Density Functional Characterization of Adsorption and Decomposition of 1-Propanethiol on the Ga-Rich GaAs (001) Surface

Abstract

Density functional calculations have been used to investigate adsorption and decomposition of 1-propanethiol on the Ga-rich GaAs (001) surface. The dissociative adsorption of 1-propanethiol on GaAs (001) to the chemisorbed propanethiolate and hydrogen was predicted to be quite facile. Followed by the C-S bond scission of the propanethiolate species, the surface propyl species was formed with a barrier of 47.2 kcal/mol for the low-energy route. The propyl species is an important precursor to propane through the C-H bond coupling and to propene via the beta-H elimination. Predicted activation free energies for the surface processes from the propyl species to propane and propene are 45.2 and 37.0 kcal/mol at 298.1 K, respectively, while the corresponding overall Gibbs free energies of reaction DeltaG are -49.3 and -21.2 kcal/mol relative to free 1-propanethiol. Therefore, both reaction routes are competitive, resulting in a product mixture, although the beta-H elimination from the propyl species is initially remarkably favorable dynamically. On the basis of our calculations, detailed mechanisms for adsorption and thermal decomposition of 1-propanethiol on the GaAs (001) surface were proposed, and the calculated results show good agreement with experimental observations.