SURFACE-STRUCTURE OF MGO(001) - A MEDIUM-ENERGY ION-SCATTERING STUDY

We have used medium-energy ion-scattering with channeling and blocking to study the surface structure of MgO(001). The ion scattering data show that UHV-cleaved crystals result in well ordered surfaces, while sputtered/annealed samples show structural disorder. Surface blocking dips in both the 0 and Mg spectra are found to occur at angles very close to the corresponding bulk blocking directions, indicating very small surface relaxation and rumpling. A detailed R-factor analysis comparing the experimental spectra with results of Monte Carlo simulations for different structures gives a surface relaxation of - 1.0% +/-1.0% and a rumpling of 0.5% +/- 1.0%. These results are in good agreement with preliminary results from all-electron total-energy calculations and imply that the surface O2- ions have small polarizations.