Low Energy Electron Diffraction Study of Epitaxial Cr2O3(0001) Films Grown on Cr(110)
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The (110) surface of Cr is somewhat unique in that its native oxide forms an epitaxial Cr2O3(0001) overlayer. Previous studies of this epitaxial surface found that a (v3xv3)R30° surface reconstruction was observed over a temperature range of 125 K to 175 K, and this has been attributed to a surface magnetic transition. To determine the nature of this surface reconstruction, we have grown an epitaxial Cr2O3(0001) surface on a Cr(110) single crystal and characterized its surface structure over a temperature range of 140 K to 675 K using low energy electron diffraction (LEED). Before growth of the epitaxial oxide, the Cr(110) surface was cleaned by performing several cycles of sputtering the surface with Ar ions followed by annealing at 725 °C to heal the surface. Although moderate surface contamination was observed on the Cr(110) surface after several sputter/anneal cycles, it was possible to grow an epitaxial Cr2O3(0001) film, which exhibited the characteristic LEED pattern of the (1x1) structure at 300 K. Our film failed to exhibit the characteristic pattern of the (v3xv3)R30° overlayer structure over the entire temperature range used in this study. It is possible that lingering impurities present in the bulk chromium prevented the reconstruction. However, it is noted that CO adsorption on this surface begins at 175 K and also results in a (v3xv3)R30° overlayer. Since CO is present in all vacuum systems and itinerate magnetic effects are very unusual, the source of the surface reconstruction is most likely not from a surface magnetic transition but from CO adsorption at low temperatures. It is probable, due to the lower base pressure of our vacuum system in comparison to the previous studies, that the cleaner environment failed to provide sufficient CO to produce the (v3xv3)R30° surface reconstruction during our measurement time.