Growth and structure of Cr on Ru(0001)-(2x2) and Cr/Ru multilayers

In-situ observations of reflection high-energy electron diffraction (RHEED) are used to study the structure and growth of epitaxial Cr films on hcp(0001) Ru buffer layers that are prepared on mica substrates under molecular beam conditions. During the growth of Cr at room temperature, we observed up to five intensity oscillations of the specular beam, indicating a layer-by-layer growth mode. Further growth results in the formation of three-dimensional islands. Simultaneously, the relaxation of the in-plane lattice parameter was recorded during growth, showing an enlarged value at 0.3 ML Cr coverage. At a coverage above 5 ML, the Cr overlayer adopts a bcc(110) structure; thereby, the Cr layers arrange into a Nishiyama-Wassermann-type epitaxy. Scanning tunneling microscopy (STM) investigations in UHV, allowing a comparison of real and reciprocal space techniques, confirm the growth behavior. A series of Cr/Ru multilayers were prepared and their magnetic properties examined by a Faraday balance. We found no resulting magnetic moment that could be expected in-between the resolution limit (>0.1 mu(B) per Cr atom) if the Cr layers were ferromagnetically ordered. (C) 1998 Elsevier Science B.V. All rights reserved.