A455 Received 23 March 1987; accepted for publication 15 April 1987 We have performed a surface X-ray diffraction study of submonolayer ~3- structures of Sn and Pb on Ge(lll). The structure factor analysis of fractional-order Bragg reflections shows a significant relaxation in the Ge substrate induced by the Sn/Pb adatoms. The registry, of the adatoms is determined from the analysis of the integer-order intensities. The adatoms are situated on top of the second layer of (3e atoms. The intensity profile normal to the surface of a subset of the fractional-order Bragg rods were measured. They display a pronounced intensity variation for both Sn and Pb, which can be explained only by a subsurface relaxation extending at least four atomic layers into the bulk.
Surface Science 189/190 (1987) 1055-1061 North-Holland, Amsterdam
GROWTH OF EPITAXIAL ULTRATHIN O N S i ( l l 1) J. H E N Z , H. V O N K A N E L ,
CoSt 2 LAYERS
M , O S P E L T a n d P. W A C H T E R
Laboratorium fiir FestkiSrperphysik, ETH Ziirich, CH-8093 Ziirich, Switzerland Received 27 March 1987: accepted for publication 14 April 1987 Perfectly smooth, pinhole-free and epitaxial CoSt3 layers of type B orientation have been grown on St(ill) with a thickness ranging from 14 to 70 ,~. The outstanding perfection of these uhrathin films was achieved by a new evaporation method, which consists in the coevaporation of Co and Si at room temperature and in a succeeding anneal. If the evaporation rates are exactly stoichiometric, an ordered structure can be detected by RHEED already at room temperature, whereas upon annealing to only 250°C a remarkable sharp Kikuchi pattern is obtained. XPS measurements of the valence band confirm that the phase is indeed CoSt 2. Films grown in such a way, retain their quality up to a temperature of 600 o C. To let thicker films grow, we use MBE at substrate temperatures which are as low as 300 o C.
Surface Science 189/190 (1987) 1062-1068 North-Holland, Amsterdam
THE SURFACE MORPHOLOGY BY THERMAL ENERGY ATOM
OF A GROWING CRYSTAL SCATTERING (TEAS)
J.J. D E M I G U E L , A. S A N C H E Z , J. F E R R O N a n d S. F E R R E R
A. C E B O L L A D A ,
Departarnento de Fisica de la Materia Condensada, C-HI, Facultad de Ciencias, Universidad Aut6norna de Madrid, Cantoblanco, 28049-Madrid, Spain Received 31 March 1987; accepted for publication 16 April 1987 The growth of a Cu(lOO) surface from its vapour has been investigated by TEAS for different surface temperatures. The specularly reflected intensity of the growing surface shows temporal oscillations for in-phase and out-of-phase scattering conditions. In-phase data have been analyzed in terms of the diffuse scattering from the surface steps whereas out-of-phase oscillations in terms of a kinematical and purely elastic description of the scattering from a random distribution of terraces. In both cases the temporal evolution of the step concentration of the growing crystal was obtained. Also, the surface diffusion coefficient of Cu adatoms was directly estimated from the experiments resulting in a preexponential of 1.4 × 10 4 cm ~ s l and an activation energy of 0.40 eV.