Investigation of the solid-liquid interface of systems with fuel cell and semiconductor applications

A combined ultrahigh vacuum/atmospheric pressure chamber was used in the investigation of the solid-liquid interface of Si(100) and Pt(111). The apparatus allowed sample transfer between atmospheric pressure and ultrahigh vacuum under ultrapure conditions. The ultrahigh vacuum environment was used for preparation and characterization of samples both before and after wet (electro) chemical treatments.; Treatment of Si(100) in HF solutions is widely used in the semiconductor industry and the chemistry of the resultant surface greatly influences subsequent processing. The Si(100) surface had both SiF and SiH species present after treatments in dilute HF and buffered HF, and upon rinsing, SiF was hydrolyzed to SiOH, resulting in a lower concentration of SiF.; Platinum is an important electrocatalyst in fuel cells and the addition of electrode modifiers can enhance its performance. Cyclic voltammetry of graphite-covered Pt(111) shows that the well-known butterfly peak of the clean surface gradually disappears with increasing carbon coverages and is eliminated at 1.0 monolayer of carbon coverage, indicating islanding of the graphite adlayers. The amount of hydrogen adsorption decreases by only 15% at carbon coverages of 1.3 monolayers. Electro-oxidation of CO is also largely unchanged on the carbon-covered surface, but formic acid electro-oxidation depends on the size of the carbon-free platinum patches. Sulfur adlayers cause a reduction of both the butterfly peak and hydrogen adsorption, with complete elimination of both at a sulfur coverage of 0.33 monolayers.; The effect of removing an electrode from solution (emersion) and transferring the electrode to UHV was also investigated by Kelvin probe measurements of the electrode outer potential. Pt(111) electrodes emersed from HClO{dollar}sb4{dollar} electrolyte containing Pb{dollar}sp{lcub}2+{rcub}{dollar} show an invariant outer potential due to a surface redox reaction that occurs upon emersion. Similarly, an invariant outer potential occurs for emersion from HClO{dollar}sb4{dollar} electrolyte containing Cu{dollar}sp{lcub}2+{rcub}{dollar} at potentials where copper adsorbs, but the outer potential accurately tracks the emersion potential at more anodic potentials where copper does not adsorb. Graphite covered Pt(111) emersed from a blank HClO{dollar}sb4{dollar} electrolyte exhibits behavior in between that of the Cu{dollar}sp{lcub}2+{rcub}{dollar} and Pb{dollar}sp{lcub}2+{rcub}{dollar} systems.