THE ADSORPTION OF BA ON AG(111)

The growth behaviour of barium on silver(111) at room temperature is i nvestigated by AES. XPS, MEIS. TDS, Work function measurements and by monitoring the secondary-electron-emission crystal current. It is show n that, for low coverage, initially a 2D monolayer is formed. For high er coverages the overlayer formed resembles a structure formed by Pois son or Stranski-Krastanov growth with small islands. As evaporation co ntinues the islands become very large or the sticking coefficient drop s to zero. Annealing the Ag with more than one monolayer of Ba on top shows a large work function decrease of 0.6 eV to an unusually low val ue of 1.9 eV. The lowering of the work function can partly be explaine d by the formation of large clusters. Coadsorption experiments with H- 2 indicate that the H-2 Sticking coefficient on Ba/Ag(111) is constant and that the H-2 adsorbs dissociatively into one binding state. From the experiments an inelastic mean free path of 11 +/- 1 angstrom for 3 51 eV electrons and 17 +/- 1 angstrom for 1113 eV and 1119 eV electron s is deduced.