Oxidation of Polycrystalline Chromium between 30°C and 400°C

The formation of coalesced oxide films on atomically clean polycrystalline chromium has been studied with Auger electron spectroscopy and secondary ion mass spectrometry at temperatures between 30°C and 400°C. The data are consistent with an initialed chemisorption of oxygen on the clean Cr followed by nucleation of chromium oxide after 2 L of exposure followed by lateral growth to form a thin, coalesced, saturated oxide film about 0.8 nm thick at 30°C. The saturated oxide was thicker at higher temperatures, being about 80 nm thick at 400°C. Detection of a CrO$\text{}^{+}$ secondary ion was associated with chemisorbed oxygen, while O¯ ion originated from chromium oxides based upon correlation with chemical changes in the low-energy Auger spectra. Keating of the coalesced oxide caused considerable changes in both the low-energy Auger spectrum as well as the secondary ion emission. Both these as well as time-dependent, reversible changes in secondary ion emission were interpreted as structural rearrangements of the chromium oxide resulting in relative changes of oxygen either adsorbed on the surface or incorporated into chromium oxide.