Growth and dynamics of ultrathin barium films on Cu(1 0 0)

The growth and dynamics of ultrathin barium films on Cu(1 0 0) have been studied by means of helium atom scattering and low energy electron diffraction. Below 200 K the films are found to grow without any epitaxial ordering and only the first monolayer exhibits a weak quasi hexagonal texture. By increasing the growth temperature above 400 K an ordered c(6×6) submonolayer phase and a well defined c(42×22)R45° monolayer structure can be prepared. With further exposure a quasi hexagonal second monolayer with a Ba bulk nearest neighbor spacing is formed indicating the crossover from the substrate mediated monolayer structure to the formation of a closely packed barium surface. For Ba films with a thickness of 1, 2 and 3 ML characteristic phonon modes were obtained, which are similar to the “organ pipe” modes previously reported for various alkali metal films.