Decomposition reactions of ethanethiol on GaAs(100)

Abstract

The adsorption and thermal decomposition reactions of ethanethiol on gallium-rich GaAs(100)–(4×1) have been investigated using the techniques of Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and thermal desorption spectroscopy (TDS) in conjunction with deuterium isotope scrambling experiments. Exposures of ethanethiol onto clean GaAs(100) at room temperature to saturation coverage followed by annealing to 750K forms a p(2×2) structure, and AES confirms that this structure is due to a pure sulfur overlayer. Upon adsorption ethanethiol undergoes S–H scission to form surface ethanethiolate and hydrogen species. Recombinative desorption of ethanethiol competes with the decomposition reaction of ethanethiolate via C–S scission to form adsorbed ethyl and sulfur species, and this C–S cleavage occurs below 500K. On the clean surface, the further reactions of the ethyl species lead to the production of a mixture of products consisting of ethene, ethane, hydrogen and butene, which all desorb below 600K. Ethene, ethane and hydrogen are formed as a direct result of β-hydride and reductive elimination reactions of the ethyl species, while butene is formed during ethyl coupling reactions on the surface. On a sulfided surface, butane, hydrogen sulfide and diethylsulfide are formed in addition to the product mixture noted above, and all desorb into the gas phase below 600K. A reaction scheme is proposed to account for the observed desorption products on both the clean and pre-sulfided GaAs(100) surfaces.