V and Cr on Ru surfaces

By molecular beam epitaxy (MBE) we have prepared (0001)-hcp Ru films on SrTiO3(111), Al2O3(0001) and Al2O3(11(2) over bar 0) surfaces. Reflection high-energy electron diffraction (RHEED) intensity oscillations are observed during the growth of the Ru films, up to temperatures of 870 K. Despite that, we found that high substrate temperatures are required for the initial deposition of Ru. Scanning tunnelling microscopy (STM) investigations show monoatomic terraces of up to 100 nm in width, and atomic resolution on Ru, although the imaging was performed under ambient conditions. The high crystallinity of the Ru films is proven by RHEED and by the appearance of interference fringes in the peak profiles of high-angle X-ray diffraction patterns. V and Cr grow pseudomorphic on Ru in the layer-by-layer growth mode for the first few monolayers (ML), afterwards island growth is obtained. In-plane lattice parameter measurements performed during the growth of the V films at room temperature show a rather slow relaxation with the first 10-15 ML to the bulk bcc value, in contrast to Cr films. (C) 1998 Elsevier Science B.V.