Density functional theory study of the adsorption of methanthiol on Au(1 1 1): Role of gold adatoms

By performing density functional theory calculations, this work clarifies the sites and energetics of both the non-dissociative and dissociated adsorptions of CH₃SH on clean Au(1 1 1) and Au(1 1 1) with intrinsic defects. It was found that the adsorption on defect-free Au(1 1 1) is most stable for non-dissociative CH₃SH. Its direct molecular dissociation to form CH₃S/Au and H/Au is barred by an activation barrier of 0.9 eV. However, the presence of neighboring Au_ad can assist the dissociation reaction to form CH₃S-Au_ad-H by lowering the energy barrier to 0.6 eV. As for the dissociated CH₃S, the surface geometry of two CH₃S joined by a Au_ad is the most favorable one.