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 degrees similar to 78 degrees; while most of the dissociated CH3S_H prefer to adsorb on bri-fcc site, and the tilt angle is around 49 degrees similar to 57 degrees. 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.