Abstract
Electron spectroscopic and diffraction results obtained in ultra-high-vacuum, combined with cyclic voltammetric data, are reported for sulfur adlayers deposited from aqueous sulfide and bisulfide media on Pt(111). The highest coverage obtained by Auger electron spectroscopy, 0.94 ± 0.05 monolayer, is very close to the coverage obtained from coulometry, and is associated with a (1×1) surface phase. This coverage is much higher than that obtained in previous electrochemical studies but is the same as found by other investigators using S2 beam dosing in vacuum. The near complete sulfur monolayer is characterized by a rapid and incomplete oxidation in a narrow potential range near 0.70 V vs a Ag/AgCl reference. Neither full sulfur monolayer coverage nor a sharp voltammetric transition could be obtained when traces of oxygen were present in the electrochemical cell. Oxidation of the (1×1) adlayer (at ≈1 monolayer) gave rise to a previously unreported (2×2) structure, at 1/2 monolayer. Further voltammetric stri...
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