H2S interaction with Cu(100)-(2 sqrt 2 x sqrt 2 )R45 degrees-O: Formation of a metastable ||05 52||-sulfur surface reconstruction.

Abstract

This paper utilizes scanning tunneling microscopy, low-energy electron diffraction, Auger-electron spectroscopy, and temperature-programmed desorption to examine a metastable ${\mathrm{\ensuremath{\Vert}}}_{0}^{5}$ $_{5}^{2}\mathrm{S}$ structure which forms after the interface reaction of ${\mathrm{H}}_{2}$S with a Cu(100)-(2\ensuremath{\surd}2 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}2 )R45\ifmmode^\circ\else\textdegree\fi{}-O surface. This preoxidized copper surface displays an enhanced reactivity towards ${\mathrm{H}}_{2}$S compared to the clean and annealed Cu(100) surface. Exposing 15 L of ${\mathrm{H}}_{2}$S onto a Cu(100)-(2\ensuremath{\surd}2 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}2 )R45\ifmmode^\circ\else\textdegree\fi{}-O surface causes all the adsorbed oxygen to desorb as ${\mathrm{H}}_{2}$O at 164 K, while leaving approximately 0.5 ML of adsorbed sulfur on the surface. When this sulfur overlayer is annealed between 525 and 600 K, a metastable ${\mathrm{\ensuremath{\Vert}}}_{0}^{5}$ $_{5}^{2}\mathrm{S}$ reconstruction forms that is not observed after annealing similar coverages of sulfur adsorbed on an initially clean Cu(100) surface. Heating the ${\mathrm{\ensuremath{\Vert}}}_{0}^{5}$ $_{5}^{2}\mathrm{S}$ surface to temperatures above 600 K converts this structure to the thermally stable Cu(100)-(\ensuremath{\surd}17 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}17 )R14\ifmmode^\circ\else\textdegree\fi{}-S (i.e., ${\mathrm{\ensuremath{\Vert}}}_{1\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}^{4}$ $_{4}^{1}\mathrm{S}$ overlayer. A model for the metastable ${\mathrm{\ensuremath{\Vert}}}_{0}^{5}$ $_{5}^{2}\mathrm{S}$ reconstruction is proposed.