${\mathrm{H}}_2$S interaction with Cu(100)-(2 √2 × √2 )R45°-O: Formation of a metastable ${\mathrm{\Vert }}_0^5$ ${}_5{}^2{}_{}{}^{}\mathrm{sulfur}$ surface reconstruction

This paper utilizes scanning tunneling microscopy, low-energy electron diffraction, Auger-electron spectroscopy, and temperature-programmed desorption to examine a metastable ${\mathrm{\Vert }}_0^5$ ${}_5{}^2{}_{}{}^{}\mathrm{S}$ structure which forms after the interface reaction of ${\mathrm{H}}_2$S with a Cu(100)-(2√2 × √2 )R45°-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√2 × √2 )R45°-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 ${\mathrm{\Vert }}_0^5$ ${}_5{}^2{}_{}{}^{}\mathrm{S}$ reconstruction forms that is not observed after annealing similar coverages of sulfur adsorbed on an initially clean Cu(100) surface. Heating the ${\mathrm{\Vert }}_0^5$ ${}_5{}^2{}_{}{}^{}\mathrm{S}$ surface to temperatures above 600 K converts this structure to the thermally stable Cu(100)-(√17 × √17 )R14°-S (i.e., ${\mathrm{\Vert }}_{1\mathrm{¯}}^4$ ${}_4{}^1{}_{}{}^{}\mathrm{S}$ overlayer. A model for the metastable ${\mathrm{\Vert }}_0^5$ ${}_5{}^2{}_{}{}^{}\mathrm{S}$ reconstruction is proposed.