Abstract
A thin Cr oxide layer has been formed on a clean Si(111) surface at 40 K via N 2O physisorption followed by Cr evaporation. In situ analysis with X-ray photoelectron spectroscopy indicated that Cr atoms arriving at the condensed N 2O layer instantly form Cr oxide but negligible Cr nitride. The Cr atoms, which preferentially consume O in the condensed N 2O layer, did not cluster themselves and the dissociated N 2 desorbed. Prolonged X-ray irradiation led to dissociation of the remaining N 2O, and the resulting dissociated O induced increased O coordination of the Cr oxide previously formed. The underlying Si substrate, on the other hand, was not oxidized until it was heated above 650°C. Such substrate disruption resulted in Cr oxide reduction at the interface. A comparative study with the reverse procedure, Cr evaporation followed by N 2O physisorption, led to conclusion that the essential condition for forming thin Cr oxide without substrate disruption is the protection of the surface with a condensed N 2O overlayer from the reactive Cr atoms.
Published Version
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