Density functional theory studies on the adsorption of methane-thiol molecule on Au (111) surface

By using the first-principles method based on density functional theory and slab model, the atomic geometries and electronic structures for the adsorptions of methane-thiol molecule on Au (111) surface were studied. A series of possible adsorption configurations constructing by S atom on different site with different orientation were studied. The adsorption energies indicate that most of the CH₃SH molecules prefer to adsorb on the top site, and the tilt angle is around 62°~78°; while most of the dissociated CH₃S_H prefer to adsorb on bri-fcc site, and the tilt angle is around 49°~57°. The comparisons between the nodissociative and dissociative adsorption show that CH₃SH prefer nodissociative adsorption on the Au (111) surface, the increase of the surface temperature and defect may make the S-H bond break. It is indicated that the bonding between S atom and substrate is much stronger in the dissociated adsorption by comparing the local density of states of S atom between the single CH₃SH and the adsorbed molecule, also the dissociated CH₃S_H. Our STM (scanning tunneling microscopy) simulations show us three distinctive pattern for the adsorption of CH₃SH and CH₃S_H on Au (111) surface.