A LEED analysis of the clean surfaces of α-Fe2O3(0001) and α-Cr2O3(0001) bulk single crystals

We analyzed the (0001) surface structures of hematite and chromia bulk single crystals by low energy electron diffraction (LEED). The hematite crystal was annealed in an O-2 atmosphere, p(O2) approximate to 3 x 10(-8) mbar, for several hours. The chromia crystal was sputtered with Ar+ ions, E = 1 keV, and afterward heated up to 900 degrees C for 5 min under ultra-high-vacuum (UHV) conditions. I (V)-curve data sets of 12 symmetrically independent diffraction spots were measured at room temperature in the energy range E = 150-500 eV. Charging effects hindered measurements at lower energies. Our analysis of the hematite single crystal surface indicates that it is terminated by a single iron layer which is occupied at approximate to 50%. Relaxation effects along the c-axis are quite large and involve several iron double layers. For the chromia surface the results indicate that termination with a single Cr seems not to hold. Most probably the surface is terminated by two partially occupied Cr sites or chromyl groups. Relaxations in deeper layers are small in contrast to alpha-Fe2O3(0001).