Symposium Organizers
Ranganathan Shashidhar Geo-Centers Inc.
James G. Kushmerick National Institute of Standards and Technology
Heiko B. Weber University of Erlangen-Nurnberg
Nongjian J. Tao Arizona State University
Symposium Support
Defense Advanced Research Projects Agency
Forschungszentrum Karlsruhe Institute for Nanotechnology
National Institute of Standards and Technology
N1: Theory of Charge Transport
Session Chairs
Tuesday PM, April 18, 2006
Room 3014 (Moscone West)
2:45 PM - **N1.1
Molecular Electronics: In Search of New Paradigms
Avik Ghosh 2 , Supriyo Datta 1
2 Electrical Engineering, University of Virginia, Charlottesville, Virginia, United States, 1 Electrical & Computer Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractTuesday, 4/18New Presenting Author1:45 pm *N1.1Molecular Electronics: In Search of New Paradigms. Avik Ghosh
3:15 PM - **N1.2
Current-induced Mechanical Effects in Nanoscale Junctions.
Massimiliano Di Ventra 1
1 , University of California, San Diego, La Jolla, California, United States
Show AbstractTransport of electrical charge across a nanoscale junction is accompanied by many effects like transfer of energy between electrons and ions [1] and consequent heating of the junction [2], and forces on ions due to current-induced variations of the electronic distribution [3, 4]. I will discuss these effects in atomic [5] and molecular wires [6] and focus on their description at the atomic level. In particular, I will discuss their relative role in the stability of nanojunctions, the bias dependence of the current and noise on heating and compare these findings with experimental results. Work supported by NSF.[1] Y-C. Chen, M. Zwolak and M. Di Ventra, “Inelastic current-voltage characteristics of atomic and molecular junctions”, Nano Lett. 4, 1709 (2004).[2] Y-C. Chen, M. Zwolak and M. Di Ventra, “Local heating in nanoscale conductors”, Nano Lett. 3, 1691 (2003).[3] Z. Yang, M. Chshiev, M. Zwolak, Y.-C. Chen, and M. Di Ventra “Role of heating and current-induced forces in the stability of atomic wires”, Phys. Rev. B 71, 041402 (2005).[4] M. Di Ventra, Y.C. Chen, and T.N. Todorov, "Are current-induced forces conservative?", Phys. Rev. Lett. 92, 1776803 (2004).[5] Y.C. Chen, M. Zwolak, M. Di Ventra, “Inelastic effects on the transport properties of alkanethiols”, Nano Lett. 5, 621 (2005).[6] Y.C. Chen and M. Di Ventra, “Effect of electron-phonon scattering on shot noise in nanoscale junctions”, Phys. Rev. Lett. 95, 166802 (2005).
3:45 PM - N1.3
First Principles Modeling of Spin-Dependent Transport Through Molecules.
Soren Smidstrup 1
1 Niels Bohr Institute, Atomistix A/S, Copenhagen Denmark
Show Abstract4:30 PM - **N1.4
Parametric Flow of Effective Hamiltonians in ab initio Transport Calculations.
Ferdinand Evers 1
1 Institute of Nanotechnology, Research Center Karlsruhe, Karlsruhe Germany
Show AbstractAb initio calculations for transport properties of single molecules based on the density functional theory (DFT) often appear to fail giving a quantitative description of the conductance that is seen in available experimental current-voltage curves (I-V). However, apart from the zero bias conductance the I-V traces contain a lot more and very important characteristic information, like step positions and inelastic satellite peaks. Many such features can be analyzed in great detail by monitoring the flow of the self consistent (Kohn-Sham) Hamiltonian (or derived quantities) under a variation of model parameters. Some examples of such parameters are the chemical potential of the leads, a gate voltage, the inter-electrode distance, the number of electrode atoms kept in the DFT calculation etc.. The talk will present results of recent studies that have utilized this idea. It will be demonstrated, that such approaches can provide a quantitative understanding not only in principle, but also in practical applications. Several examples of the latter will be presented.
5:00 PM - N1.5
Ab inito Calculation of Electron Transport Through Single Molecules by the RTM/NEGF Method.
Kenji Hirose 1 , Nobuhiko Kobayashi 2
1 Fundamental Research Laboratories, NEC Corporation, Tsukuba, Ibaraki, Japan, 2 Nanotechnology Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
Show Abstract5:15 PM - N1.6
π-logic: A New Approach Allowing for all Boolean Logic Operations to be Performed in Single Molecules.
Marleen van der Veen 1 , Harry Jonkman 1 , Jan Hummelen 1
1 Molecular Electronics, Materials Science Centre Plus, University of Groningen, Groningen Netherlands
Show Abstract5:30 PM - N1.7
Microscopic Near-field Physics of Single-molecules.
Yongqiang Xue 1
1 College of nanoscale Science & Engineering, University at Albany-SUNY, Albany, New York, United States
Show AbstractRecent developments in single-molecule measurements offer the possibility to observe and manipulate single experimental realization of quantum systems without requiring ensemble average. Single-molecule signals provide significant insights into the interaction of single-molecules with their nanoenvironments. In the device context, the detection of single-molecule signals often implies the exploitation of the different kinds of near-fields existing spontaneously or artificially in immediate proximity to the surface of electrodes/substrates. In this talk we show that the concept of near-field provides a unifying theme covering numerous domains of single-molecule science and technology (electronics, photonics, phononics, . . .), which mainly concerns phenomena involving evanescent fields (electronic density surface wave, evanescent light, local electrostatic and magnetic fields, . . .) or localized interatomic or molecular interactions. A major task in single-molecule science and technology is thus to realize control and optimization of such fields and local interactions through bottom-up atom-engineering. In particular, the physics associated with all near-field concepts may serve as a general framework for the design of physical or chemical nanostructures (photonic and electronic) able to control the fundamental electronic and photonic processes in the near-field interaction zone. Microscopic theoretical and computational frameworks will be introduced that enable detailed analysis of the near-field concepts.
5:45 PM - N1.8
Electronic Transport Properties through Nanoscale Materials by First Principles Calculations.
Hiroshi Mizuseki 1 , Rodion Belosludov 1 , Amir Farajian 1 , Olga Pupysheva 1 , Chiranjib Majumder 2 , Jian-Tao Wang 3 , Hao Chen 4 , Nobuaki Igarashi 1 , Tomoki Uehara 1 , Yoshiyuki Kawazoe 1
1 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, 2 Novel Materials and Structural Chemistry Division, Bhabha Atomic Research Center, Mumbai India, 3 Institute of Physics, Chinese Academy of Sciences, Beijing China, 4 Physics Department, Fudan University, Shanghai China
Show AbstractFor many years, progress in microelectronics has been associated with a reduction in the minimum feature size of integrated circuits. However, this trend, as described by Moore's Law, seems to be ending due to process and physical limitations, and therefore a new paradigm shift has been expected. Molecular devices are potential candidates for this next step, and they would make it possible to realize the most advantageous devices. However, a major predicament and source of expenditure is necessary that such a large number of organic molecules can be obtained by synthetic chemistry, so any means of exploring their properties and behavior in order to predict the relevant properties of a molecule in advance of its synthesis would be extremely useful. One established approach is to use the computational methods developed for the prediction of a stable molecular structure and conductance properties.Our group has covered a wide range of molecular systems which have potential application in molecular electronics using first-principles calculations [1]; supramolecular enamel wires (covered wires) [2], connection between organic molecules and metal electrodes [3], self-assembled nanowires on silicon surface [4]. Moreover we examine electronic transport properties through small molecules for a building block, such as benzene [5], bent carbon nanotube [6], DNA, porphyrin and ferrocene molecules and so on. In this presentation, we will present recent investigations related to nanoscale devices, using molecular orbital analysis.[1] http://www-lab.imr.edu/~mizuseki/nanowire.html[2] R. V. Belosludov, A. A. Farajian, H. Baba, H. Mizuseki, and Y. Kawazoe, Jpn. J. Appl. Phys., 44, 2823 (2005).[3] C. Majumder, H. Mizuseki, and Y. Kawazoe, J. Chem. Phys., 118, 9809 (2003).[4] J.-T. Wang, E. G. Wang, D. S. Wang, H. Mizuseki, Y. Kawazoe, M. Naitoh, and S. Nishigaki, Phys. Rev. Lett., 94, 226103 (2005).[5] F. Jiang, Y. X. Zhou, H. Chen, R. Note, H. Mizuseki, and Y. Kawazoe, Phys. Rev. B, 72, 155408 (2005).[6] A. A. Farajian, B. I. Yakobson, H. Mizuseki, and Y. Kawazoe, Phys. Rev. B, 67, 205423 (2003).
Symposium Organizers
Ranganathan Shashidhar Geo-Centers Inc.
James G. Kushmerick National Institute of Standards and Technology
Heiko B. Weber University of Erlangen-Nurnberg
Nongjian J. Tao Arizona State University
N2: Transport in Molecular Electronics
Session Chairs
Wednesday AM, April 19, 2006
Room 3014 (Moscone West)
9:00 AM - **N2.1
Single Molecule, Single Electron Transistors and Self-assembled Molecular Electronic Circuitry.
Thomas Bjornholm 1
1 Nano-Science Center & Dept of Chemistry, University of Copenhagen, Copenhagen Denmark
Show AbstractOrganic molecules are becoming increasingly important as the active component in electronic devices both in the form of low-tech high market volume applications (e.g. organic light emitting diodes) and, on a single molecule level, in basic research test systems. The presentation will present the most recent results on single molecule transport measurements at 4 Kelvin through single oligo-p-phenylenevinylene and C60 molecules physiosorbed or chemisorbed in a gap of about 2 nm between source and drain electrode of a single electron transistor device (SET) [1-2]. The measurements reveal the intimate relation between transistor characteristics and the position of the molecular redox states, vibronic structure, spin, electronic coupling to electrodes and image charges in the electrodes resulting in charge localization on the molecule. The possibilities to self-organize entire molecular electronic circuitry will be discussed [3-5] and recent structural studies of rotaxane based nanomechanical switching in condensed Langmuir films will be presented [6].Key references:[1A] ]Kubatkin, S., Danilov, A., Hjort, M., Cornil, J., Brédas, J-L., Stuhr-Hansen, N., Hedegård, P. & Bjørnholm, T. Single-electron transistor of a single organic molecule with access to several redox states. Nature 425, 698-701 (2003);[1B] Hedegård, P & Bjørnholm T. Charge transport through image charge stabilized states in a single molecule single electron transistor. Chem. Phys. (2005) in press.[2] Danilov, A.V., Kubatlin. S.E., Kafanov, S.G., Bjørnholm T. Strong electronic coupling between single C60 molecules and gold electrodes prepared by quench condensation at 4 Kelvin. A single molecule three terminal device study. Faraday Discussions (in press)[3] Hassenkam, T., Moth-Poulsen, K., Stuhr-Hansen, N., Nørgaard, K., Kabir, M.S., Bjørnholm T. Self-assembly and conductive properties of molecularly linked gold nanowires. Nano Letters 4, 19-22 (2004).[4] Nielsen, L. K., Bjørnholm, T. & Mouritsen, O. G. Fluctuations caught in the act. Nature 404, 352 (2000).[5] Nørgård, K., Bjørnholm, T., Supramolecular Chemistry on Water – Towards Self-Assembled Molecular Electronic Circuitry. Chem. Commun. Feature Article 1812 – 1823 (2005).[6] Nørgaard, K., Laursen, B.W., Sygaard, S., Kjaer, K., Tseng, H-R., Flood, A.H., Stoddart, J.F., Bjørnholm T. Structural Evidence of Mechanical Shuttling in Condensed Monolayers of Bistable Rotaxane Molecules. Angewandte Chemie (accepted)
9:30 AM - **N2.2
A Statistical Approach for Electrical Transport Investigations through Single Molecules.
Emanuel Loertscher 1 , Heiko Weber 2 , Heike Riel 1
1 Science & Technology, IBM Research GmbH, Rueschlikon Switzerland, 2 , University of Erlangen-Nuremberg, Erlangen Germany
Show AbstractThe fundamental understanding of charge carrier transport through metal-molecule-metal junctions is a key challenge of molecular electronics and a prerequisite for future applications. In that respect, detailed investigations of the electrical contact between an individual molecule and the electrodes is essential.We performed statistical investigations of charge carrier transport through metal-molecule-metal junctions by the mechanically controllable break-junction (MCBJ) technique [1,2]. Current-voltage curves are acquired automatically during repeated cycles of stepwise opening and closing of the junction. This approach requires an excellent mechanical stability which, in our case, is testified by the observation of quantized conductance of quantum point contacts at room temperature. The entity of all acquired data provide an excellent basis for statistical analysis. For example, conductance histograms evidence that single molecules can be contacted by this method. A further advantage of our approach is that every single current-voltage characteristics represents one specific configuration of the metal-molecule-metal system.A model system consisting of 1,4-phenyl-dithiol, 1,4-biphenyl-dithiol, 1,4-terphenyl-dithiol, and 1,4-quaterphenyl-dithiol, i.e., one, two, three, and, four phenyl units terminated symmetrically by acetyl protected thiol groups [3] has been investigated. The extensive data set of reproducible and stable current-voltage curves reveals characteristic transport properties of the individual molecules. Conductance studies at different temperatures are compared to results achieved by other techniques [4,5] and theoretical predictions.[1] J. Moreland and J. Elkin, J. Appl. Phys. 58, 3888 (1985).[2] C. J. Muller, J. M. van Ruitenbeek, and L. de Jongh, Physica C 191, 485 (1992).[3] Courtesy of the Institute for Nanotechnology, Forschungszentrum Karlsruhe, Germany.[4] S. Hong, R. Reifenberger, W. Tian, S. Datta, J. Henderson, and C. P. Kubiak, Superlattices and Microstructures 28, 289 (2000).[5] M. A. Reed, C. Zhou, C. Muller, T. Burgin, and J. Tour, Science 278, 252 (1997).
10:00 AM - **N2.3
Intrinsic Electron Conduction Mechanisms in Molecules
Mark Reed 1
1 , Yale University, New Haven, Connecticut, United States
Show AbstractElectron devices containing molecules as the active region have been an active area of research over the last few years. This talk presents measurements in a variety of molecular systems to elucidate the transport mechanisms, specifically in self-assembled monolayers (SAMs) using nanometer scale devices. Detailed kinetic studies are necessary to distinguish between different conduction mechanisms; for example, in alkanes temperature-independent electron transport is observed, proving tunneling as the dominant conduction mechanism when defects are eliminated from the device structure. This is distinct from Langmuir-Blodgett films, where only defect or filamentary conduction has been observed. Inelastic electron tunneling spectroscopy of the molecules in the junction exhibits well-defined modes of the molecules in the junction, and yield a measurement of the intrinsic linewidths of these modes. Deviation from this classic behavior for more complex molecule structures, and a comparison of the differences and pitfalls of various fabrication and characterization approaches, will be discussed.
10:30 AM - **N2.4
Transport Mechanisms and Inelastic Tunneling in Molecular Junctions.
Jeremy Beebe 1
1 Process Measurements Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractWednesday, 4/19Title Change9:30 am *N2.4Transport Mechanisms and Inelastic Tunneling in Molecular Junctions. Jeremy M. Beebe
11:30 AM - **N2.5
The Nature of "Conduction Channels" Through Molecular Electronic Devices.
Jeffrey Reimers 1 , Gemma Solomon 1 , Noel Hush 2 , Alessio Gagliardi 3 4 , Alessandro Pecchia 5 , Thomas Frauenheim 3 , Aldo Di Carlo 5
1 School of Chemistry, The University of Sydney, Sydney, New South Wales, Australia, 2 School of Molecular and Microbial Biosciences, The University of Sydney, Sydney, New South Wales, Australia, 3 Institute for Theoretical Physics, University of Paderborn, Paderborn Germany, 4 PaSCO Graduate School, University of Paderborn, Paderborn Germany, 5 INFM- Dipartimento di Ingegneria Elettronica, University di Roma Tor Vergata, Rome Italy
Show Abstract12:00 PM - **N2.6
Temperature Dependence of Conductance in Single Molecule Junctions.
Joshua Hihath 1 , Xiulan Li 1 , Fang Chen 1 , Nongjian Tao 1
1 Electrical Engineering, Arizona State University, Tempe, Arizona, United States
Show AbstractUnderstanding the fundamental electron transport mechanism in single molecules is a necessary step towards the ultimate goal of molecular electronics. We have determined the conductance of single molecules covalently bound to two gold electrodes by varying the temperature of the system during measurements in order to elucidate the transport mechanism. These measurements have been carried out on a variety of molecules including alkanedithiols of different lengths, conjugated redox molecules, and biologically relevant molecules such as DNA. The dependence of the conductance on temperature is different for each of the molecules. For example, the conductance of alkanedithiols is independent of temperature while the conductance of the redox molecules increases with temperature. The temperature dependence, together with other external parameters such as solvent, help us to elucidate the differences between coherent tunneling and thermally activated processes.
12:30 PM - **N2.7
Simple Molecules as Benchmark Systems for Molecular Electronics.
Darko Djukic 1 , Jan van Ruitenbeek 1
1 Kamerlingh Onnes Laboratorium, Universiteit Leiden, Leiden Netherlands
Show AbstractOver the past decade several techniques have been developed aimed at contacting individual organic molecules with metal leads. Although there has been some success, the experiments often cannot be interpreted uniquely. This is not surprising since nearly all the information needs to be deduced from the current and voltage only. There is often very little agreement between experiments by different groups and between experiments and theory.This motivated us to concentrate on simple molecular systems that can be characterized in more detail and that may provide benchmarks for computations. Our most studied system is dihydrogen, H2, contacted between Pt leads. We use break junction techniques at low temperatures. This allows us to obtain a lot of statistics over many contacts. The molecular junction can be characterized through conductance, the number of conduction channels, and –most significantly- the vibration modes. The vibration modes are seen through point contact spectroscopy (dI/dV). For hydrogen three vibration modes have been observed, their shift upon isotope substitution (D2 and HD) was obtained, and their dependence on stretching of the contact was measured. Shot noise measurements demonstrate that the current is carried by a single channel, thus confirming that the characteristics are due to a single molecule. The results agree very well with calculations by K. Thygesen and K.W. Jacobsen (Lyngby), but disagree with other approaches, suggesting that there is no consensus yet on the proper method for molecular electronics computations. The experiments are being extended towards other molecules, including CO, H2S, C2H2, benzene, and others.
N3: Molecules and Monolayers
Session Chairs
Wednesday PM, April 19, 2006
Room 3014 (Moscone West)
2:30 PM - **N3.1
Designing, Measuring and Controlling Molecular- and Supramolecular-Scale Properties for Molecular Devices
Paul Weiss 1
1 Chemistry and Physics, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractWe use molecular design, tailored syntheses, intermolecular interactions and selective chemistry to direct molecules into desired positions to create nanostructures, to connect functional molecules to the outside world, and to serve as test structures for measurements of single or bundled molecules. Interactions within and between molecules can be designed, directed, measured, understood and exploited at unprecedented scales. We look at how these interactions influence the chemistry, dynamics, structure, electronic function and other properties. Such interactions can be used to advantage to form precise molecular assemblies, nanostructures, and patterns, and to control and to stabilize function. These nanostructures can be taken all the way down to atomic-scale precision or can be used at larger scales. We select and tailor molecules to choose the intermolecular interaction strengths and the structures formed within the film. We selectively test hypothesized mechanisms for electronic switching by varying molecular design, chemical environment, and measurement conditions to enable or to disable functions and control of these molecules with predictive and testable means. Critical to understanding these variations has been developing the means to make tens to hundreds of thousands of independent single-molecule measurements in order to develop sufficiently significant statistical distributions, comparable to those found in ensemble-averaging measurements, while retaining the heterogeneity of the measurements. We quantitatively compare the conductances of molecule-substrate junctions. We demonstrate the importance of these junctions in conductance switching of single molecules.
3:00 PM - **N3.2
Molecules in Electronic Circuits - from Integrated Single Molecules to SAMs in CMOS Technology.
Marcel Mayor 1 2
1 Department of Chemistry, University of Basel, Basel Switzerland, 2 FZK Karlsruhe GmbH, Institute for Nanotechnology, D-76021 Karlsruhe Germany
Show AbstractThe integration of molecular structures in electronic circuits is a concept that has already been proposed in the sixties, when Hans Kuhn presented his vision of molecular engineering. Limited by the available techniques, Kuhn and coworkers mainly investigated molecular monolayers deposited on electrodes.[1]In the last few years, the tools to investigate nsnoscale objects have improved tremendously. Furthermore, the feature sizes in semiconductor technology have been reduced very fast and continuously that Gordon Moore dares to describe it as a law. However, this feature size reduction seems to hit soon both, physical and economical limits. With that background the revival of the idea to integrate molecules in electronic circuits is not surprising.Molecules are well defined nanoscale objects consisting of a definite structure leading to particular electronic properties. As these structures can be tailored by chemical synthesis, the visionary concept of molecular electronics is geared by the hope that electronic functions can be realized by carefully designed molecular structures.[2] Apart from the huge variety given by the immenseness of possible molecular structures, the incredible smallness of a functional unit based on a molecule is a main driving force. However, integration of molecular structures in electronic circuits is still an experimental challenge and the field is still at the level of exploring the potential as well as the limitations.In close cooperation with physicists and engineers from academics and industry, single molecules and assemblies of molecules have been integrated in electronic circuits. Correlations between the molecular structure and the observed 1/V characteristics have been investigated. The findings allow to further optimize the molecules for particular electronic functions. Several molecular systems have been synthesized and studied to collect the required comprehension to design particular electronic functions. Recently, a molecular rod acting as s single molecule rectifier has been designed, synthesized and integrated.[3] Indeed rectification was observed, however, it does not yet match the rectification ratios known from its silicon opponents.In conclusion, the concepts of molecular electronics will be presented and illustrated with several experiments displaying the interesting perspectives but also the remaining problems of the concept.[1]H. Kuhn, D. Möbius, Angew. Chem. Int. Ed. (1971) 10, 460. [2]a) M. Mayor, H. B. Weber, R. Waser in Nanoelectronics and Information Technology. Advanced Electronic Materials and Novel Devices (Ed.: R. Waser), Wiley-VCH, Weinheim (2003) 501. b) M. A. Reed, J. M. Tour, Scientific American (2000) 282, 86. c) C. Joachim, J. K.Gimzewski, A. Aviram, Nature (2000) 408, 541. [3]M. Elbing, R. Ochs, M. Koentopp, M. Fischer, C. von Hänisch, F. Weigend, F. Evers, H. B. Weber, M. Mayor, Proc. Natl. Acad. Sci. U.S.A. (2005) 102, 8815.
3:30 PM - **N3.3
Correlating Electronic Structure and Transport in Molecular Junctions Based on Conjugated Molecules
C. Daniel Frisbie 1 , Xioayang Zhu 2 , BongSoo Kim 2
1 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 Chemistry, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThis talk will describe the use of conducting probe atomic force microscopy (CP-AFM) and ultraviolet electron spectroscopy (UPS) to understand the correlation between electron transport and energy levels in molecular junctions. We have synthesized a series of rigid aromatic molecules (oligoacenes and oligophenylenes) that are end-functionalized with surface linking groups. Self-assembled monolayers of these films on gold have been extensively characterized and the spectrum of filled electronic states has been measured by UPS. We have measured transport through metal-molecule-metal junctions based on these SAMs using the CP-AFM method. Transport measurements as a function of molecular length allow determination of the transport efficiency (beta value) and contact resistance. We will describe this technique in some detail and then discuss the correlation of the transport measurements with the electronic structure of the junctions.
4:30 PM - N3.4
Vapor Phase Deposition of OPEs.
Nadine Gergel-Hackett 1 , Michael Cabral 1 , Timothy Pernell 1 , Lloyd Harriott 1 , John Bean 1 , Bo Chen 2 , Meng Lu 2 , James Tour 2
1 Charles L. Brown Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, Houston, Texas, United States
Show AbstractTo address problems in molecular electronics that include low yields of working devices and inconsistencies in device results, we have developed a process to improve the control, uniformity and purity of molecular monolayers. Rather than using the traditional solution phase self-assembly method, we first purify the molecular source materials in-situ and then vaporize the molecules in an ultra-high vacuum system under conditions that result in a pure, dense, well-ordered monolayer. The molecule that we have used for this work, oligo(phenylene ethynylene) (OPE), is commonly used as a simple conducting “wire” in molecular devices, and is the backbone for molecules that have shown electrical switching behavior(1,2,3,4). We vaporized the OPEs using a special low temperature sublimation cell and controlled the molecular exposure by varying the vaporization temperature and time. We were thus able to establish the conditions for dense monolayer deposition. Based on ellipsometry data, exposure conditions are given for assembly of a single monolayer of OPE molecules standing upright on Au. X-ray photo spectroscopy (XPS) confirmed that the monolayer was uncontaminated and that the molecules were bound to the Au substrate. Additionally, scanning tunneling microscopy (STM) results confirmed that the monolayer is composed of molecules that are in the desired dense standing up phase, commonly referred to as the C (4 x 2) phase. By establishing vapor phase deposition as a viable assembly technique for the simple OPE molecule, we are setting the framework for a process offering enhanced yields and greater compatibility with conventional microelectronic fabrication.Acknowledgements: We would like to thank Giovanni Zangari and Gyana Pattanaik for their help with imaging and use of their STM. The work at Uva was supported by the National Science Foundation (NIRT 0210585) and DARPA/ONR MoleApps program (N00014010706). The work by J. M. Tour was funded by DARPA/ONR Moletronics program (N000140110657) and DARPA/ONR MoleApps (N000140410765).1.M.A. Reed et al, Appl. Phys. Lett. 78, 3735 (2001).2.C. Zhou et al, Applied Physics Letters 71, 611 (1997).3.N. Gergel et al, J. Vac. Sci. Technol. A. 23 (4), 880 (2005).4.A. S. Blum, Nature Materials 4, 167 (2005).
4:45 PM - N3.5
Atomically-Flat Nanophotonic Antennae: Optically Resonant Gold Nanoparticle Substrates for Single-molecule Optoelectronics.
Lloyd Bumm 1
1 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma, United States
Show AbstractSupported flat gold nanoparticles (FGNPs) are optically resonant substrates for high-resolution scanning tunneling microscopy (STM). These are atomically-flat single-crystal plates with large {111} faces that are composed of only a few atomic terraces. The nanoparticles are prepared using standard solution techniques and then deposited on indium tin oxide (ITO) coated glass substrates. The nanoparticles range in size from tens to thousands of nanometers and have been characterized by STM, NSOM, SEM, TEM, and dark-field spectroscopy. These are excellent substrates for molecularly-resolved STM imaging of alkanethiol self-assembled monolayers (SAMs). We demonstrate that these FGNP/ITO substrates can be used as photonic antenna for STM single-molecule optoelectronic measurements of guest molecules supported by the host SAM.
5:00 PM - N3.6
The Effects of Hydration on Molecular Junctions.
David Long 1 , Jason Lazorcik 1 , Brent Mantooth 1 , Martin Moore 2 , Mark Ratner 3 , Alessandro Troisi 4 , James Tour 5 , Ranganathan Shashidhar 1
1 Research and Development Center, SAIC, Manassas, Virginia, United States, 2 Center for Bio/Molecular Science and Engineering, NRL, Washington, District of Columbia, United States, 3 Dept. of Chemistry, Northwestern University, Evanston, Illinois, United States, 4 Dept. of Chemistry, University of Warwick, Coventry United Kingdom, 5 Nanoscale Science and Technology, Rice University, Houston, Texas, United States
Show Abstract5:15 PM - N3.7
Dithiocarbamates: Functional and Versatile Linkers for the Formation of Self-assembled Monolayers.
Peter Morf 1 , Fabio Raimondi 2 , Heinz-Georg Nothofer 3 , Bernhard Schnyder 2 , Akio Yasuda 3 , Jurina Wessels 3 , Thomas Jung 1
1 Laboratory for micro- and nanotechnology, Paul Scherrer Institute, Villigen Switzerland, 2 Laboratory for Electrochemistry, Paul Scherrer Insitute, Villigen Switzerland, 3 Materials Science Laboratories, Sony Deutschland GmbH, Stuttgart, Stuttgart Germany
Show AbstractIn this Work a functional and versatile SAM forming linker group the dithiocarbamate (DTC) is re-visited; Complete layer formation of mono-functional acyclic and bifunctional cyclic dithiocarbamates on Au(111) with new and distinctly different layer properties as found for the thiol systems are demonstrated by X-ray photoelectron spectroscopy, cyclic voltammetry and scanning tunneling microscopy. Characteristic and new properties of these SAM layers derive from the bi-dentate structure of the linker and its resonant structure. Furthermore, the chemical adsorption and voltammetric desorption reactions are quantitatively determined and the adsorption / desorption and etching on the Au(111) surface has been investigated for different DTC derivatives. Conjugation between phenyl substituents, the bi-dentate linker and metallic electron states is discussed in relation to molecular electronics.
5:30 PM - **N3.8
Highly Functional Molecular Wires Through Rational Chemical Design.
Dwight Seferos 1 , Alexander Hexamer 1 , Edward Kramer 1 , James Kushmerick 2 , Guillermo Bazan 1
1 Department of Chemistry and Materials, UC Santa Barbara, Santa Barbara, California, United States, 2 Surface and Microanalysis Science Division, NIST, Gatherberg, Maryland, United States
Show AbstractIt is clear that slight structural modifications can play a tremendously influential role in the morphology, photophysics and bulk transport properties of conjugated organic semiconductors. However, the role that molecular structure plays in molecules of interest for molecular electronics is less well understood. Inspired by the efforts of examiners of conjugated polymer oligomers, we have embarked on a careful examination of how molecular structure can influence molecular charge-transport and the self-assembled monolayer structure of molecular wire molecules. Specifically, we have synthesized a series of dithiol molecules based on the oligo(phenylene-vinylene) (OPV) and oligo(thienylene-vinylene) (OTV) motifs. Our structures include liner and [2.2] paracyclophane containing ridig-rods, and OPVs with 0, 1, and 2 methylene units between the conjugated fragment and thiol points of surface attachment. Surface analysis was probed by electrochemical methods, layer thickness analysis, X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Molecular conductivity measurements performed using scanning probe microscopy correlated with monolayer conductivity measurements using the cross-wire tunnel-junction technique will be discussed. Our studies provide fundamental insight towards the rational design of molecules that form high-quality monolayers and achieve good charge-transport properties.
Symposium Organizers
Ranganathan Shashidhar Geo-Centers Inc.
James G. Kushmerick National Institute of Standards and Technology
Heiko B. Weber University of Erlangen-Nurnberg
Nongjian J. Tao Arizona State University
N4: Semiconductor Based Molecular Electronics
Session Chairs
Thursday AM, April 20, 2006
Room 3014 (Moscone West)
9:30 AM - **N4.1
Forming Molecular Monolayers and Molecular Diodes on GaAs.
Julia Hsu 1 , Wenjie Li 2 , Yong Jun 3 , Clark Highstrete 1 , Carolyn Matzke 1 , Karen Kavanagh 2 , X. Y. Zhu 3 , A. Alec Talin 4 , Sergey Faleev 4 , Francois Leonard 4
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Physics, Simon Fraser University, Burnaby, Alberta, Canada, 3 Chemistry, University of Minnesota, Minneapolis, Minnesota, United States, 4 , Sandia National Laboratories, Livermore, California, United States
Show AbstractIntegrating molecular functions with conventional semiconductors opens up new possibilities for future devices. However, the formation of molecular monolayers and the study of molecular diodes on semiconductors are much less mature than their counter parts on metals. In this talk, the formation of alkanethiol or alkanedithiol monolayers on (001) GaAs and electronic transport across these molecular layers by ballistic electron emission microscopy (BEEM) will be discussed. X-ray photoemission spectroscopy and ellipsometry indicate that alkanethiols and alkanedithiols behave drastically differently in forming monolayers on GaAs, unlike on Au. For example, even though hexadecanethiols (C16MT) have a molecular length almost twice that of octanedithiols (C8DT), the monolayer thicknesses for these two molecules on GaAs are approximately the same. Using BEEM, we examined transport properties of Au/molecule/GaAs and Au/molecule/metal/GaAs diodes where molecule = C16MT or C8DT. BEEM is one of the very few experimental techniques that are capable of measuring the local electronic transport through such buried interfaces. The barrier heights determined from BEEM are compared with Schottky barrier heights determined from current-voltage (I-V) measurements. A major difference between the two measurements is that the local barrier height determined from BEEM is without applying a bias across the molecular layer while a large field could exist across the molecules. We found that the presence of the molecule dramatically increases the BEEM threshold voltage compared to reference Au/GaAs diodes while the I-V barrier height increases are much smaller. The results will be discussed within the framework of a 1D model with two tunneling barriers, sheding light on the electronic structure of the moleculer diodes. Research at SFU supported by the Natural Science and Engineering Research Council of Canada. Work done at Sandia is partially supported by a jump-start program from DOE’s Center for Integrated Nanotechnology (CINT). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
10:00 AM - N4.2
Hot Electron Transport in Si and GaAs Molecular Diodes.
Wenjie Li 1 , M. Kuikka 2 , H.-Z. Yu 2 , C.M. Matzke 3 , J.W.P. Hsu 3 , C. Highstrete 3 , A.A. Talin 4 , F. Leonard 4 , S. Faleev 4 , Karen Kavanagh 1
1 Physics, Simon Fraser University, Burnaby , British Columbia, Canada, 2 Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 4 , Sandia National Laboratories, Livermore, California, United States
Show AbstractInvestigation of electron transport across individual, or small numbers of organic molecules has attracted a great deal of attention and controversy in the past five years. Ballistic electron emission microscopy (BEEM) offers a way to study local transport through a buried layer, such as a thin molecular layer, without biasing the molecule and with nanometer lateral resolution. In BEEM a biased STM tip is used to inject non-equilibrium (hot) electrons into a thin (5 – 10 nm) surface metallic film. A small fraction of these carriers reach the underlying substrate interface without scattering. If the substrate is a semiconductor, when the tip bias exceeds the interfacial barrier energy BEEM current in the semiconductor is detected. Unlike STM there is no bias applied across the molecular layer. In this talk, we present a study of electron transport through Au /Molecule/GaAs (001) and Au/Molecule/Si (111) samples where the molecule (alkanes or alkanethiols or alkandithiols, carbon number 8 – 16) is bonded directly to the substrate via either a S-GaAs bond or a C-Si bond. These diodes were compared to sandwich structures: Au/Molecule/Au/GaAs (001) and reference Au/GaAs, Au/Si(111), or Hg/Si(111) diodes. We find that the threshold for ballistic transport is increased from 0.85 V to 1.1 or 1.4 V (GaAs) and from unstable 0.82 to stable 0.82 to 0.96 eV (Si) due to the presence of a molecular layer. The molecular layers are continuous with no evidence of Au/GaAs shorts. The BEEM current is largest through sandwiched molecular layers (50 - 60% that of the reference diodes) and through alkanes or alkanemonothiol directly bonded to Si or GaAs, respectively. However, for the Au/dithiol/GaAs diodes where one end is a S-GaAs and the other end S-Au, transmission was negligible. However, when detected these diodes had the largest increase in threshold voltages (1.4 V). Interestingly, the presence of a surface Au-S bond is correlated with a strong suppression in the BEEM transmission. These results are combined with structural and compositional evaluations of the molecules by XPS, Auger, ellipsometry, I-V, C-V, and Hg probe measurements, and modeling to discuss the possible role of the molecular layer at the interface.We thank the Natural Science and Engineering Research Council of Canada for partial support of this work. Work done at Sandia is partially supported by a jump-start program from DOE’s Center for Integrated Nanotechnology (CINT). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
10:15 AM - N4.3
A New Approach for Silicon-based Single Molecular Device Based on Dopant-Molecule Interaction.
Jixin Yu 1
1 Department of Electrical Engineering and USC NanoCenter, University of South Carolina, Columbia, South Carolina, United States
Show AbstractSilicon-based hybrid molecular electronic device represents a promising alternative for continuing Moore’s law. Due to the random nature of ion implantation, dopant diffusion, and other processes that are involved in the doping of silicon material, the dopant number in the silicon substrate is subject to stochastic variations. Although macroscopically silicon sample remains neutral, active (ionized) dopants that reside in a few layers below silicon surface will locally change the electrical properties of the silicon surface at atomic scale, thus affect the electric properties of the covalently linked molecules on the surface. Ultrahigh vacuum scanning tunneling microscopy (UHV-STM) experiments on the Metal Phthalocyanine (MPc) molecules that were absorbed on Si(100) surface have shown that the electronic properties of molecules were greatly affected by substrate-molecule interaction. Such interaction will be dramatically increased when molecules are placed close to dopants and their electronic properties will vary notably depending on the distance between molecules and underlying dopants. Utilizing dopant-molecule interaction, a new approach for fabricating silicon-based single molecular devices is presented, employing STM-based feedback control lithography (FCL), self-assembly of dopant precursors, low-temperature silicon overgrowth, and molecule self-assembly. The device density produced by this scheme is decided by the dopant distribution, and can reach up to 1014 bit/cm2.
10:30 AM - **N4.4
Role of Interfaces on the Direct Tunneling and the Inelastic Tunneling Behaviors in metal/alkylsilane/silicon Junctions.
Dominique Vuillaume 1 , Dinesh Aswal 1 3 , David Guerin 1 , Stephane Lenfant 1 , Christian Petit 2 , Guy Salace 2 , Jatinder Yakhmi 3
1 , IEMN-CNRS, Villeneuve d Ascq France, 3 , BARC, Mumbai India, 2 , Univ. de Reims, Reims France
Show AbstractIn molecular electronics, the role of interfaces remains the subject of many controversies. In fact, frequently the interface can explain the electrical behavior measured in the molecular device.We compared the tunneling behavior of metal/alkylsilane/silicon junctions by measuring their current density-voltage (J(V)) characteristics. For some junctions, depending on the chemical nature of the alkyl/metal interface, the results are in excellent agreement with the theory of Simmons for tunneling current between dissimilar electrodes separated by a thin insulating film. With this model, we extracted the effective mass (m*) and the barrier height of the junctions. For a deeper physical characterization of these junctions, we reported inelastic electron tunneling spectroscopy (IETS) measurements of the electrons-molecular vibrations coupling, recognized as a key point in molecular electronic devices.The metal/alkylsilane/silicon junctions were prepared on highly-doped silicon covered by an ultra-thin native dioxide (ca. 1nm) films. Self-assembled monolayers constituted of alkylsilanes chains from 3 to 11 carbon atoms, and bearing different terminal groups were deposit by chemisorption in solution. Metal electrodes (aluminum or gold) were gently evaporated to complete the junction. The metal/terminal group combinations were chosen allowing specific chemical interactions at the interface, to test their influence on the electrical behavior and IETS.Since the thiol group at the interface avoids diffusion of gold into the molecule even for a 3 carbons chain, we observed pure tunnel conduction with barrier height of 2.4-2.5 eV and an effective mass parameter m* = 0.16 m0. This extends the demonstration of the excellent tunnel dielectric behavior of organic monolayers down to 3 carbon atoms with a thiol/Au couple at the interface. Other SAMs without the thiol end-group (i.e. CH3 terminated) do not follow a pure tunneling behavior.IETS confirms the quality of the thiol-Au interface; we observed a strong S-Au vibration peak at 25.1 mV. Moreover for all the different systems, we are able to distinguish and identify the most intense vibration modes of the alkyl chains: (i) the CH2 rocking mode at 95.2 mV; (ii) the C-C vibration at 134.3 mV and (iii) the CH2 vibration at 187.9 mV. These peaks are clearly distinguished from those of the Si and ultra-thin SiO2 phonons.In conclusion, we demonstrated that the thiol/gold couple at the interface avoids gold diffusion and damage creation in junctions during the evaporation of the metal for alkyl chains as short as 3 carbon atoms. For this device, the good electrical contact permits observing a perfect tunneling current behavior in the junction in agreement with Simmons’s model.
12:00 PM - **N4.6
Metal-Molecule-Semiconductor Device Structures
David B Janes 1
1 , Purdue Univ., W. Lafayette, Indiana, United States
Show AbstractIn the field of molecular electronics, the contacts to the molecular elements are critical interfaces. The use of semiconductor contacts allows direct covalent bonding, provides an additional degree of freedom due to the semiconductor states, and, in certain circumstances, can minimize the effects of electrical shorting due to direct metal/substrate contacts. This talk will describe the development and electrical characterization of metal/molecule/semiconductor device structures on both GaAs and Si substrates. The devices are lithographically defined and fabricated using an indirect evaporation technique for the metal (top) contact and doped semiconductor layers for the bottom contact. In order to observe the conductance of the molecular species, rather than that of the semiconductor barrier, the semiconductor layers used in this study are generally highly doped. In these structures, the electronic conduction between the metal and semiconductor can be modulated by choice of molecular species. Several alkyl thiol and aromatic thiol molecules have been employed in order to determine the effects of molecular length, conjugation and intrinsic dipole moment. In certain molecules, conductance peaks or memory/switching effects have been observed. The current-voltage characteristics and conductance versus temperature both indicate that the molecular layers change the transport mechanism, generally involving a lower effective barrier height than that of a metal/semiconductor Schottky barrier. Studies on both n- and p- type substrates, including those with nanometer scale cap layers, allow the effects of the molecular and semiconductor barriers to be isolated. A basic conduction model has been developed, based on the electrostatics of the structure and thermionic-field-emission analysis of the semiconductor portion of the barrier.
12:30 PM - N4.7
Electronic Structure of Si-bound Alkyl Monolayers.
Fabrice Amy 1 , Antoine Kahn 1 , Calvin Chan 1 , Adi Salomon 2 , David Cahen 2
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel
Show AbstractN5: Molecular Spectroscopies
Session Chairs
Thursday PM, April 20, 2006
Room 3014 (Moscone West)
2:30 PM - **N5.1
Electronic Transport through Organic Monolayer Devices
Duncan Stewart 1 , Jason Blackstock 1 , Carrie Donley 1 , Douglas Ohlberg 1 , Zhiyong Li 1 , R. Stanley Williams 1
1 , Hewlett-Packard Labs, Palo Alto, California, United States
Show Abstract We report experimental studies of electronic transport through molecular monolayers. Particular emphasis is placed on combining detailed chemical, physical and electronic characterization in a single test structure, and to whatever degree possible, fabricating well-defined interfaces that enable quantitative chemical and physical analysis. To this end, physical characterization of ultra-flat template-stripped Au and Pt metal electrodes including UHV-STM imaging of the surface atomic configuration and incorporation into a new stencil-based nanopore device is described in detail at this meeting by J.J. Blackstock. In-situ XPS and IR spectroscopy of organic monolayers and the buried inorganic/organic interfaces is described in detail at this meeting by C.L. Donley. Using this well-characterized device structure, here we present detailed I-V characterization including temperature dependence and IETS spectroscopy of several alkane self-assembled and Langmuir-Blodgett monolayers, correlating both electrical switching behavior and IETS spectral response to the measured chemical and physical structure of the device.
3:00 PM - N5.2
Simulating IETS: The Molecular Signature In Single Molecule Conduction.
Gemma Solomon 1 , Alessio Gagliardi 2 3 , Alessandro Pecchia 4 , Thomas Frauenheim 2 , Aldo Di Carlo 4 , Jeffrey Reimers 1 , Noel Hush 1 5
1 School of Chemistry, The University of Sydney, Sydney, New South Wales, Australia, 2 Institute for Theoretical Physics, University of Paderborn, Paderborn Germany, 3 PASCO Graduate School, University of Paderborn, Paderborn Germany, 4 INFM- Dipartimento di Ingegneria Elettronica, Universita di Roma "Tor Vergata", Rome Italy, 5 School of Molecular and Microbial Biosciences , The University of Sydney, Sydney, New South Wales, Australia
Show AbstractWe present results for a simulated inelastic electron tunneling spectra (IETS) from calculations using the ‘gDFTB' code. The geometric and electronic structure is obtained from calculations using a local-basis density-functional scheme and a non-equilibrium Green's function formalism is employed to deal with the transport aspects of the problem. The calculated spectrum of octanedithiol on gold(111) shows good agreement with experimental results and suggest further details in the assignment of such spectra. We show that some low energy peaks, unassigned in the experimental spectrum, occur in a region where a number of molecular modes are predicted to be active, suggesting that these modes are the cause of the peaks rather than a matrix signal, as previously postulated. The simulations also reveal the qualitative nature of the processes dominating IETS. It is highly sensitive only to the vibrational motions that occur in the regions of the molecule where there is electron density in the low voltage conduction channel. This result is illustrated with an examination of the predicted variation of IETS spectra with binding site and alkane chain length.
3:15 PM - **N5.3
Energy-level Alignment of Self-Assembled Monolayers on Metals
Roger van Zee 1
1 , NIST, Gaithersburg, Maryland, United States
Show AbstractThe energy of the Fermi level relative to the molecular transport states is one of the critical elements in determining the current-voltage characteristics of any molecule-based electronic device. We have measured this energy-level alignment for conjugated molecules (“molecular wires”) chemisorbed on metal surfaces. Specifically, one- and two-photon photoemission have been used to determine the valence electronic structure of oligo(phenylene-ethynylene)thiols, oligo(phenylene-vinylene)thiols and naphthalenethiols. The alignment of these valence states relative to the Fermi level is obtained from these spectra too. The nature of the valence states has been established using valence effective Hamiltonian calculations; the charge-transport states have been identified with these calculations. This identification allows the hole-injection barrier, electron-injection barriers and the transport gap to be calculated. The effects of oligomer length and chemical substitution have been studied. Charge transfer and the intrinsic molecular dipole are found to be key components of the energy-level alignment of these systems.
3:45 PM - N5.4
Electronic Level Alignment at Metal-molecule Interfaces from First Principles.
Jeffrey Neaton 1 , Mark Hybertsen 2 3 , Steven Louie 1 4
1 The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Center for Transport in Molecular Nanostructures, Columbia University, New York, New York, United States, 3 Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York, United States, 4 Department of Physics, University of California at Berkeley, Berkeley, California, United States
Show AbstractElectronic transport properties of nanoscale molecular junctions must depend on the energetic alignment of frontier molecular states with the contact Fermi levels; yet many fundamental issues controlling the nature of this alignment remain unresolved. In this work, first-principles many-electron perturbation theory is used to explore how molecular states are modified at metal-molecule interfaces. The electronic structure of a model metal-molecule interface, benzene (C6H6) on graphite (0001), is computed within the GW approximation. The benzene HOMO-LUMO gap is predicted to be 7.2 eV in this environment, a large reduction relative to its calculated gas-phase value of 10.5 eV, and slightly smaller than its computed solid-phase gap of 7.5 eV. This decrease is attributed to electrostatic correlations between the molecule and substrate. Implications for experiments probing the electronic properties of organic and molecular nanostructured systems in contact with metallic and semiconducting surfaces, such as cyclopentene on Si(001), will also be discussed. This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the DOE under Contract No. DE-AC03-76SF00098; by the NSF grant DMR04-39768; by the Nanoscale Science and Engineering Initiative of the NSF under Award Number CHE-0117752; and by the New York State Office of Science, Technology, and Academic Research (NYSTAR). Computational resources have been provided by NERSC.
4:30 PM - **N5.5
Spectroscopic Probes of Electron Transport at Thiolate SAM/Au(111) Interfaces.
Xiaoyang Zhu 1
1 Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractAlkanethiol self-assembled monolayers (SAMs) on Au(111) are model systems for molecular electronics. We probe the role of the chemisorption bond on electron dynamics at the SAM/Au interface using time-resolved two-photon photoemission spectroscopy. Formation of the Au-S bond is evidenced by a localized σ* resonance, which broadens and shifts upward in energy when the lying-down chemisorbed molecules stand up. We also observed a delocalized electron resonance confined to the thiolate/Au interface, independent of the alkyl chain length. The localized chemisorption bond does not affect the electronic coupling between delocalized electronic resonances and the metal substrate. Instead, lifetimes of these resonances are decreased due to scattering with S atoms.
5:00 PM - N5.6
Measurement of Bond Strength in gold-alkanedithiol-gold Junctions.
zhifeng huang 1 2 , Bingqian Xu 2 , Nongjian Tao 2 1
1 SEM, Arizona State Univ., Tempe, Arizona, United States, 2 EE, Arizona State Univ., Tempe, Arizona, United States
Show Abstract5:15 PM - N5.7
Chemical and Physical Structure of Buried Inorganic/Organic Interfaces From In-Situ X-Ray Photoelectron Spectroscopy and Infrared Spectroscopy.
Carrie Donley 1 , Jason Blackstock 1 , William Stickle 2 , Doug Ohlberg 1 , Duncan Stewart 1
1 Quantum Science Research, Hewlett Packard, Palo Alto, California, United States, 2 , Hewlett Packard , Corvallis, Oregon, United States
Show Abstract In molecular-scale electronic devices the critical active layer is typically only a few nanometers thick. Detailed physical and chemical characterizations of this layer and adjacent interfaces are essential for understanding electronic behavior. Unfortunately, this active region is almost always buried within a potentially complex materials stack formed in a series of process steps, many of which induce physical and chemical modifications in the preceding materials layers. Reliable chemical information on the as-built devices can only be extracted from challenging in-situ analysis. We present a combination of such in-situ x-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy experiments designed to chemically and physically characterize the buried active region inside a molecular electronic device. A technique was developed to cleave the device stack at a critical buried inorganic/organic interface in an ultra-high vacuum environment, enabling XPS analysis of the material structure on both sides of the cleaved interface. We have applied these techniques to a series of nominally straightforward platinum/organic monolayer/titanium devices that show useful electrical behavior. Complete fabrication and electronic behavior details of these same devices are presented at this meeting by J.J. Blackstock and D.R. Stewart, respectively. Previous studies have indicated that these devices are chemically much more complex than originally expected, including platinum oxide at the bottom electrode interface and titanium carbide and oxide incorporated at the top electrode interface. Our in-situ analysis allows us to characterize the final as-built device structure, and shows a surprising interaction between deposited Ti and the PtOx from the bottom interface, mediated through the organic monolayer.
5:30 PM - N5.8
The Electronic Structure of Diamondoids Measured with NEXAFS and Soft X-ray Emission
Trevor Willey 1 , Christoph Bostedt 2 , J. Dahl 3 , R. Carlson 3 , S. Liu 3 , R. Meulenberg 1 , T. van Buuren 1 , L. Terminello 1 , Thomas Moller 2
1 Chemistry and Materials Science, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 , Technische Universitat, Berlin Germany, 3 , MolecularDiamond Technologies, ChevronTexaco, Richmond, California, United States
Show AbstractRecently, higher diamondoids have been isolated from petroleum sources[1]. Derivatives of the smallest diamondoid, adamantane, already are used in pharmaceuticals and other industries, and show promise for molecular electronic applications. The larger diamondoids and their derivatives will certainly open opportunities within molecular electronics and nanotechnology with potential uses in field emission, for nanometer scale constructs, and for nucleating the growth of diamond. We will present the first Near-Edge X-ray Absorption Fine Structure (NEXAFS) measurements of both gas-phase and solid-state diamondoids. The Carbon K-edge reveals rich information on the surface states, and shows emergence of a diamond-like band structure in non-interacting, gas-phase diamondoids[2]. Various calculations have now been performed to predict the HOMO-LUMO gap in these materials, and we will compare predictions to our measurements using x-ray absorption and soft x-ray emission, which probe the LUMO and HOMO respectively. [1] J. E. Dahl, S. G. Liu, R. M. K. Carlson, Science, 299, 96-99 (2003)[2] T.M. Willey, C. Bostedt, et al., Phys. Rev. Lett. 95, 113401 (2005)
5:45 PM - N5.9
Simultaneous Spectroscopic and Electronic Characterization on a Simple Molecular Electronics Test Platform.
David Robinson 1 , A. Talin 1 , Paul Dentinger 1 , Richard Anderson 1
1 , Sandia National Laboratories, Livermore, California, United States
Show AbstractMany published molecular electronics experiments are difficult to understand and reproduce due to a dependence on exotic, expensive, low-throughput fabrication techniques and geometries that prohibit use of independent characterization methods. Among the most tractable device geometries that have been demonstrated is one consisting of an array or superlattice of particles spanning electrode pairs. We have developed a molecular electronics test platform based on this geometry that is especially simple, relying only on standard and other parallel, low-cost techniques including solution-based self assembly, and that provides reproducibility through adequate control and characterization of device geometry. We have studied the electronic and photonic properties of junctions including a number of aliphatic and aromatic bridge molecules using cyclic voltammetry, surface-enhanced Raman spectroscopy, UV-visible reflectance spectroscopy, Auger electron spectroscopy, and electron microscopy. Simultaneous study with these methods offers insights into the charge transport mechanisms through molecules and particle arrays.
N6: Poster Session: Molecular-Scale Electronics Poster Session
Session Chairs
Friday AM, April 21, 2006
Salons 8-15 (Marriott)
9:00 PM - N6.1
Nanosized Paramagnetic Transition Metal Complexes with Redox Active Ligands.
Lahcene Ouahab 1
1 , Universite de Rennes, Rennes France
Show Abstract9:00 PM - N6.10
Ab-initio Green's Function Method with GAUSSIAN for Electrical Transport through Atomic and Molecular Wires.
Tomofumi Tada 1 2 , Satoshi Watanabe 1 2
1 Department of Materials Engineering, The University of Tokyo, Tokyo Japan, 2 CREST, Japan Science and Technology Agency, Saitama Japan
Show Abstract9:00 PM - N6.2
Two-Dimensional Self-Assembly of 1-Pyrylphosphonic Acid: Transfer of Stacks on Structured Surface
Hin-Lap Yip 1 , Hong Ma 1 , Alex K.-Y. Jen 1 2 , Jianchun Dong 3 , Babak Parviz 3
1 Materials Science and Engineering, University of Washington, Seattle, Washington, United States, 2 Chemistry, University of Washington, Seattle, Washington, United States, 3 Electrical Engineering, University of Washington, Seattle, Washington, United States
Show AbstractStrong hydrogen bonding and π-π stacking between 1-pyrylphosphonic acid (PYPA) molecules were exploited to create self-assembled two-dimensional supramolecular structures. Stacked polycrystalline films of these laminate crystalline PYPA bilayers were easily deposited on solid supports through a simple spin-coating technique. Atomic force microscopy reveals that processing parameters, such as solvent, concentration, and surface of the substrate are critical factors in determining the final morphology of the stacked film. Robust laminate structures could be obtained only when short alkyl chain protic solvents (methanol or ethanol) and a non-hydrophobic substrate surface were used. Stacked polycrystalline films were formed through the nucleation and growth of PYPA molecules into laminate structures at the air/solvent interface before they land on the substrate during the spin-coating process. These films possess good mechanical properties and were easily transferred onto a SiO2/Si substrate that was patterned with Au electrodes without breaking their crystalline structures. The successful transfer of the laminate crystals allows us to probe their electrical properties through a field effect transistor device. A gating effect on the charge transport of the stacked films indicates that PYPA laminate crystal possesses p-typed semiconductor characteristics.
9:00 PM - N6.4
Synthesis and Characterization of Novel 2D Oligomers and Polymers for Molecular Electronics
Suresh Valiyaveettil 2
2 Department of Chemistry, National University of Singapore, Singapore Singapore
Show AbstractMolecular electronics, in particular single molecule electronics, is beginning to show potential for future electronic device applications. Recently, intensive efforts have focused on the design and fabrication of single molecular memories, switches and rectifiers using techniques such as cross-bar structures, nanopore, break junctions, cross-wire junctions, and Hg-drop junctions. The need for high speed and more power for our electronic devices are pushing the demand to accelerate the development of molecular electronics devices for building a molecular CPU.One of the key steps in fabricating such devices is to assemble molecules with appropriate electronic states for “current flow” through tunneling onto conductor or semiconductor substrates. In molecular electronics, the property of transferring electrons from one molecule to another is being manipulated to build electronic circuits and other components of a molecular computer to process information at a higher speed and maximum efficiency. In this preseentation, we will discuss our recent efforts in designing novel molecules with interesting elctronic structures. Both oligomers and polymers with 2D electronic conjugation have been synthesized and their properties were investigated.
9:00 PM - N6.5
Valence Electronic Structure of Oligo(phenylene vinylene)Thiolate Self-assembled Monolayers on Gold.
Laura Picraux 1 , Christopher Zangmeister 1 , Steven Robey 1 , Lawrence Sita 2 , Roger van Zee 1
1 Chemical Science and Technology Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Department of Chemistry, University of Maryland, College Park, Maryland, United States
Show AbstractRecent studies have shown that oligo(phenylene vinylene)thiolate (OPVs) self-assembled monolayers are more conductive than the well-characterized oligo(phenylene ethynylene)thiolate monolayers, implying that devices with improved performance may be created using OPVs. This finding prompted a careful investigation of monolayers of OPVs in an effort to determine what factors are improving the transport properties. Three OPV molecules were synthesized, and monolayers of these OPVs were prepared on vapor-deposited gold films. The structural properties of these monolayers were characterized, and the electronic structure was investigated with ultraviolet photoemission spectroscopy. The data show that these compounds form ordered, upright monolayers. The valence states of these monolayers can be understood by comparison to that of the well-studied para-(phenylene vinylene) polymer and charge-injection barriers estimated from this comparison. To further understand the factors that influence band line-up, new systems are being explored which change the substrate-molecule linking chemistries. With these new systems, we hope to better understand the orbital nature of the charge transport chemistry and be able to better predict how changing the structure of the molecule or the substrate will affect the observed transport properties.
9:00 PM - N6.6
Controlled Nanogap Manufacturing for Single Molecule Contacts by Electromigration.
Arne Hoppe 1 , Joerg Seekamp 1 , Veit Wagner 1
1 School of Engineering and Science, International University Bremen, Bremen Germany
Show AbstractElectrical measurements at single molecules require a pair of electrodes separated by a nanogap of only a few nanometers corresponding to the size of the molecule. Various approaches like mechanical controlled break-junctions, crossed-wire junctions, nanopores and conducting atomic force microscopy are well known to be able to realize such nanogaps. However, an desirable additional gate electrode at the molecule is difficult to achieve following these approaches. A less frequently used technique for this purpose is nanogap formation by electromigration, where an additional gate electrode can easily be realized via the substrate. For the nanogap formation a small metal wire of typically 100 nm width is broken by imposing a high current density at liquid helium temperature. At room temperature this approach usually leads to gaps much larger than molecular sizes. Recently Strachan et al. reported on successful nanogap production at room temperature by using an active control scheme for the applied voltage in dependence of the measured conductivity of the wire. Following this approach we present an alternative control scheme, which includes in addition to the measured conductivity, the time derivative of the conductivity and the average noise level as parameters to control the applied voltage.In our experiments gold nanowires of 100 nm width and 20nm height with a Ti adhesion layer on a SiO2-surface were prepared by e-beam lithography. A current level of about 5 mA is usually sufficient to start the electromigration process at room temperature. We test different wire shapes as a long thin wire of constant thickness or a thick wire with lithographically defined short narrowing. We find the long thin wire to be more demanding for our control loop than a wire with a short narrowing.The regulation behavior of our control loop for the various regions of the electromigration process occurring until a nanogap is achieved will be discussed. With our approach we can reproducibly manufacture gaps at room temperature with given gap size smaller than 10 nm.
9:00 PM - N6.8
Electrical Properties of Alkyl Monolayers on Silicon.
S. Fishwick 1 , N. Wright 1 , A. Houlton 2 , B. Horrocks 2
1 School of Electrical, Electronic and Computer Engineering, University of Newcastle Upon Tyne, Newcastle Upon Tyne United Kingdom, 2 School of Natural Sciences, University of Newcastle Upon Tyne, Newcastle Upon Tyne United Kingdom
Show AbstractOrganic thin films can be used to tailor the electrical properties of metal-semiconductor junctions present in many microelectronic devices by acting as a highly controllable interfacial layer. We report on the formation of alkyl monolayers attached to the hydrogen-terminated surface of silicon (111) in both mercury drop and lithographically patterned Schottky diodes. Electrical measurements were performed at a range of temperatures to establish the mechanisms of charge transport through the organic material and demonstrate how varying alkene chain length can tune the monolayer thickness, layer conductivity and ultimately the behaviour of the final device. Chemical etchants and high temperature atoms associated with metal deposition have the potential to damage organic films through the formation of pin-hole defects. Monolayer damage due to repeated deposition/etch cycling was imaged using atomic force microscopy and devices using these films were tested for early breakdown. The produced alkyl monolayers have demonstrated thickness control with molecular precision and reliable operation as insulators below the physical limitations of SiO2.
9:00 PM - N6.9
DNA Templated CdS Nanowires as Microelectronic Interconnects.
T. Hollis 1 , S. Fishwick 1 , L. Dong 2 , B. Connolly 2 , A. Houlton 2 , B. Horrocks 2 , N. Wright 1
1 School of Electrical, Electronic and Computer Engineering, University of Newcastle Upon Tyne, Newcastle Upon Tyne United Kingdom, 2 School of Natural Sciences, University of Newcastle Upon Tyne, Newcastle Upon Tyne United Kingdom
Show AbstractDNA molecules represent an ideal nanowire scaffold material for molecular electronic devices, due to a combination of nanoscale diameters and highly controllable microscale lengths. We report on the conductivity of individual strands of λ-DNA coated with cadmium sulphide. Pairs of thin gold electrodes, separated by a range of micrometer lengths, were manufactured with large contacts on each electrode to allow testing signals to be applied. Each pair of electrodes was connected using a DNA templated CdS nanowire. Current-voltage measurements were used to determine the resistance of the synthesised nanowires over the various lengths and physical parameters were imaged using AFM and SEM techniques. These nanowires represent not only fundamental building blocks for “bottom-up” systems but are presented as a connection method between emerging molecular systems and traditional macroscopic environments.
Symposium Organizers
Ranganathan Shashidhar Geo-Centers Inc.
James G. Kushmerick National Institute of Standards and Technology
Heiko B. Weber University of Erlangen-Nurnberg
Nongjian J. Tao Arizona State University
N7: Bio-Electronics and Carbon Nanotubes
Session Chairs
Friday AM, April 21, 2006
Room 2000 (Moscone West)
9:30 AM - N7.1
Engineering of Semiconductor Oxide Surfaces and Interfaces for Biosensing Applications
Edward Eteshola 1 5 , Matthew Keener 4 1 5 , Dharma Tokachichu 6 , Benjamin Cipriany 4 , Min Gao 4 , Philip Barnes 1 5 , Leonard Brillson 4 , Bhushan Bharat 6 , Stephen Lee 1 3 5
1 Biomedical Engineering, Ohio State University, Columbus, Ohio, United States, 5 Davis Heart and Lung Research Institute, Ohio State University, Columbus, Ohio, United States, 4 Electrical Engineering, Ohio State University, Columbus, Ohio, United States, 6 Nanotribology Center, Ohio State University, Columbus, Ohio, United States, 3 Chemical Engineering, Ohio State University, Columbus, Ohio, United States
Show AbstractResearch involving the study of biomolecules (peptides, proteins, antibodies, antigens, etc) attachment and interactions at semiconductor oxide-liquid surfaces and interfaces is of significant bio/technological importance, and consequently has become an increasingly important and growing area of research activity. A better understanding and the ability to control/manipulate such phenomena is crucially essential for any investigation in the field of micro- or nanobiosensor technology, because the attachment of peptides/proteins and interactions of receptor/ligands on such solid surfaces govern performance and reliability of these devices in real-world situation applications. We are involved in a systematic research program that utilize modern protein and antibody engineering approaches to engineer the protein sensing interface of a subset of biochemically modified field effect transistor (BioFET) sensors, namely immunologically modified FET (ImmunoFET). To date, we have used self-assembled monolayers incorporating model receptor proteins to both modify and functionalize the FET SiO2 sensing gate, and demonstrated functionality of the FET sensor. We have also used phage display to identify short peptides that recognize and bind to thermally grown SiO2 layers; our primary interest is in use of these peptides as nanoscale affinity domains inserted as translational fusions to heterologous proteins to drive affinity interaction between the heterologous proteins and FET SiO2 sensing surfaces. In addition, we have developed a protein engineering technology (circular permutation of protein) that allows us to alter protein topography in a way that lets us manipulate the position of the ends of the protein and any point on the protein surface relative to the FET sensing surface. These results would be discussed/presented.
9:45 AM - **N7.2
Single Molecule Conductance Determination Using the I(s) and I(t) STM Methods.
Richard Nichols 1
1 The Department of Chemistry, The University of Liverpool, Liverpool, Merseyside, United Kingdom
Show AbstractMethods for forming stable molecular wires between a gold surface and a gold STM tip will be discussed and compared in this presentation. The resulting single molecule conductance (SMC) values for a variety of dithiol molecules, including more complex molecules with redox active groups along the molecular wire, will be discussed. Methods for obtaining single molecule conductance during current-distance and current-time experiments will be described. For instance, spontaneous formation of stable molecular wires between a gold scanning tunnelling microscopy (STM) tip and substrate is observed when the sample has a low coverage of dithiol molecules and the tunnelling resistance is made sufficiently small without touching the tip against the surface. The versatility of the techniques is demonstrated on a variety of molecule wires ranging for simple alkanedithiols [3] to redox active molecular wires [1,2,4] single and double stranded DNA [5]. The temperature dependence of molecule conductance is also discussed for both simple alkanedithiol molecules as well as conjugated molecular wires [6].1.Haiss, W.; van Zalinge, H.; Higgins, S. J.; Bethell, D.; Hobenreich, H.; Schiffrin, D. J.; Nichols, R. J., Redox state dependence of single molecule conductivity. Journal Of The American Chemical Society 2003, 125, (50), 15294-15295.2.Haiss, W.; Nichols, R. J.; Higgins, S. J.; Bethell, D.; Hobenreich, H.; Schiffrin, D. J., Wiring nanoparticles with redox molecules. Faraday Discussions 2004, 125, 179-194.3.Haiss, W.; Nichols, R. J.; van Zalinge, H.; Higgins, S. J.; Bethell, D.; Schiffrin, D. J., Measurement of single molecule conductivity using the spontaneous formation of molecular wires. Physical Chemistry Chemical Physics 2004, 6, (17), 4330-4337.4.Haiss, W.; van Zalinge, H.; Hobenreich, H.; Bethell, D.; Schiffrin, D. J.; Higgins, S. J.; Nichols, R. J., Molecular wire formation from viologen assemblies. Langmuir 2004, 20, (18), 7694-7702.5.van Zalinge, H.; Schiffrin, D. J.; Bates, A. D.; Haiss, W.; Ulstrup, J.; Nichols, R. J., Single molecule conductance measurements of single and double stranded DNA oligonucleotide, Harm van Zalinge, David J. Schiffrin, Andrew D. Bates, Wolfgang Haiss, Jens Ulstrup and Richard J. Nichols. ChemPhysChem, in press 2005.6.Haiss, W.; van Zalinge, H.; Bethell, D.; Ulstrup, J.; Schiffrin, D. J.; Nichols, R. J., Thermal Gating of the Single Molecule Conductance of Alkanedithiols. Faraday Discussion, FD131, 2005.
10:15 AM - N7.3
Theoretical Analysis of metallo-DNA Electrical Conductivity.
Olga Pupysheva 1 , Amir Farajian 1 , Boris Yakobson 1
1 Dept. of ME&MS, and Dept. of Chemistry, Rice University, Houston, Texas, United States
Show AbstractUnique self-assembling and self-recognition properties of DNA make it appealing as a building block for molecular electronics. However, low DNA conductance remains the main obstacle preventing its utilization. One of the ways to improve the electrical transport properties of DNA is introduction of metallic atoms between the nucleotide bases. In particular, artificial metallo-DNAs with copper-mediated base pairing hydroxypyridone-Cu(II)-hydroxypyridone have been synthesized recently by Tanaka and Shionoya. We theoretically study the electronic structure of relatively short fragments of such metallo-DNA double helix containing few copper atoms. Spatial localization and energies of the molecular orbitals (MO) are calculated (mainly using Gaussian03 software), with and without constant external electric field applied along the DNA axis. We compare the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), as well as the electric-field dependences of their energies, for metal-containing and natural DNA molecules. Furthermore, we address the effect of the number of copper atoms in metallo-DNA on the HOMO-LUMO energy gap. The most probable conduction mechanisms, namely, copper-copper hopping versus nucleotide π-π overlap, are considered. Based on our results, we evaluate the possibility to use artificial metallo-DNA as nanowire-interconnects. This work is supported by the Robert Welch Foundation and by the Office of Naval Research.
10:30 AM - N7.4
Oligonucleotide Based Self Assembly of Carbon Nanotubes.
Cengiz Ozkan 1 , Xu Wang 2 , Senthil Gurusamy-Thangavelu 1
1 Mechanical Engineering, University of California at Riverside, Riverside, California, United States, 2 Chemical and Environmental Engineering, University of California, Riverside, California, United States
Show AbstractWe describe self assembly processing of functional carbon nanotubes using single strand deoxyribonucleic acid (DNA) and peptide nucleic acid (PNA) fragments. Previous research has shown the self assembly of carbon nanotubes to quantum dots via a simple peptide bonding. Here, we make use of the DNA for self assembly of nanoscale components because of its spatial encoding capabilities which will be eventually useful for the integration of devices. During self assembly, first multiwalled carbon nanotubes have been functionalized via oxidation to introduce COOH groups at the nanotube ends. Amine functionalized ss-DNA fragments were attached to the COOH groups via the (1-ethyl-3-dimethylaminopropyl) carbodiimide HCl (EDC) coupling reaction. The resulting heterostructures have been characterized using Fourier transform infrared spectroscopy, Raman spectroscopy, scanning and transmission electron microscopy and energy dispersive spectroscopy. We have also conducted platinum metallization of DNA and PNA (peptide nucleic acid) fragments to study the properties conductive biological linkages to inorganic components. Current-voltage measurements of the metallized and bare structures will also be presented. Metallized nanotube-DNA and nanotube-PNA complexes could have potential applications for nanoelectronics and sensors.
10:45 AM - N7.5
UHV-STM Characterization of Protein Functionalized SWNTs on the Si(100) surfaces
Wei Ye 1 3 , Joseph Lyding 2 3
1 Materials Science & Engineering, University of Illinois, Urbana, Illinois, United States, 3 Beckman Institute for Advanced Science and Technology, University of Illinoins, Urbana, Illinois, United States, 2 Electrical and Computer Engineering, University of Illinoins, Urbana, Illinois, United States
Show AbstractImmobilization of biomolecules on single-walled carbon nanotubes (SWNTs) has prospects for new bioelectronic devices. Understanding the electronic properties of these systems on clean silicon surfaces is important in integrating biomolecules with conventional silicon-based devices. Here, we use STM to study the electronic properties of protein functionalized-SWNTs on atomically clean Si(100)-2×1 surfaces prepared in UHV.Saccharomyces cerevisiae (yeast) iso-1-cytochrome c was immobilized on the sidewalls of single-walled carbon nanotubes (SWNTs) via a bifunctional molecule, 1-pyrenebutanoic acid, succinimidyl ester [1]. The sample was freeze dried and deposited onto Si(100) surface by dry contact transfer (DCT) in UHV [2]. A UHV STM was used to acquire topographical images as well as spatially resolved tunneling current-voltage (I-V) spectra. Current imaging tunneling spectroscopy (CITS) was also performed on the cytochrome c protein bound to the Si(100) surface.The cytochrome c protein molecules have round shapes found both on the SWNTs and on the substrate. They are irregularly spaced on the side wall of the SWNTs. The size of the protein molecules attached to the nanotubes is comparable to the diameter of the nanotubes and the height is around 0.8 nm – 1.5 nm. The electronic properties of the protein molecules on SWNTs and on substrate were compared. The band gap of the molecules is always narrower than that of SWNTs and silicon substrate. Topographical images indicate the substructure of the protein molecule. Scanning tunneling spectroscopy shows both metallic and semiconducting areas inside of the protein molecule. [1] Chen, R. J.; Zhang, Y.; Wang, D.; Dai, H. J. Am.Chem. Soc. 2001, 123, 3838.[2] Albrecht, P. M. and Lyding, J. W., Appl. Phys. Lett. 2003, 83, 5029
11:30 AM - **N7.6
Electrically-Induced Infrared Emission from Carbon Nanotube Devices.
Jia Chen 1 , V. Perebeinos 1 , M. Freitag 1 , J. Tsang 1 , Ph. Avouris 1
1 , IBM T. J. Watson Reserach Center, Yorktown Heights, New York, United States
Show Abstract The optical properties of carbon nanotubes (CNTs) are currently the focus of intense study. CNTs are direct band gap materials and their optical spectra have long been attributed to transitions between free particle bands. We show that studies of electrically-excited infrared (IR) emission from single nanotube molecules provide new insights into the electron-hole interactions in quasi-1D systems. We demonstrate strongly-enhanced EL from a partially suspended CNTFET operated under unipolar transport conditions. In our devices, carriers are generated locally, when a single type of carrier is accelerated under high local electric fields to energies sufficient to create strongly correlated e-h pairs (excitons). This excitation mechanism contrasts with emission from radiative recombination of carriers (electrons and holes) injected from the opposite ends (source and drain) of a CNTFET operated under ambipolar transport conditions. We find not only an increase in emission efficiency by 2-3 orders of magnitude in the suspended CNTs, but a completely different dependence of the light emission on the electrical properties of the CNTFET. We show that the light emission intensity increases exponentially with the drive current in partially suspended CNTFETs, while in 3D materials light emission is usually proportional to the product of the electron and the hole currents. The strong Coulomb interaction between electrons and holes in a 1D CNT creates bound excitons whose binding energies are more than an order of magnitude larger that those in 3D materials, preventing them from dissociating under electrical fields thus contributing little to drive current compared with that in 3D. Finally, the much higher exciton density achieved in our devices than that in typical photoluminescence experiments allows us to detect emission from higher excitation states in CNTs.
12:00 PM - N7.7
Nonvolatile Carbon Nanotube Memory Device With Molecular Charge Storage
Volker Sorger 1 , Zhen Yao 1
1 Physics, Center for Nano- and Molecular Science and Technology and Texas Materials Institute, University of Texas, Austin, Texas, United States
Show AbstractWith Moore’s Law approaching the point where miniaturization of established “top-down” fabricated devices reach fundamental issues within the next one or two decades, researcher are avidly pursuing alternatives to fulfill the demand for increasing computing power. “Bottom-up” approaches to nano-electronics can potentially reach far beyond the limits of “top-down” manufacturing. Floating gate flash-memories are a dominant type of information storage devices on the market; however, scaling issues limit device performance. Similar to the floating dot single electron memories with a thin Si channel, here, a memory device consisting of a cabon nanotube (CNT) channel functionalized with charge storing, redox-active molecules, Cobalt Porhyrin (CoP) is reported. A critical scaling parameter for conventional flash memories is the tunnel oxide thickness. In the device geometry reported here, the tunnel thickness is in the sub-nanometer range, essentially only half the diameter of a CoP molecule. Remarkably, retention time and endurance tests show excellent device performance compared to Si-floating dot memories. Furthermore, the device can be programmed as a multi-bit storage system increasing the density for integrated device applications. Single electron charging behavior has been demonstrated upon cooling the device down to 4.2 K.
12:15 PM - N7.8
Thermoelectric Properties of a Nanocontact.
Keivan Esfarjani 1 , Mona Zebarjadi 2 , Ali Shakouri 2
1 Physics, Sharif University of Technology, Tehran Iran (the Islamic Republic of), 2 Electrical Engineering, UC Santa Cruz, Santa Cruz, California, United States
Show AbstractThermoelectric properties of a nanocontact made of two capped single wall carbon nanotubes (SWCNT) are calculated within the tight-binding approximation and by using Green's function method. It is found that doped semiconducting nanotubes can have high Seebeck coefficients. This in turn leads to very high figures of merit(ZT) for p-doped tubes which turn out to have also a large electrical to thermal conductivity ratio. Transport in the nanocontact device is dominated by quantum interference effects, and thus it can be tuned by doping (charge transfer and/or impurity potential) or application of a (nano-)gate voltage, or a magnetic field. Another reason for high ZT in this device is the absence of phonon transport as there is barely a contact between the two sides.
12:30 PM - N7.9
Probing Optoelectronic Properties of Functionalized Carbon Nanotubes Through Field Effect Transistor Response.
Jordan Poler 1 2 , Harsh Chaturvedi 2 1
1 Chemistry, UNC Charlotte, Charlotte, North Carolina, United States, 2 Center for Optoelectrics and Optical Communications, UNC Charlotte, Charlotte, North Carolina, United States
Show AbstractCarbon nanotubes and nanowires are important materials for new nanotechnology devices and sensors. Future opotoelectronic devices can be made from assemblies of nanostructured materials. One difficulty in preparing these assemblies from nanotubes is the lack of site-specific points of contact and the subsequent compliance of the linkage between nanoparticles. Using molecular mechanics and dynamics calculations, we have modeled the assembly process of two-dimensional and three-dimensional structures of carbon nanotubes. The linkers between the nanotubes consist of novel metalodendrimers. These dendrimers have multiple binding sites with chemically specified chirality. Most importantly, they are mechanically rigid. This enables the multidimensional constraints and geometry, required for advanced electronic and optoelectronic devices.We have fabricated back-gated single walled carbon nanotube field effect transistors. Devices were processed with standard optical lithography and high resolution e-beam lithography. We are using these devices to study charge injection into the nanotubes and the resultant effect on the tube’s transport properties. Organometalic based molecular adsorbates onto the nanotubes effect the transistor response. We believe this is due to charge transfer from the metal center through the ligand and finally onto the nanotube. Ruthenium centered phenanthroline complexes exhibit a strong metal to ligand charge transfer. We believe that the nanotube quenches charge from the ligand after the complex has been optically excited. This results in the potential for optically altering the carrier density, and therefore the transport properties of the nanotubes.E-beam lithography and molecular combing of functionalized carbon nanotube FETs will be presented. Imaging of the assemblies with SEM and AFM indicate molecular organization along the nanotubes. Nanomanipulation of the assembled tubes is accomplished with the AFM in order to study single molecule/ single nanotube electronic behavior.
12:45 PM - N7.10
A Novel Nanotube-on-Insulator (NOI) Approach toward Single-Walled Carbon Nanotube Devices
Xiaolei Liu 1 , Song Han 1 , Daihua Zhang 1 , Koungmin Ryu 1 , chongwu zhou 1
1 Electrical Engineering, University of Souther California, Los Angeles, California, United States
Show AbstractWe present a novel nanotube-on-insulator (NOI) approach to produce high-yield nanotube devices based on aligned single-walled carbon nanotubes. First, we managed to grow aligned nanotube arrays with controlled density on crystalline, insulating sapphire substrates, which bear analogy to industry-adopted silicon-on-insulator substrates. Based on the nanotube arrays, we demonstrated registration-free fabrication of both top-gated and polymer-electrolyte-gated field-effect transistors with minimized parasitic capacitance. In addition, we have successfully developed a way to transfer these aligned nanotube arrays to flexible substrates. Our approach has great potential for high-density, large-scale integrated systems based on carbon nanotubes for both micro- and flexible electronics.
N8: Devices and Molecular Switching
Session Chairs
Friday PM, April 21, 2006
Room 2000 (Moscone West)
2:30 PM - N8.1
A Novel Non-destructive Interfacing Technique for Molecular Scale Switching Junctions.
Chad Johns 1 , Ibrahim Kimukin 1 , M. Saif Islam 1 , Doug Ohlberg 2 , Duncan Stewart 2 , Carrie Donley 2 , Shih-Yuan Wang 2 , R. Stanley Williams 2
1 Electrical Engineering, UC Davis, Davis, California, United States, 2 Quantum Science Research, Hewlett Packard Laboratories, Palo Alto, California, United States
Show Abstract2:45 PM - N8.2
Self-Assembled Monolayer Sandwich Electronic Junctions
Xiaojuan Fan 1 , Dat T. Tran 1 , Daniel P. Brennan 1 , Tolulope O. Salami 1 , Scott R. J. Oliver 1
1 Dept. of Chemistry and Biochemistry, UC Santa Cruz, Santa Cruz, California, United States
Show AbstractWe report sandwich metal-SAM-metal junctions patterned into microscale arrays by contact printing. A metal-coated Si wafer was immersed into an a,w-alkanedithiol solution to self-assemble a monolayer of one molecule thickness. A nanoscale coating of metal was then evaporated on a polydimethylsiloxane (PDMS) stamp, and subsequently transferred onto the thiol SAM surface by contact printing. We have successfully fabricated the first examples of Ag-SAM-Ag and Co-SAM-Co molecular electronic junctions. Microscopic images show excellent edge resolution. The IV behavior of Ag-SAM-Ag sandwich junctions is non-linear. For Co-SAM-Co sandwich junctions, a large hysteresis was found in the IV curve, indicative of charge trapping and current bistability. These data along with the magnetic field-dependent transport properties will be discussed.
3:00 PM - N8.3
Etched Edge of Metal/Insulator/Metal Pattern for Molecular Scale Contacts
Bruce Hinds 1 2 , Pawan Tyagi 1 , Steve Holmes 2
1 Chemical and Materials Engineering, Univ. of Kentucky, Lexington, Kentucky, United States, 2 Chemistry, Univ. of Kentucky, Lexington, Kentucky, United States
Show AbstractProducing reliable electrical contacts with gaps having the dimensions of molecular lengths is a difficult challenge for molecular electronics. As a promising alternative to break-junctions, we use conventional film deposition and photolithography to form an exposed edge of a thin film multilayer structure (metal/insulator/metal). Molecules can self-assemble on the exposed edge offering an alternative conduction path through the molecules with angstrom-scale dimensional control. Critical to this approach is to have minimal background tunnel current between metal planes. We find the role of stresses to be the primary factor in reducing background current Electrodes were successfully fabricated with this strategy with current measured through a metal coordination compound cluster composed of a cube with cyano linked Ni or Fe at the corners. Thiolacetate ligand tethers come off of the cluster core and bind the complex to the metal leads, allowing the molecule to span the insulator gap on the surface of the etched pattern. Molecules that do not bridge the gap are not electrically active. Along the 10um pattern edge approximately 6000 molecules are involved in conduction. 10nA per molecule is seen at 10mV bias. Tunnel current through the molecules is analyzed with Simmons model and barrier height is found to be 1.1 eV and tunnel length of 1.2nm. Photo-enhancement of current is also seen. Control experiments show the controlled removal and attachment of the surface bound molecules. The electrode allows a simple and scalable technique to electrically contact molecules from end to end.
3:15 PM - N8.4
Large-area Molecular Diodes
Hylke B. Akkerman 1 , Paul W. M. Blom 1 , Dago M. de Leeuw 2 , Bert de Boer 1
1 Molecular Electronics, Materials Science Centre, University of Groningen, Groningen Netherlands, 2 , Philips Research Laboratories, Eindhoven Netherlands
Show AbstractOrganic materials have become important building blocks for electronics circuits. The use of a single molecular layer in a two-terminal diode has found tremendous interest by both academic and industrial research groups since first proposed in the mid-70s by Aviram and Ratner. Most of the measurements done on molecular diodes use scanning probes, break junctions, and metallic crossbars. From application point of view a crossbar circuitry is the preferred geometry for two-terminal molecular devices. However, since the active layer is only 1-2 nm thick, these crossbar devices are sensitive to short circuits through the self-assembled monolayers (SAMs) due to filamentary growth during deposition of the metal top contact, which is limiting the applicability of these molecular diodes. The only reliable data in literature so far are achieved on alkane(di)thiols in so-called nanopores by Reed et al., preventing short circuits by using a very small device diameter of only 45 nm. We demonstrate a novel technology, using conventional photolithography, for the facile and highly reproducible fabrication of large-area electronic metal-insulator-metal (MIM) diodes based on SAMs of alkanedithiols. The alkanedithiols are used as a reliable reference and thus essential for verifying the validity of a new technological approach for manufacturing molecular diodes. By using an organic conductor as a top electrode, which is not penetrating into the SAM, devices with unprecedented size up to 100 μm in diameter could be made with a high yield of working devices (> 95 %). The devices are stable after storage for at least 75 days in air and no degradation or hysteresis is observed for 100 consecutive I–V scans. When scaled to molecular dimensions our results are in good agreement with the earlier work on the nanopores but with a ~ 5 million times larger device area.
3:30 PM - N8.5
Molecular-Electronic Device Fabrication Enabling Complete Chemical and Physical Characterization
Jason Blackstock 1 , Duncan Stewart 1 , Zhiyong Li 1 , Carrie Donley 1 , Douglas Ohlberg 1 , Pamela Long 1 , Sehun Kim 1 , Regina Ragan 1 , R. Williams 1
1 Quantum Science Research, Hewlett-Packard Labs, Palo Alto, California, United States
Show AbstractOne of the main limitations of many nanoscale molecular-electronic devices is the lack of physical and chemical characterization accompanying electrical data. This lack of characterization is due in large part to the device geometries and fabrication processes being incompatible with the use of conventional characterization tools; frequently the critical layers and interfaces are inaccessibly buried in the device structure. Nonetheless, understanding the internal physical and chemical properties of the active layer(s) and interfaces inside the devices is essential for accurately correlating device structure and electronic behavior.Herein we present a set of new fabrication techniques that enable a range of conventional characterization tools to be employed both during and after nanoscale device fabrication. These techniques include: the fabrication of atomically-flat, patterned template-stripped bottom metal electrodes with well-defined atomic structure (elucidated by UHV-STM); and the formation of a new stencil-based nanopore device geometry that enables detailed characterization of the internal physical and chemical nanoscale properties of the final device structures. The combination of these techniques with other standard processing allows the generation of molecular-electronic devices over a range of lateral device sizes, from tens of nanometers to hundreds of microns. Details on fabricated device components and on complete devices (including UHV-STM, SEM and AFM data) will be presented, along with descriptions of how these techniques allow conventional physical and chemical characterization tools (including in-situ UHV-STM, XPS and IR) to be successfully employed.Our goal at HP is to couple detailed physical characterization and detailed electrical characterization of molecular device structures. This presentation focuses specifically on the fabrication techniques developed to enable this coupling. Presentations at this meeting by C.L. Donley and D.R Stewart respectively present complete in-situ physical/chemical characterization and complete electronic behavior of molecular-electronic devices fabricated using these techniques.
4:15 PM - N8.6
A Soft Top Contact Deposition Technique for Forming Large Area Molecular Junctions.
Jason Fabbri 1 , Ken Shimizu 1 , Jim Jelincic 1 , Nicholas Melosh 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractCross-bar electrical junctions are necessary for molecular electronics yet traditional approaches to depositing the top electrical contact such as e-beam evaporation can cause damage to molecular monolayers. In particular, for large area electrodes which could be useful for in-situ optical spectroscopy on molecular junctions, top contact deposition induced damage presents a major problem. We have developed a new technique that involves the flotation of cross-bar top contacts held together by a polymer backing onto molecular monolayer films. The polymer backing is spin-cast on top of the electrodes then lifted off from a substrate and floated onto a molecular device. This polymer layer enables cross-bar patterns, retention of pattern registry, and ability to scale device sizes from 10 μm to 2 mm length scales. In addition, interfacial energetics resulting from the polymer induce a drying process that leads to wrinkle free electrodes. Non-shorting (>90% yield), mm-scale junctions of alkane chain molecules deposited via the LB technique were fabricated and the tunneling current measured. A tunneling decay constant of 0.86 Å-1 was found, in good agreement with single molecule measurements on alkanethiols. Various microscopy and spectroscopy techniques are used to demonstrate the high quality of these top contacts and their potential applications.
4:30 PM - N8.7
Solid Electrolyte Based Switching Junctions Fabricated Using an Organic Monolayer for Nanoscale Separation Between Electrodes.
Doug Ohlberg 2 , Duncan Stewart 2 , Shih-Yuan Wang 2 , R. Stanley Williams 2 , Chad Johns 1 , Long Do 1 , Ibrahim Kimukin 1 , M. Saif Islam 1
2 Quantum Science Research, Hewlett Packard Laboratories, Palo Alto, California, United States, 1 Electrical Engineering, UC Davis, Davis, California, United States
Show AbstractGrowth and shrinkage of nanoscale metal protrusions, from solid electrolytes such as metal sulphides, across a nanometer sized gap were recently found to controllably generate high and low conducting states with varying electrical bias voltages. We report a novel technique of using a Langmuir-Bloggett film of Cadmium Stearate or disteroyl phosphatidyl Choline / Stearic, to create the nano-sized gap between an inert electrode and a Cu2S or Ag2S solid electrolyte. The formation and annihilation of an atomic bridge at the crossing point between two electrodes were facilitated by using the LB flim with ~1nm thickness. Switching was observed to be similar, with typical device yields 70%+, regardless of the choice for the LB film. Most devices consistently switched in the 0.5V-0.9V range, while others exhibited switching in the 2V-5V range. This technique of using LB film offers the distinct benefit of maintaining precise control over the gap size contributing to higher yields and repeatability in devices.
4:45 PM - N8.8
Low Temperature Transport Study of the "nitro" Molecules.
Nabanita Majumdar 1 , Zena Martin 1 , Nathan Swami 1 , L. Harriott 1 , Y. Yao 2 , James Tour 2 , Dave Long 3 , R. Shashidhar 3
1 Electrical and Computer Engineering, University of Virginia, Charlottesville , Virginia, United States, 2 Department of Chemistry and Center for Nanoscale Science and Technology, Rice University, Houston, Texas, United States, 3 , Geo-Centers R&D Center, Arlington, Virginia, United States
Show Abstract5:00 PM - N8.9
In-Situ Surface Plasmon Spectroscopy of Molecule-based Switching Devices
Kentaro Shimizu 1 , Ragip Pala 1 , Jason Fabbri 1 , Jim Jelincic 1 , Mark Brongersma 1 , Nicholas Melosh 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractA central architecture towards fabricating molecular-electronics memory elements have employed a cross-bar array in which electrically active molecules sandwiched between two metal contacts are switched by an applied voltage. Although current-voltage measurements show non-capacitive hysteresis, for conventional spectroscopic techniques, the presence of the top opaque metal electrode prevents optical analysis to verify the mechanism behind this switching behavior. Surface plasmon polaritons, however, can resonantly couple into the organic layer between two metal films allowing for a sensitive in-situ investigation. In these devices, the top metal film not only serves as the electrode, but also as a source for surface plasmon generation and coupling. We have exploited this resonance effect to measure changes in the refractive index of organic molecules, including rotaxanes and Ru(Bipy)3, in molecular devices. We find the refractive indices, indeed, reveal correlation in optical absorption between solution and the solid state. Furthermore, we report optical transitions along with electrical switching that support a model of molecular reconfiguration in a metal-molecule-metal junction.
5:15 PM - N8.10
Interfacial Molecular Charge Transport in Patterned Monolayer Films for OLED Applications
Lucile Teague 1 , James Kushmerick 1
1 Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractUnderstanding charge transport in molecular systems and molecular thin films is crucial for the development of molecule-based device structures. As such, we present a study of the interfacial charge transport for known hole and electron transport materials tethered to SiO2 surfaces. Molecular attachment has been achieved by multi-step reaction chemistry on self-assembled silane monolayers from the literature 1,2.. The relationship between the structure and charge transport properties of these films is characterized by FTIR, ellipsometry and AFM methods, and will be compared to theoretical models of these monolayer films. Additionally, micro- and nanoscale lithographic methods, including AFM based nanolithography, for the creation of mixed hole and electron transport films will be discussed. In particular, we are interested in the charge transport characteristics at the interface of the patterned hole transport and electron transport regions and their subsequent relationship to the efficiency and performance of molecular scale devices such as organic light-emitting diodes.1Wasserman, S.R.; Tao, Y.; Whitesides, G. M. Langmuir, 1989, 5, 1074-1087. 2Kooi, S. E.; Baker, L. A.; Sheehan, P. E., Whitman, L. J. 2004, 16, 1013-1016.
5:30 PM - N8.11
Electrical Conductivity Measurements on Functionalized, Mn12 Acetate-based complexes, for Potential use as Molecular Wires Integrated with Storage Devices.
Prabhakar Bandaru 1 2 , Chinung Ni 1 2 , Chris Beedle 3 , David Hendrickson 3 , Sonali Shah 3
1 MAE, UC, San Diego, La Jolla, California, United States, 2 Materials Science Program, UC, San Diego, La Jolla, California, United States, 3 Department of Chemistry, UC, San Diego, La Jolla, California, United States
Show Abstract