Unimolecular electronic monolayer

For now, unimolecular electronic devices must be tested with inorganic electrodes, thinned out to atomic or oligoatomic sharp tips. Molecules either singly, or in parallel as a monolayer array (one molecule thick), have been shown to be either passive or active electronic components. There are two ways to connect a molecule to an inorganic metal electrode physisorption, and chemisorption. 

Molecular electronics" (ME) (sensii stricto), or molecular-scale electronics" or unimolecular electronics" (UE) is the study of electrical and electronic processes measured or controlled om a molecular scale or on the nanometer scaleJ A wider definition of molecular electronics sensu lato), or "molecule-based electronics" encompasses electronic p ocesses by molecular assemblies of any scale, including macroscopic crystals and conducting polymers/ This article deals with UE and focuses on electrical conduction (asymmetric or not), through single molecules or through a monolayer of molecules measured in parallel. 

In principle, molecules can be either passive or active electronic components, either singly or in parallel as a one-molecule-thick monolayer array. This may lead to electronic devices with dimensions of 1-3 nm. Unimolecular electronics (UE) or molecular electronics sensu stricto, or molecular-scale electronics evolved from studies of organic crystalline metals, superconductors, and conducting polymers the idea is to exploit the electronic energy levels of a single molecule, and most importantly its HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), which can be tuned, or modified by incorporation of electron-donating... 

Cytochrome c can be strongly adsorbed in its native state on tin oxide electrodes at coverages of several tenths of a monolayer. Measurements of unimolecular electron transfer rate constants for adsorbed cytochrome c can be readily made in the absence of solution cytochrome c using cyclic voltammetry. The kinetic results are consistent with an interfacial model involving electrostatic interaction between the tin oxide and the exposed heme edge of the cytochrome as well as an electrostatically driven adsorbate reorientation capability to account for the anomalous dependence of rate constant on scan rate. Other possible explanations for the... 

Fig. 16 Eleven unimolecular rectifiers studied at the University of Alabama as monolayers between Au electrodes (except for 36d and 36e see text). The arrows indicate the experimentally observed direction favored electron transfer however the direction is reversed for 36d and 36e...

The formation of monolayers of cerotic, be-henic, and stearic acids adsorbed from cis-decahydronaphthalene and w-hexadecane solutions onto glass was studied by electron microscopy. Platinum preshadowed carbon replicas of the monolayered glass surfaces were examined in a JEM 6-A electron microscope. The acids adsorb initially in discrete patches the average patch diameter depends on the length of the acid molecule, becoming smaller for shorter acids. The area covered by the unimolecular film increases as the adsorption time or concentration of adsorbate solution increases. Contact angle measurements on partially monolayered surfaces show the contact angle to be dependent upon the fraction of substrate covered. Direct evidence of metastable incorporation of hexadecane in acid mono-layers was obtained. 

U (for unimolecular ) rectifiers occur when the current passing through a molecule, or monolayer of molecules, involves electron transfers involving molecular orbitals, whose significant probability amplitudes are asymmetrically placed within the chromophore." ... 

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