Analysis of intensity data for rheed by the MgO(001) surface

Rocking curves for elastic diffraction of 10 keV electrons incident on the MgO(001) surface, in the [010] azimuth, are computed and compared with experimental data. Very good agreement with experiment is obtained in spite of some uncertainty about the inelastic component of the data. Assuming that the possible presence of an inelastic component does not affect the subsequent analysis allows the spacing of the topmost atomic layers of the MgO(001) surface to be determined. The most likely value is found to be identical to the bulk layer spacing and the upper limit on any deviation from the bulk spacing is found to be a 3% expansion. This is consistent with the accepted LEED result. Further calculations are then used to show that RHEED could be used to find the rumpling of the MgO(001) surface as well as the topmost layer spacing. It is shown that the RHEED intensities are insensitive to rumpling when the incident beam azimuth lies in one of the [n10] directions with n even, but that they are very sensitive to rumpling when it lies in other directions. Use of this effect would enable the topmost spacing and rumpling to be determined by a systematic procedure for which the computational cost is particularly low. Some reasons for the apparent insignificance of inelastic scattering in the analysis of the RHEED data for diffraction by the MgO(001) surface are considered and the prospects of using RHEED as a general surface structure analysis technique are discussed.