Change of surface structures of Ba deposited on Mo(110) surface

The change of the surface structures of barium (Ba) deposited on a Mo(110) surface has been investigated by means of a reflection high-energy electron diffraction (RHEED) apparatus. Based on our RHEED observation, it has been clarified that the surface atomic density of Ba increased continuously in proportion to the increase of the film thickness, and there are no critical film thicknesses related to the structural phase transition. This means that the surface structures which appear in the Ba/Mo(110) system do not exhibit any drastic phase transition at any film thickness. The change of the surface structures of the Ba/Mo(110) system occurs in two steps and results in the c(2 × 2), (1.6 × 2) and (1.5 × 1.8) structures that form a boundary. In either of the two steps, surface structures appear in the balance between the energetic stability of the coherency with the atomic arrangement of the Mo substrate and the energetic stability achieved by surface structures themselves forming triangle lattices.