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 him thicknesses related to the structural phase transition. This means tha t the surface structures which appear in the Ba/Mo(110) system do not exhib it any drastic phase transition at any film thickness. The change of the su rface structures of the Ba/Mo(110) system occurs in two steps and results i n the c(2 x 2), (1.6 x 2) and (1.5 x 1.8) structures that form a boundary. In either of the two steps, surface structures appear in the balance betwee n the energetic stability of the coherency with the atomic arrangement of t he Mo substrate and the energetic stability achieved by surface structures themselves forming triangle lattices.