Overview of Nanoelectronic Devices <s> A. Molecular Electronic Switching Devices <s> Properties of synthetic electroactive and photochromic molecular systems are described, with particular emphasis on microscopic processes controlling these properties. Both low-molecular weight and polymeric materials can be (and many have already been) used as conducting systems. The chemical flexibility of many molecular systems also allows for using them as information-processing materials, whose action is based on their photochromic properties. A relation between properties of individual molecules and those of macroscopic molecular systems allows one to envisage construction of molecular-scale devices. However, due to limitations associated with technological problems (construction of molecular-scale elements, their addressing, quantum-mechanical (size) limitations, etc.), the construction of such elements is still a problem that awaits solution. > <s> BIB001 </s> Overview of Nanoelectronic Devices <s> A. Molecular Electronic Switching Devices <s> Several protein-based molecular biodevices have been made possible by the molecular interfacing technology that enables proteins to electronically communicate with the conventional electronic materials, such as metals or semiconductors. The molecular interfacing technology, however, should be extensively improved to allow for precise designs at the single-molecule level. The molecular-scale design of protein-based molecular biodevices may be accomplished by further innovation in molecular interfacing technology. It is also important to pursue the possibility of utilizing the self-organization of biomolecules for information processing, and to make it possible to create a molecular network-based biodevice without any preprogrammed wiring among its molecules. Major advances have recently been made in basic technology. Yet, it will take some time to construct a prototype neurodevice in which neurons are utilized as components. Further investigations should focus on the development of molecular interfaces that offer bilateral communication between neurons and conventional electronic materials. > <s> BIB002 </s> Overview of Nanoelectronic Devices <s> A. Molecular Electronic Switching Devices <s> Abstract The golden-rule expression for the non-adiabatic electron-transfer rate constant in donor/acceptor system is analyzed using a Fourier (time-dependent) representation. The rate constant is written in terms on an evolving overlap of wavepackets on initial and final state potential-energy surfaces. By the following the explicit time-dependence of these functions, we can obtained both standard results of electron-transfer theory for the specific case of a standard polaron-type model (including inverted-region behavior, temperature dependence, nuclear tunneling effects, energy sharing) and some important generalizations, including situations of breakdown of the Condon approximation, analysis of the effects of the frequency changes, and simplifications of the relevant vibrational modes due to solvent, to intra-molecular vibrations, or to both. The correlation-function method is briefly described, and results of a number of calculations are discussed. Analysis includes the effect of inhomogeneous broadening and energy flow into solvent and vibrational degrees of freedom. Analysis of two particular cases, subjects of recent elegant experimental investigation, are included to show the applicability of the technique. <s> BIB003 </s> Overview of Nanoelectronic Devices <s> A. Molecular Electronic Switching Devices <s> Diverse space-related applications have been proposed for microscopic and sub-microscopic structures, mechanisms, and 'organisms'. To govern their functions, many of these tiny systems will require even smaller, nanometer-scale programmable computers, i.e. 'nanocomputers' on-board. This paper provides an overview of the results of a nearly two-year study of the technologies and designs that presently are in development for electronic nanocomputers. Strengths and weaknesses of the various technologies and designs are discussed, as well as promising directions for remedying some of the present research issues in this area. The presentation is a synopsis of a longer MITRE review article on the same subject. <s> BIB004 </s> Overview of Nanoelectronic Devices <s> A. Molecular Electronic Switching Devices <s> We describe the first single-molecule electromechanical amplifier, the active element of which is one fullerene molecule (C60) with a junction length and width of ∼ 1 nm. Forces in the nano-Newton range are generated by a metallic tip pressing on the molecule in its adsorbed state. This working nanodevice is based on the modulation of virtual resonance tunneling through the molecule by electromechanical deformation of the C60 cage. <s> BIB005 </s> Overview of Nanoelectronic Devices <s> A. Molecular Electronic Switching Devices <s> During the past decade, the speed of computer processors has increased as much as 1,000 times. Information now flies through tiny circuits in quan? tities and at speeds that were inconceiv? able in the early 1980s. But where is all of the information stored? The density of conventional storage media?the random-access memory that serves as temporary working space and the hard disks used for long-term storage?has increased also, but only by about 10 times. We have entered an era in which <s> BIB006
After more than two decades of work, at least four broad classes of molecular electronic switching devices can be distinguished in the research literature: • electric-field controlled molecular electronic switching devices, including molecular quantum-effect devices BIB001 ; • electromechanical molecular electronic devices, employing electrically or mechanically applied forces to change the conformation BIB005 or to move a switching molecule or group of atoms  ,  to turn a current on and off; • photoactive/photochromic molecular switching devices  , BIB001 , BIB006 ,  -  , which use light to change the shape, orientation, or electron configuration of a molecule in order to switch a current; • electrochemical molecular devices BIB002 , BIB003 ,  , which use electrochemical reactions to change the shape, orientation, or electron configuration of a molecule and hence to switch a current. Many examples and details about the various types of molecular electronic devices are provided in the references cited above and elsewhere  , BIB004 . Here, however, we shall focus primarily on the first two categories of molecular electronic devices. The electricfield controlled molecular electronic switches are most closely descended from the solid-state microelectronics and nanoelectronic devices described above and promise to be the fastest and most densely integrated of the four categories. The electromechanical molecular switching devices are also promising, since they too could be laid down in a dense network on a solid substrate. Each of the other two categories, while quite promising in general, has a major drawback for use in nanocomputers. Photoactive devices in a dense network would be difficult to switch individually, since light cannot be easily confined on length scales very much below its wavelength (approximately 500 to 1000 nm). Electrochemical molecular devices would likely require immersion in a solvent to operate. Before we discuss specific device designs, however, we provide some additional background information, plus a discussion on the key topic of the molecular wires that will be needed to link together such molecular switches.