title: A LEED analysis of the clean surfaces of α-Fe(2)O(3)(0001) and α-Cr(2)O(3)(0001) bulk single crystals.
abstract: 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(O(2))≈3 × 10(-8) mbar, for several hours. The chromia crystal was sputtered with Ar(+) ions, E = 1 keV, and afterward heated up to 900 °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 ≈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 α-Fe(2)O(3)(0001).
authors.affiliation: Department of Earth and Environmental Sciences, Section Crystallography, Ludwig-Maximilians-Universität München, Theresienstraße 41, 80333 Munich, Germany.
authors.forename: Maike
authors.initials: M
authors.lastname: Lübbe
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Moritz