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Molecular Electronics is self-contained and unified in its presentation. It can be used as a textbook on nanoelectronics by graduate students and advanced undergraduates studying physics and chemistry. In addition, included in this new edition are previously unpublished material that will help researchers gain a deeper understanding into the basic concepts involved in the field of molecular electronics.
In this thesis we studied the conductance of single molecule junctions. We focused on the consequences of nuclear motion on the transport characteristics of the junction and investigated the switching behavior of tautomeric molecules. Two different theoretical methods were used: scattering and density matrix theory. Scattering theory was applied to to two classes of molecules. In the benzene-thiolate systems we demonstrated the importance of respective time/energy scales, comprising the lifetime of the hole on the molecule, the size of the vibronic coupling, and the vibrational frequency, which determine vibrational effects. For the tautomers switching behavior depended significantly on the chemical nature of the hydrogen carrying unit. Density matrix theory was used to compute the current-voltage curve of a 'two electronic states'-'one mode' system, which we compared to similar results, obtained from scattering theory.
Charge Transport in Organic Semiconductors, by Heinz Bässler and Anna Köhler. Frontiers of Organic Conductors and Superconductors, by Gunzi Saito and Yukihiro Yoshida. Fullerenes, Carbon Nanotubes, and Graphene for Molecular Electronics, by Julio R. Pinzón, Adrián Villalta-Cerdas and Luis Echegoyen. Current Challenges in Organic Photovoltaic Solar Energy Conversion, by Cody W. Schlenker and Mark E. Thompson.- Molecular Monolayers as Semiconducting Channels in Field Effect Transistors, by Cherie R. Kagan. Issues and Challenges in Vapor-Deposited Top Metal Contacts for Molecule-Based Electronic Devices, by Masato M. Maitani and David L. Allara. Spin Polarized Electron Tunneling and Magnetoresistance in Molecular Junctions, by Greg Szulczewski.
As the size scale of electrical devices approach the atomic scale. Moore’s law is predicted to be over for semiconductor devices. Studies into the replacement of semiconductor technology with organic devices was first predicted by Avriam and Ratner[1] in 1974. Since then significant research into molecular based organic devices has been conducted. The work presented in this dissertation explores the theoretical frameworks used to model transport through molecular junctions. We present studies which seek to garner a better understanding of the charge transport through molecular junctions and how the conduction properties can be optimized. We show that a single atom can change a molecule from an insulator to a conductor. We also study the effects of sigma and pi bridges on molecular rectification. We will then show molecular devices that act as viable electrical static and dynamic switches. The studies presented here help to demonstrate the viability of organic devices in the forms of rectifiers and switches with applications ranging from the replacement of traditional semiconductor devices to neuromorphic computing.
In recent years, ever more electronic devices have started to exploit the advantages of organic semiconductors. The work reported in this thesis focuses on analyzing theoretically the energy level alignment of different metal/organic interfaces, necessary to tailor devices with good performance. Traditional methods based on density functional theory (DFT), are not appropriate for analyzing them because they underestimate the organic energy gap and fail to correctly describe the van der Waals forces. Since the size of these systems prohibits the use of more accurate methods, corrections to those DFT drawbacks are desirable. In this work a combination of a standard DFT calculation with the inclusion of the charging energy (U) of the molecule, calculated from first principles, is presented. Regarding the dispersion forces, incorrect long range interaction is substituted by a van der Waals potential. With these corrections, the C60, benzene, pentacene, TTF and TCNQ/Au(111) interfaces are analyzed, both for single molecules and for a monolayer. The results validate the induced density of interface states model.
Quantum tunnelling is one of the strangest phenomena in chemistry, where we see the wave nature of atoms acting in “impossible” ways. By letting molecules pass through the kinetic barrier instead of over it, this effect can lead to chemical reactions even close to the absolute zero, to atypical spectroscopic observations, to bizarre selectivity, or to colossal isotopic effects. Quantum mechanical tunnelling observations might be infrequent in chemistry, but it permeates through all its disciplines producing remarkable chemical outcomes. For that reason, the 21st century has seen a great increase in theoretical and experimental findings involving molecular tunnelling effects, as well as in novel techniques that permit their accurate predictions and analysis. Including experimental, computational and theoretical chapters, from the physical and organic to the biochemistry fields, from the applied to the academic arenas, this new book provides a broad and conceptual perspective on tunnelling reactions and how to study them. Quantum Tunnelling in Molecules is the obligatory stop for both the specialist and those new to this world.