ru-(bipy)3+2] and methyl viologen [MV+2], was studied in a U-tube permeation cell with flux quantified by UV-vis Spectroscopy. Relative selectivity of the permeates was seen to vary from 1.9 to 3.6 as a function of tip-functionalization chemistry. Anionic charged functional groups are seen to sharply increase flux of cationic permeates. This effect is reduced at higher solution ionic strength consistent with shorter Debye screening length. Using a hindered diffusion to model observed selectivities was consistent only with a geometry of only CNT tip functionalization, not along the length of CNT core. Biologically active desthiobiotin was also shown to be reversibly coordinated to stretavidin, showing a reduction in ionic flux through CNT. Pressure driven flux of a variety of solvents (H2O, hexane, decane ethanol, methanol) are 4-5 ORDERS OF MAGNITUDE FASTER than conventional Newtonian flow. There are also experimental indications of the ordering of polar solvents inside CNT pores. Dual functional CNTs (that is different functionality at each end of a CNT) have also been produced by reacting each side of the membrane with different functional solution, then subsequent removal of polymer matrix.
9:15 AM - U3.2
Fast Mass Transport Through Sub-2nm Carbon Nanotubes
Jason Holt 1 , Hyung Gyu Park 1 , Aleksandr Noy 1 , Olgica Bakajin 1
1 Biosecurity and Nanosciences Laboratory, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractWe report gas and water flow measurements through microfabricated membranes with sub-2 nm aligned carbon nanotubes as pores. The measured gas flow exceeds predictions of the Knudsen diffusion model by at least an order of magnitude. The measured water flow rate exceeds values calculated from continuum hydrodynamics models by two to three orders of magnitude and agrees with flow rates extrapolated from molecular dynamics simulations. The gas and water permeabilities of these nanotube-based membranes are orders of magnitude higher than those of commercial polycarbonate membranes, despite having an order of magnitude smaller pore size. These properties should enable more energy-efficient nanoscale filtration, as well as fundamental studies of mass transport in confined environments.
9:30 AM - U3.3
Atomistic Simulations on Transport of Water inside Nanotubes of Varying Hydrophobicity and Size.
Daejoong Kim 1 , Artit Wangperawong 1 , Eric Darve 1
1 Mechanical Engineering, Stanford University, Stanford, California, United States
Show Abstract9:45 AM - U3.4
Inorganic Nanotube Nanofluidics for Single Molecule Detection and Manipulation
Rong Fan 1 , Rohit Karnik 2 , Arun Majumdar 2 3 , Peidong Yang 2 3
1 Department of Chemistry, University of California at Berkeley, Berkeley, California, United States, 2 Department of Mechanical Engineering, University of California, Berkeley, California, United States, 3 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractInorganic nanotubes represent a new class of one-dimensional nanostructures towards multi-functionalities and complexities. A nanowire-template approach has been developed to synthesize high quality inorganic nanotubes that are mechanically robust and free of pinholes. Vertically aligned silica nanotube arrays were synthesized through a controlled oxidation-etching approach using silicon nanowires as templates. These nanotubes were integrated with microfluidic channels to create nanofluidic systems for single DNA molecule sensing. These nanofluidic devices are unique in their high aspect ratio and exhibit different DNA translocation mechanisms from biological nanochannels, e.g. ion channel proteins. Transient changes of ionic current indicate single molecule translocation events. Ionic current crossover was observed with the change of the buffer solution ionic strength, which is indicative of the interplay of electrostatic effect and geometric effect. Furthermore, single molecule manipulation and controlled delivery can be realized in nanotube nanofluidic systems assisted with external electrostatic control. Moreover, complex nanofluidic circuits have been created in a custom-designed fashion through a self-assembled VLS growth process. These multiplexed nanofluidic circuits can be used to simultaneously perform genomic-sized polynucleotide sorting, and trapping, manipulating or delivering individual biomolecules. This work represents the first time that inorganic nanotubes were utilized as functional components in complex nanofluidic systems. These systems represent a novel platform for studying single molecule biology and biophysics, and presage their potential in the large-scale integration of nanofluidic systems.
10:00 AM - **U3.5
Gramicidin Channels.
Roger Koeppe 1
1 Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractGramicidin channels are mini-proteins which catalyze the passive transport of monovalent cations across lipid bilayer membranes at rates approaching 10 million ions per second. Two tryptophan-rich subunits associate by means of transbilayer dimerization to form the conducting channels. Respective subunits are tethered to the bilayer/solution interface through hydrogen bonds that involve the indole NH groups with water and the phospholipid backbone. The channel’s permeability characteristics are particularly well-defined: ions and water move through a pore whose wall is formed by the peptide backbone; gramicidin channels are selective for monovalent cations, with no measurable permeability to anions or polyvalent cations; the single-channel conductance and cation selectivity vary when the amino acid sequence is varied, even though the permeating ions make no contact with the amino acid side chains. The channel structure is known at atomic resolution. Given the plethora of available experimental information for both the wild-type and amino-acid-substituted channels, gramicidin channels provide important insights into the microphysics of ion permeation through bilayer-spanning channels.
10:30 AM - **U3.6
Synthetic Multifunctional Pores.
Stefan Matile 1
1 Department of Organic Chemistry, University of Geneva, Geneva Switzerland
Show AbstractThe general objective of the concept of synthetic multifunctional pores is to combine molecular translocation with molecular recognition and catalysis [1]. Todays synthetic multifunctional pores are rigid-rod beta-barrels, i.e., barrel-stave supramolecules composed of para-oligophenyls as “staves” and beta-sheets as “hoops.” Design strategies for the construction of pores that either close (blockage) or, more recently, open response to chemical stimulation are available (ligand-gating) [2], voltage-sensitive rigid-rod push-pull beta-barrels as well [1]. Recent highlights concerning the practical application of synthetic multifunctional pores concern catalysis as well as multicomponent sensing in complex matrixes. An illustrative and timely example for the latter topic is sugar sensing in soft drinks, with synthetic multifunctional pores serving as “universal” transducers of chemical reactions into color [3]. Beyond the classical rigid-rod beta-barrel [1-3], transmembrane rigid-rod π-stack architecture will be introduced for the creation of ligand-gated ion channels [4] as well as for ligand- and voltage-sensitive photoinduced electron transfer across bilayer membranes.1. Sakai N., Mareda J. and Matile S., Acc. Chem. Res., 38, 79-87 (2005).2. Gorteau V., Perret F., Bollot G., Mareda J., Lazar A.N., Coleman A.W., Tran D.H., Sakai N. and Matile S., J. Am. Chem. Soc., 126, 13592-13593 (2004).3. Litvinchuk S., Sordé N. and Matile S. J. Am. Chem. Soc., 127, 9316-9317 (2005).4. Talukdar P., Bollot G., Mareda J., Sakai N. and Matile S. J. Am. Chem. Soc., 127, 6528-6529 (2005).Acknowledgement: This research is supported by the Swiss NSF.
U4: Bioinspired and Organic Tubes I
Session Chairs
Wednesday PM, April 19, 2006
Room 2002 (Moscone West)
11:30 AM - **U4.1
Self-Assembly of Biomimetic and Bioactive Nanostructures
Samuel Stupp 1
1 Materials Science & Engineering, Department of Chemistry, and Feinberg School of Medicine, Northwestern University, Evanston, Illinois, United States
Show AbstractSelf-assembly directed by covalent structure and environment generates the functionally sophisticated supramolecular structures of biology. A contemporary challenge is to achieve this type of self-assembly with synthetic molecules to create organic objects that emulate proteins. This lecture describes the self- assembly of peptide-based molecules into high molar mass one-dimensional nanostructures that can serve as bioactive nanostructures to signal cells or to sense the presence of biological analytes. One form of these nanostructures involves the self-assembly of peptide amphiphiles on carbon nanotubes.
12:00 PM - **U4.2
Tubular Assemblies Prepared from Cyclic Peptides Composed of β-Amino Acids.
Shunsaku Kimura 1
1 Dept. of Material Chemistry, Kyoto University, Kyoto Japan
Show AbstractCyclic tri- and tetra-β-peptides (CTPs) having cyclohexane or pyranose rings were synthesized. Various spectroscopic measurements and computational geometry optimization revealed that these compounds take planer conformation with all amide groups vertically orientated to the ring plane in one direction. The CTP with cyclohexane rings forms a regular rod-like structure in solution as revealed by transmission electron microscopy, and the electron diffraction analysis showed that the rod is composed of tubular assemblies formed by intermolecular hydrogen bondings among the amide groups. The CTP with pyranose rings also forms a tubular assembly. Notably, the surface of the assembly provides binding sites for lectins.
12:30 PM - **U4.3
Conformation-Controlled Inversion, Propagation, and Memory of Supramolecular Chirality
Hicham Fenniri 1 2
1 National Institute for Nanotechnology, University of Alberta, Edmonton, Alberta, Canada, 2 Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
Show AbstractA remarkable level of control over supramolecular chirality (SC) has been achieved under the effect of an asymmetric molecular input using the sergeant and soldier effect, molecular recognition, chiral memory, circularly polarized light, chiral vortex forces, redox- and photo-switches, and photoinduced electron transfer. The ability to control SC allowed for the design of sensors, chiral cholesteric phases, catalysts, asymmetric synthesis of materials with electromagnetic and optoelectronic applications, information storage, display systems and photochromic materials, and for the design of materials with unique chiral light-emitting and non-linear optical properties. However, for SC inversion to occur in both natural and synthetic systems, the symmetry of the molecular input must also be inverted. Here we introduce supramolecular atropisomerism (chiromerism) as a novel property of supramolecular systems whose chiroptical properties can be reversibly and controllably driven in mirror-image directions upon self-assembly of conformers of a single, homochiral molecular module. Extensive physical and computational studies led us to the conclusion that the solvation free energy of the self-assembling module determines its conformational states, which in turn control the SC output. We have also shown that the resulting supramolecular atropisomers (chiromers) are not only thermodynamically stable, but they can also memorize and propagate their chirality in an achiral environment. These results underscore the fundamental role of achiral environmental chemical/physical factors in determining SC, and establish that absolute molecular chirality does not necessarily determine SC. SC should thus be viewed as the result of a supramolecular chain reaction whose pathways could be rationalized by invoking the Curtin-Hammett principle in the context of supramolecular systems.
U5: Bioinspired and Organic Tubes II
Session Chairs
Toshimi Shimizu
Makoto Takafuji
Wednesday PM, April 19, 2006
Room 2002 (Moscone West)
2:30 PM - **U5.1
Supramolecular Nanotube Hosts for Encapsulation of 10-nm-Scale Objects.
Toshimi Shimizu 1 2
1 Nanoarchitectonics Research Center (NARC), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan, 2 SORST, Japan Science and Technology Corporation (JST), Tsukuba, Ibaraki, Japan
Show AbstractLipid nanotubes (LNTs) with 10-100-nm-scale hollow cylinders have been again receiving much interest due to their resemblance to multi-wall carbon nanotubes in size dimensions, their unique shapes, and prospective technological applications.[1] Though a limited number of synthetic lipid molecules have been well documented to self-assemble into tubular structures, there have been no definitive guiding principles to manipulate the nanotube morphologies.[2] Discrete, organic, hollow cylinder architectures are also of great interest in nanomaterials science due to the continuing interest in nano-space-specific fundamental phenomena. Here we describe chiral self-assembly of synthetic glycolipid molecules into uniform hollow cylinder structures in approximately 100% yields. Optimization of the introduction position of a cis-double bond in the unsaturated hydrocarbon chains enabled us to get such uniform nanotubes among a series of glucopyranosylamide lipids.[3] In addition, we have succeeded in the confined organization of gold nanocrystals or ferritin at room temperature by filling a vacant glycolipid nanotube hollow cylinder with aqueous solutions of hydrogen tetrachloroaurate or ferritin, respectively.[4,5] The lipid N-(11-cis-octadecenoyl)-beta-D-glucopyranosylamine 1 proved to produce the nanotubes with the narrowest distribution of outer diameters (av. = 200 nm, s.d. = 23 nm) among several lipid homologues synthesized.[3] To get a one-dimensional vacant LNT hollow, we removed the water filled in the LNT hollow cylinder of 1. An aqueous solution of hydrogen tetrachloroaurate (III) was immersed into the LNT hollow cylinder by capillary action and the aurate anion was then photochemically reduced to Au(0) by UV irradiation in the confined nanospace. We confirmed that the present LNTs can keep their tubular structures without any destruction even after the lyophilization process. TEM images revealed that the gold nanocrystals of 3-10 nm well generated in the one-dimensional nano-space of the LNT.[4] The EDX spectroscopy and the SAED pattern revealed the exact presence of Au nanocrystals with a fcc phase in the LNT. By applying the similar methodology, we next tried to encapsulate ferritin (12 nm) within the LNT from 1. The TEM and EDX revealed that ferritins are well encapsulated in the hollow cylinder. We were able to see ferrihydrite cores as black dots.[5] Thus, the hollow cylinder of the LNT from 1 provides an effective, supramolecular nanotube host for the confined organization of 10-nm-scale objects.References[1] a) T. Shimizu et al., Chem. Rev. 105, 1401 (2005). b) J.M. Schnur, Science, 262, 1669 (1993). [2] a) G. John et al., Adv. Mater., 3, 715 (2001). b) J.H. Jung et al., J. Am. Chem. Soc., 124, 10674 (2002).[3] S. Kamiya et al., Langmuir, 21, 743 (2005).[4] a) B. Yang et al., Chem. Commun., 500 (2004). b) B. Yang et al., Chem. Mater., 16, 2826 (2004).[5] H. Yui et al., Chem. Lett., 34, 232 (2005).
3:00 PM - U5.2
Self-Assembled Lipid Tubules: Synthesis, Characterization, and Ordered Arrays.
Yue Zhao 1 , Nidhi Mahajan 1 , Jiyu Fang 1
1 , University of Central Florida, Orlando, Florida, United States
Show AbstractThe rolling of lipid bilayer sheets into hollow cylindrical tubules have emerged as a group of interesting supramolecular nanostructures. The hollow cylindrical shape and the crystalline molecular order of the bilayer walls make lipid tubules attractive as a template for the synthesis of inorganic materials, a substrate for the helical crystallization of proteins, and a controlled release system for drug deliver. Here, we image the molecular orientation order in the lipid tubules using liquid crystals as an optical amplification probe. We find that the organization of the molecular tilt azimuth in the lipid tubules can induce an azimuthal orientation in the liquid crystals. A modulated tilt state of the lipid tubules is observed after liquid-crystal optical amplification. Atomic force microscopy studies show that the modulated tilt can induce nanoscale ripples with a periodicity of ~ 200nm for the tubules with the diameter in the range from 200 nm to 650 nm. The angle of the ripples with respect to the equator of the tubule shows a bimodal distribution with centers at ~ 28° and ~ 5 °. We develop a method that combing surface patterning and moving contact line to produce 2-D ordered arrays of parallel aligned lipid tubules on substrates. The patterned and aligned tubules are used as templates for synthesizing silica films with specific morphologies and patternes. References:1. Y. Zhao, N. Mahajan, R. Lu, J. Y. Fang, “Liquid-Crystal Imaging of Molecular-Tilt Organization in Self-Assembled Tubules of Chiral Phospholipids” Proceedings of the National Academy of Sciences USA 2005, 102, 7438. 2. N. Mahajan, J. Y. Fang, “Two-Dimensional Ordered Arrays of Aligned Lipid Tubules on Substrates with microfluidic networks” Langmuir 2005, 21, 3153.
3:15 PM - U5.3
Self-assembled Lipid Nanotube: Inner Diameter and Surface Control by Using Wwedge-shaped Bipolar Amphiphiles.
Mitsutoshi Masuda 1 2 , Toshimi Shimizu 1 2
1 Nanoarchitectonics Research Center, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan, 2 CREST, Japan Science and Technology Agency, Tsukuba Central 4, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan
Show AbstractLipid nanotubes with different inner- and outer membrane surfaces are intriguing nano-architectures applicable to the specific modification of internal and external surfaces, selective filling of nanomaterials into the hollow cylinder [1], controlled release, and creation of templates for the fabrication of inorganic nanomaterials [2]. The most direct way to construct an unsymmetrical lipid membrane is to make use of the asymmetry of heteroditopic 1,omega-bipolar amphiphiles having headgroups differing in size or properties, that is, “unsymmetrical bolaamphiphiles”. The wedge-shape of the lipids also affords us to control inner diameter of the self-assembled nanotubes. So far, there have been no reliable approaches for controlling their diameters until now. Here we would like to present the lipid nanotubes self-assembled from the unsymmetrical bolaamphiphile, and control of the inner diameter and inner/outer surfaces of them [3].Unsymmetrical bolaamphiphiles 1(n) (n = 12, 14, 16, 18, and 20) self-assembled in water to form lipid nano- and microtubes. The nanotubes were separated by centrifugation and examined by TEM and X-ray diffraction (XRD) to study the molecular packing within the tubular membranes. TEM observation revealed that the nanotubes have hollow cylinder structures up to several hundred micrometers long with 30-43-nm outer diameters and 14-29-nm inner diameters. By comparing the membrane stacking periodicity obtained from XRD analysis of the tubes with the molecular packing within single crystals [4], we found that the nanotubes consist of an unsymmetrical monolayer lipid membrane, in which the molecules are packed in parallel. This suggests that the inner surface of the nanotubes is covered with carboxy headgroups and the outer surface with 1-glucosamide headgroups. The inner diameters of the lipid nanotubes could be controlled in the range of 17.7 to 22.2 nm in steps of ~1.5 nm/2 carbons by varying the oligomethylene spacer length. References[1] N. Kameta, M. Masuda, H. Minamikawa, N.V. Gotev, J.A. Rim, J.H. Jong, and T. Shimizu, Adv. Mater., in press.[2] T. Shimizu, M. Masuda, and H. Minamikawa, Chem. Rev. 105, 1401 (2005).[3] M. Masuda and T. Shimizu, Langmuir, 20, 5969 (2004).[4] M. Masuda, K. Yoza, and T. Shimizu, Carbohydr. Res., 340, 2502 (2005).
4:00 PM - **U5.4
Template Wetting – A Construction Kit for 1D Nanostructures.
Martin Steinhart 1 , Markus Geuss 5 1 , Olaf Kriha 3 , Klaus Rademann 5 , Petra Goering 1 , Andreas Greiner 3 , Joachim Wendorff 3 , Ralf Wehrspohn 4 , Elke Hempel 2 , Ulrich Goesele 1 , Thomas Thurn-Albrecht 2
1 , Max-Planck-Institute of Microstructure Physics, Halle Germany, 5 Department of Chemistry, Humboldt-University, Berlin Germany, 3 Department of Chemistry, Philipps-University, Marburg Germany, 4 Department of Physics, University of Paderborn, Paderborn Germany, 2 Department of Physics, Martin-Luther-University, Halle Germany
Show AbstractA plethora of functional materials has been formed into non-carbon nanotubes and nanorods by means of porous templates. The properties of the one-dimensional nanoobjects depend to a great extent on their internal mesoscopic fine structures, but little is known on the underlying physico-chemical phenomena governing the generation of these features. Wetting ordered porous alumina with polymeric melts and solutions allows not only realizing new nanotube architectures, but enables also a systematic investigation of structure formation processes inside the pores. Polymer nanotubes with a longitudinal gradient in composition have been prepared by face-to-face wetting, where different polymeric solutions simultaneously infiltrate porous alumina from the two opposite template surfaces. One-dimensional composite structures containing a block copolymer rod segment and a homopolymer tube segment can be prepared in such a way that the length of both segments is adjustable. Based on an X-ray analysis, we show how coherent kinetic control over the crystal orientation in macroscopic ensembles of nanotubes and nanorods inside porous alumina templates wetted by partially crystalline polymers is attained. We have identified two clear limiting cases. If the entities inside the template pores are crystallized in the presence of a connecting surface film, crystallization will start in this film. Exclusively those crystals grow along the template pores that have their dominant growth direction aligned with the long axes of the pores, resulting in large arrays of the nanostructures with uniform crystal orientation. In the absence of a surface film, crystallization is separately initiated within each pore by homogeneous nucleation, and any crystal orientation allowing the growth of the lamella crystals along the pores appears statistically. As an example of structure/property relationships thus arising, the native polarization and domain structure of ferroelectric polymer nanotubes as well as their local poling on the 100-nm scale are discussed. We believe that the concepts presented here are of general validity and potentially useful to control mechanical, electronic or piezoelectric properties of 1D nanostructures made of polymeric or even more generally organic materials. They might be components of bio-inspired adhesive structures, sensors, and nano-actuator arrays.
4:30 PM - U5.5
Gas Storage in Aromatic Nanochannels.
Roberto Simonutti 1 , Piero Sozzani 1 , Silvia Bracco 1 , Angiolina Comotti 1 , Lisa Ferretti 1 , Michele Mauri 1
1 Materials Science, University of Milan-Bicocca, Milan, Mi, Italy
Show AbstractThe application of the principles of self-assembly and crystal engineering permits the shaping of nanoscale environments lined with specific receptors for absorbing gases and vapors. We could obtain novel nanochannels held together by a network of weak van der Waals interactions that fabricate the zeolite-like host structure and cooperatively stabilize the in-diffusing gases. The molecular crystal can store at low pressure large amounts of carbon dioxide and methane selectively over nitrogen, oxygen and hydrogen. Carbon and proton Magic Angle Spinning NMR spectroscopy could recognize the specific interactions that contribute to the overall stabilization. The impressive upfield shifts caused by the aromatic ring currents on gas molecules at the van der Waals close contacts provide a tool for measuring the intermolecular distances, proving the formation of CH-π interactions and understanding the preferred topology of the gases interacting with the fully aromatic nanochannels. This provides one of the rare detailed description of gas molecules trapped into crystals. Also, the open nanochannels can be explored by the hyperpolarized xenon gas. In fact, the sensitivity of 129Xe NMR can be strongly enhanced by hyperpolarization (HP), a recent technique that, exploiting spin-exchange optical pumping, produces such a remarkable xenon nuclear polarization that a significant xenon signal can be detected by a few scans and minor amount of material. Anisotropic xenon signals are observed demonstrating the squeezing of the xenon atoms into the aromatic nanochannels. Furthermore, in the narrow nanochannels of porous crystals xenon atoms cannot bypass each other realizing a particular case of one-dimensional diffusion, called single-file diffusion. HP 129Xe NMR in the Continuous-Flow set-up made it possible to monitor single-file diffusion over a time-scale of tens of seconds.Reference: P. Sozzani, S. Bracco, A. Comotti, L. Ferretti, R. Simonutti “Methane and Carbon Dioxide Storage in a Porous van der Waals Crystal” Angew. Chem. Int. Ed., 2005, 44, 1816-1820 (VIP paper).
4:45 PM - U5.6
Relation Between Structure and Physical Properties for Conjugated Polymer Nanowires Prepared by the Template Method.
Jean-Luc Duvail 1 , Patrice Retho 1 , Yunze Long 1 , Vincent Fernandez 1 , Philippe Molinie 1 , Guy Louarn 1 , Olivier Chauvet 1
1 , Institut des Materiaux, Nantes France
Show Abstract5:00 PM - U5.7
Microtubular Structure Composed of Self-assembled Nanofibrous Aggregates from Mono-alkylated L-Glutarimide Derivative.
Yoshiko Kira 1 , Hirotaka Harada 1 , Makoto Takafuji 1 , Hirotaka Ihara 1
1 Department of Applied Chemistry and Biochemistry, Kumamoto University, Kumamoto Japan
Show AbstractU6: Composites of Carbon Nanotubes I
Session Chairs
Wednesday PM, April 19, 2006
Room 2002 (Moscone West)
5:15 PM - U6.1
Metal-insulator Transition in DNA-functionalized Single-wall Carbon Nanotubes.
Vadim Puller 1 , Slava Rotkin 1
1 Physics Department, Lehigh University, Bethlehem, Pennsylvania, United States
Show Abstract5:30 PM - U6.2
Reversible Control of Carbon Nanotube Microstructure Using Poly(acrylic acid).
Jaime Grunlan 1 2 3 , Lei Liu 3 2 , Yeon Seok Kim 1 2
1 Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Polymer Technology Center, Texas A&M University, College Station, Texas, United States, 3 Materials Science and Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractSingle-walled carbon nanotubes (SWNTs) are an exciting material due to their small size, high modulus, and high intrinsic conductivity. As a result, nanotubes hold significant promise for imparting electrical conductivity, mechanical strength, and thermal conductivity to polymeric materials. Despite this potential, the ability to stabilize nanotubes in solution remains a significant hurdle to their widespread use. This has led to significant research efforts on the use of stabilizing agents and chemical modification of the nanotubes to impart solubility. Once stabilized, these nanotubes lend themselves to chemical modification, spectroscopic study, and/or incorporation into ink-based systems. Nanotube suspensions are currently being studied for use in drug and gene delivery applications. Solid films of SWNT-filled polymers are being studied for a variety of uses including thermal management, humidity sensing, and corrosion resistance. The present work demonstrates a method to control the microstructure of carbon nanotubes in aqueous solution and dry composite films using poly(acrylic acid). As the pH of an aqueous mixture containing 1 wt% PAA and 0.1 wt% SWNT is raised from 2 to 9, a significant increase in viscosity is observed that suggests improved exfoliation of nanotube bundles. Drying these mixtures into composite films reveals heavy aggregation of SWNTs at low pH and a well-dispersed network at high pH. These results are due to the de-protonation that occurs with PAA as pH increases, which enhances its ability to hydrogen bond and interact with SWNTs. Trends in mechanical properties and electrical conductivity confirm this idea of increasing polymer-nanotube interaction with pH. Additionally, these microstructural changes are fully reversible by simply reducing pH. This behavior has significant implications for the processing of carbon nanotubes and tailoring of composite properties. Many of the relationships uncovered here could be applied to other types of hydrophobic nanotubes and nanowires.
5:45 PM - U6.3
Chemical Vapor Deposition of Carbon Nanotube-Reinforced Polymer Composites.
Chi-Hwa Wu 1 2 , David Harding 1 2
1 Laboratory for Laser Energetics, University of Rochester, Rochester, New York, United States, 2 Department of Chemical Engineering, University of Rochester, Rochester, New York, United States
Show AbstractMultiwalled carbon nanotube (MWNT)- reinforced polymer composite films were synthesized at low temperature by a two-step process using (i) microwave-assisted electron-cyclotron-resonance chemical vapor deposition (ECR-CVD) to make a MWNT mat at 450 °C on a catalyst-coated substrate with gas mixture of methane and hydrogen, and (ii) chemical vapor infiltration (CVI) of polymers into the nanotube mat. In this study, parylene and glow-discharge polymerization (GDP) polymers were utilized to infiltrate the nanotube mat at temperature below 200 °C. Sequentially depositing MWNT and then infiltrating with polymer requires low temperature for sustaining the polymer matrix. By taking advantages of the ECR-CVD system, e.g. high plasma density at low growth temperature, it is possible to prepare such composite films and a fully-dense material. A strong interfacial adhesion between the carbon nanotubes and the polymer matrix is a major factor that determines the reinforcement performance of such nanocomposites. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies showed that nanotubes embedded with the polymer matrix enhance interfacial adhesion by simple mechanical attaching or interlocking. The feasibility of making nanotube-reinforced composite depends on the processing parameters, including the effect of polymer vapor infiltration and the volume density of the nanotube mat. Characterizations of these composite films have been conducted and it was found that a fully-dense composite film was synthesized using a 40 vol.% MWNT mat vapor-deposited with parylene polymer, while the GDP polymer was found less than 3 μm infiltration with the same mat. In addition, the mechanical behaviors of these composites, including hardness and elastic modulus, were investigated using nano-indentation.
U7: Poster Session: Organic and Inorganic Nanotubes
Session Chairs
Oliver Hayden
Kornelius Nielsch
Thursday AM, April 20, 2006
Salons 8-15 (Marriott)
9:00 PM - U7.1
Comparison of Piezoelectric and Carbon Nanotube-Based Actuators.
Hossein Golnabi 1 , Mahmod Ghorannevis 1 , Masoud Golnabi 1
1 Plasma Physics Research Center, Islamic Azad University, Tehran Iran (the Islamic Republic of)
Show Abstract9:00 PM - U7.10
Carbon Nanotube – Polymer Composites as Field Emission Cathodes.
David Carey 1 , Richard Smith 1 , Ravi Silva 1 , Robert Murphy 2 , Werner Blau 2 , Jonathan Coleman 2
1 Advanced Technology Institute, University of Surrey, Guildford United Kingdom, 2 School of Physics, Trinity College Dublin, Dublin Ireland
Show AbstractCarbon nanotubes have significant potential as large area cathodes for field emission displays. The use of carbon nanotube – polymer composites offers an important route to control the nanotube content and the properties of the cathode as a whole. Arc discharge multiwall carbon nanotubes have been incorporated into PmPV, a derivative of the conjugated polymer PPV. By successive dilutions of nanotube concentration, a range of samples with nanotube mass fractions up to 7 % was prepared and the resultant composites spin cast to form nanotube-polymer cathodes. Large area electron field emission characterisation was made as a function of nanotube mass fraction using phosphor coated anodes where electron emission at low applied electric fields was observed. From the resultant emission site maps and threshold electric fields, the transport and emission of electrons is discussed. Surrounding each nanotube is a polymer coating that acts as a tunnel barrier and the fluctuation induced tunnelling between the nanotubes in a disordered percolation network is shown to play an important role. Factors affecting the potential use of carbon nanotube – polymer composites for field emission based displays are also discussed.
9:00 PM - U7.11
Developments in Nanomanipulation for Field Emission from Carbon Nanotubes.
Richard Smith 1 , David Carey 1 , David Cox 1 , Ravi Silva 1
1 Advanced Technology Institute, University of Surrey, Guildford United Kingdom
Show AbstractField emission (FE) based devices using carbon nanotubes, such as displays and high current density microwave sources are beginning to emerge. It is well known that the fraction of nanotubes emitting in such devices can be quite low and in some cases below 10%. Most measurements techniques, such as current-field characterisation using phosphor coated anodes, tend to reflect the density of emitting nanotubes with the lowest local threshold fields for emission. An alterative method is to measure the FE characteristics using local probe electrodes attached to high precision manipulators. We show that by performing such measurements within a scanning electron microscope, complementary electrical and structural information about the nanotube can be obtained. In a two terminal arrangement, by varying the position of the anode electrode, information about local electric field and field enhancement factor can be obtained. By incorporating a third electrode and using a focussed ion beam system to produce a circular aperture, a gate electrode can be produced to provide three terminal characterisation. We show that such an arrangement is able to characterise an individual carbon nanotube. Estimates of the anode field screening factor due the presence of the metallic gate and the gate transparency factor can be obtained. Methods for local probe measurements for nanotubes are also discussed.
9:00 PM - U7.12
Catalytic Growth of Single-Walled Carbon Nanotubes: Effect of Catalyst Composition and Synthesis Parameters.
Elena Mora 1 , John Pigos 1 , Toshio Tokune 1 , Avetik Harutyunyan 1
1 , Honda Research Institute, Columbus, Ohio, United States
Show AbstractThe growing interest to use carbon single-walled nanotubes (SWNTs) for fundamental science and applications demands a reasonably pure and homogeneous (diameter, chirality) material. To achieve this, it is necessary to have a full understanding of the effect of the catalyst composition and the synthesis parameters on the growth of the tubes.In this work, a series of catalysts (Fe, Fe/Mo and their corresponding oxides), supported on alumina, were examined for the growth of SWNTs using chemical vapor deposition method (CVD) with methane gas under different conditions. To discuss the growth mechanism, experimental results from calorimetric measurements of the catalysts melting points, in situ mass spectrometer studies of the gases evolved during the synthesis, and thermogravimetrical and Raman measurements of the synthesized materials were used. The findings support a growth mechanism based on the liquefaction of the catalyst particles due to carbon diffusion into the nanoparticles [1,2] and termination of the process caused by the formation of stable carbide phases and amorphous carbon.The presence of Mo in the composition was found to modify the characteristics of the Fe catalyst by improving the efficiency of the hydrocarbon decomposition, assisting the carbon-induced liquefaction and affecting the catalyst “lifetime”. Consequently, the growth of SWNTs was observed to initiate earlier and prolong for longer times, resulting in higher yields. Moreover, results point to the formation of an alloy between both metals (Fe and Mo). On the other hand, the use of metal oxides catalyst particles was found surprisingly to exhibit similar catalyst activity as the reduced forms. However, it was observed earlier [3] that higher temperatures were required to initiate the nucleation and growth of the nanotubes.Finally, the effect of the carbon feedstock on the synthesis was analyzed. We found that the hydrocarbon (methane) flow rate has a dramatic impact on the catalyst activity, “lifetime” and efficiency of nanotubes formation. Particularly, the increase of the flow rate up to 15 cm3min-1mg-1Fe increased the resulted carbon concentration and decreased the period of time that the catalyst was active. Meanwhile, a flow rate of 220 cm3min-1mg-1Fe decreased the catalyst “lifetime” by almost 10 times, and assisted the formation of amorphous carbon and/or stable Fe carbide solid phases resulting in an early termination of the growth.1. A. R. Harutyunyan, E. Mora, T. Tokune, Appl. Phys. Lett. 86, 153113, 2005.2. A. R. Harutyunyan, E. Mora, T. Tokune, Appl. Phys. Lett. 87, 051919, 2005.3. A. R. Harutyunyan, B. K. Pradhan, U. J. Kim, G. Chen, P. C. Eklund, Nano Letters 2, 525, 2002.
9:00 PM - U7.13
Ab-Initio Modeling of Contact Formation in Carbon Nanotube Devices.
Karthik Ravichandran 1 , Wolfgang Windl 1 , Leonardo Fonseca 2
1 Materials Science & Engineering, The Ohio State University, Columbus, Ohio, United States, 2 Center for Semiconductor Components, Universidade Estadual de Campinas, Campinas, SP, Brazil
Show AbstractThe continuing miniaturization of semiconductor devices has currently reached a stage where further progress does not seem to be feasible for much longer without changing the traditional device structure. Several dimensions are about to meet their physical limits (like the thickness of the gate oxide or dopant concentration vs. junction depth in ultrashallow junctions) and require novel solutions. Among other challenges, these novel nanoelectronic devices require an unprecedented attention to the detailed geometry and electronic properties on the atomic scale. In this paper, we will discuss the simultaneous process and electron-transport modeling on the atomic scale for the example of carbon nanotube and graphene Schottky devices, using temperature-accelerated ab-initio molecular dynamics methods and atomistic transport modeling based on the Landauer theory. Our results show that finite-temperature contact formation can result in severely distorted nanotubes in contact with, e.g., titanium, and conductance values two orders of magnitude smaller than for the optimum case. Furthermore, surface defects and surface oxygen can strongly influence the contact formation. Our transport results for the finite-temperature formed contacts are in excellent agreement with experiments.
9:00 PM - U7.14
Tuning of Diameter of SWCNTs.
Miro Haluska 1 , Martin Hulman 2 , Bjorn Hornbostel 1 , Siegmar Roth 1 , David Carroll 3
1 von Klizing, Max Planck Institute for Solid State Research, Stuttgart Germany, 2 Institute for Materialphysics , Vienna University, Vienna Austria, 3 Center for Nanotechnology, Wake Forest University, Winston-Salem, North Carolina, United States
Show Abstract9:00 PM - U7.15
Scratching Nanotubes onto Si Substrates.
Ying Chen 1 , Jun Yu 1
1 Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australian Capital Territory, Australia
Show AbstractAligned carbon nanotubes (CNTs) can be readily synthesized on quartz or silicon-oxide coated Si substrates using a chemical vapor deposition method, but it is difficult to grow them on pure Si substrates without predeposition of metal catalysts. We report that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000oC on the templates created on Si substrates with simple mechanical scratching. This simple technique does not require a pre-deposition of metal catalysts. Scanning electron microscopy and X-ray energy spectroscopy analysis revealed that the fractured Si atomic planes at the scratched areas sink FePc vapor due to capillarity effects and act as the preferred nucleation sites for CNT growth. Two-step pyrolysis process avoids reactions between catalyst Fe particles and Si surface with the formation of inactive FeSi catalysts [1].[1] Y. Chen and J. Yu, APPLIED PHYSICS LETTERS 87, 033103, 2005
9:00 PM - U7.16
Relatively Low Temperature Growth of Carbon Nanotubes by Thermal Chemical Vapor Deposition using Novel Catalysts.
Han-Chung Tai 1 , Tsung-Ying Chuang 1 , Chuan-Ping Juan 1 , Yao-Ren Chang 1 , Rui-Ling Lai 1 , Kao-Chao Lin 1 , Jiun-Kai Shiu 1 , Wen-Pin Wang 1 , Huang-Chung Cheng 1
1 Electronics Engineering, National Chiao Tung University, Hsinchu Taiwan
Show Abstract9:00 PM - U7.17
Carbon Nanotubes For Micro Batteries Devices.
Rouviere Emmanuelle 1 , Salot Raphael 1 , Faucherand Pascal 1 , Bancel Stephane 1 , Gaillard Frederic 1
1 DTEN/STN/LTME, Commissariat A L'Energie Atomique, Grenoble France
Show Abstract9:00 PM - U7.18
Selective Placement of Carbon Nanotubes.
Ali Afzali 1 , James Hannon 1 , Christian Klinke 1 , Phaedon Avouris 1
1 Research Division, IBM, Yorktown Heights, New York, United States
Show AbstractThe electronic properties of carbon nanotubes (CNT) makes them specially well-suited for nanoelectronics. Field-effect transistors incorporating CNT as channel material have shown superior performance to that of Si devices. However, a major obstacle for large-scale integration of CNT in circuits is the lack of control in placement of CNTs on the substrates. In this talk we present selective placement of CNTs on metal oxide surfaces through functionalization of CNT with diazonium salts having organic acid end-cap groups. Spectroscopic analysis of functionalized CNT along with electron microscopy and fabrication of field-effect transistors are described.
9:00 PM - U7.19
Electrochemical Properties of Supercapacitors from Carbon Nanotube Electrodes by EPD.
Chunsheng Du 1 , Ning Pan 1
1 , University of California at Davis, Davis, California, United States
Show Abstract9:00 PM - U7.2
Super-compressible, Resilient Carbon Nanotube Films.
Anyuan Cao 1 , Pamela Dickrell 2 , W. Sawyer 2 , Mehrdad Ghasemi-Nejhad 1 , Pulickel Ajayan 3
1 Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii, United States, 2 Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, United States, 3 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractWe report that vertically aligned carbon nanotube films can be reversibly compressed to less than 15% of film thickness and return to nearly original thickness upon the release of the compressive load. Under compression, the nanotubes collectively form wave-like zigzag buckles along the tube axis which can be folded like compression springs, and can fully unfold to their free length after load release. While the compression behavior is similar to conventional low density flexible foams, the nanotube films possess hundreds times higher compressive strength, fast recovery rate, high sag factor, and the excellent breathability due to the open-cell nature of the nanotube arrays. There is a drop of maximum compressive strength of about 30% after thousands of compression cycles, but the permanent deformation (thickness that can not be recovered after load release) is less than 15% of initial film thickness. These results demonstrated that nanotubes have high flexibility/resilience and can be bent through large angles (strains) repeatedly without structural failure, as predicted by previous experimental and theoretical work. Furthermore, the aligned nanotube arrays act with collective response, with all nanotubes buckling at the same wavelength. The nanotube films present a novel class of open-cell foam structure, with individual nanotubes acting as strong nanoscale struts and the inter-nanotube space as interconnected open-air cells. Such light-weight, resilient systems consisting of well ordered nanoscale units (nanotube struts) could have many interesting applications such as flexible electromechanical systems, compliant interconnect structures, actuators, and coatings for mechanical damping and energy absorbing services.
9:00 PM - U7.20
Carbon Nanotube Synthesis Using Fe-containing Mesoporous Silica Catalysts.
Jeong-Rae Ko 1 , Wha-Seung Ahn 1
1 Chemical Engineering, Inha University, Incheon Korea (the Republic of)
Show AbstractCNTs (Carbon nanotubes) were prepared by catalytic CVD (chemical vapor deposition) using Fe-MCM-41 with 4 mol % Fe loading prepared by direct synthesis route. SBA-15 impregnated with uniform 5 nm size iron oxide nano-particles were also prepared for CNTs synthesis for comparison. The characterization of the catalysts prepared was performed using XRD, SEM/TEM, N2 physisorption, UV-Vis diffuse reflectance and FT-IR spectroscopies and TGA. These studies established that catalytic materials with high dispersion of Fe species were successfully prepared. To start CNTs synthesis, a quartz boat holding the dry 0.1 g Fe-MCM-41 sample was placed into the middle of a horizontal tubular reactor and temperature was raised to 823 K in Ar atmosphere. After catalyst reduction, the reactor temperature was increased to 923 – 1123 K to proceed graphitization using a feed mixture composed of Ar : H2 : hydrocarbon = 8 : 1 : 1 [160 sccm Ar, 20 sccm H2, and 20 sccm C2H2] for 10 – 60 min. Typical MWNTs were produced under the given reaction condition as demonstrated by the SEM/TEM and FT-Raman spectroscopic analysis of the product obtained. Initially, 1023 K was established to be the optimum synthesis temperature based on the total carbon yield and qualities of CNTs obtained. Significant amount of amorphous carbon was also formed and was believed to cause deactivation of the catalyst and no further increase in the total carbonaceous product was detected beyond 30 min reaction. Purification was conducted using a combination of thermal treatment with enhanced heating rate (10 K/min) followed by acid etching using HF (50 wt %). The effect of the H2/C2H2 mole ratio on the CNTs formation was also examined, and the gas mixture of Ar : H2 : C2H2 = 14 : 5 : 1 was found to be the optimum. Finally, we have examined the effect of cobalt co-catalyst on the CNTs production. For this purpose cobalt acetate dissolved in ethanol was wet-impregnated to Fe-MCM-41 (Co/Fe weight ratio of 1/3 to 1/1). Among these catalyst, Co-impregnated Fe-MCM-41 with Co/Fe = 1 was shown to produce a small fraction of SWNTs with ca. 2 nm diameter with MWNTs being the major product. These studies revealed that Fe-MCM-41 is a promising catalyst/host material to grow uniform sized MWNTs, primarily because of the high dispersion of Fe species within the mesoporous silica frame work.
9:00 PM - U7.22
Carbon Nanotubes Catalysis by Metal Silicide: Resolving Inhibit Versus Growth.
Santiago Esconjauregui 1 2 , Caroline Whelan 1 , Karen Maex 1 2
1 , IMEC, Leuven Belgium, 2 Department of Electrical Engineering, Katholieke Universiteit Leuven, Leuven Belgium
Show Abstract9:00 PM - U7.23
Optical Anisotropy of Aligned Single Wall Carbon Nanotubes
Jeffrey Fagan 1 , Barry Bauer 1 , Matthew Becker 1 , Erik Hobbie 1
1 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractThe optical properties of single wall carbon nanotubes (SWCNTs), particularly for fractions containing well defined tube lengths and chiralities, are of significant importance for a variety of applications. In this work, separated fractions of DNA wrapped SWCNTs were aligned and their optical anisotropy measured through polarized light spectroscopy combined with small-angle neutron scattering (SANS). Alignment was achieved using several methods that generated centimeter scale samples with near uniform alignment. By determining the degree of alignment independently using SANS, we obtain the intrinsic optically anisotropy of the SWCNTs as a function of such parameters as tube length and band structure.
9:00 PM - U7.24
High Current Density Field Emission from Arrayed Bundles of Carbon Nanotubes: Parametric Studies of Growth and Field Emission
Michael Bronikowski 1 , Harish Manohara 1
1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, United States
Show AbstractWe have found that Carbon Nanotubes (CNT) arranged in arrays of bundles, with bundle diameter and spacing of a few microns, give much greater field emission current densities that either isolated CNT or dense mats of CNT. We have observed current densities of many Amp/cm^2 at fields of approximately 4 Volts/micron. As part of ongoing efforts to fabricate high-intensity electron-beam devices based on these arrayed CNT bundles, we have studied CNT bundle growth (by Chemical Vapor Deposition, CVD) as a function of the various CVD processing parameters, and field emission intensity as a function of CNT bundle array geometric parameters such as bundle size, spacing, and CNT length and diameter. Results will be presented from these parametric studies, in which we have optimized both CNT growth and field emission of electrons from arrayed bundles of CNT.
9:00 PM - U7.25
Fe-Co Magnetic Alloy Catalysts for the Synthesis of Vertically Aligned Carbon Nanofibers.
Kate Klein 1 2 , A.V. Melechko 1 2 , J.D. Fowlkes 1 , I.M. Anderson 3 , K.D. Sorge 4 , T. Leventouri 4 , J.R. Thompson 5 , P.D. Rack 1 2 , T.E. McKnight 1 , M.L. Simpson 1 2
1 Molecular Scale Engineering & Nanoscale Technologies Research Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Engineering, Univeristy of Tenneessee, Knoxville, Tennessee, United States, 3 Microscopy, Microanalysis, Microstructures, Metals & Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Physics, Florida Atlantic University, Boca Raton, Florida, United States, 5 Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstract9:00 PM - U7.26
Electrical and Tribological Behavior of Metal-infiltrated MWNT Contact Brushes
Sunil Pal 1 , Pamela Dickrell 2 , Linda Schadler 1 , Pulickel Ajayan 1 , W Sawyer 2
1 Materials Science & Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractThis presentation examines the contact resistance and tribological properties of oriented capped carbon multiwalled nanotube (MWNT) films. Highly anisotropic tribological behavior of MWNT films oriented in mutually orthogonal directions is observed. The average values of coefficient of friction varied from high values (0.795) for vertically aligned nanotubes grown on rigid substrates to low values (0.090) for the same nanotubes dispersed flat on the same substrates. The results were insensitive to humidity, which is in contrast to graphite materials. The multiwalled nanotube layers also had a monotonic decrease in friction coefficient with increased surface temperature in both orientations, having a 32% drop in friction coefficient over a 73°C temperature rise. Orientation and temperature friction trends are examined in regards to activation energies for interfacial surface sliding. Using e-beam evaporation method, metal such as gold and copper were infiltrated into the film and a well adhered backing was made. Vertically aligned MWNT films backed with conductive layers were tested for hot switching and electrical sliding applications. The MWNT films were cycled for 3000 cycles of hot electrical switching under a low force contact with no degradation in the electrical contact resistance, which is in contrast to traditionally used noble metal alloys which realize signal degradation and arcing under repeated hot switching contacts. The gaseous environment insensitivity, orientation and temperature dependent and potentially tunable tribological properties, and sustainable electrical hot switching makes oriented MWNT promising as components in multifunctional coatings and composite materials for air and space applications.
9:00 PM - U7.27
Single-walled Carbon Nanotube Growth Enhanced by Reduction Layers for Carbon Nanotube Field-Effect Transistor Applications
Tsung-Yeh Yang 1 , Tri-Rung Yew 1
1 Dept. of Material Science & Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractThis paper presents the growth of the semiconducting single-walled carbon nanotubes (SWCNTs) enhanced by implementing reduction layers for field-effect transistor applications. The reduction layers, proposed to play a role of consuming the oxygen that might degrade the single-walled CNT growth, were deposited before the nickel catalyst. To verify the role of the reduction layers and the mechanism for CNT growth enhancement, various reduction materials were investigated. The results showed that the single-walled carbon nanotubes synthesized with reduction layer enhancement contributed better crystallization and good field-effect properties.For CNT growth and field-effect transistor fabrication, the size of the catalyst was modified by Ar and H2 plasma pre-treatment in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system before the SWCNT growth. A test structure with electrodes separated at various spacing was used to measure the CNT length and field-effect transistor characteristics as well. In addition to electrical characteristics, the scanning electron microscope (SEM), high resolution transmission electron microscope (HR-TEM), atomic force microscope (AFM), and Raman spectrum will be also used to characterize the SWCNT physical properties.
9:00 PM - U7.28
Carbon Nanotube Field Emitters Grown in the Anodic Aluminum Oxide Pore Channel Array
Fu-Ming Pan 1 , Chen-Chun Lin 1 , Kai-Chun Chang 1 , Cheng-Tzu Kuo 1 , Mai Liu 2 , Chi-Neng Mo 2
1 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan, 2 , Chunghwa Picture Tubes, Ltd., Taoyuan Taiwan
Show AbstractCarbon nanotubes (CNTs) have been grown in the anodic aluminum oxide (AAO) pore channel array, and their field emission properties were studied. For the CNT field emitter fabrication, the AAO pore channel array was first prepared in a triode structure, which was fabricated on the Si wafer using conventional integrated circuit processes. The cobalt catalyst was then electrochemically deposited in the AAO pore bottom, and the growth of CNTs followed. The CNT growth was carried out in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system using the gas mixture of CH4 and H2 as the plasma source. The triode structure fabricated on the Si wafer were 4μm in diameter and 2μm in depth. After Al anodization, due to the volume expansion, a large stress built up in the triode structure, leading to a disordered pore arrangement near the periphery of the triode. However, reasonably ordered pore channels still occupied a very large portion of the AAO film. The pore diameter ranged from 60 nm to 100 nm. The highly ordered AAO pore channels provided benign growth conditions for vertically aligned CNTs with controllable tube density and tube diameters. After extending out of the AAO pores, overgrown CNTs retained the vertical growth direction. The field-emission characteristics of the AAO-CNT triodes have been studied and will be presented in the meeting.
9:00 PM - U7.29
Effects of Metal Coating on the Field Emission Properties of Carbon Nanotubes.
Youngmi Cho 1 , Changwook Kim 1 , Heesung Moon 1 , Sohee Park 2 , Seungwu Han 2
1 Corporate R&D Center, Samsung SDI Co, Ltd, Youngin-si, Gyeonggi-do Korea (the Republic of), 2 Department of Physics and Division of Nano Science, Ewha Womans University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - U7.3
Low Temperature Synthesis of CNTs on Glass Substrate by Direct Catalyst-microwave Interaction.
Wang Chih-Yung 1 , Chen Zong-Han 1 , Chang Shih-Chin 1 , Chin Tsung-Shune 1
1 material science and engineering, National Tsing Hua University, Hsinchu Taiwan
Show Abstract9:00 PM - U7.30
Development of a Single-Walled Carbon Nanotube Thin-Film Sensor for Air Pollutant Monitoring
Winadda Wongwiriyapan 1 , Shin-ichi Honda 1 , Hirofumi Konishi 1 , Tomoaki Mizuta 1 , Takafumi Ohmori 1 , Yoshito Kishimoto 1 , Tatsuya Ito 2 , Toru Maekawa 2 , Kengo Suzuki 2 , Hiroshi Ishikawa 2 , Kenjiro Oura 3 , Mitsuhiro Katayama 1
1 Dept. of Electronic Eng., Osaka Univ., Osaka Japan, 2 , New Cosmos Electric Co., Ltd., Osaka Japan, 3 Research Center for UHVEM, Osaka Univ., Osaka Japan
Show Abstract Single-walled carbon nanotubes (SWNTs) have attracted considerable attention in a wide range of scientific research fields. Their small dimensions and unique properties make SWNTs the most promising nanomaterials for the building blocks of future devices for information-, environment and energy-, and bio-technologies. SWNTs have served as single-function devices in areas such as thin-film transistors, field emitters, energy storage devices and gas sensors. In recent years, efforts have been devoted to creating gas sensors with a sensitivity on the ppb order using microarray SWNTs. However, its fabrication complexity makes it difficult to produce in large-scale production. Thus, development of a novel sensing technique with a simple architecture for ultrasensitive gas detection has been stringently required. In this study, we demonstrated ultrasensitive gas detection using single-walled carbon nanotube (SWNT) thin-film sensor. An alumina substrate which is a platform of a conventional metal oxide thin-film sensor was used as a substrate for a growth of SWNT thin film. The SWNTs were grown by Fe/Al catalyst-assisted chemical vapor deposition. The sensor response of the as-grown SWNT thin film was investigated. NO2 was detected down to the ppb level (~ 5 ppb) under room-temperature operation with a fast response. The test cycle of gas adsorption and desorption using a heater set at the bottom of the sensor showed a short recovery in the activation of the sensor. The fabricated SWNT sensor was insensitive to ethanol, acetone and toluene even when exposed to extremely high gas concentrations of more than 1,000 ppm. Using an electrical breakdown technique, gas response sensitivity was improved by an order of magnitude. The relationship between gas concentration and sensor response was derived based on the Langmuir adsorption isotherm. The proposed SWNT thin-film gas sensor exhibits merits over other types of sensors by virtue of its simplicity in fabrication and feasible application to the presently used commercial sensor process. This work was partly supported by Grant-in-Aids for Scientific Research from Japan Society for the Promotion of Science.
9:00 PM - U7.31
Self-assembled Carbon Nanotube Field Effect Transistor with Silicide Contacts
Wei-Chang Yang 1 , Tri-Rung Yew 1
1 Materials Science and Engineering, National Tsing-Hua University, Hsinchu Taiwan
Show AbstractControlled growth of single-walled carbon nanotubes (CNTs) are synthesized between predefined catalytic silicide pads by chemical vapor deposition (CVD) from 600 degree C to 900 degree C. Self-assembled field-effect transistors fabricated with these controlled-growth nanotubes between silicide electrodes show high-level compatibility with current silicon CMOS process. Silicide pads are formed by rapid thermal annealing (RTA) process of multi-layer thin film consisting of catalytic metal, supporting materials, and silicon with various crystalline structures. Before the synthesis process, silicide pads are pretreated by thermal and plasma to enhance its catalytic ability. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM), Raman spectroscopy, and electrical measurement are employed to characterize the physical, chemical, and electrical properties of the self-assembled field-effect transistors. Furthermore, these self-assembled field-effect transistors will be fabricated for sensor applications.
9:00 PM - U7.32
Purification and Functionalization of Single-Walled Carbon Nanotubes for the Fabrication of Electrospun Biocompatible Fibers.
Bin Zhao 1 , Alex Puretzky 1 , Ilia Ivanov 1 , David Styers-Barnett 1 , Hui Hu 1 , Chris Rouleau 1 , Hongtao Cui 1 , Meng-Dawn Cheng 2 , David Geohegan 1
1 Center of Nanophase MAterial Science and Condensed Matter Science Division, Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 2 Environmemtal Science Division, Oak Ridge National Lab, Oak Ridge, Tennessee, United States
Show AbstractSingle-walled carbon nanotubes (SWNTs) have attracted great attentions because of their unique structure and properties. In this work we discuss the purification of SWNTs synthesized by high-power laser vaporation, and the fabrication of SWNT/polymer fibers as scaffolds for biological applications. SWNTs were synthesized by laser ablation of carbon targets with Ni and Co as catalysts using a high-power (600 W) industrial Nd:YAG laser facility at Oak Ridge National Laboratory. The as-prepared SWNTs were purified by treatments with nitric acid, controlled-pH water-extraction and hydrogen peroxide. The efficiency of purification was estimated by using SEM, TEM, TGA, and solution phase NIR spectroscopy techniques. A sonication/vapor-deposition technique was used to produce individual or small bundles of SWNTs on TEM grid. Purified SWNTs were used to make nanotubes/polymer composite fibers by an electrospinning technique. Biocompatible polymers, such as polyethyleneimine and poly (lactic acid), were mixed with the SWNTs to form stable dispersions via sonication. Electrospinning was used to produce nano- and micro-size nanotube/polymer fibers. The application of these fibers as scaffolds for growing cells is currently under investigation.Research supported by the U. S. Department of Energy (EERE) through the Center on Carbon-Based Hydrogen Storage and by the U. S. Department of Energy, Division of Material Science, Basic Energy Sciences.
9:00 PM - U7.34
Effect of Ion Irradiation on Transport Properties of FET Devices made of SWNT Networks.
Viera Skakalova 1
1 Von Klitzing department, Max Planck Instituteof Solid State Research, Stuttgart Germany
Show Abstract9:00 PM - U7.35
Single-walled Carbon Nanotubes Decorated by sub-10 nm Gold Nanoparticles.
Qingling Hang 1 , Matt Maschmann 2 , Timothy Fisher 2 , David Janes 1
1 Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States
Show Abstract9:00 PM - U7.36
Integration of Single-Walled Carbon Nanotubes with III-V(110) Surfaces.
Laura Ruppalt 1 2 , Joseph Lyding 1 2
1 Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show Abstract In an effort to further elucidate the nature of carbon nanotube-substrate interactions, we have used ultrahigh vacuum (UHV) scanning tunneling microscopy (STM), spectroscopy (STS), and STM nanomanipulation to probe individual single-walled carbon nanotubes (SWNTs) transferred in situ to the InAs(110) and GaAs(110) surfaces. Recent work [1,2] suggests that for supported nanotubes, the nature of the underlying substrate can play a significant role in determining the properties of the nanostructure. The STM, with its ability to yield correlated topographic and electronic information at a subnanometer length-scale, provides a means to study, with atomic detail, the influence of the local substrate character on individual nanotube properties in these hybrid nanotube/III-V systems. The III-V compound semiconductors represent a technologically relevant class of materials recently utilized as templates for carbon nanotube device and structure fabrication[3,4]. Our studies are carried out on clean, atomically flat (110) InAs and GaAs surfaces obtained though cleavage in UHV. An UHV Dry Contact Transfer (DCT) technique is employed to deposit HiPCO-produced SWNTs onto the ambient-incompatible III-V(110) substrates with minimal perturbation to tube or substrate. Subsequent STM imagery and STS spectra confirm the sensitivity of the detected nanotube character to the electrical and physical properties of the supporting III-V platform. Furthermore, the precise manipulation of individual SWNTs by the STM tip enables an investigation of the dependence of STM and STS measurements on a nanotube's proximity to specific substrate features. In particular, an enhanced mechanical stability of isolated SWNTs on the III-V substrates is observed when the tubes are aligned along the sublattice rows, potentially indicative of the increased binding between SWNTs and the surface cations of these compound semiconductors[5]. Additionally, semiconducting nanotubes on In- and GaAs(110) generally exhibit energy gaps in agreement with theoretically predicted values though with differing fermi-level shifts, suggesting a link between the extent of charge transfer in these SWNT/III-V systems and the nature of the III-V substrate. [1] R.H. Miwa, W. Orellana, and A. Fazio, APL 86 213111 (2005).[2] E. Pop, et. al., PRL 95 155505 (2005).[3] A. Jensen, et. al., NanoLett. 4 349 (2004).[4] T. Tsukamoto, et. al., JAP 98 076106 (2005).[5] Y.-H. Kim, M. J. Heben, and S. B. Zhang, PRL 92 176102 (2004).
9:00 PM - U7.39
Electron Spin Resonance of Peapods and Peapod-derived Multi-Layer Nanotubes.
Younghyun Kim 1 , Norbert Nemes 2 , Balint Nafradi 3 , Titusz Feher 3 , Laszlo Forro 3 , David Luzzi 1
1 Dep. of materials science and engineering, Univ. of Pennsylvania, philadelphia, Pennsylvania, United States, 2 , Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain, 3 , Institute of Physics of Complex Matter, EPFL, CH-1015 Lausanne Switzerland
Show Abstract9:00 PM - U7.40
Method for Carbon Nanotubes with Iron Obtaining by Microwave Heating.
Oxana Kharissova 1 , Ubaldo Mendez 2
1 FCFM, UANL, Monterrey Mexico, 2 FIME, UANL, Monterrey Mexico
Show Abstract9:00 PM - U7.41
Controlling the Height of CVD-grown Multi-wall Nanotube Arrays
Michael Stadermann 1 , Sarah Sherlock 1 , Brian Dick 1 , Hyung-gyu Park 1 , Alexander Artyukhin 1 , William Pitz 1 , Alexander Noy 1 , Olgica Bakajin 1
1 Chemistry & Materials Science, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractDue to various difficulties, carbon nanotube arrays have seen only limited use in industrial applications to date. One of the difficulties is the reproducible growth of these arrays, let alone a good measure of control over the obtained height. In this work, we have preformed a parametric study of multi-wall carbon nanotube (MWNT) growth. The investigated parameters were gas flow rate, process pressure, and water content of the feed gas. We were able to identify a region in the parameter space that yields stable and highly reproducible growth of tall nanotubes arrays. As a result, we can controllably grow MWNT forests to any height between 1 μm and 1 mm by choosing the right combination of pressure, humidity, flow rate, and growth time. Additionally, we were able to perform kinetic studies of the carbon nanotube growth, and our results suggest that the precursor for nanotube growth is formed in the gas phase.
9:00 PM - U7.42
A Simple Combinatorial Method to Discover Co-Mo Binary Catalysts that Grow Vertically Aligned Single-walled Carbon Nanotubes.
Suguru Noda 1 , Hisashi Sugime 1 , Toshio Osawa 1 , Yoshiko Tsuji 1 , Shohei Chiashi 2 , Yoichi Murakami 2 , Shigeo Maruyama 2
1 Department of Chemical System Engineering, The University of Tokyo, Tokyo Japan, 2 Department of Mechanical Engineering, The University of Tokyo, Tokyo Japan
Show AbstractSingle-walled carbon nanotubes (SWNTs) are attracting much attention owing to their unique properties and potential applications. To establish their fabrication process, preparation of metal catalyst nanoparticles is a key issue, from which SWNTs grow during catalytic chemical vapor deposition (CCVD). Considering possible structural changes in catalyst nanoparticles on substrate surfaces at high temperatures during CCVD, we have proposed to utilize nanoparticles spontaneously forming from submonolayers of catalyst metals at the CCVD temperatures. By using our combinatorial method [1], we have discovered in a single experimental run that 0.05-0.1-nm-thick Co on SiO2 spontaneously forms Co nanoparticles that grow high-quality SWNTs during alcohol CCVD (ACCVD [2]) [3]. In this work, we extended our combinatorial method to binary catalysts and applied to the Co-Mo catalyst, which we previously prepared by dip-coating and found so active as to grow vertically-aligned SWNTs [4]. A mask with a slit simply set above a substrate during sputter-deposition yields thickness profiles of deposits in one-dimension perpendicular to the slit. We prepared thickness profiles of Mo (0.2- 4 nm) and Co (0.2- 8 nm) orthogonally on a SiO2/Si wafer. ACCVD changed the color of the catalyst wafer remarkably. By micro-Raman scattering measurement, we confirmed the formation of SWNTs and quantified their relative yield at 100 different points. When the nominal thickness of catalyst metals were converted into atomic concentrations, an interesting tendency was found; the relative yield was high for points with Co concentration slightly higher than the Mo concentration. This tendency is consistent with the model previously proposed [5] that the CoMoOx layer is formed and then the residual Co forms Co nanoparticle catalysts at a high number density on this layer. Then we analyzed the catalyst point with 1.5 nm Co and 1.4 nm Mo in more detail. Transmission electron microscope showed that the products were mainly SWNTs with some double-walled carbon nanotubes and amorphous carbon. Scanning electron microscopy revealed that the SWNTs were vertically aligned and formed a 2-um-thick film.To realize SWNT-based devices, SWNTs should be grown under widely varied conditions and proper catalysts should be chosen for each condition. Our combinatorial method, which can yield an exhaustive catalyst library on a substrate, will accelerate the development of SWNTs growth processes.[1] S. Noda, Y. Kajikawa and H. Komiyama, Appl. Surf. Sci.225, 372 (2004).[2] S. Maruyama, R. Kojima, Y. Miyauchi, S. Chiashi and M. Kohno, Chem. Phys. Lett. 360, 229 (2002).[3] S. Noda, Y. Tsuji, Y. Murakami, and S. Maruyama, Appl. Phys. Lett. 86, 173106 (2005).[4] Y. Murakami, S. Chiashi, Y. Miyauchi, M. Hu, M. Ogura, T. Okubo, S. Maruyama, Chem. Phys. Lett. 385, 298 (2004).[5] M. Hu, Y. Murakami, M. Ogura, S. Maruyama, T. Okubo, J. Catal. 225, 230 (2004).
9:00 PM - U7.43
Carrier Injection Properties of Solution-processed Carbon Nanotube Transistors with Nonmagnetic and Ferromagnetic Electrodes.
Tomohiro Fukao 1 , Kazuhiro Saito 1 , Nobuyuki Toda 1 , Hiromichi Kataura 2 , Masashi Shiraishi 1 3
1 Department of Materials Engineering Science, Osaka university , Toyonaka, Osaka, Japan, 2 , National Institute of Advanced Industrial Science and Technology (AIST), Tukuba, Ibaraki, Japan, 3 , CREST-JST, Kawaguchi, Saitama, Japan
Show Abstract9:00 PM - U7.44
PECVD Grown Vertically Embedded CNTs for Field-emission Displays and Gated Transistors.
Yaser Abdi 1 2 , Javad Koohsorkhi 1 , shamsoddin Mohajerzadeh 1 , M Robertson 3 , R Thompson 3
1 electrical, thin film lab, tehran, tehran, Iran (the Islamic Republic of), 2 physics, university of tehran, Tehran Iran (the Islamic Republic of), 3 physics, Acadia University, Wolfville, Quebec, Canada
Show Abstract9:00 PM - U7.45
Ultra-low Loading of Electrocatalysts Supported on CNTs-based Electrode for DMFC
Chen-Hao Wang 1 , Yu-Tai Tsai 2 , He-Yun Du 2 , Li-Chyong Chen 3 , Kuei-Hsien Chen 3 4 , Han-Chang Shih 1 2
1 Materials Science and Engineering, National Tsing Hua Univ., Hsinchu Taiwan, 2 Institue of Materials Science and Nano Technology, Chinese Culture University, Taipei Taiwan, 3 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 4 Institue of Atomic and Molecular Science, Academia Sinica, Taipei Taiwan
Show AbstractThe direct methanol fuel cell (DMFC) is a power source which generates electrical power by the redox reaction feeding methanol fuel and oxygen directly to the anode and cathode respectively. In the recent years, the development of DMFC is mainly focused on higher performance but lower cost. For these reasons, the approaches of nano size electrocatalysts and high conductible carbon materials are applied to the manufacturing of membrane electrode assemblies (MEA) for DMFCs. The methanol oxidation is thought of a slower step in the reaction, and further work is required.Carbon nanotubes (CNTs) which have high surface area and good electronic conductance are suitable for electrocatalysts supports. In our case, CNTs were directly grown on carbon cloth (gas diffusion layer) and electrocatalysts (ie. Pt-Ru) were deposited on as-grown CNTs using physical vapor deposition (PVD). We assume that direct growth of CNTs not only has the above mentioned advantages, but the interfacial resistance between CNTs and carbon cloth can also be reduced comparing traditional catalyst inks screen-printed method. From scanning electron microscope (SEM) images, the CNTs are directly and densely grown on carbon cloth. From high resolution transmission electron microscope (HRTEM) images, the character of as-grown CNT is a bamboo-like structure and the diameter of CNT is about 20 nm. For the anodic application of MEA, the nano-size of Pt-Ru at atomic ratio 1:1 (0.40 mg/cm2 metal loading) electrocatalysts is deposited on the as-grown CNTs. E-TEKSM standard gas diffusion electrode (4.0 mg/cm2 Pt black) is used for the cathodic application. The membrane of MEA is Nafion® 117. The cell temperature is maintained at 80 C, and 1 M methanol (20 ml/min) and pure oxygen (1.0 l/min) are supplied to the respective anode and cathode. The cell performance shows that maximum power density is 102 mW/cm2.
9:00 PM - U7.46
Effect of Radicals on Carbon Nanotube Growth in CH4/H2 Plasma-enhanced Chemical Vapor Deposition
Atsushi Okita 1 , Yoshiyuki Suda 1 , Akinori Oda 2 , Junji Nakamura 3 , Atsushi Ozeki 1 , Hirotake Sugawara 1 , Yosuke Sakai 1
1 Graduate school of information science and technology, Hokkaido university, Sapporo, Hokkaido, Japan, 2 Graduate school of engineering, Nagoya insititute of technology, Nagoya Japan, 3 Graduate school of pure and applied sciences, Tsukuba university, Tsukuba Japan
Show AbstractCarbon nanotube (CNT) attracts great interest in its potentials such as high mechanical strength, heat capacity, elastic force and electronic properties and current density [1, 2]. Therefore, CNT applications are now being investigated and developed in LSI interconnection [3], transistor [4] and network-like interconnections [5]. These applications demand the accurate control of CNTs. But these controls have been not achieved yet. We used plasma-enhanced chemical vapor deposition (PECVD) for CNT growth because it can grow CNTs at lower temperature than the other methods. It is believed that plasma promotes gas dissociation and produces a lot of radicals and then these radicals promote CNT growth. However, PECVD is so complicated reaction that it is difficult to determine the plasma parameter. We focus on the correlation between CNT growth and plasma chemistry. In our previous work, we grew CNTs by CH4 RF plasmas and simulated its plasmas [6]. We compared experiment and simulation results in terms of the amount of carbon. We showed the total amount of carbon atoms calculated from simulation and deposited as CNTs were corresponding to the order. In this work, we have used CH4/H2 RF plasmas for CNT growth. We should reveal the role of radicals for the control of CNT properties. We compared experimental results with simulation ones. The detail of experimental setup and simulation model are described in our previous reports [6]. Gases are kept at pressures ranging from 1 to 10 Torr under the substrate temperature at 650oC. We used triple-layered catalysts (Al2O3/Fe/Al2O3 = 3/3/3 nm) for CNT growth. We evaluated the CNT parameters by a scanning electron microscope and transmission electron microscope. We analyzed CH4/H2 plasmas by one-dimensional fluid modeling. We calculated number densities and fluxes of plasma species. As the results, we obtained CNTs grown by CH4/H2 plasma at 10 Torr: CNT length = 4.85 μm , number density = 1.58×1011 cm-2 and diameter = 8-12 nm. In the simulation results, the most dominant radical for the CH4/H2 plasma at 10 Torr is CH3. Compared to the growth experiment by CH4 plasmas [6], CH4/H2 plasmas provided better CNTs with less impurities. We think that this is due to catalyst reduction and removing amorphous carbon by a effect of H radicals. In the simulation results, CH4 dissociation is promoted mainly by H radicals. This recombination reaction (CH4 + H → CH3 + H2) is dominant more than electron dissociative reaction (CH4 + e → CH3 + H + e). [1] M. S. Dresselhaus, G. Dresselhaus, Ph. Arouris (Editors), “Carbon Nanotubes Synthesis, Structure, Properties, and Applications”, Springer (2001) 287-425 [2] M. Meyyappan, et al., Plasma Sources Sci. Technol. 12 (2003) 205-216 [3] M. Nihey, et al., Jpn. J.Appl. Phys. 43 (2004) 1856-1859 [4] A. Javey, et al., Nature. 424 (2003) 654-657 [5] Y. Homma, et al., Appl. Phys. Lett. 81 (2002) 2261-2263 [6] A.Okita, et al., submitted
9:00 PM - U7.47
Production Of Carbon Nanofibers Using Sodium Chloride Supported Catalysts.
Ahu Dumanli 1 , Yuda Yurum 1
1 Materials Science and Egineering, Sabanci University, Istanbul Turkey
Show AbstractWednesday, April 19New presenting authorPoster U7.49Production Of Carbon Nanofibers Using Sodium Chloride Supported Catalysts. Emine Begum Gulsoy
9:00 PM - U7.48
Solid Phase Synthesis of Carbon Nanotubes From Organometallic Compounds at Ambient Pressure
Matthew Laskoski 1 , Teddy Keller 1 , Syed Qadri 1
1 , Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractCarbon nanotubes (CNTs) are formed in a bulk solid from thermal decomposition of metal-containing organometallic compounds in the presence of a carbonizing compound at ambient pressure. The method permits the large-scale production of CNTs in a solid, film, fiber, or powdered form. Heat treatment of various precursor compositions up to 1400 C results first in the decomposition of the organometallic compound and the formation of metal nanoparticles and ultimately the formation of carbon nanotubes at carbonization temperatures. In the synthesis, only a minute quantity of metal nanoparticles is required to initiate the formation of CNTs in the developing carbonaceous media. Characterization studies by X-ray diffraction, thermogravimetric analyses, Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) confirmed the formation of CNTs in the developing carbon composition above 600 C. The compositions exhibit interesting magnetic properties as a result of the presence of metal nanoparticles embedded in the CNT domain. The shaped compositions have structural integrity, which enhances their importance for potential nanoelectronic, electrical, magnetic, sensor, and structural composite applications.
9:00 PM - U7.49
Single Walled Carbon Nanotubes Synthesized by the Pyrolysis of Pyridine over Catalysts
Jiwen Liu 1 , David Carroll 1 , Jiri Cech 2 , Siegmar Roth 2
1 Physics, The Center for Nanotechnology and Molecular Materials , Wake Forest University, Winston Salem, North Carolina, United States, 2 , Max-Planck-Institute for solid state research, Stuttgart Germany
Show AbstractSingle walled carbon nanotubes are successfully synthesized by pyrolysis of pyridine over MgO supported Fe-Mo or Co-Mo catalysts in the presence of different atmosphere, pure H2 or mixture of H2 and NH3. The average diameters of SWNTs are ~1.5 nm and ~3nm for pure H2 and the mixture of H2 and HN3, respectively. Scanning tunneling spectroscopy (STS) studies show that the SWNTs grown from different atmospheres are doped with nitrogen in pyridine-type structure, and the donor feature occurs at different energy on the conduction band in local density of states due to the low nitrogen doping concentration.
9:00 PM - U7.50
Electron Transport in Semiconducting Chiral Carbon Nanotubes.
M. Kauser 1 , A. Verma 2 , P. Ruden 1
1 Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 2 School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractCarbon nanotubes have demonstrated potential to be key building blocks in the next generation of nano-scale electronic and opto-electronic devices [1,2]. However, good control over the nanotube fabrication process is one of the major challenges facing efforts that aim at practical uses of these materials. In particular, the chirality of carbon nanotubes is difficult to control, and at present transport experiments are often performed on tubes of unknown chirality. This gap in structural characterization is currently being filled by various theoretical modeling techniques. A reasonably detailed understanding of the behavior of electron transport in semiconducting zigzag (n,0) nanotubes at various temperatures and electric fields has been obtained from analytical models [3] and Monte Carlo simulations [4-6]. The primary scattering mechanisms explored are phonon assisted. Semiconducting chiral (n,m) carbon nanotubes have not been investigated, primarily because of their complicated electron and phonon dispersions associated with low symmetry. In this paper, we report on ensemble Monte Carlo simulations for electrons in chiral carbon nanotubes. The electronic band structure is evaluated within the framework of a tight-binding model. The principal electron scattering mechanisms are due to coupling to longitudinal acoustic, longitudinal optical, and radial breathing mode phonons. Both steady-state and transient phenomena are explored for various electric fields and temperatures. In addition, the Boltzmann transport equation is solved iteratively for very low applied fields to obtain low-field transport parameters. The results obtained for various chiral (n,m) carbon nanotubes are compared with semiconducting zigzag (n,0) carbon nanotubes of similar diameter, and with other carbon nanotubes, zigzag and chiral, of different diameters. Our calculations attempt to complete the picture of charge transport in single-walled semiconducting carbon nanotubes and to shed light on the diameter dependence of the low-field mobility and of the high-field electron velocity. References:[1] A. P. Graham, G. S. Duesberg, W. Hoenlein, F. Kreupl, M. Liebau, R. Martin, B. Rajasekharan, W. Pamler, R. Seidel, W. Steinhoegl, and E. Unger, Appl. Phys. A 80, 1141 (2005).[2] J. A. Misewich, R. Martel , P. Avouris, J. C. Tsang, S. Heinze, and J. Tersoff, Science 300, 783 (2003).[3] V. Perebeinos, J. Tersoff, and P. Avouris, Phys. Rev. Lett. 94, 086802 (2005).[4] G. Pennington and N. Goldsman, Phys. Rev. B 68, 045426 (2003).[5] A. Verma, M. Z. Kauser, and P. P. Ruden, J. Appl. Phys. 97, 114319 (2005).[6] A. Verma, M. Z. Kauser, and P. P. Ruden, Appl. Phys. Lett. 87, 123101 (2005).
9:00 PM - U7.51
High Yield Synthesis of Boron-Doped Single-Walled Nanotubes by Pulsed Laser Vaporization and Their Optical and Vibrational Properties
Jeff Blackburn 1 , Timothy McDonald 1 , Thomas Gennett 2 1 , Yanfa Yan 1 , Kim Jones 1 , Chaiwat Engtrakul 1 , Kelly Knutsen 1 , Randy Ellingson 1 , Anne Dillon 1 , Michael Heben 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 chemistry, Rochester Institute of Technology, Rochester, New York, United States
Show AbstractControl of the electronic properties of carbon single-wall nanotubes (SWNTs) is highly desirable for a variety of applications. Specifically, the ability to produce large quantities of highly pure n- and p-type nanotubes should allow the fabrication of sensors, hydrogen storage media, and optoelectronic devices such as solar cells. SWNTs doped with boron are conceptually appealing since boron should substitute in the carbon lattice without the generation of bonding defects. To date, however, attempts to produce high quality boron-doped SWNTs (B-SWNTs) by laser vaporization have been unsuccessful. Also lacking in the literature are comprehensive reports on the effects that boron doping has on the optical and vibrational properties of SWNTs. To this end, we have recently developed the first synthetic procedure for the high yield synthesis of B-SWNTs by pulsed laser vaporization. Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) confirm boron incorporation as sp2 bonded species at doping levels of 1 – 2% in the laser-produced B-SWNTs. Boron doping leads to enhanced solubility relative to pure carbon SWNTs in colloidal solutions, allowing for a detailed analysis of solvated B-SWNTs with steady state and time-resolved spectroscopies. We find that boron incorporation into the SWNT lattice modifies the Raman vibrational modes, especially for metallic nanotubes, inducing a Breit-Wigner-Fanno lineshape below the G-band even for de-bundled SWNTs.1 The absorption cross-section and photoluminescence quantum yield of the semiconducting B-SWNTs are also modified. These results shed light on how boron controls the SWNT electronic structure and modifies the electron-phonon coupling, and highlight the great potential of these materials for a variety of adsorption and optoelectronic applications.(1)Paillet, M.; Poncharal, P.; Zahab, A.; Sauvajol, J. L.; Meyer, J. C.; Roth, S. Physical Review Letters 2005, 94, 237401.
9:00 PM - U7.52
Fabrication and Characterization of a Multi-walled Carbon Nanotube Ionization Source.
Srividya Natarajan 1 , Charles Parker 1 , Scott Wolter 1 , Jeffrey Glass 1 , Brian Stoner 2 , Chris Bower 2
1 Department of Electrical & Computer Engineering, Duke University, Durham, North Carolina, United States, 2 , RTI International, Research Triangle Park, North Carolina, United States
Show AbstractMass spectrometers find application in a variety of fields from criminology to medical research. Miniaturizing a mass spectrometer would add features like portability, lower cost and lower power consumption. The three principal parts of a mass spectrometer are the ion source, mass sensor and ion detector. Carbon nanotubes have been proven to be excellent sources of field emission and should also serve as good sources for impact ionization. As part of the design of a microfabricated mass spectrometer, we have fabricated and investigated a carbon nanotube ionization source. Vertically aligned multi-walled carbon nanotubes (MWNTs) were deposited on a catalyst-deposited Si substrate using microwave plasma enhanced chemical vapor deposition (MPECVD). A 50 Å-thick layer of Fe (catalyst) was used. Our growth process uses an ammonia plasma pretreatment followed by the addition of methane during growth. Stable growth conditions have been established over temperatures ranging from 750 - 850 °C to yield aligned MWNTS with good control over length. The growth rate was calculated to be about 100nm/s. A test system with the ability to make current-voltage as well as emission profile measurements is used to characterize the MWNTs in this study. The stability of the MWNTs and emission currents as monitored by analyzing the residual gas content of the test chamber will be reported. The current-voltage characteristics of as-grown MWNTs, for different ambient gases (for example, nitrogen and argon), at pressures ranging from 1E-8 to 1E-4 Torr, will be presented. The ion currents for these gases, measured using a faraday cup array, will be reported. Further, we will present the emission profiles of these MWNTs for these gases and pressures.
9:00 PM - U7.53
Stability of Electron Field Emission from Various Types of Carbon Nanotubes Films.
Vijaya Kayastha 1 , Benjamin Ulmen 1 , Yoke Khin Yap 1
1 , Michigan Technological University, Houghton, Michigan, United States
Show AbstractCarbon Nanotubes (CNTs) are known to have excellent properties for electron field emission. Their high aspect ratio enables large electric field enhancement at their tips and initiates electron emission at relatively low applied field. However, commercial products based on the field emission of CNTs have not been demonstrated. The main reason is the absent of long-term emission stability from CNTs. The fundamental factors that contribute to the emission stability have not been well studied. Here, we found that stability of emission current from CNTs is directly related to their graphitic orders. We have tested various types of CNTs grown by thermal Chemical Vapor Deposition (CVD) and plasma enhanced CVD (PECVD). All multiwalled CNT films were grown on in a circular pattern of 0.385 cm2 on low resistance Si substrates. The field emission measurements were conducted in planar diode configuration, with cylindrical brass electrodes at a vacuum level of 2.0 X 10-7 mbar. The gap between the two electrodes was fixed at 1000 ± 10 µm to prevent possible arcing between the electrodes. As electrons are preferentially emitted from the tips of CNTs, vertically aligned nanotubes are considered as the idea cold cathode materials. Also, as they possess lower screening effect, evenly separated CNTs are preferred for this purpose. Thus CNTs grown by PECVD are seemingly ideal for field emission. However, our results shown that the emitted currents from these PECVD CNTs degraded by as much as 70% within an emission period of 20 hours. In contrast, randomly distributed CNTs grown thermal CVD can emit electrons at a threshold electric field as low as 1.3 V/micron. Furthermore, the initial emitted current is maintained within the tested period of 20 hours. Both Raman spectroscopy and transmission electron microscopy indicate that graphitic order of thee CNTs determines the field emission stability of CNTs. We also found that the field emission stability is strongly depends on the emitted current density. From these results, the upper performance limits of these CNTs for stable electron emission are determined. Details of these results will be discussed in the meeting.Y.K.Y acknowledges supports from the Michigan Tech Research Excellence Fund, Army Research Office (W911NF-04-1-0029), CNMS at ORNL, and NSF CAREER Award (0447555).
9:00 PM - U7.54
Fast, Position-Controlled Growth of Single-walled Carbon Nanotubes
Zuqin Liu 1 , David Styers-Barnett 1 , Alex Puretzky 1 , Christopher Rouleau 1 2 , Hongtao Cui 2 , Kai Xiao 1 , Ilia Ivanov 1 , Dongning Yuan 3 , Jie Liu 3 , David Geohegan 1 2
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Chemistry , Duke University, Durham, North Carolina, United States
Show AbstractWe have developed a novel laser-assisted CVD technique to synthesize single-walled carbon nanotubes (SWNTs) in a localized fashion with very high growth rates. The technique utilizes laser irradiation as a localized heat source to provide precise control over growth conditions in an area that is nominally a function of both laser spot size and substrate catalyst composition. The heating time, as measured in situ by a fast optical pyrometer, can be controlled precisely by choosing the proper laser power, repetition rate, pulse width, and numbers of laser pulses. Temperature profiles of a Si/SiO2 substrate, for example, showed controlled heating to CVD temperatures occurring in a few seconds. We note, however, that the heating efficiency can be improved further by using SiN membranes or TEM grids as a substrate. Present studies have focused primarily on the following: 1. Pushing the SWNT growth rate, which is currently ~20 microns/laser pulse under un-optimized conditions, to even higher levels; 2. Investigation of the lower limit of the time / temperature required for the formation of individual SWNTs and subsequent measurement of their electrical properties. We note that different thermal energies result in different SWNT chiralities and distinct electron transport properties (semiconductive vs. metallic), so this portion of our work may provide a vehicle to deliberate production SWNTs of a particular type in a particular area. Such work would accelerate insights into the physics of SWNTs.Research on Functional Nanomaterials at the Center for Nanophase Materials Sciences is supported by the U. S. Department of Energy, Division of Materials Science, Basic Energy Sciences.
9:00 PM - U7.55
Reversible Doping for Nanotube Sensors and Electronic Applications.
Satishkumar Chikkannanavar 1 , Leif Brown 1 , Hsing-Lin Wang 1 , Stephen Doorn 1
1 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractBandgap fluorescence from single-walled carbon nanotubes presents an opportunity for use of nanotubes for optically-based sensing. Because emission wavelengths are in the near-infrared region, nanotube optical sensing may be a useful approach for in-vivo applications as well. Reversible energy and charge-transfer bleaching of optical transitions will be demonstrated as signal transduction methods for sensing applications. Reversible doping through redox chemistry will also be demonstrated as an effective means of modulating nanotube conductivity properties.
9:00 PM - U7.56
Determination of Single Walled Carbon Nanotube Chirality by Probing the Empty and Filled States Using STM and Spectroscopy: Theory and Experiments.
Noureddine Tayebi 1 2 , Joseph Lyding 1 2
1 Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractA tight-binding approach that allows for the prediction of scanning tunneling microscopy (STM) images and scanning tunneling spectroscopy (STS) of carbon nanotubes (CNTs) at room temperature (RT) is used in conjunction with experimental RT STM images and STS to precisely determine the chirality of CNTs deposited on a silicon substrate. By applying a positive bias between the STM tip and the CNT, the empty states of the CNT are probed and bright stripes are observed around semiconducting CNTs. The direction of these stripes is reversed upon probing the filled states of the CNT (i.e., applying a negative bias between the tip and the CNT). The direction of the bright stripes is highly dependent on the chirality of the CNT and is due to the current enhancement that arises from the increase of the density of states of C-C bonds parallel to the CNT axis near the conduction band. This phenomenon is reversed under negative bias, where the density of states of the parallel C-C bonds is reduced and that of nonparallel bonds dominates. We take advantage of this phenomenon to determine the chirality of CNTs by comparing simulated and experimental STM images and STS.
9:00 PM - U7.57
Micro- and Nano-Scale Graphite Tubes and Cones from the Kola Peninsula, Russia.
John Jaszczak 1 2 , Svetlana Dimovski 3 , Stephen Hackney 4 , George Robinson 2 , Yury Gogotsi 3
1 Physics, Michigan Technological University, Houghton, Michigan, United States, 2 A. E. Seaman Mineral Museum, Michigan Technological University, Houghton, Michigan, United States, 3 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 4 Materials Science and Engineering, Michigan Technological University, Houghton, Michigan, United States
Show AbstractDespite its common occurrence in natural geological environments, new and unusual naturally occurring forms of graphite continue to be discovered. Several highly unusual forms of natural graphite have been found to occur in an alkaline syenitic pegmatite in the Hackman Valley, Khibiny Massif, Kola Peninsula, Russia. The morphologies and paragenesis of these unusual graphite forms suggest a possible hydrothermal origin.The graphite occurs macroscopically in two forms: as spherical aggregates up to 2 cm in diameter composed of friable, radially-aligned fibers ~20 μm in cross section, and as fine-grained surface coatings in cavities covering other minerals, including aegirine, strontian-apatite and K-feldspar. Optical microscopy and field emission scanning electron microscopy (FESEM) has revealed that the fibers are actually hollow channels whose walls are composed of tabular graphite crystals greatly elongated in the direction of the fiber axis and with their basal planes oriented parallel to the channel walls. Inside and among the channels occur graphite whiskers up to 2 μm in diameter and up to 15 μm in length. The fine-grained graphite coating on the surfaces of cavities is comprised almost solely of micro- and nano-scale graphite whiskers. The largest graphite whiskers are hollow scrolls, with the c-axis predominantly perpendicular to the whisker axis. Conical whiskers occur at the micro- and nano-scales. Nano-scale cones tend not to be hollow and may have a cone-helix structure. Transmission electron microscopy (TEM), Raman spectroscopy, and FESEM indicate that the whiskers are composed of well-ordered graphitic layers but are commonly coated by amorphous carbon. TEM also shows evidence of the occurrence of carbon nanotubes. The carbon nanotubes, which are dispersed in amorphous carbon and therefore difficult to image, are approximately 3 to 6 nm in diameter and can reach up to 100 nm in length. Although metal catalysts are commonly used in laboratory growth of carbon nanotubes, no evidence for metal catalyst particles in the Kola whiskers have been observed by TEM or by energy dispersive x-ray spectroscopy. More work is currently underway to try to extract these nanotubes from the amorphous carbon matrix for further characterization.
9:00 PM - U7.59
Construction of Supramolecular Nanotubes with Cationic Inner Surface and the Encapsulation Ability Toward Anionic Nanoparticles.
Naohiro Kameta 1 , Mitsutoshi Masuda 1 2 , Toshimi Shimizu 1 2
1 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan, 2 , CREST, Japan Science and Technology Agency (JST), Tsukuba Japan
Show AbstractGlycolipids self-assembled into nanotubes with controllable size dimensions.[1] Those nanotubes consist of bilayer structure, therefore, the inner and outer surfaces are covered with nonionic sugar hydroxy groups. We have reported that gold nanoparticles and spherical protein were encapsulated into the hollow cylinder structure of the nanotube by using capillary action. Nanotubes functionalized with different outer and inner surfaces should encapsulate nano- and bio-materials in a selective and effective manner. Herein we describe new methodology for selective formation of the supramolecular nanotube with a cationic innermost surface via self-assembly of a novel unsymmetrical bolaamphiphile 1 having 1-glucosamide group at one end of oligomethylene chain and an aminoethylamide group at the other end. We succeeded in the encapsulation of anionic nanoparticles and proteins into the hollow cylinder of the resultant nanotubes without capillary action.[2]In order to control the self-assembled morphologies of 1, we prepared two different types of solid of 1 prior to the self-assembly in water: One is a powder reprecipitated from methanol solution, and the another is a film prepared by solvent evaporation of dimethylformamide solution of 1. Self-assembly was carried out by allowing the hot aqueous dispersion of each solid of 1 to cool to room temperature at pH 10. Scanning transmission electron microscopic observation revealed that the self-assembly of the powder gave a tape-like structure, whereas the film mainly nanotube with 70-80 nm in inner diameters. Characterization of the molecular packing of the powder, the film, the resultant self-assembled tapes and nanotubes was performed by powder X-ray diffraction and IR spectroscopy. The powder and the self-assembled tape consisted of symmetrical monolayer lipid membranes (MLMs), in which molecules packed in antiparallel fashion. On the other hand, the film and the self-assembled nanotube consisted of unsymmetrical MLM with parallel molecular packing. The packing polymorphism of the MLM self-assembled from 1 strongly depends on the initial molecular packing, which are controllable by the solvent condition. All the results obtained suggested that the innermost surfaces of the nanotube should be covered with amino headgroup charged positively at neutral pH, and the outermost surfaces with sugar headgroup. This nanotube with positively charged hollow cylinder is expected to encapsulate anionic molecular objects and biopolymers via electrostatic interactions. Actually, the nanotube was able to effectively encapsulate anionic latex beads (20-40 nm) or spherical protein, ferritin (12 nm), into the hollow cylinder merely by mixing both aqueous dispersions.[1] T. Shimizu et al., Chem. Rev., 105, 1401 (2005), T. Shimizu et al., Chem. Mater., 16, 2826 (2004), Chem. Lett., 34, 232 (2005). [2] N. Kameta, M. Masuda, H. Minamikawa, N. V. Goutev, J. A. Rim, J. H. Jung, and T. Shimizu et al., Adv. Mater., in press.
9:00 PM - U7.6
Ferrocene and Tin-Center Functionalized Carbon Nanotubes for Nanoelectronics
Cengiz Ozkan 1 , Senthil Gurusamy-Thangavelu 1 , Chunglin Tsai 2 , Faruk Yilmaz 2 , Mihri Ozkan 2
1 Mechanical Engineering, University of California at Riverside, Riverside, California, United States, 2 Electrical Engineering, University of California, Riverside, California, United States
Show Abstract Functionalized SWCNTs are potential precursors, which exhibit versatile reactivity. We are efficiently using its reactive feature to develop the potential materials. In particular, the incorporation of Tin centers and ferrocene units on the surface of the SWCNT could exhibit improvement in solubility, semiconducting and redox properties. The oxidized SWCNTs attached with tin centers improve the solubility of the SWCNTs in organic solvents. Venturing into the further reactivity of functionalized CNTs affords the materials with special property. Array of ferrocene units in the walls of SWCNTs supposed to exhibit potential redox property. Characterization of these materials by SEM, EDS, FT-IR and Cyclic Voltammetry gives valuable information about the property of the same. These fabricated nanotubes are good candidates for applications in nanoelectronics.
9:00 PM - U7.60
Fabrication of Nanoporous Titania on Glass and Transparent Conducting Oxide Substrates by Anodization of Titanium Films.
Andrew Leenheer 1 2 , Alexander Miedaner 2 , Calvin Curtis 2 , Maikel van Hest 2 , David Ginley 2
1 Materials Science, Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show Abstract9:00 PM - U7.62
Self-Assembly Mechanisms of Synuclein Nanofibers
Sonal Padalkar 1 , Robert Colby 1 , Lia Stanciu 1
1 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractThe synuclein protein is of interest due to its capacity to self-assemble into long amyloid-like fibrils and function as a scaffold for metal nanowire formation. Synuclein is a 14.5 kDa protein found in brain. When fibrillation finds favorable conditions in-vivo, it leads to diseases such as Parkinson Disease, dementia and Hallervorden-Spatz disease. The goal of the present paper is to study the self-assembly mechanisms of synuclein into nanofibers, under various experimental conditions.The α-synuclein was self-assembled into fibers at 37 and 4 degree Celsius and different pH conditions, with gentle “rolling”. After the self-assembly experiments, the resulted samples were imaged by cryo-electron microscopy to confirm fiber formation. Cryo-Transmission Electron Microscopy is largely used for characterization of biological structures, such as tubular peptides, due to the necessity for electron beam damage minimization when imaging soft materials. Cryo-electron microscopy encompasses not only imaging of biological macromolecules, but also single particle, helical and tomography three-dimensional reconstructions. The samples were deposited on 3mm diameter quantifoil microscopy grids and embedded in a think vitreous ice layer by fast plunging into liquid ethane and then imaged under low dose conditions. The images of the synuclein self-assembled at 37 degree Celsius show the presence of nanofibers with a twisted morphology and diameter of about 8nm. The effects of metal cations and different pH values on the self-assembly mechanisms of synuclein were also investigated. At the temperature of 4 degree Celsius the self-assembly process slowed down. Hence, the cryo-electron microscopy imaging experiments were performed every 24 hours, to dynamically follow the kinetics of the self-assembly of the protein nanofibers. The morphology of the fibers at different moments during the self-assembly process suggested the synuclein fiber formation is a nucleation and growth process that is accelerated by the presence of metal cations such as Co2+ and Ca2+. The nucleation and growth process is enhanced by seeding the fibrillation solutions with pre-formed short synuclein fibers, which act as nucleation sites for the growth of new fibers.
9:00 PM - U7.63
Magnetic Nanotubes Prepared by Atomic Layer Deposition.
Mihaela Daub 1 , Mato Knez 1 , Kornelius Nielsch 1 , Ulrich Goesele 1
1 , Max-Planck-Institute for Microstructure Physics, Halle Germany
Show AbstractThe synthesis and study of magnetic nanostructures is an exciting and fast growing field, mainly because of their broad range of potential applications. Among these applications, a special interest represents nowadays magnetic data storage, microelectronics, or biomedical uses like cell separation or biosensing. Atomic layer deposition (ALD), is a very suitable method for the conformal deposition of oxide or metallic thin films in high aspect ratio pore structures, while offering the precise tuning of the layer thickness and high uniformity. We have used atomic layer deposition inside the pores of self-ordered or perfectly ordered alumina membranes to obtain magnetic nanotubes. The pores had the following dimensions: diameter 40-180 nm, pore length 1-20 µm and 210 nm interpore distance. Ni nanotubes with thickness of 5-40 nm were obtained by exposing the surface of the membrane to alternating cycles of NiCp2 (nickelocene) and hydrogen. After the Ni ALD, we deposited a layer of noble metal on top of the membrane, or we covered it with polymeric thin film in order to protect the tubes against oxidation. The physical properties of the Ni nanotubes were investigated by SEM and TEM. The influence of the layer thickness onto the magnetic anisotropy of the magnetic tubes was studied by using the SQUID. We also examined in this study CoCp2 (cobaltocene) as a potential precursor for obtaining Co nanotubes.Acknowledgement: This work was supported by the German Federal Ministry for Education and Research (BMBF), project number 03N8701.
9:00 PM - U7.64
Electron Diffraction on Boron Nitride Nanotubes
Raul Arenal 1 , Mathieu Kociak 2 , Annick Loiseau 3 , Dean Miller 1
1 MSD, Argonne National Laboratory, Argonne, Illinois, United States, 2 , LPS, University Paris Sud - CNRS, Orsay France, 3 LEM, ONERA- CNRS, Chatillon France
Show AbstractBoron nitride nanotubes (BNNTs) have been the subject of a significant scientific interest in recent years due to their unique physical properties, which make them a possible alternative to their carbon brethren in regards to possible applications. Nevertheless, in contrast to carbon nanotubes for which many studies have shown their atomic structure, for BNNTs there is a lack of detailed knowledge of their atomic structure. This structural knowledge is key to understanding the growth mechanism.Electron diffraction (ED) is a powerful technique that can provide information on both helicity and diameter, the two parameters that describe the atomic structure of a NT. In this communication, the ED and imaging techniques for the determination of the atomic structure of BNNTs will be presented. The intensities of ED patterns from individuals BNNTs (single-walled and multi-walled) as well as from bundles of these tubes have been recorded using a nanometer-sized coherent electron beam in the nano-area ED geometry [1]. To identify the structure of the nanotubes the experimental measurement of the helicities will be compared with the simulated diffraction images [2].This work was supported by the U. S. Department of Energy, Office of Science, under Contract W-31-109-ENG-38.[1] R. Arenal, M. Kociak, A. Loiseau and D.J. Miller (in preparation).[2] Ph. Lambin and A. A. Lucas, Phys. Rev. B, 56, 3571 (1997)
9:00 PM - U7.66
Noise in Carbon Nanotube Field Effect Transistors
Fei Liu 1 , Kang Wang 1 , Daihua Zhang 2 , Chongwu Zhou 2
1 EE, UCLA, Los Angeles, California, United States, 2 EE, USC, Los Angeles, California, United States
Show AbstractSingle-wall carbon nanotubes (SWNTs) are synthesized using a standard chemical vapor deposition method. CNT-FETs used in the study are backside gated with Ti/Au as metal contacts. In time domain, random telegraph signals (RTSs) have been studied in detail for different kinds of carbon nanotubes, including p-type semiconducting CNTs and ambipolar CNTs. It is believed that the random telegraph signals are due to the charge and discharge of defect centers located at the interface of carbon nanotube and SiO2 or underneath SiO2. Depending on the properties of the defect centers, random telegraph signals may be classified into Coulomb repulsive and Coulomb attractive ones. For a Coulomb repulsive RTS, the gate dependence of emission and capture constants show an exponential dependence in a p-type SWCNT-FET, which follows detailed balance relation. For a Coulomb attractive RTS, however, the emission and capture time constants show a non-exponential gate dependence. Furthermore, the Coulomb attractive center gives a small activation energy with the temperature varying from 0.25 K to 24 K. These seem to suggest that the mechanism of the Coulomb attractive random telegraph signal is attributed to the tunneling process between the CNT channel and the Coulomb attractive defect. In frequency domain, low frequency noise power spectra at different gate and source-drain bias were measured from 4.2 K up to room temperature, which shows 1/f behavior. The noise mechanisms as a function of voltage bias and device temperature are analyzed. The work was in part supported by MARCO Focus Center on Functional Engineered Nano Architectonics – FENA
9:00 PM - U7.67
Synthesis and Properties of Tungsten Disulfide Nanotubes.
Rita Rosentsveig 1 , Allexander Margolin 1 , Ifat Kaplan-Ashiri 1 , Ronit Popovitz-Biro 1 , Reshef Tenne 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel
Show Abstract9:00 PM - U7.8
Electrochemically Induced Dimensional Change in Individual Single-walled Carbon Nanotube/polypyrrole Heterostructures.
James Ly 1 , Alexander Lee 1 , Song Han 3 , Xiaolei Liu 3 , Daihua Zhang 3 , Mark Thompson 2 1 , Ari Requicha 4 , Chongwu Zhou 3 2
1 Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California, United States, 3 Electrical Engineering, University of Southern California, Los Angeles, California, United States, 2 Chemistry, University of Southern California, Los Angeles, California, United States, 4 Computer Science, University of Southern California, Los Angeles, California, United States
Show AbstractThe conducting polymer polypyrrole has the unique ability to reversibly change its physical size by the application of electrical stimuli; this electrochemical switching process results from both mass and charge transfer and is dependent on factors as the counterion, solvent, and nature of the monomer. However, published studies have focused on polypyrrole films approaching or exceeding one micron. Interest in nanoscale architectures and properties have led us to develop polypyrrole coated single-walled carbon nanotube heterostructures whose change in size may similarly be controlled by electrochemical means. The polymer growth was carried out electrochemically and conditions were explored to controllably produce a polypyrrole sheath of thickness ranging from 140 nm to 750 nm over single-walled carbon nanotubes as determined by AFM. These heterostructures of varying thicknesses were then electrochemically cycled to record thickness changes of 2-35%. Our results show that a direct correlation can be drawn between increasing polypyrrole thicknesses and resultant changes in size.
Symposium Organizers
Kornelius Nielsch Max-Planck-Institute of Microstructure Physics
Oliver Hayden IBM Research GmbH
Hirotaka Ihara Kumamoto University
Deli Wang University of California-San Diego
U8: Composites with Carbon Nanotubes II
Session Chairs
Thursday AM, April 20, 2006
Room 2002 (Moscone West)
9:00 AM - U8.1
Light Actuation of Polymer-nanotube Composites.
Samit Ahir 1 , Ali Tajbakhsh 1 , Eugene Terentjev 1
1 Physics, Cambridge University, Cambridge United Kingdom
Show AbstractRubbery composites containing multi-walled carbon nanotubes exhibit a reversible photo-mechanical actuation under irradiation with near infrared light. We demonstrate that this IR-actuation is reproducible across differing polymer systems, and that the nanotube response to photon absorption is predominantly responsible for the observed effect. We show that the speed of the nanocomposite actuation mechanism is faster than classical Debye relaxation. The magnitude, and most spectacularly - the sign of the response, are directly related to the degree of uniaxial alignment of the nanotubes in the matrix. We study this stress-induced alignment in some detail, both theroretically and experimentally (using synchrotron WAXS). The actuation stroke depends on the polymer being tested, however, the general response features are qualitatively identical for all nanotube-rubber systems tested. We propose a theoretical model for the reversible actuation behavior. The possible mechanism by which the nanotubes respond to low-energy photon stimulation involves the charge carrier separation and polaron formation around high defect density zones, leading to significant shape change of the tube - and the resulting macroscopic mechanical response of the composite. This approach, and underlying concepts should be applicable to various other (non-carbon) nanotube systems. [The early part of this work has appeared in Nature Mater. v.4 2005]
9:15 AM - U8.2
Nanotube-polymer Composites for Ultra-fast Photonics.
Alex Rozhin 1 , Vittorio Scardaci 1 , Frank Wang 1 , Ian White 1 , Bill Milne 1 , Andrea Ferrari 1
1 Engineering, University of Cambridge, Cambridge United Kingdom
Show AbstractCarbon nanotubes (CNTs) are at the centre of nanotechnology research. A variety of possible uses are suggested for this unique form of carbon, such as transistors, composites and field emission devices. However, many key applications of CNTs in electronic devices require individual tubes with given chirality for their optimum performance. Here we show how to exploit the electronic properties of composites made of CNTs with uncontrolled chirality and polymers to realise ultra-fast photonics devices. These devices are based on the nanotubes non-linear optical properties. CNTs behave as efficient saturable absorbers, i.e. they are pass-high filters for light, becoming transparent for sufficiently high power [1,2]. Saturable absorption is optimised by minimising the non-saturable losses, i.e. the scattering losses on bundles and the non-saturable absorption in the CNT themselves, the surfactant and the polymer matrix. We report the fabrication and characterisation of CNT-based transparent films, produced from water solutions and organic solutions. We characterize spray-coated pure single wall CNTs films and CNTs-polymer (Polyvinyl Alcohol (PVA), Polyvinyl Pyrrolidone (PVP) and polycarbonate (PC)) composites using UV-VIS-IR absorption and micro-Raman spectroscopy at different excitation wavelengths. Optical microscopy reveals areas with a homogeneous distribution of CNTs (over visible light wavelengths), which generate a strong Raman signal even though the individual nanotubes cannot be optically resolved. Saturable absorption is investigated using the Z-scan technique. We demonstrate that these composites can be used as passive photonic devices for fiber optics communications and for different laser systems. In particular we use CNTs–polymers composites for pulse shape control in erbium doped fibre lasers. 1.A.G. Rozhin et al. Chem. Phys. Lett. 405, 288 (2005).2.A. G. Rozhin et al. Thin Solid Films 464-465, 36 (2004).
U9: Separation of Carbon Nanotubes
Session Chairs
Thursday PM, April 20, 2006
Room 2002 (Moscone West)
9:30 AM - U9.1
Chromatographic Separation of Single Wall Carbon Nanotubes.
Barry Bauer 1 , Vardhan Bajpai 1 , Jeffrey Fagan 1 , Matthew Becker 1 , Erik Hobbie 1
1 Polymers Division, NIST, Gaithersburg, Maryland, United States
Show AbstractSize exclusion chromatography (SEC) has been used to separate single wall carbon nanotubes (SWNT) dispersed by chemical modification in organic solvents and by DNA in aqueous solution. The chromatographic detection includes size sensitive detectors, multi-angle light scattering (MALS) and intrinsic viscosity (IV), which can provide information on the size and shape of the SEC fractions. The dispersions were also characterized by small angle neutron scattering (SANS) and atomic force microscopy (AFM). Chemical modification was accomplished by covalent attachment of octadecyl amine to acid treated SWNT and by covalent attachment of butyl groups through free radical grafting. Both covalent attachment methods produced dispersions that contained impurities or clusters of SWNT. The DNA dispersions produced the best dispersions, being predominately single nanotubes.
9:45 AM - U9.2
Chiral-selective Separations of Single-walled Carbon Nanotube Suspensions.
Timothy McDonald 1 2 , Jeffrey Blackburn 1 , Chaiwat Engtrakul 1 , Marcus Jones 1 , Garry Rumbles 1 , Michael Heben 1
1 Basic Science, National Renewable Energy Lab, Golden, Colorado, United States, 2 Applied Physics, Columbia University, New York, New York, United States
Show AbstractCollections of single-walled carbon nanotubes with the same physical structure and electronic type will likely be required for many applications, including solar energy conversion. An obstacle is that current nanotube synthesis methods result in a distribution of metals and semiconductors with structure-dependent band gaps[1, 2]. Obtaining homogenous collections of a single nanotube type through purification of as-produced samples is a current goal of nanotube research. Purification of single-walled carbon nanotube (SWNT) distributions might be obtained by employing chirality-selective interactions with common surfactants. With this approach purification could be scaled up to obtain bulk quantities of specific SWNT species. Towards this end we have measured the interfacial binding energy of nanotubes in contact with various aqueous surfactant molecules as a function of tube type. The measurements are afforded by a sensitive Fourier-transform photoluminescence excitation (PLE) spectroscopy apparatus that permits continuous excitation from 350 to 950 nm and allows time dependent measurements as a function of temperature. Dynamic PL studies show that single-walled carbon nanotubes in suspensions diluted below the critical micelle concentration re-bundle at different rates depending on the nanotube’s chirality. Using information gained from these studies we describe processes for “sculpting” the PLE maps for solubilized SWNT species. For example, one approach uses oxidation of the surfactant molecules suspending the SWNTs to remove all but one semiconducting carbon nanotube from the full PLE spectrum. Optical absorption and PL studies indicate that the other nanotube types have been selectively bundled. Efforts to complete the chirality-selective purification by removing the bundled nanotubes will be described. 1.Iijima, S. and T. Ichihashi, Nature, 1993. 363(6430): p. 603-605.2.Haddon, R.C., et al., Mrs Bulletin, 2004. 29(4): p. 252-259.3.O'Connell, M.J., et al., Science, 2002. 297(5581): p. 593-596. The U.S. Department of Energy (DOE) Solar Photochemistry program funded by the Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences supported this work.
U10: Growth of Carbon Nanotubes
Session Chairs
Hirotaka Ihara
Ernesto Joselevich
Thursday PM, April 20, 2006
Room 2002 (Moscone West)
10:00 AM - *U10.1
Recent Development of Carbon Nano-technology
Sumio Iijima 1
1 Materials Science and Engineering, Meijo University, Nagoya, Aichi, Japan
Show AbstractCarbon nanotube is quite interesting nano-material applicable for logical circuit, electrical wiring and field emitter so on. Such applications are all aimed at nanotube itself. On the other hand, nanotube and related material of carbon nanohorn can be used as the nanoscale reaction chamber or nanocapsule for drug-delivering.Recently, we succeeded to immobilize the nano-sized Gd-oxide cluster in the nano-space of nanohorns, which may use as the probe material for the MR imaging. Futhermore, Biomolecular materials of DNA and some kind of proteins well interact with the nanotube and nanohorn, so that the carbon nano-technology widely covers the biochemical engineering. Interaction between carbon nano-materials and biomolecular materials is attracting subject, which broadens our understanding of bioprocess.
11:00 AM - U10.3
In-Flight Length Classification and Growth Kinetics of Aerosol Grown Carbon Nanotubes.
Soo Kim 1 2 , Michael Zachariah 1 2
1 Mechanical Engineering, University of Maryland, College Park, Maryland, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractWe describe an on-the-fly kinetic study and length classification of the aerosol growth of carbon nanotubes. The methodology employs electrical mobility classification of the CNT, which enable a direct measure of CNT length distribution in an aerosol reactor. The specific experiment employs two mobility classification steps. In the first step we mobility classify the nickel particle created by pulsed laser ablation so that a stream of monodisperse nickel particles were obtained. These predetermined particles were seeded to grow uniform diameter CNTs, which were grown with the addition of hydrocarbon and hydrogen in a heated aerosol reactor. A second mobility classification step allows us to determine the length distribution of the CNTs. By varying the temperature of the growth we were able to extract Arrhenius growth parameters. We found an activation energy (Ea) for growth ~80kJ/mol from acetylene, which is considerably lower than previous works for substrate grown CNTs (Ea=110~150 kJ/mol). Furthermore we observed that our aerosol CNT growth rate were about two orders of magnitude higher than substrate grown CNTs. On the basis of lower activation energy found in this approach, we proposed that the possible mechanism of gas-phase growth of CNT is correlated with both surface (Ea=29kJ/mol) and bulk diffusion (Ea=145kJ/mol) of carbon on nickel aerosol particles.
11:30 AM - **U10.4
Fullerene as a Supramolecular Shape-Shifter for Dimensionally-Regulated Nanostructures.
Katsuhiko Ariga 1 , Takashi Nakanishi 1
1 Supermolecules Group, National Institute for Materials science, Tsukuba Japan
Show Abstract The introduction of carbon nano-clusters such as fullerenes into electronic devices and the objective to construct functional, molecular-based electronic systems requires deep understanding of the interactions between the individual nano-size carbon building blocks and is currently one of the most challenging scientific research areas. One of the approaches is to fabricate dimension regulatable novel nano/mesoscopic architectures which exploit the advantageous intrinsic properties of their carbon-based building blocks. Our research is focused on the development of a facile way to fabricate carbon-rich materials with desirable dimensionality. Here we report the first example that the dimensionality and nanostructures of hierarchical fullerene architecture can be regulated by variation of the nature of the solvent system. Note that the newly synthesized fullerene derivative (1) serves as solvophilic hybrid material consisting of a π-conjugated sp2-carbon fullerene moiety and three sp3-C16 alkyl chains. Compound (1) forms hierarchical supramolecular objects in different solvents. The fullerene (1) in toluene/2-propanol (1/1) mixture self-assembles into spherical vesicle aggregates with an average diameter of 250 nm. TEM analysis reveals a wall thickness of 8-9 nm which is in agreement with a two-lamellae bilayer arrangement of (1). 1-Propanol directs the assembly of (1) to 1-D structures. The resulting fibers (possibly tubes) reveal lengths of over 20 μm and appear as partially twisted 2-D tape structures. When 1,4-dioxane is used, the brown-colored supernatant contains self-assembled 2-D single bilayer disks. The layer thickness determined from AFM is about 4.4 nm which corresponds to the thickness of an interdigitated bilayer of (1). When (1) was dispersed in a THF/ H2O (1/1) mixture, 3-D cone-shaped objects with submicron size were obtained. The XRD pattern of a cast film of (1) showed well-defined peaks with a d spacing of 4.28 nm. This value is again consistent with the interdigitated bilayer structure model where center-to-center separation of C60 moieties is estimated to be 4.3 nm. IR spectra of the cast films of 1 indicated all-trans conformation for CH2 vibrations. In relation to these observations, DSC displayed endothermic peaks. These data supports the hypothesis that the supramolecular assemblies of (1) can be based on the self-assembled bilayer structure. The obtained hierarchical supramolecular objects include vesicles, fibers (possibly tubes), disks and cones, providing hints for synthetic methodologies towards dimension regulatable novel carbon materials.
12:00 PM - U10.5
Direct Observation of Single-walled Carbon Nanotube Growth Using in-situ Transmission Electron Microscope.
Ming Lin 1 , Peiying Tan 1 , Yonglim Foo 1 , Chris Boothroyd 1 , Engsoon Tok 2
1 , Institute of Materials Research and Engineering, Singapore Singapore, 2 Department of Physics, National university of Singapore, Singapore Singapore
Show AbstractThe complete understanding of nucleation and growth mechanism of carbon nanotubes (CNTs) plays key role in the massive production of high-quality CNTs with controlled helicity and diameters. Although the CNTs have been studied extensively and are produced routinely by various of methods, the formation of CNT, especially for single-wall CNT (SWNT) is still unknown. Herein, we will present real-time observation of SWNT growth using an in-situ ultra-high vacuum transmission electron microscope at 650 C. We observe an isolated SWNT growth process in the TEM and provide direct evidence that catalyst remains as metallic Ni during steady growth state. The SWNTs preferentially grow on small sized catalysts (diameter ≤ 6 nm), and their diameter ratio of SWNT to catalyst is ~ 0.5-1. In our experimental condition, SWNT growth rate is determined and limited by the supply of the carbon reactant from the gas phase. During steady state growth, the Ni catalyst does not change to intermediate Ni3C phase. These SWNTs grow primarily through base-growth mechanism with C surface diffusion as main pathway on Ni catalyst. Under the same experimental conditions, larger Ni catalysts (diameter > 6 nm) result in nanocages formation. This is the first time where the growth of high-quality SWNTs has been studied in real-time under high vacuum growth conditions to minimize contamination effect. This insight developed through the in-situ TEM experiments, suggests that we can grow clean and large array SWNTs with controlled diameter for technological application through engineering monodispersed nanoscale catalyst.
12:15 PM - U10.6
Epitaxial Approaches to Carbon Nanotube Organization
Ernesto Joselevich 1 , Ariel Ismach 1 , David Kantorovich 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel
Show AbstractThe organization of carbon nanotube arrays on surfaces is a critical prerequisite for their large-scale integration into nanocircuits. We found that single-wall carbon nanotubes (SWNTs) catalytically produced on miscut c-plane sapphire wafers grow along the 0.2 nm-high atomic steps of the vicinal α-Al2O3 (0001) surfaces, yielding highly aligned, dense arrays of discrete nanotubes on a dielectric material. The nanotubes reproduce the atomic features of the surface, including steps and kinks. We also demonstrate the aligned growth of SWNTs by periodically nanofaceted surfaces, leading to the formation of either unprecedentedly straight and parallel nanotubes, or to wavy nanotubes loosely conformal to sawtooth-shaped faceted nanosteps. It is also possible to create carbon nanotube crossbar arrays in one growth step by simultaneous nanofacet-directed and field-directed growth in perpendicular directions. Lattice-oriented, atomic step-templated and nanofacet-directed nanotube growth may be rationalized as nanotube-extended versions of incommensurate lattice-directed epitaxy, ledge-directed epitaxy, and graphoepitaxy, respectively. These different modes of “nanotube epitaxy” open up many possibilities of assembling nanotube architectures from the bottom up by surface engineering.1. Ismach, A; Segev, L.; Wachtel, E.; Joselevich, E. Angew. Chem. Int. Ed. 2004, 43, 6140.2. Ismach, A; Kantorovich, D.; Joselevich, E. J. Am. Chem. Soc. 2005, 127, 11554.
12:30 PM - U10.7
Metal Ultrathin Film Catalyzed Ethanol Chemical Vapor Deposition of Single-Walled Carbon Nanotubes and Applications
Limin Huang 1 4 , Brian White 2 4 , Matthew Sfeir 2 4 , Mingyuan Huang 3 4 , Henry Huang 3 4 , Shalom Wind 1 4 , James Hone 3 4 , Stephen O'Brien 1 4
1 Applied Physics, Columbia University, New York, New York, United States, 4 , the Columbia Nanoscale Science & Engineering Center, New York, New York, United States, 2 Chemistry, Columbia University, New York, New York, United States, 3 Mechanical Engineering, Columbia University, New York, New York, United States
Show AbstractGrowth of high purity single-walled carbon nanotubes (SWNTs) with control over the tube orientation, location, diameter and length is a continued challenge for fundamental research and future nanotube-based device applications. Previous work on oriented growth required complicated sample preparation and growth procedures. We report a simple and efficient, laminar-flow-assisted chemical vapor deposition (CVD) process that can grow oriented and long single-walled carbon nanotubes (SWNTs) using a Co ultrathin film (~ 1 nm) as the catalyst and ethanol/water as carbon feedstock. No external electrical field guide or “fast heating” technique was used for the tube alignment. In the process, millimeter to centimeter-long, oriented and high quality SWNTs can grow horizontally on various flat substrate surfaces such as SiO2/Si, Si, Si3N4, Al2O3, traverse slits as large as hundreds of microns wide, or grow over vertical barriers as high as 20 mm, demonstrating that the carbon nanotubes are floating in the gas flow during the growth. The approach takes advantage of thin film technology and CVD growth using ethanol. Metal Co ultrathin films (1 nm) were used as the catalyst because they can be deposited by e-beam evaporation or sputtering, which is compatible with fabrication process in semiconductor industry. During the CVD, the as-deposited Co ultrathin film (~ 1 nm) balled up to form individual nanoparticles catalyst (~ 2-10 nm in diameter). This thin film deposition was also combined with ultrahigh resolution lithographic patterning to isolate individual ultrathin catalyst islands, which can be used to grow individual SWNTs with precise control over location and orientation. We use ethanol with trace amount of self-contained water (0.2-5 wt%) as the carbon source. The combination of ethanol and water may produce cleaner carbon nanotubes. The trace amount of self-contained water in ethanol may act as a mild oxidizer to clean the nanotubes and to elongate the lifetime of the catalysts. We also found that lifting up Co ultrathin film catalysts can grow longer carbon nanotubes.The controlled growth of high quality SWNTs is useful for fundamental research on individual carbon nanotubes. For instance, the suspended tube geometry allows characterization by multiple techniques, including Rayleigh scattering, Raman scattering, high-resolution transmission electron microscopy and electron diffraction, etc. The controlled growth will also benefit the development of nanotube-based devices for future applications, such as FETs, sensors, NEMS, etc. In terms of the applications, we will talk about (1) a technique that allows us to place a nanotube with the desired properties in a predetermined location by direct mechanical transfer; (2) SWNT-FET-based sensors for sensing changes in molecular conformation; and (3) preparation of transparent conducting thin films.
12:45 PM - U10.8
Assembly of Vertically Aligned Carbon Nanotube Multi-layers.
Xuesong Li 1 , Lijie Ci 1 , Pulickel Ajayan 1
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractBecause of their excellent properties and potential applications, many techniques have been developed to assemble carbon nanotubes. However, to assemble three dimensional structures with controlled length still remains a big challenge. In the present work we report a way to assemble vertically aligned carbon nanotube multi-layers by a multi-step chemical vapor deposition processes involving vapor phase catalyst delivery by an unprecedented bottom-up growth mechanism: the growth of every layer occurs on the silicon oxide substrate, even if previously grown layers entirely covers the substrate, indicating a very unique buried growth process that always forms at the bottom of the multiple layer assembly, lifting the rest up as it grows. This process can be repeated several × we have grown up to 8-layers in this fashion. It is shown that the carbon source can diffuse into the previous carbon nanotube forest and reach the substrate through both the top and the sides since the late layer can still grow even if the top or the sides of the previous layer are covered. Our results demonstrate a simple repeating growth process to assemble multiple layers of nanotube arrays with controlled length and number of layers. As each layer was produced in a different CVD run, it is possible to modify the growth parameters (e.g., the carbon source or the catalyst) to grow different structures in different runs to form a heterostructure, i.e., the singlewalled/multiwalled carbon nanotube multilayers, which was also already realized by our results. This multi-layer nanotube structure, with controlled length, could serve as long vertical via interconnects.
U11: Carbon Nanotube Devices
Session Chairs
Thursday PM, April 20, 2006
Room 2002 (Moscone West)
2:30 PM - **U11.1
Carbon Nanotube Field-Effect Transistors - Recent Observations
Joerg Appenzeller 1
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractOver the last years carbon nanotubes (CNs) have attracted an increasing interest as building blocks for nano-electronics applications. Due to their unique properties enabling e.g. ballistic transport at room-temperature over several hundred nanometers,[1,2,3] high performance CN field-effect transistors (FETs) have become feasible.[4,5,6] The successful improvement of CNFET performance however is merely a result of the application of established concepts. It is indeed a consequence of the detailed study of the material specific properties that have guided the research on CN-based transistor applications. An example of this is the critical observation that CNFETs in fact behave as Schottky barrier devices.[7,8] It was found that switching in nanometer size semiconductors, such as carbon nanotubes, contacted with source/drain metal electrodes is determined entirely by the metal/semiconductor interfaces and their field-dependence. Making use of this particular type of nanotube property, we have been able to gain important insights into the topic of multi-mode transport in CNFETs[9] and, more recently have related the performance of nanotube devices with their diameters.[10] Another important milestone has been the successfully fabrication of the first band-to-band tunneling CNFET with a much more abrupt switching behavior than can be obtained with any conventional transistor approach,[11] evidence that nano-materials can be used to create drastically different and more efficient switches in principal. [1] M. Fuhrer, H. Park, and P.L. McEuen, IEEE Trans. on Nanotech. 1, 78 (2002).[2] A. Javey, J. Guo, Q. Wang, M. Lundstrom, and H. Dai, Nature 424, 654 (2003).[3] S. Wind, J. Appenzeller, Ph. Avouris, Phys. Rev. Lett. 91, 058301 (2003).[4] A. Bachtold, P. Hadley, T. Nakanishi, and C. Dekker, Science 294, 1317 (2001).[5] A. Javey, H. Kim, M. Brink, Q. Wang, A. Ural, J. Guo, P. McIntyre, P. McEuen, M. Lundstrom, and H. Dai, Nature Materials 1, 241 (2002).[6] S. Wind, J. Appenzeller, R. Martel, V. Derycke, and Ph. Avouris, Appl. Phys. Lett. 80, 3817 (2002).[7] S. Heinze, J. Tersoff, R. Martel, V. Derycke, J. Appenzeller, and Ph. Avouris, Phys. Rev. Lett. 89, 106801 (2002).[8] J. Appenzeller, J. Knoch, V. Derycke, R. Martel, S. Wind, and Ph. Avouris, Phys. Rev. Lett. 89, 126801 (2002).[9] J. Appenzeller, J. Knoch, M. Radosavljevic, and Ph. Avouris, Phys. Rev. Lett. 92, 226802 (2004).[10] Z. Chen, J. Appenzeller, J. Knoch, Y.-M. Lin, and Ph. Avouris, Nano Letters 5, 1497 (2005).[11] J. Appenzeller, Y.-M. Lin, J. Knoch, and Ph. Avouris, Phys. Rev. Lett. 93, 196805 (2004).
3:00 PM - U11.2
Ambipolar Single Electron Transistor Using Side-Contacted Single-Walled Carbon Nanotube
Kenta Matsuoka 1 , Haruo Tomita 1 , Hiromichi Kataura 2 , Masashi Shiraishi 1 3
1 Department of Material Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka Japan, 2 , Nanotechnology Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan, 3 , CREST, Japan Science and Technology Corp., Kawaguchi Japan
Show Abstract A single-walled carbon nanotube (SWNT), which has a quasi-one-dimensional molecular structure with semiconducting or metallic properties, has been vigorously investigated, and it is recognized to be a considerably potential molecule in future nano-electronics devices. However, one of the largest obstacles that impedes the realization of nano-structured devices using SWNTs is difficulty in aligning SWNTs. In a chemical vapor deposition method, aligned growth of SWNTs can be achieved, but this method could easily introduce more defects in SWNTs compared with a laser ablation method. The introduced defects induces scattering of electrons, which prevents larger carrier mobility and longer spin coherency. Here, in this work, we report on the estimation of the ballistic conduction length in laser synthesized SWNT by measuring characteristics of side-contacted aligned SWNT single electron transistors (SETs) [1] fabricated by using an alternating current (ac) dielectrophoresis method. The sample was fabricated as follows. After the SWNTs were synthesized, they were purified by a conventional method [2]. After the purification, the SWNTs were ultrasonicated in ethanol for 10 h to dissolve bundles. Then centrifugation at 5000 rpm for 15 min was carried out to select well-dispersed narrow bundle SWNTs, and they were dispersed onto Si substrates with FET structures by using an ac dielectrophoresis method [3]. The source/drain electrodes were Au, and channel length was about 2 μm. From AFM observations, a radius of the SWNT bundle was estimated to be 11 nm. The aligned SWNT bundle wasn’t burnt out by an excess voltage in these experiments. From the temperature dependence of the resistance, the SWNT bundle was semiconductive, and also it showed ambipolar characteristics in FET operations. At 5 K, Coulomb staircase, Coulomb oscillation and Coulomb diamonds in both electron injection and hole injection were observed. To the best of our knowledge, this is the first report on an SET using an aligned-fabrication methodology and a solution process. The Coulomb island length was calculated by using an equation CΣ=2πLε(SiO2)ε0/ln(2L/r), where CΣ is total capacitance, L the Coulomb island length, ε(SiO2) the relative permittivity of SiO2, ε0 the electric constant and r the radius of the SWNT bundle. From a contour plot of ISD as a function of VSD and VG, CΣ was calculated to be 10.7 aF. For CΣ= 10.7 aF, L was estimated to be 200-300 nm, here the Coulomb island length in the device can be regarded as ballistic conduction length in the SWNTs, and hence it can be considered that the ballistic conduction length is 200-300 nm [1]. This result indicates that the laser-synthesized SWNTs are applicable to spin valve devices when 200 nm gap devices are fabricated.[1]K. Matsuoka et al., Chem. Phys. Lett. Accepted. [2]M. Shiraishi et al., Chem. Phys. Lett. 394 (2004), 110. [3]R. Krupke et al., Science 301 (2003), 344.
3:15 PM - U11.3
Doping Characteristics of Network Single-walled Carbon Nanotube Transistors by Molecule Encapsulation.
Masashi Shiraishi 1 4 , Shuichi Nakamura 1 , Tomohiro Fukao 1 , Megumi Ohishi 1 , Taishi Takenobu 2 4 , Yoshi Iwasa 2 4 , Hiromichi Kataura 3
1 Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan, 4 , CREST-JST, Kawaguchi, Saitama, Japan, 2 Institute of Materials Research, Tohoku University, Sendai, Miyagi, Japan, 3 Nanotech. Res. Inst., AIST, Tsukuba, Ibaragi, Japan
Show AbstractRecent several years, studies on molecular electronics using single-walled carbon nanotubes (SWNTs) have attracted many people. Especially, a field effect transistor (FET) application of SWNTs can be regarded as one of the best candidates of SWNT applications. There are two different approaches for realizing SWNT-FETs, that is, towards individual SWNT-FETs [1] and random network SWNT-FETs (RN-SWNT-FETs) [2]. The former has shown as high device performance as that of Si-based transistors, while the latter has opened the door towards plastic device applications of SWNTs because no heating processes are needed. In this sense, the RN-SWNT-FETs can be a potential device in a field of organic FETs. Our group has vigorously investigated the device characteristics of the RN-SWNT-FETs, succeeded in establishing a fabrication process without heating and obtained comparably high device performance (μ~3.6 cm2/Vs, on/off ratio ~ 100000) [3]. The next important milestone of the RN-SWNT-FETs is an achievement of carrier doping because the polarity control of FETs is an indispensable technique for realization of C-MOS logic circuits. In this work, we report on the doping characteristics of the RN-SWNT-FETs. The doping was carrier out by molecular encapsulation as proposed by Takenobu and co-workers [4]. We have selected TCNQ for a p-type dopant and TMTSF for an n-type dopant, and these dopant molecules were encapsulated inside of the SWNTs. The SWNTs were synthesized by a laser ablation method using Ni/Co catalytic metals at 1473 K, and were purified by a conventional method [5]. The doping procedure was shown in detail in the literature [4]. The doped SWNTs were dispersed onto Si substrates with back gate FET structures. Although undoped RN-SWNT-FETs always show ambipolar FET characteristics in vacuum because of desorption of oxygen, the doped RN-SWNT-FETs have shown a p-type character even after 60 h evacuation. This indicates the dopant was stable even in vacuum. As widely accepted, SWNT-FETs operate as a Schottky FET, which means the injected carriers can be controlled by a relationship between the Schottky barrier, gate voltage and a source-drain voltage. Thus the evaluation of the barrier height is important. The barrier height for holes was evaluated by measuring temperature dependence of resistance [6], the barrier was evaluated to be about 70 meV, while that of the undoped FETs was about 170 meV [3], which indicates the band structure of the SWNTs can be definitely modulated by the doping. We will also discuss the device performance of the doped FETs in detail and in addition, discuss carrier injection mechanisms in case of n-doping. [1] S.J. Tans et al., Nature 393 (1998), 49.[2] M. Shiraishi et al., CPL 394 (2004), 110.[3] T. Fukao et al., in preparation.[4] T. Takenobu et al., Nature Mat. 2 (2003), 687.[5] M. Shiraishi et al., CPL358 (2002), 213.[6] J. Appenzeller et al., PRL, M. Shiraishi et al., APL 87 (2005), 93107.
3:30 PM - U11.4
Experimental Analysis on Gate Capacitance in SWNT Electrochemical Transistor
Hidekazu Shimotani 1 2 , Takayoshi Kanbara 1 , Kazuhito Tsukagoshi 3 , Yoshinobu Aoyagi 3 4 , Hiromichi Kataura 5 , Yoshihiro Iwasa 1 2
1 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, 2 CREST, Japan Science and Technology Agancy, Kawaguchi, Saitama, Japan, 3 , RIKEN, Wako, Saitama, Japan, 4 Department of Information Processing, Tokyo Institute of Technology, Nagatsuda, Kanagawa, Japan, 5 Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Show Abstract Electrochemical transistor (ECT) is a kind of field-effect transistor (FET), where a gate voltage is applied via electrolyte instead of an dielectric layer in FET's. In an ECT configuration, an active layer is immersed in an electrolyte. A gate capacitor of an ECT is made of an electric double layer at the interface between the active layer and the electrolyte. Because a typical thickness of the electric double layer is as thin as ∼1 nm, gate couplings in ECT's are much more effective than those of thick dielectric layers (∼100 nm) in back-gated FET. Therefore, ECT is expected as a novel method to dope more carriers by low gate voltage than FET does. Especially, single-walled carbon nanotube (SWNT)-ECT's have created considerable interest for their potential application to chemical sensors. For applications of SWNT-ECT's to scientific research or practical use, it is necessary to understand how the gate voltage controls the charges in the SWNT. The aim of this research is to make the first demonstration of SWNT-ECT's with a four-terminal configuration including a reference electrode and to reach comprehensive understanding of the operation mechanism. In our experiments, a SWNT device with a source and a drain electrode was immersed in an electrolyte (0.1 M of LiClO4 in propylene carbonate) and the gate voltage applied by a Pt-coil counter electrode is precisely controlled with a Ag/Ag+ reference electrode. Because of the large capacitances and mesoscopic scales of SWNT-ECT's, the gate capacitances (C) of them are not simply equal to their electrostatic geometrical capacitances (Cgeom). In a SWNT-ECT, the charge accumulation by the gate voltage significantly shifts the Fermi energy of the SWNT. Indeed, multi-subband transports in SWNT-ECT's were observed in our experiments, which mean the Fermi energy was shifted to the second subband. Therefore, there must be voltage drop between the SWNT and the source and the drain electrodes to match their Fermi energy. The voltage drop is related to the accumulated charge by a factor called quantum capacitance (Cq). As a result, C of a SWNT-ECT is a series of Cgeom and Cq, which means C-1 = Cgeom-1 + Cq-1. In FET's C is approximated by Cgeom, because Cq is much larger than Cgeom. On the other hand, our experiments showed that Cgeom is comparable to Cq in SWNT-ECT's. In conclusion, we performed the first quantitative experimental analyses of SWNT-ECT's with a four-terminal configuration. We found that Cq and Cgeom are comparable to each other in the SWNT-ECT's.
3:45 PM - U11.5
Experimental Electron Phonon Coupling in Nanotubes
Andrea Ferrari 1 , Michele Lazzeri 2 , Stefano Piscanec 1 , John Robertson 1 , Francesco Mauri 2
1 Engineering, University of Cambridge, Cambridge United Kingdom, 2 Institut de Mineralogie et de Physique des Milieux Condenses, Universite Pierre et Marie Curie, Paris France
Show AbstractElectron-phonon coupling (EPC) is a key physical parameter in nanotubes. Ballistic transport, superconductivity, excited state dynamics, Raman intensity and phonon dispersions fundamentally depend on the electron phonon coupling. We present the direct experimental measurement of the optical phonons EPC in graphite and nanotubes [1-3]. We demonstrate that the EPCs for nanotubes of arbitrary chirality can be derived from graphite as well as directly fitted from their Raman spectra. The graphite EPCs are measured in four independent ways: from the optical phonon dispersions around Gamma and K [1], from the width of the G peak and from the Raman D peak dispersion [1]. We analytically prove that width and position of the Raman G- peak in metallic nanotubes are proportional to the square of the graphite electron phonon coupling and inversely proportional to the tube diameters. This explains the difference in the Raman spectra of metallic and semiconducting nanotubes and their trends as a function of tube diameter. We then directly fit the EPCs for nanotubes in the 0.8-2 nm diameter range. Our six independent experimental EPC measurements are validated by accurate DFT calculations in nanotubes and graphite [1-3]. Our results show that previous calculations significantly underestimated the experimental EPCs. 1.S. Piscanec et al. Phys. Rev. Lett. 93, 185503 (2004)2.M. Lazzeri et al. cond-mat/05087003.M. Lazzeri et al. Phys. Rev. Lett. in press (2005), cond-mat/0503278
4:15 PM - U11.6
First-Princiles study of workfunctions of SWNTs and DWNTs
Bin Shan 1 , Kyeongjae Cho 2
1 Applied Physics, Stanford University, Stanford, California, United States, 2 Mechanical Engineering, Stanford University, Stanford, California, United States
Show AbstractCarbon nanotube (CNT) electronics has been studied by many experimental groups, and the nature of source/drain contact to CNT has been a controversial research topic [1]. Many experimental and theoretical researches are mainly focused on metal electode/CNT interface study without examining the work function variation of different CNTs. To develop a detailed understanding on the metal/CNT interface electronic structures, we have performed first principles calculations to study work functions of single wall carbon nanotubes (SWNTs) and double wall nanotubes (DWNTs). Work functions of SWNTs show qualitatively different behavior depending on tube diameter [2]. Work functions of large SWNTs (diameter larger than 1nm) are practically identical to the graphene WF (4.7 eV). For smaller diameter tubes (diameter smaller than 1nm), work functions show strong dependence on the chirality. Surface dipoles and hybridization effects are shown to be responsible for the observed work function change in SWNTs. Work functions of DWNTs with outer shell dimeter larger than 1nm are also investigated and are found to change up to 0.5 eV from the grapheme WF. This WF change is explained by a chemical hardness and softness model which desctibes the charge equilibriation between the outer shell and smaller inner shell of DWNTs. The predicted work function variation on nanotube chirality can provide a possibility of engineering the electronic properties of SWNTs and DWNTs.[1]B. Shan and K. Cho, “Schottky Barrier at Metal/Nanotube Contact,” Phys. Rev. B 70, 233405 (2004).[2]B. Shan and K. Cho, “First principles study of work functions of single wall carbon nanotubes,” Phys. Rev. Lett. 94, p.236602 (2005).
4:30 PM - U11.7
Template-directed Self-assembly of Carbon Nanotube Field-Effect Transistors.
Stephen McGill 1 , Saleem Rao 1 , Pradeep Manandhar 1 , Seunghun Hong 2 , Peng Xiong 1
1 Physics and MARTECH, Florida State University, Tallahassee, Florida, United States, 2 Physics and Nano-Systems Institute, Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe pattern self-assembled monolayers (SAMs) of organic molecules to control the interactions between carbon nanotubes and inorganic surfaces.1 Deposition of the SAMs forms a template that directs the placement and alignment of nanotubes on lithographically defined electrodes to create field-effect transistors (FETs). Our assembly process is highly scalable and we demonstrate parallel fabrication of five FETs on a single substrate. These FETs exhibit large “on” currents of ~1μA with “on/off” ratios as high as 106. Furthermore, our devices exhibit novel functionality by operating hysteresis-free without passivation of the nanotube or electrode surfaces. These features may lead to enhanced performance for delicate sensing applications utilizing these devices. We discuss the electrical characteristics of these FETs and contrast them with other state-of-the-art devices and assembly strategies. This work has been supported by NSF NIRT grant ECS-0210332.1 S.G. Rao, L. Huang, W. Setyawan, and S. Hong, Nature 425, 36 (2003).
4:45 PM - U11.8
Electrical Transport in Carbon Nanotube Y-junctions- a Paradigm for Novel Functionality at the Nanoscale.
Prabhakar Bandaru 1 2 , Chiara Daraio 1 2 , Sungho Jin 1 2 , Apparao Rao 3
1 MAE, UC, San Diego, La Jolla, California, United States, 2 Materials Science Program, UC, San Diego, La Jolla, California, United States, 3 Physics department, Clemson University, Clemson, South Carolina, United States
Show AbstractCarbon Nanotube (CNT) based electronics offer significant potential, as a nanoscale alternative to silicon based devices, for novel molecular electronics technologies. So far, the elucidation of fundamental properties of nanotubes and nanowires and their applicability for electrical devices has mainly focused on adopting the MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) paradigm, where a nanotube serves as the channel between lithographically fabricated electrodes (viz., Source and Drain), and an electrically insulated gate modulates the channel conductance. In other demonstrations, cumbersome Atomic Force Microscope (AFM) manipulations of nanotube properties have been utilized. To realize a truly nanoelectronic architecture, it is desirable to have a fully integrated nanotube based technology, where both devices and interconnects are based on CNTs. Additionally, it would be attractive, in proposing new nanoelectronic elements, to harness new functionalities, peculiar to novel CNT forms such as Y-junctions. We report on the electrical properties of CNT based Y-junctions, with the ultimate aim of implementing a nanotube based circuit topology and electronics. The Y-junction morphologies have a natural asymmetry at the junction region due to the presence of non-hexagonal defects which are required for energy minimization. The carrier delocalization and the inevitable presence of catalyst particles, introduced during growth, at the bend induce a net charge and scattering which can be exploited in constructing electronic devices. Our preliminary electrical measurements on these CNT Y-junctions reveal the possibilities of using these for switching and transistor related applications1. We have assembled and electrically characterized the DC resistance and the AC impedance of several Y-junctions 2. The observation of inverting/switching in a three-terminal Y-junction, up to 42 kHz, alerts us to the vast potentialities of the Y-junction devices in the development of nanoelectronic components including inverters, logic gates, and frequency mixers. An electrical impedance model of a MWNT Y-junction will be presented which will help gain an understanding of the current transport mechanisms in these structures.1. P. Bandaru et al, “Novel electrical switching behavior and logic in carbon nanotube Y-junctions”, Nature Materials, vol. 4(9), 663-666, (2005)2. N. Gothard, et al. “Controlled growth of Y-junction nanotubes using Ti-doped vapor catalyst”, Nanoletters 4, 213-217 (2004).
5:00 PM - U11.9
Engineering the Electronic Properties and Mechanical Configurations of Carbon Nanotubes Interfaced With Silicon Surfaces Using the UHV-STM.
Peter Albrecht 1 , Joseph Lyding 1
1 Electrical and Computer Engineering, University of Illinois, Urbana, Illinois, United States
Show AbstractA room-temperature UHV-STM is used for the imaging, electrical characterization, and mechanical manipulation of single-walled carbon nanotubes (SWNTs) adsorbed onto Si surfaces. We have developed a dry contact transfer (DCT) technique for the in situ deposition of isolated SWNTs which preserves the cleanliness of the UHV-prepared Si surface [1]. A pristine SWNT-Si interface is critical to elucidating the sensitivity of both metallic and semiconducting SWNTs to subtle fluctuations (both naturally occurring and STM-mediated) in the local topographic and electrostatic environments.We will demonstrate how nanolithographic patterning of the H-passivated Si(100)-2x1 surface [2] offers intriguing opportunities for enhancing the mechanical coupling between the SWNT and the Si substrate and tuning the conductance of the hybrid SWNT-Si system. For semiconducting SWNTs on degenerately doped n-type Si(100)-2x1:H, recent results suggest that negatively charged Si dangling bonds positioned in close proximity to the SWNT shift the Fermi level towards the valence band edge – an effective p-type electrostatic doping of the nanotube locally gated by the depassivated Si. Piva and coworkers have observed a similar energetic shift in the onset of conduction through individual styrene molecules bound to Si(100) after modifying the charge state of a proximal Si surface atom [3].Current Imaging Tunneling Spectroscopy (CITS), where a full dc I-V characteristic is acquired at each pixel of a topographic image, allows us to visualize the electronic structure of a hybrid SWNT-Si(100) surface. From these spatial maps of the tunneling current and conductance, we will detail the energy and length scales associated with these local STM-induced modifications to the SWNT and their implications for nanotube-based devices and interconnects on semiconductor surfaces.We will also show how the STM tip can be leveraged for the manipulation of SWNTs having a wide range of lengths (tens to hundreds of nm). Such mechanical actuation capabilities allow us to vary the orientation of the SWNT with respect the underlying Si dimer rows in order to probe registration-dependent electronic phenomena predicted theoretically [4]. For an isolated SWNT on Si(100)-2x1, a pronounced modification of the tunneling conductance accompanies the transition from parallel to perpendicular alignment. By combining selective patterning of H-Si(100) with STM manipulation, we can also stabilize individual SWNTs in strained configurations for subsequent electrical measurement. [1] P.M. Albrecht and J.W. Lyding, APL 83, 5029 (2003).[2] J.W. Lyding et al., APL 64, 2010 (1994).[3] P.G. Piva et al., Nature 435, 658 (2005).[4] S. Barraza-Lopez, P.M. Albrecht, N.A. Romero, K. Hess, cond-mat/0510477 (2005).
5:15 PM - U11.10
Highly Flexible and Transparent Single Wall Carbon Nanotube Network Gas Sensors Fabricated on PDMS Substrates.
Seung-Beck Lee 1 2 , Chi-Won Cho 1 , Chae-Hyun Lim 2 , Ju-Fan Zhang 2 , Bong-Hyun Park 2 , Hyung-Seok Jeon 2 , Heongkyu Ju 2 , Cheol-Jin Lee 3
1 Electronics and Computer Engineering, Hanyang University, Seoul Korea (the Republic of), 2 Nanotechnology, Hanyang University, Seoul Korea (the Republic of), 3 Electronics and Computer Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractWe report on the fabrication of thin-film gas sensors on PDMS substrates using networked thin-film of single walled carbon nanotube (SWCNT) bundles. The catalytic CVD synthesized SWCNT bundles were dispersed in sodium dodecyl sulfate (SDS) solution at various ultrasonic power. SWCNT network thin-film was initially formed, using vacuum filteration, on ~20 nm pore alumina membrane filter surfaces. To transfer the SWCNT bundle thin-film onto a flexible substrate, PDMS was cured directly on the filter. After filter removal, a highly flexible SWCNT thin-film was formed on the PDMS surface. Thin-film resistances ranging from 0.2 kΩ/sq to 2.8 kΩ/sq with optical transparency of 40 to 80 % at 400 nm wavelength was produced by changing SWCNT density with no noticeable fluctuation in conductance at 180 degree bending, demonstrating high flexibility. When exposed to NH3 gas, the change in thin-film conductance increases by 10% when SWCNT density was reduced by 50%, which may be due to the higher percentage of SWCNTs partially freed from the surface during PDMS transfer for lower SWCNT density films increasing surface area. It was also found that reducing the bias voltage from 1 V to 0.3 V resulted in reduced sensor recovery times (from 30% after 5 min to 80%), which we attribute to SDS surfactant remaining on the SWCNT surface decreasing adhesion strength of NH3 gas molecules. We will present flexible thin-film’s SWCNT bundle density and average length dependent optical, mechanical and electrical characteristics. Gas sensing operation of the SWCNT flexible thin-film depending on thin-film preparation will also be presented
5:30 PM - U11.11
Axial Strain Induced Torsion in Single Walled Carbon Nanotubes as the Basis for High Quality, Integrated NEMS Devices.
Moneesh Upmanyu 1 , Haiyi Liang 1
1 Engineering Division, Materials Science Program, Colorado School of Mines, Golden, Colorado, United States
Show AbstractUsing classical molecular dynamics and empirical potentials, we show that the axial deformation of single-walled carbon nanotubes (SWCNTs) is coupled to their torsion. The axial strain induced torsion (a-SIT) is limited to chiral nanotubes - graphite sheets rolled around an axis that breaks its symmetry. Small strain behavior is consistent with chirality \& curvature-induced elastic anisotropy (CCIEA) - CNT rotation is equal and opposite in tension and compression, and decreases with curvature and chirality. The large-strain compressive response is remarkably different. The coupling progressively decreases, in contrast to the tensile case, and changes its sign at a critical compressive strain. Thereafter, it untwists with increasing axial strain and then rotates in the opposite direction, i.e. the same sense as under tension. This suggests that the response is now dictated by a combination of non-linear elasticity and CCIEA. The implications of the richness of this behavior are discussed.
5:45 PM - U11.12
Thermal Conductivity of Multi-walled Carbon Nanotube Heat Removal Pillars Measured by the Delta Vgs Method.
Hiroki Shioya 1 2 , Taisuke Iwai 1 2 3 , Daiyu Kondo 1 2 , Mizuhisa Nihei 1 2 , Yuji Awano 1 2
1 , Nanotechnology Research Center, Fujitsu Laboratories Ltd., Atsugi Japan, 2 , Fujitsu Ltd., Kawasaki Japan, 3 , Compound semiconductor Device Laboratory, Fujitsu Laboratories Ltd., Atsugi Japan
Show Abstract