LEED STUDY OF THE STRUCTURE OF THE (100) SURFACE OF CAO

The structure of the (100) surface of UHV cleaved CaO has been determined at room temperature by LEED. The experimental data set consists of 39 beams obtained between 120 and 400 eV in seven diffraction geometries. The calculations were based upon rumpled ionic models and used the CAVLEED library of LEED programs. Up to 57 beams and nine phase shifts were used. Very good agreement was obtained between theory and experiment, the best fit yielding a rumple of less than 2% and a surface layer contraction of 1% of an interlayer spacing. The R factor computed for this solution was 0.156. A shell-model calculation of the surface structure is in general agreement with this result in that it predicts a rumple of 5% and a surface contraction of 3% of an interlayer spacing.