Adsorption kinetics of hydrogen sulfide and thiols on GaAs (001) surfaces in a vacuum

Adsorption mechanisms of hydrogen sulfide and alkanethiols on GaAs (001) surfaces prepared in a vacuum were studied using first principles calculations. The need for a physisorbed precursor was confirmed based on energetic arguments and molecular dynamics simulations of the transition from a physisorption to a chemisorption state. The preference for S-Ga bond formation was found, resulting from a weak non-dissociative chemisorption state formed by the overlap of a sulfur lone pair orbital with an empty Ga dangling bond. Physisorption energies and the height of the transition barrier from physisorption to chemisorption on GaAs were found to be very similar to those on gold, while the main difference from gold was that hydrogen remains on the GaAs surface upon S-H cleavage. Obtained results allowed for a more advanced interpretation of experimental data concerning H2S and thiol adsorption on GaAs.