GROWTH MODES OF W AND MO THIN EPITAXIAL (110)FILMS ON (11(2)OVER-BAR0)SAPPHIRE

Growth modes of W(110) and Mo(110) epitaxial thin films grown with pul sed laser deposition (PLD) on (11(2)over-bar0) sapphire were studied. The films properties were studied both in reciprocal space using refle ction high energy electron diffraction (RHEED) and X-ray diffraction a nd in real space using atomic force microscope (AFM). The conventional ly used high temperature growth process, usually considered to be the best process - according to reciprocal space characterization - to min imize in-plane crystallites twinning and mosaicity,is proved to yield three-dimensional growth and rough surfaces. A sample continuously wed ged up to a thickness of 600 A was studied and only partial islands co alescence was observed. An alternative optimized growth process is pro posed, based on 200 degrees C deposition, subsequent annealing, and fu rther high temperature deposition, that enables the elimination of in- plane twinned-crystallites while yielding to nearly perfect W(110) or Mo(110) surfaces, from both crystallographically and geometrically poi nts of view. Throughout the paper we discuss information gained respec tively from RHEED and AFM characterization, and analyse their relation ships and complementarity. The comparison with MBE grown films suggest s that what we report on is not a PLD-specific behavior. Eventually we report on a R(15x6)Mo surface reconstruction, which had never been ob served before to our knowledge. (C) 1998 Elsevier Science B.V. All rig hts reserved.