Macro- and microstructural characterization of organosulfur monolayers adsorbed at gold

Lamp, Brian
Major Professor
Marc D. Porter
Committee Member
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Monolayers derived from the adsorption of sulfur-containing organic compounds at metal surfaces have become popular model systems for the study of interfacial processes[superscript]1,2. While a large base of information has been assembled, several areas still require further investigation. Areas of interest include such topics as monolayer structure and stability, intermolecular interactions in the monolayer film itself, the nature of monolayer binding chemistry, and analytical applications of these materials;This dissertation is aimed at strengthening the knowledge base regarding these materials by examining the fundamental characteristics of organosulfur based monolayer films. The dissertation reports the results of four studies. The first examines the micro- and macrostructural character of monolayers adsorbed from symmetric di-alkyl disulfides at gold electrodes, and compares the results to films adsorbed from the corresponding alkanethiols. While the average structure of the two types of assemblies are essentially indistinguishable, monolayers formed from disulfide precursors exhibit smaller regions of molecular order and slightly lower overall coverage;The second section of the dissertation presents results from an in situ infrared spectroelectrochemical study which examines the structure of alkanethiolate monolayers at extremely cathodic potentials. For methyl terminated films, the strength if the intermolecular interactions, combined with relative instability in the electrolyte solution prevents changes in the chain structure at these potentials. Monolayers terminated with hydroxy-functionalities, however, exhibit marked structural changes with applied potential;The third section examines the propensity for adsorption/desorption of alkanethiolate monolayers at step versus terrace sites on the gold surface. This study indicates that the thiolate adsorbes preferentially adsorb at step sites, before covering the remaining terrace sites;The final study examines the stability of monolayer films adsorbed from several mercaptopyridine compounds, and examines implications of their stability to the utility of these films in facilitating the electron transfer reaction of cytochrome c. With short immersion time in the precursor solution, pyridinethiolate monolayers are formed which are effective in facilitating cytochrome c electron transfer. With increasing immersion time, instability in the film structure leads to monolayers which strongly resemble films of mono- and oligomeric sulfur, and exhibit poor facilitator characteristics. ftn[superscript]1Ulman, A. An Introduction to Ultrathin Organic Films: From Langmuir-Blodgett to Self-Assembly, Acadamic: Boston, 1991. [superscript]2Dubois, L. H; Nuzzo, R. G. Annu. Rev. Phys. Chem. 1992, 43, 437-463.