The layer structure of Ag on a Ni/Pt(111) surface after high temperature annealing was studied by Auger electron spectroscopy, depth profile of Ar ion sputtering, and low-energy electron diffraction (LEED). A structural phase p(2 X 2) LEED pattern was observed in one atomic monolayer (ML) on I ML Ni/Pt(111) surface after annealing at 800 K. Based on observations of the change of ion sputtering, rates for the Ag overlayers, the LEED pattern, and minimum strain energy, we propose a layer structure of Ag for 1 ML Ag/l ML Ni/Pt(111) after the 800 K annealing. The compositions in the subsurface region are 0.25 ML Ag in p(2 X 2) structure on the topmost layer, Ag75Ni25 alloy in the second layer, and Ni-Pt alloy in the remaining layers of the subsurface regions. (c) 2006 American Vacuum Society.