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 on Ni(111) and Co(0001) were studied by means of the ECT-BFS method. The 1ML deposit appears to be very stable on both substrates. Platinum can diffuse at high temperature only, the large activation barrier being represented by the first substrate layer. On the contrary, the stability of the 2ML deposit is poor so that alloying is easily obtained. In both cases, the platinum diffusion produces metastable states. The lowest-energy states exhibit a propensity for platinum dilution in a limited region below the surface. The initial platinum thickness determines not only the features of the alloyed region, but also the surface concentration. The surface alloys have features qualitatively similar to those reported for the (111) surface of bulk Pt–Ni and Pt–Co alloys: a platinum-rich surface and oscillating concentration profiles.