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"Molecular electronics"
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Electron Transport in Molecular Wire Junctions
Molecular conductance junctions are structures in which single molecules or small groups of molecules conduct electrical current between two electrodes. In such junctions, the connection between the molecule and the electrodes greatly affects the current-voltage characteristics. Despite several experimental and theoretical advances, including the understanding of simple systems, there is still limited correspondence between experimental and theoretical studies of these systems.
Journal Article
A Single-Molecule Diode
We have designed and synthesized a molecular rod that consists of two weakly coupled electronic π-systems with mutually shifted energy levels. The asymmetry thus implied manifests itself in a current-voltage characteristic with pronounced dependence on the sign of the bias voltage, which makes the molecule a prototype for a molecular diode. The individual molecules were immobilized by sulfur-gold bonds between both electrodes of a mechanically controlled break junction, and their electronic transport properties have been investigated. The results indeed show diode-like current-voltage characteristics. In contrast to that, control experiments with symmetric molecular rods consisting of two identical π-systems did not show significant asymmetries in the transport properties. To investigate the underlying transport mechanism, phenomenological arguments are combined with calculations based on density functional theory. The theoretical analysis suggests that the bias dependence of the polarizability of the molecule feeds back into the current leading to an asymmetric shape of the current-voltage characteristics, similar to the phenomena in a semiconductor diode.
Journal Article
Nanoelectronics : a molecular view
\"This is a reference book for graduate students and researchers in the areas of nanomaterials, nanoelectronics, solid state physics and solid state devices. Segments of this book are also useful as textbook for a course in nanoelectronics\"-- Provided by publisher.
Book
Molecular Electronics: Some Views on Transport Junctions and beyond
The field of molecular electronics comprises a fundamental set of issues concerning the electronic response of molecules as parts of a mesoscopic structure and a technology-facing area of science. We will overview some important aspects of these subfields. The most advanced ideas in the field involve the use of molecules as individual logic or memory units and are broadly based on using the quantum state space of the molecule. Current work in molecular electronics usually addresses molecular junction transport, where the molecule acts as a barrier for incoming electrons: This is the fundamental Landauer idea of \"conduction as scattering\" generalized to molecular junction structures. Another point of view in terms of superexchange as a guiding mechanism for coherent electron transfer through the molecular bridge is discussed. Molecules generally exhibit relatively strong vibronic coupling. The last section of this overview focuses on vibronic effects, including inelastic electron tunneling spectroscopy, hysteresis in junction charge transport, and negative differential resistance in molecular transport junctions.
Journal Article
Logic Gates and Computation from Assembled Nanowire Building Blocks
Miniaturization in electronics through improvements in established \"top-down\" fabrication techniques is approaching the point where fundamental issues are expected to limit the dramatic increases in computing seen over the past several decades. Here we report a \"bottom-up\" approach in which functional device elements and element arrays have been assembled from solution through the use of electronically well-defined semiconductor nanowire building blocks. We show that crossed nanowire p-n junctions and junction arrays can be assembled in over 95% yield with controllable electrical characteristics, and in addition, that these junctions can be used to create integrated nanoscale field-effect transistor arrays with nanowires as both the conducting channel and gate electrode. Nanowire junction arrays have been configured as key OR, AND, and NOR logic-gate structures with substantial gain and have been used to implement basic computation.
Journal Article
Logic Circuits with Carbon Nanotube Transistors
We demonstrate logic circuits with field-effect transistors based on single carbon nanotubes. Our device layout features local gates that provide excellent capacitive coupling between the gate and nanotube, enabling strong electrostatic doping of the nanotube from p-doping to n-doping and the study of the nonconventional long-range screening of charge along the one-dimensional nanotubes. The transistors show favorable device characteristics such as high gain (>10), a large on-off ratio (>105), and room-temperature operation. Importantly, the local-gate layout allows for integration of multiple devices on a single chip. Indeed, we demonstrate one-, two-, and three-transistor circuits that exhibit a range of digital logic operations, such as an inverter, a logic NOR, a static random-access memory cell, and an ac ring oscillator.
Journal Article
Field regulation of single-molecule conductivity by a charged surface atom
Electrical transport through molecules has been much studied since it was proposed1 that individual molecules might behave like basic electronic devices, and intriguing single-molecule electronic effects have been demonstrated2, 3. But because transport properties are sensitive to structural variations on the atomic scale4, 5, 6, 7, further progress calls for detailed knowledge of how the functional properties of molecules depend on structural features. The characterization of two-terminal structures has become increasingly robust and reproducible8, 9, 10, 11, 12, and for some systems detailed structural characterization of molecules on electrodes or insulators is available13, 14, 15, 16, 17. Here we present scanning tunnelling microscopy observations and classical electrostatic and quantum mechanical modelling results that show that the electrostatic field emanating from a fixed point charge regulates the conductivity of nearby substrate-bound molecules. We find that the onset of molecular conduction is shifted by changing the charge state of a silicon surface atom, or by varying the spatial relationship between the molecule and that charged centre. Because the shifting results in conductivity changes of substantial magnitude, these effects are easily observed at room temperature.
Journal Article
The fabrication, characterization and functionalization in molecular electronics
Developments in advanced manufacturing have promoted the miniaturization of semiconductor electronic devices to a near-atomic scale, which continuously follows the ‘top-down’ construction method. However, huge challenges have been encountered with the exponentially increased cost and inevitably prominent quantum effects. Molecular electronics is a highly interdisciplinary subject that studies the quantum behavior of electrons tunneling in molecules. It aims to assemble electronic devices in a ‘bottom-up’ manner on this scale through a single molecule, thereby shedding light on the future design of logic circuits with new operating principles. The core technologies in this field are based on the rapid development of precise fabrication at a molecular scale, regulation at a quantum scale, and related applications of the basic electronic component of the ‘electrode–molecule–electrode junction’. Therefore, the quantum charge transport properties of the molecule can be controlled to pave the way for the bottom-up construction of single-molecule devices. The review firstly focuses on the collection and classification of the construction methods for molecular junctions. Thereafter, various characterization and regulation methods for molecular junctions are discussed, followed by the properties based on tunneling theory at the quantum scale of the corresponding molecular electronic devices. Finally, a summary and perspective are given to discuss further challenges and opportunities for the future design of electronic devices. Molecular electronics is a science that studies the quantum behavior of electrons tunneling in molecules, in which the electric property of a single molecule is an intrinsic fingerprint property strongly correlated to its structure, offering opportunities to develop new operating strategies for electronic devices for future possible solutions to suppress beyond Moore’s Law. The electrode–molecule–electrode junction (molecular junction) is the basic unit and model of molecular electronics, which can be produced by precise fabrication and regulation methods. The basic aspects of fabrication, characterization and functionalization in molecular electronics are described.
Journal Article