Functionalization of Indium Tin Oxide
NAVAL RESEARCH LAB WASHINGTON DC
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The preparation and functionalization of ITO surfaces has been studied using primarily X-ray photoemission spectroscopy and infrared reflection-absorption spectroscopy IRRAS and the reagents n-hexylamine and n-octyltrimethoxysilane OTMS. Particular attention has been paid to characterization of the surfaces both before and after functionalization. Surfaces cleaned by ultraviolet UVozone treatment and subsequently exposed to room air have 0.5-0.8 monolayers ML of adsorbed impurity C. Most is in the form of aliphatic species, but as much as one-half is partially oxidized and consists of C-OH, C-O-C, andorCO groups. The coverage of these species can be reduced by cleaning in organic solvents prior to UVozone treatment. The OH coverage on the ITO surfaces studied here is relatively small 1.0 OH nm-2, based on the Si coverage after reaction with OTMS. A satellite feature in the O Is XPS spectrum, often suggested to be a quantitative measure of adsorbed OH, receives a significant contribution from sources not directly related to hydroxylated ITO. n-Hexylamine adsorbs, at a saturation coverage of 0.08 ML, via a Lewis acid-base interaction. The particular acid site has not been conclusively identified, but it is speculated that surface Sn sites may be involved. For OTMS, a saturation coverage of about 0.21 ML is found, and the CSi atom ratios suggest that some displacement of preadsorbed organic impurities occurs during adsorption. The alkyl chain of adsorbed OTMS is disordered, with no preferred stereoisomer. However, the chain appears to lie mainly parallel to the surface with the plane defined by the terminal CH3-CH2-CH2- segment oriented essentially perpendicular to the surface.
- Inorganic Chemistry