Structural Characterization of Sulfur-Based Monomolecular Thin Films: I. Langmuir-Blodgett Films Derived From Multisulfur Heterocycles. II. Second Harmonic Generation Studies of Alkanethiolates on Ag and Au

135 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1997.Optical second-harmonic generation (SHG) has been used as a very sensitive surface probe to study metal-electrolyte interfaces at potentials within the double layer charging region. In this work, the potential dependence of second harmonic (SH) signal from metal/thin film/electrolyte systems have been studied. Self-assembled monolayers (SAMs) of alkanethiolates have been prepared on Ag and Au surfaces, both SHG and AC impedance measurements of the Ag-alkanethiolate-electrolyte systems have been performed for alkanethiols with different chain lengths. The capacitance of the alkanethiolate SAMs is found inversely proportional to the chain length of the alkanethiol. For both Au and Ag electrodes, the SH signal is found less sensitive to the potential change after alkane-thiolate monolayer formation. The coverage dependent SH signal intensity from Au-alkanethiolate-electrolyte systems has been measured. Ozonolysis is used to obtain partially covered hexadecanethiolate (HDT) monolayers on Au surfaces, with the coverage being controlled by the ozone exposure time and monitored by surface plasmon resonance (SPR) technique. A linear relationship between the film coverage and SH intensity has been observed.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD