Growth and dynamics of ultrathin barium films on Cu(100)

The growth and dynamics of ultrathin barium films on Cu(100) 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 x 6) submonolayer phase and a well defined c(4 root2 x 2 root2)R45 degrees 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. (C) 2001 Elsevier Science B.V. All rights reserved.