Surface modification of co-evaporated thin films upon oxygen and air exposure

Ru and Ti have been co-evaporated onto a SiC substrate in an ultrahigh vacuum chamber. The formation of the RuTi film and its interaction with oxygen by exposure to 100 L of pure oxygen and exposure to air was investigated by X-ray photoelectron spectroscopy (XPS). The results are compared with those of the monoatomic Ru and Ti films. XPS analysis of the bimetallic film shows that there is a shift in the peak position of Ru and Ti towards lower and higher binding energy values, respectively, indicating that an alloy is formed. Upon exposure to air at room temperature, the Ru/(Ru + Ti) surface concentration decreases from 0.65 to 0.54, indicating that Ti atoms migrate to the surface of the film. Ti associated to Ti(IV) increases significantly in air-exposed RuTi, accounting for 65% of all Ti emissions. This value is three times higher than that observed on air-exposed Ti monoatomic film. Correspondingly, the thickness of the oxide layer at the surface of air-exposed RuTi is ∼3 times as thick as that found at the surface of air-exposed Ti monoatomic film.