Platinum overlayers on Co(0001) and Ni(111): numerical simulation of surface alloying

The surface alloying of one and two monolayers (ML) of platinum deposited o n Ni(lll) and Co(0001) were studied by means of the ECT-BFS method. The 1 M L deposit appears to be very stable on both substrates. Platinum can diffus e at high temperature only, the large activation barrier being represented by the first substrate layer. On the contrary, the stability of the 2 ML de posit is poor so that alloying is easily obtained. In both cases, the plati num diffusion produces metastable states. The lowest-energy states exhibit a propensity for platinum dilution in a limited region below the surface. T he initial platinum thickness determines not only the features of the alloy ed region, but also the surface concentration. The surface alloys have feat ures qualitatively similar to those reported for the(lll) surface of bulk P t-Ni and Pt-Co alloys: a platinum-rich surface and oscillating concentratio n profiles. (C) 1999 Elsevier Science B.V. All rights reserved.