Molecular synthesis and modification of surfaces for electronic device applications
Corley, David Allen
Tour, James M.
Doctor of Philosophy
This dissertation focuses on the synthesis of molecules and their grafting onto surfaces in order to modify the physical properties and behavior of various substrates and devices. For gold, first presented is the self-assembly of synthesized dipolar molecules onto OFET electrodes, demonstrating a powerful technique to tune the device's work function for electron injection. Discussed next is a multimodal study using SERS analysis of synthesized OPV and OPE molecules self-assembled within single-molecule electrical junctions, providing a rare glimpse of how tunneling electrons affect molecular structure during conduction. Lastly, STM studies are presented for self-assembled supramolecular wires composed of synthesized azobenzene molecules, demonstrating exciting cooperative UV- and bias-driven switching behavior. For silicon electronic studies where current does not pass through molecules, the synthesis and covalent grafting of a unique POM-species is first presented. Next, a combination XPS, UPS, IPS, and Kelvin Probe study is presented for a series of grafted aryl diazonium salts, offering a model for observed changes in the substrate's work function based on grafting-induced changes its surface band bending and electron affinity. Presented last is a powerful method utilizing diazonium salt grafting to impurity dope an FET device from the surface, demonstrating effects on electronic transport that penetrate even a ∼5 microm-thick device layer. For "through-molecule" electronic studies on silicon, presented is an investigation of C60 films solvent-grafted into nanogap devices, yielding bistable switching behavior possessing ON:OFF ratios >103 . Also presented is the attachment of Au nanoparticles to device surfaces using synthesized molecular tethers. Finally, the grafting of a synthesized alkoxyarylaminyl radical is discussed. For the protection of silicon devices from environmental conditions, the combined use of diazonium salt grafting and alkene thermal hydrosilylation is presented, demonstrating enhanced resistance of the surface to oxidation relative to diazonium grafting alone. Also discussed is a method to increase surface hydrophilicity using alkene hydrosilylation grafting in the presence of dilute HF, effectively protecting MEMS devices from capillary collapse during exposure to liquid water and humidity. For carbon, the functionalization of graphene devices using synthesized aryl diazonium salts is presented, yielding a model for the kinetics of diazonium salt graphene functionalization.
Chemistry; Organic; Physical chemistry