CHARACTERIZATION OF EPITAXIAL RUBIDIUM FILMS WITH HELIUM-ATOM SCATTERING

The growth of thin rubidium films on a nickel(001) substrate has been investigated for coverages of between one and six monolayers using hel ium-atom scattering (HAS). Two different growth modes were found by mo nitoring the specular reflectivity during deposition which, at 50 K, d isplayed oscillations indicating layer-by-layer growth, whereas at 90 K the onset of step flow is observed. Information concerning the morph ology of the him surface and the Debye-Waller factor was obtained by m easure the intensity of the specularly scattered helium beam as a func tion of the incident energy. The experiments showed that, for beam ene rgies between 9 and 66 meV, the Debye-Waller factor is proportional to Delta k(z)(2), with Delta k(z) denoting the perpendicular momentum tr ansfer to the surface. The average terrace width of the annealed films was measured to be of the same order as that of the substrate, which is larger than 230 Angstrom. The step height distribution was found to depend on the preparation process: annealing the rubidium film reduce s the density of monatomic rubidium steps, whereas the height modulati on induced by steps on the nickel substrate remains unchanged and can be observed up to a film thickness of six monolayers. The Debye temper ature of the him surface has been determined at various stages of him preparation and for various coverages. In the case of annealed films i t was found to decrease from 96 K to 62 K as the coverage was raised f rom 1.3 to 6.1 monolayers. (C) 1998 Elsevier Science B.V. All rights r eserved.