AES, XPS and EELS study of the initial oxidation of polycrystalline chromium

Abstract

The interaction of oxygen with a clean polycrystalline chromium surface has been studied at 300 K in the 10 −8 – 10 −6 Torr pressure range by means of AES, XPS and EELS. From the chemical information obtained by these analytical techniques, the reaction of the oxygen with the chromium surface has been found to occur in three stages: Dissociative chemisorption of oxygen up to 1–2 L exposures. Nucleation of cr 2o 3 islands which grow laterally until coalescence up to ~10 L exposures. Beyond 10 L the thickening of the oxide becomes slow and follows a logarithmic law. The beginning of the second stage is characterized by abrupt changes in the chromium AES, XPS and EELS spectra. Also, changes in the energetic position of the AES oxygen peak and of the Ols band have been found during this stage. After the coalescence is reached the average thickness of the film is ~3.8 monolayers. The beginning of the third stage is characterized by an abrupt decrease in the reaction rate leading to a logarithmic type growth law.