A LEED study of the MgO (100) surface: identification of a finite rumple

Abstract

The first unambiguous identification of a finite rumpling of the ions in the (100) face of a rocksalt-structure compound has been made by means of an extension of a previous LEED theory/experiment comparison for MgO (100) carried out using a new and extensive I(V) data set recorded over the energy range between 20 and 150 eV. These data were obtained from an air-cleaved sample using a novel, computer-controlled spectrum acquisition system, surface charging effects being eliminated by application of a primary energy modulation technique. An R-factor analysis was used to locate the optimum structural solution. This involves a differential relaxation of the top layer ions of 0.04 AA with an associated mean surface relaxation of zero, a result which agrees well with the most recent shell model calculations. This finding is discussed in relation to the postulated existence of a structural phase transition at the MgO (100) surface and its implications for the type of chemical bonding operative in the region are assessed.