Surface Science Letters 250 (1991) L363-L367 L363 North-Holland Surface Science Letters Epitaxial submonolayer cobalt films on Cu(100) studied by X-ray diffraction S. Ferrer European Synchrotron Radiation Facility, B.P. 220, 38043 Grenoble Cedex, France E. Vlieg 1 and I.K. Robinson AT& T Bell Laboratories, Murray Hill, NJ 07974, USA Received 23 January 1991; accepted for publication 12 April 1991 The surface morphology of submonolayer Co deposits on Cu has been investigated by analyzing the profiles of surface X-ray diffracted beams along parallel momentum transfer directions. The profiles may be decomposed in two components of different width. The wide component contains direct information on the sizes of the cobalt islands. A two-level model gives a good description of the data for coverages below 0.5 ML. The kinetics of the island rearrangement involving the growth of large islands at the expense of small ones has also been investigated. 1. Introduction The suitability of diffraction techniques to study the disorder and defects of crystalline surfaces has been recognized since many years [1,2]. Imperfec- tions on a surface broaden a diffracted beam, which contains information on the statistical dis- tribution of surface defects [3,4]. The control and characterization of the surface perfection is very important in different areas of surface science. In epitaxial growth of thin films or superlattices, imperfections may alter in an undesirable way the electronic properties of the films. The most utilized techniques to characterize growth perfection are electron diffraction either LEED or RHEED. These techniques are relatively simple from the experimental point of view but have the disad- vantage that the interpretation is complicated by multiple scattering effects. Recently, the advent of high resolution LEED apparatus with transfer 1 Present address: FOM Institute, Kruislaan 407, 1098 SJ Amsterdam, Netherlands. widths as large as 200 nm has given new breath to these studies [5,6]. On the other hand, neutral atom scattering for low defect densities and X-ray diffraction are purely kinematical techniques that allow, in a simple way, the extraction of quantita- tive information on the distribution of surface defects [7,8]. In this Letter we present an X-ray diffraction study on the early stages of growth of cobalt on Cu(100). From previous work [9,10] it is known that Co grows in a layer by layer mode when it is deposited on the copper substrates at tempera- tures in the range 270-450 K. The film is pseudo- morphic with the fcc substrate, and has sometimes been (incorrectly) termed "fcc" cobalt, although in fact it is not cubic (a--b 4: c) because of the lattice strain. We have performed transverse scans of dif- fracted beams from a surface consisting of Co islands on the Cu substrate to get information on the island size distribution. Also, the degree of surface perfection has been evaluated by utilizing previously published analytical results for the dif- fraction from two-level surfaces [11]. Finally, the 0039-6028/91/$03.50 © 1991 - Elsevier Science Publishers B.V. (North-Holland)