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

Abstract

We analyzed the (0001) surface structures of hematite and chromia bulk single crystals bylow energy electron diffraction (LEED). The hematite crystal was annealed in anO2 atmosphere, pO2≈3 × 10−8 mbar, for several hours. The chromia crystal was sputtered withAr+ ions,E = 1 keV, and afterwardheated up to 900 °C for 5 min under ultra-high-vacuum (UHV) conditions.I(V)-curve data sets of 12 symmetrically independent diffractionspots were measured at room temperature in the energy rangeE = 150–500 eV. Charging effects hindered measurements at lower energies. Our analysis of the hematitesingle crystal surface indicates that it is terminated by a single iron layer which is occupied at≈50%. Relaxationeffects along the c-axis are quite large and involve several iron double layers. For the chromiasurface the results indicate that termination with a single Cr seems not tohold. Most probably the surface is terminated by two partially occupied Crsites or chromyl groups. Relaxations in deeper layers are small in contrast toα-Fe2O3(0001).