Molecular Electronics: Analysis and Design of Switchable and Programmable Devices Using Ab Initio Methods
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The process of scaling down modern semiconductor devices faces serious obstacles, mainly because of device-addressing problems. Practical limitations in fabrication and extraordinary increases in production costs will also be limiting issues. Small molecules, easy to tailor, are the natural candidates to complement semiconductor components in the generation of hybrid circuits, giving birth to a completely new area of electronics, molecular electronics or Moletronics. Experimental characterization is highly challenging, and only a few experiments in which only one molecule is addressed have been performed, because technical possibilities of success become greatly diminished with the minuscule system size. Fortunately, modern quantum-chemistry-theoretical-based computational techniques are able to accurately solve molecular systems using precise natural laws, and this ability increases substantially as systems become smaller.
This review investigates recent results on molecular systems that can potentially be used as electronic devices. It is particularly focused on molecules that can behave as controllable switches (a characteristic that allows programmability) and the theoretical techniques available for their analysis, design, and simulation. Switching has been studied before but not with the purpose of programmability. For instance, Collier et al. studied switching based on the translation degrees of freedom of mechanical bonds, and more elaborate molecular circuits have being proposed, such as a flash-like, single-electron memory cell; however, they are hardly useful for a paradigm of a chemically random assembly of molecules governed mostly by thermodynamic and some kinetic controls where programmability features at the level of devices are of paramount importance. The studies cited focused on electrical features and their correlation to conformational properties, the metallic contacts characterization, and the metal–molecule interface. Determining the correlation between transport characteristics and molecular electronic and geometrical configuration is particularly important, because this correlation provides a mechanism to control electron transport in molecular and atomistic systems.