Oxygen induced dissolution and segregation of silicon in platinum single crystals

The segregation of silicon in platinum flat (111), stepped (553) and (332) surfaces is studied as a function of crystal temperature. Silicon segregates below 1000°C with a segregation energy between 17 and 20 kcal/mol. In the retarding field mode, the maximum amount of segregated Si corresponds to a Si (93 eV)/Pt (242 eV) Auger peak ratio of about 5. In the presence of O2, Si dissolves into the bulk at T≳600°C. The rate of Si dissolution increases with O2 pressure and crystal temperatures. At an O2 pressure of 5×10−7 Torr, the activation energy for the dissolution process is 16±2 kcal/mol. Continued exposure to O2 results in the reappearance of Si at the Pt surface as a new phase, SiOx, characterized by Auger peaks of Si (84 eV) and O (515 eV).