Studies of structure and reactivity in monolayer assemblies: 1. Ozonolysis of alkanethiolate self assembled monolayers on Au. 2. In-plane resistivity of ultrathin gold films as a high sensitivity, molecularly differentiated probe of chemisorption at the

This research focused on the chemistry of self-assembled monolayers (SAMs) and is written in two parts. Part I addresses the mechanism by which UV radiation produces photo oxidation at alkanethiol SAMs, and Part II addresses the use of in-plane resistivity measurements as a sensitive technique to monitor self-assembly at liquid-metal interfaces.; Ozonolysis, from UV-photosynthesized O₃, has been found to be the primary cause of the sulfonation and labilization of self-assembled hexadecanethiol (HDT) monolayers on Au, which takes place following irradiation with a low pressure Hg-arc lamp in air. Surface Plasmon Resonance was employed to compare the efficacy of HDT SAM stripping under various irradiation conditions and upon exposure to O₃ generated ex situ. Sixty minutes of irradiation in vacuum and N₂ led to undetectable (<2%) and ∼5% labilization of the SAMs respectively. In contrast, treatment with UV in air for 30 min or with O₃ alone in the dark for 10 min labilizes 100% of the chemisorbed HDT. Infrared reflection-absorption spectroscopy indicates that a major product from both O₃ exposure and UV-irradiation in air is an alkanesulfonate.; Ultrathin gold films, with thicknesses between the onset of conductivity (d ∼ 5 nm) and the electron mean free path ( d ∼ 80 nm), display surface-sensitive resistivities, which have been exploited to follow the adsorption and desorption of molecular monolayers at the metal solution interface with high precision. For nominal Au film thicknesses (d ∼ 40 nm), strongly chemisorbed thiolate monolayers increase the resistivity of the thin Au films by ca. 4%, but weakly adsorbed species, such as pyridine or phenolate at open circuit, induce no observable change in the Au film resistance. Resistivity measurements implemented with a high stability current source and high-precision digital voltmeter sampling at 1 Hz resulted in 3 σ uncertainties in alkanethiolate coverage of 1.4 × 10–4 monolayer. Correlating chemical manipulations with changes in surface morphology as characterized by AFM indicates a significant morphology-related contribution to resistivity which must be controlled to extract meaningful information related to the electronic interaction of adsorbate and substrate.