Methylthiol adsorption on GaAs(100)-(2x4) surface: Ab initio quantum-chemical analysis

Quantum-chemical cluster calculations within the density functional theory are performed to study the mechanism of adsorption of the methylthiol molecule CH3SH on an As-As dimer on a GaAs (100) surface. It is shown that the adsorption of the molecule can proceed through dissociation of either the S-H or C-S bond. The lowest energy has the state of dissociative adsorption with the rupture of the C-S bond resulting in the formation of a methane molecule and sulfur adatom incorporated between surface arsenic atoms constituting the dimer. A somewhat higher energy has the state of dissociative adsorption with the rupture of the S-H bond. In this state the CH3S-radical is adsorbed at an arsenic atom constituting dimer and the hydrogen atom is adsorbed at a gallium atom bonded to this arsenic atom. These two states provide chemical and electronic passivation of the semiconductor surface.