Synthesis and analysis at the chemical interface of novel oligomers as candidates for molecular electronics
Tour, James M.
Doctor of Philosophy
New oligomers, intended for use as potential molecular electronics devices have been synthesized based on rational design principles. A large number of chemically and conformationally diverse molecules have been synthesized, in order to manipulate two physical characteristics of the oligomer: the molecular junction with the bulk phase material, and the molecular electronic behavior due to the conformational and electronic nature of the molecular backbone. For the former characteristic, the new oligomers contained various substrate linkers or "alligator clips", such as thioacetyl and free thiols, isonitriles, nitriles, pyridines groups, as well as diazonium salts for direct substrate attachment. For the latter characteristic, different molecular geometries were synthesized that contained electron-withdrawing groups such as fluorine atoms and nitro groups. These variations are meant to address redox processes, electron-localization and conformational restrictions of the conjugated oligomer, features that are thought to play active roles in the electrical responses of molecular electronic devices. The direct reaction of arenediazonium salts with the solid bulk phase allowed us to extend the molecular electronics field toward the preparation, characterization and use of organically grafted materials that are technologically important such as silicon and gallium arsenide semiconductors, palladium metallic surfaces and individual single-walled carbon nanotubes. The goals of this work include higher current densities, lower conductivity barriers and improved matching between molecular orbitals and the Fermi level from the bulk phase. Finally, through the synthetic work presented here, the importance of a complete and systematic analytical elucidation of the chemisorbed organic films made with these novel oligomers is emphasized, so that the quality and integrity of the chemical interface is better understood before the molecules are assigned as active elements in molecular electronic devices.