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In order to evaluate the interfacial monolayer order on copper surfaces in two-dimensions, the tilt angle distribution and orientation-conformation correlation maps were investigated using sum frequency generation imaging microscopy (SFGIM). In this paper, these methods of analyses were further utilized in evaluating the effect of the formation of a thin oxide film on the monolayer order of octadecanethiol (ODT) deposited on Cu. By chemically stripping the native oxide of the copper surface using amidosulfonic acid (ASA), the spontaneous atmospheric oxidation of Cu from an initial reduced state was observed as a change in the nonresonant phase response of the sum frequency generation (SFG) spectral line shape obtained from the SFGIM setup configured with a 1064 nm probe beam. Statistical calculations and contour maps for the CH-stretch modes of the terminal methyl and methylene group showed the overall decrease in the mean tilt angle and increase in the amount of alkyl gauche defects as a result of the oxidation of the metal surface underneath ODT. With the growth of the oxidized film, the changes in the methyl group tilt orientation are spatially correlated to the changes in the nonresonant phase. Regions with the highest concentration of reduced surface Cu registered lower gauche defect signals and low relative nonresonant phases. Over the exposure time, these regions of well-ordered monolayers were observed to gradually undergo Cu oxidation, initiating from the domain boundaries moving inward.
Santos et al. (Thu,) studied this question.