An unusual composition profile:: a LEED-TBIM study of Pt25Cu75(111)

The structure and composition of a disordered N25Cu75(1 1 1) sample was studied by low energy electron diffraction. The r-factor, D-1 = 0.096, illustrates a very good agreement between experimental and theoretical spectra. The Pt concentration versus depth oscillates around the bulk value (C-1, C-2, C-3, C-4 = (28, 8, 48, 8 at.% Pt). The most striking result is the quite large and unusual Pt enrichment in layer 3 (C-3 = 48%) followed by the still important Pt depletion in layer 4 as opposed to the damped oscillations observed for similar Pt-Ni(1 1 1) and Pt-Co(1 1 1) alloys. This result, which is in contradiction with a previous LEIS study, is interpreted within the Tight Binding Ising Model and is related to a termination of the L1(1) phase, which exists only in the Cu-Pt system. (C) 2003 Elsevier Science B.V. All rights reserved.