ELSEVIER Surface Science 339 (1995) 323-328 ...... % ~ !~ ~!iY~t~it~ ........ surface science Alloying at the Co/Pt(111)interface: a study by crystallographic low energy electron diffraction Andrea Atrei 1, Ugo Bardi *, Monica Galeotti, Gianfranco Rovida, Marco Torrini, Ermanno Zanazzi Dipartimento di Chimica, Universit?t di Firenze, Firenze, 1-50121, Italy Received 27 January 1995; accepted for publication 19 May 1995 Abstract After depositing a single atomic layer of cobalt on the Pt(lll) surface, annealing at 600 K leads to the formation of a surface alloy of stable composition and structure. This phase was examined by crystallographic low energy electron diffraction finding that of the two topmost layers the first layer contains 20 at% of cobalt and the second one 80 at% of cobalt. No significant amounts of cobalt could be detected below the second atomic layer from the surface. Keywords: Alloys; Cobalt; Electron-solid interactions, scattering, diffraction; Low energy electron diffraction (LEED); Low index single crystal surfaces; Metallic films; Platinum; Surface relaxation and reconstruction 1. Introduction The cobalt/platinum interface has been object of a number of studies in view of the magnetic proper- ties of cobalt thin films and layered phases [1-3]. The structure of systems formed depositing ultra-thin films of cobalt on platinum has been studied by various techniques [4-6] as well as the surface struc- ture of bulk Co-Pt alloys [7-10]. Interdiffusion phe- nomena occur at the Pt-Co interface at relatively low temperatures with the formation of surface al- loys [11]. When starting from a single layer of cobalt deposited on Pt(lll) we observed by X-ray photo- * Corresponding author. E-mail: bardi@mailserver.idg.fi.cnr.it. 1 Present address: Laboratorium ftir Festk6rperphysik, ETH, Ziidch, Switzerland. electron diffraction (XPD) [12] that diffusion of cobalt into the platinum bulk is limited to the two topmost surface layers only. Measurements by low energy ion scattering (LEIS) [11,12] showed that the topmost layer in this phase is composed principally of platinum. However, a direct measurement of the layer-by-layer composition was not possible by these techniques, and the LEIS results for the topmost layer needed to be quantified and verified by an independent technique. Hence, in the present study we used quantitative low energy electron diffraction for this purpose. LEED analysis has been shown to be able to determine the composition of the first few atomic layers of several alloys [13], including Co-Pt ones [7,8]. The results of the present work confirm that the surface alloy at the Co/Pt(lll) interface is two atomic layers thick. The composition was found to be 20 at% cobalt in the topmost layer and 80 at% in the second. 0039-6028/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0039-6028(95)00631 - 1