LEED-investigations and work-function measurements of the first stages of epitaxy of tungsten on tungsten (110)

The arrangement of tungsten atoms (0.2–4 monolayers) evaporated onto W(110) has been studied with LEED and work-function measurements in ultrahigh vacuum. For temperatures of T=300–430 K island growth has been derived from rings, which are visible at characteristic energies, around each spot of the LEED pattern. By increasing substrate temperature the islands coalesce in the [001] direction. For T=520–800 K the surface shows microfacets with step edges in the [11̄0] direction. Step-free epitaxial growth has been observed at T=950 K. The decrease of work function during evaporation confirms the formation of islands and facets. The average dipole moment per edge atom has been determined by combination of LEED and work-function data. Quantitative evaluation of the LEED pattern yields the distance between islands, size of islands, and number of rows of atoms per terrace. The results show that the LEED pattern provides information on epitaxial growth which is not available with any other technique.