Very-high-quality MgO(001) surfaces: roughness, rumpling and relaxation

The structure of MgO(001) single crystal surfaces that are of very high crystalline quality, extremely flat, clean and stoichiometric, was investigated by grazing incidence X-ray scattering. A new procedure for preparing these surfaces is described, which includes high-temperature annealing in air followed by high-temperature ion bombardment, and annealing under partial oxygen pressure. The relaxation, -0.56+/-0.35%, and rumpling, 1.07+/-0.5%, were determined with a much better accuracy than in any previous experimental study. These values are compared with those given in previous experimental and theoretical studies. The atomic structure of the Ca-segregated MgO(001) surface was also investigated. The most likely structure is the theoretically predicted (root 2 x root 2)R45 degrees reconstruction. Atomic displacements within this unit cell were determined. (C) 1998 Elsevier Science B.V. All rights reserved.