Interactions at the Ni 3 Al(111)−S−Al 2 O 3 Interface at Elevated Temperatures: Ordering of Al 2 O 3 on an S-Modified Substrate

Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM) have been used to investigate the growth, morphology, and thermal stability of the oxide prepared on a (2 × 2)-S-covered Ni 3 Al(111) surface. The results demonstrate that although sulfur significantly alters the oxidation rate and oxide morphology on the Ni 3 Al(111) substrate at room temperature, it does not inhibit the formation of the ordered γ‘-Al 2 O 3 at elevated temperatures. The oxide formed on the S-modified Ni 3 Al(111) surface at room temperature is stable up to at least 1100 K. Sulfur remains at the oxide−Ni 3 Al(111) interface during oxygen exposure at ∼300 K. During annealing, however, sulfur is removed from the oxide−alloy interface. Annealing from 300 to 1100 K results in the segregation of aluminum to the oxide−alloy interface, as evidenced by an enhancement in the Al (1396) /Ni (848) atomic ratio, and the appearance of a metallic aluminum peak in the Auger spectra.