First principles study of gallium atom adsorption on the α-Al ₂O₂(0001) surface

The adsorption of Ga atoms in low coverage on the Al-terminated α-Al₂O₃(0001) surface has been studied theoretically by using first principles periodic boundary condition (PBC) calculations within the framework of the generalized gradient approximation (GGA). Eight possible adsorption sites are investigated, but only two are found to correspond to stationary points. Both of these locations are characterized as hollow sites, with three surrounding surface O atoms and an Al atom in the center located deeper within the A1₂O₃ slab. The slight difference in the stability of these two sites is due to a difference in the chemical interactions between the Ga atom and the surface O atoms. Strong interactions between the Highest Occupied Molecular Orbital (HOMO) of the Ga atom and the surface state of the Al₂O₃ surface are observed. This interaction promotes charge transfer from the Ga to the surface Al atoms, which in turn causes the surface Al atoms to move up from the surface.