Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session L11: Focus Session: Transport Properties of Nanostructures III: Molecular Junctions II |
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Sponsoring Units: DMP Chair: Dan Ralph, Cornell University Room: 305 |
Tuesday, March 17, 2009 2:30PM - 3:06PM |
L11.00001: Electron Transport in Single Molecule Junctions: Stability, Electron-Phonon Interactions and Current-Induced Local Heating Invited Speaker: Understanding electron transport in a single molecule connected to two electrodes is as basic task in molecular electronics. A widely used approach is to attach the molecule with two linkers that can bind to the electrodes. Thiol is the most studied linker because of its well known capability to bind strongly to metal electrodes, such as Au, although several other linkers, such as isocyanide, amine, pyridine, carbon-carbon and carboxylic acid, have also been used to establish a molecule-electrode contact. It has been concluded that the linkers can play an important or even dominant role in the conductance and other electron transport properties of molecular junctions. Since the molecule-electrode contact is often the weakest link in a molecular junction, an important question that has not yet been well studied is: \textit{How stable is a molecular junction due to the finite lifetime of the linker-electrode bond?} Another important question is: \textit{How hot does a molecular junction get when passing a current through it?} In the present work, we investigate the stability and breakdown mechanism of a single molecule covalently attached to two gold electrodes via Au-S bonds. We report on an experimental study of current-induced local heating in single molecules covalently attached to two gold electrodes as a function of applied bias and molecular length We also discuss the related electron-phonon interactions in single molecule junctions. [Preview Abstract] |
Tuesday, March 17, 2009 3:06PM - 3:18PM |
L11.00002: Electron Transport and Thermoelectricity in Alkanethiol Molecular Junctions Yu-Chang Chen, Chun-Lan Ma, Diu Nghiem, Yu-Shen Liu We investigate the electron transport properties of alkanethiol molecules in the two- and three-terminal junctions by using first-principles approaches. We observe that novel states around the Fermi levels are introduced in the amino-substituted butanethiol junction. It leads to a sharp increase of the current owing to the resonant tunneling. We also describe a field-theoretic theory combined with first principles approaches to calculate the thermoelectricity. The dependence of the Seebeck coefficient on the biases, gate voltages, and temperatures is systematically investigated. Due to the novel states introduced by the amino-substituted butanethiol junction, the Seebeck coefficient could be easily controlled by using gate voltages and biases. When the temperature in one of the electrodes is set to zero, the Seebeck coefficient could vary pronouncedly with the temperature in the other electrode, and such dependence could be enhanced by varying gate voltages. At finite biases, we also find richer features in the Seebeck coefficient related to the density of states in the vicinity of the left and right Fermi levels. [Preview Abstract] |
Tuesday, March 17, 2009 3:18PM - 3:30PM |
L11.00003: Ab initio transport calculations of molecular wires with electron-phonon couplings Kenji Hirose, Nobuhiko Kobayashi Understanding of electron transport through nanostructures becomes important with the advancement of fabrication process to construct atomic-scale devices. Due to the drastic change of transport properties by contact conditions to electrodes in local electric fields, first-principles calculation approaches are indispensable to understand and characterize the transport properties of nanometer-scale molecular devices. Here we study the transport properties of molecular wires between metallic electrodes, especially focusing on the effects of contacts to electrodes and of the electron-phonon interactions. We use an ab initio calculation method based on the scattering waves, which are obtained by the recursion-transfer-matrix (RTM) method, combined with non-equilibrium Green's function (NEGF) method including the electron-phonon scatterings. We find that conductance shows exponential behaviors as a function of the length of molecular wires due to tunneling process determined by the HOMO-LUMO energy gap. From the voltage drop behaviors inside the molecular wires, we show that the contact resistances are dominant source for the bias drop and thus are related to local heating. We will present the electron-phonon coupling effects at contact on the inelastic scattering and discuss on the local heating and local temperature, comparing them with those of metallic atomic wires. [Preview Abstract] |
Tuesday, March 17, 2009 3:30PM - 3:42PM |
L11.00004: Transport properties and stability of molecular break junctions Nikolai Sergueev, Leonidas Tsetseris, Kalman Varga, Sokrates Pantelides The electrode-molecule interface in a break junction is known to be crucial to understand its electronic and transport properties. Using first-principles calculations we first probe a comprehensive set of mechanisms responsible for the stability of the prototype junction of a benzene-dithiol (BDT) between gold electrodes. We find that by pulling the electrodes apart the geometry of the molecule depends drastically on the electrode-surface morphology. We next report results of the quantum transport calculations for several stable junction configurations. The calculations are performed using the recently developed technique based on density functional theory and complex absorbing potentials[1]. The molecular junction is treated as a closed system with a set of complex potentials mimicking the source and the drain electrodes. We find that the conductance of the BDT molecule varies significantly within the different junction configurations. We will compare the results with recent experiments on BDT break junctions. [1]. K. Varga and S.T. Pantelides, PRL 98, 076804 (2007). [Preview Abstract] |
Tuesday, March 17, 2009 3:42PM - 4:18PM |
L11.00005: Electrical Conductance and Reversible Conductance Switching in Molecular Junctions Invited Speaker: A technology is demonstrated to fabricate reliable molecular metal-molecule-metal junctions with unprecedented device diameters up to 100 $\mu $m. The yield of these molecular junctions is close to unity. Stability investigations have shown a shelf life of years and no deterioration upon cycling. Key ingredients are the use of a conducting polymer layer (PEDOT:PSS) sandwiched between the self-assembled monolayer (SAM) and the top electrode to prevent electrical shorts, and processing in lithographically defined vertical interconnects (vias) to prevent both parasitic currents and interaction between the environment and the SAM [1--3]. Furthermore, a fully functional solid-state molecular electronic switch is manufactured by conventional processing techniques. The molecular switch is based on a monolayer of photochromic diarylethene molecules sandwiched between two electrodes. The monolayer reversibly switches the conductance by more than one order of magnitude between the two conductance states via optical addressing. This bidirectional conductance switch operates as an electronic ON/OFF switch and as a reprogrammable data storage unit that can be optically written and electronically read [4]. \\[4pt] [1]\textit{ Nature}, \textbf{441}, 69--72 (2006). \\[0pt] [2] \textit{Proc. Natl Acad. Sci USA, }\textbf{104}, 11161-11167 (2007). \\[0pt] [3] \textit{Nature} \textit{Nanotechn.}, \textbf{3}, December issue (2008) \\[0pt] [4] \textit{Adv. Mater. }\textbf{20}, 1467--1473. [Preview Abstract] |
Tuesday, March 17, 2009 4:18PM - 4:30PM |
L11.00006: Reversible, mechanically-activated switching in pyridine single molecule junctions Maria Kamenetska, Su Ying Quek, Michael L. Steigerwald, Hyoung Joon Choi, Steven G. Louie, Mark S. Hybertsen, J.B. Neaton, Latha Venkataraman We measured the conductance of single pyridine-terminated molecules by mechanically forming and breaking Au point contacts with a modified STM in a solution of molecules. Conductance traces recorded while stretching the junction reveal two distinct steps at different conductance, both due to the formation of a single molecule junction between gold electrodes. To better understand the origin of this bi-stable conductance signature, we devise a new method to experimentally determine the distance between the gold electrodes for any given molecular conductance. We find a clear correlation between the level of conductance and the distance between gold electrodes, with the lower conductance corresponding to a molecule fully stretched between the contacts and the higher conductance to a molecule bound at an angle. The dependence of conductance on metal-molecule contact geometry allows us to reversibly switch between conductance states by elongating and compressing the junction. [Preview Abstract] |
Tuesday, March 17, 2009 4:30PM - 4:42PM |
L11.00007: First-Principles Studies of Single-Molecule Junctions: Conductance and Mechanically-Controlled Switching Su Ying Quek, Hyoung Joon Choi, Steven G. Louie, Mark S. Hybertsen, Latha Venkataraman, J.B. Neaton We explore the conductance of amine- and pyridine-Au single-molecule junctions, in the context of recent experiments, with a density-functional theory (DFT)-based scattering state approach. Using a physically motivated self-energy correction, we compute conductance values in good agreement with experiment, in contrast to DFT values that are too large[1]. We investigate quantitatively conductance trends, and demonstrate, together with experiment, that reversible conductance switching can result from mechanically-induced changes in the metal-molecule contact geometry in pyridine-Au junctions. [1] Quek et al, Nano Lett 7, 3477 (2007) [Preview Abstract] |
Tuesday, March 17, 2009 4:42PM - 4:54PM |
L11.00008: Conductance of Molecular Wires Measured by STM- Break Junction Jonathan R. Widawsky, Maria Kamenetska, Adam C. Whalley, Jennifer E. Klare, Colin Nuckolls, Mark S. Hybertsen, Latha Venkataraman We present a comparison of the measured conductances of short molecular wires attached to gold electrodes in ambient conditions. The junctions are fabricated using a modified STM to repeatedly form and break Au point contacts, characterized by the quantum of conductance, in a solution of molecules. Specifically, we study how the conductance of three molecules -- 4,4'-diaminoazobenzene, 4,4'-diaminostilbene, and bis-(4-aminophenyl)acetylene -- depends on the voltage bias applied across the electrodes. In order to determine a statistically most-probable value of conductance, each measurement is obtained from data sets of approximately 10,000 individual conductance pull-out traces obtained over a few hours. In addition, we measure the conductance of solutions irradiated with ultraviolet light to induce photoisomerization of the azobenzene and stilbene from their \textit{trans} to the \textit{cis} configurations. [Preview Abstract] |
Tuesday, March 17, 2009 4:54PM - 5:06PM |
L11.00009: Molecular orbital theory of ballistic electron transport through molecules Matthias Ernzerhof, Philippe Rocheleau, Francois Goyer Electron transport through molecules occurs, for instance, in STM imaging and in conductance measurements on molecular electronic devices (MEDs). To model these phenomena, we use a non-Hermitian model Hamiltonian [1] for the description of open systems that exchange current density with their environment. We derive qualitative, molecular-orbital-based rules relating molecular structure and conductance. We show how side groups attached to molecular conductors [2] can completely suppress the conductance. We discuss interference effects in aromatic molecules [3] that can also inhibit electron transport. Rules are developed [1] for the prediction of Fano resonances. All these phenomena are explained with a molecular orbital theory [1,4] for molecules attached to macroscopic reservoirs. [1] F. Goyer, M. Ernzerhof, and M. Zhuang, JCP 126, 144104 (2007); M. Ernzerhof, JCP 127, 204709 (2007). [2] M. Ernzerhof, M. Zhuang, and P. Rocheleau, JCP 123, 134704 (2005); G. C. Solomon, D Q. Andrews, R P. Van Duyne, and M A. Ratner, JACS 130, 7788 (2008). [3] M. Ernzerhof, H. Bahmann, F. Goyer, M. Zhuang, and P. Rocheleau, JCTC 2, 1291 (2006); G. C. Solomon, D. Q. Andrews, R. P. Van Duyne, and M. A. Ratner, JCP 129, 054701 (2008). [4] B.T. Pickup, P.W. Fowler, CPL 459, 198 (2008); P. Rocheleau and M. Ernzerhof, JCP, submitted. [Preview Abstract] |
Tuesday, March 17, 2009 5:06PM - 5:18PM |
L11.00010: Quantum transport in Molecular Device Partha Pratim Pal, Brandon Johnson, Ranjit Pati Researchers have taken a lot of interest in designing electronic circuits using molecules ever since the pioneering work of Aviram and Ratner that showed that an organic molecule can be used as a rectifier. Organic molecules with their abundant availability, structural flexibility coupled with their versatile electronic properties are promising candidates for miniaturized electronic devices. To be able to predict the behavior of different organic molecules in an electronic circuit under applied bias, we need to have a detailed knowledge of the electronic structure of the molecule under the influence of the applied electric field. Thus first principles calculations are the best way to get to the root of this problem. In this talk, we report a new approach to model electron transport in single molecular junction, which gives results that match closely with the experimental counterparts. We believe this new approach would give a tremendous boost to the predictive capability of electronic properties of molecular devices. [Preview Abstract] |
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