Microstructure of theα−Al2O3(112¯0)surface

The microstructure of the $\alpha -{\mathrm{Al}}_2{\mathrm{O}}_3\left(112\mathrm{}¯0\right)$ surface has been investigated by means of He-atom scattering (HAS), low energy electron diffraction (LEED), atomic force microscopy, and x-ray photoelectron spectroscopy. Heating the samples at 1600 K in air results in atomically smooth surfaces which are, however, covered by a carbon layer. No diffraction pattern could be obtained for these contaminated surfaces. Additional cleaning by sputtering and annealing under UHV conditions yielded highly ordered surfaces characterized by a well defined $(1\mathrm{}\times 1)$ diffraction pattern in HAS and LEED. Annealing above 1400 K caused a structural transition to a $(12\mathrm{}\times 4)$ phase, which is characterized by an ordered arrangement of oxygen vacancies. At room temperature the surface was found to be unreactive with regard to molecular and, surprisingly, atomic hydrogen.