Atomic Structure of theα−Al2O3(0001) (31×31)R±9°Reconstruction

The projected atomic structure of the $\alpha -{\mathrm{Al}}_2{\mathrm{O}}_3\mathrm{}\left(0001\right)(\sqrt{31}\times \sqrt{31})R\pm 9°$ reconstruction has been analyzed by means of the grazing incidence x-ray diffraction technique, which is not limited by the surface insulating character. It consists of two Al planes whose structure is close to that of metallic Al(111). This overlayer is rotationally reconstructed, is commensurate with the substrate, and displays strong nonlinear static distortion waves. This layer, oxygen depleted, explains why the surface properties are dramatically changed.