Breakup of oxide films on a Ni-Fe(100) surface by S 2 impingement

Abstract

Impingement of S 2 molecules onto the oxidized (100) surface of Ni 60Fe 40 at 500°C disrupts the coalesced oxide morphology. LEED and AES observations suggest that sulfur penetrates the oxide to the alloy interface forming chemisorbed c(2X2)S regions upon which sulfides subsequently nucleate and eventually grow over the rearranged oxide. The sulfur-induced change in the oxide morphology may be explained by a model involving a balance of surface tensions between the oxide and c(2X2)S phases to minimize the total surface free energy. In addition, S 2 and O 2 co-dosing experiments on the clean Ni 60Fe 40(100) surface reveal that O 2 sticking is greatly reduced by the presence of the c(2X2)S or sulfide phases during the initial scale growth.