ELECTRON-DENSITY MAPS FOR THE SI(1-1-1) 7X7 SURFACE CALCULATED WITH THE MAXIMUM-ENTROPY TECHNIQUE USING X-RAY AND ELECTRON-DIFFRACTION DATA

Maximum-entropy electron-density maps have been calculated for the fir st time for a two-dimensional surface structure using X-ray and electr on-diffraction data. The maps clearly resolve all the 102 atoms of the Takayanagi dimer-adatom-stacking-fault model. The atomic positions de termined from the map are in good agreement with those from a least-sq uares refinement, Electron bondings between atoms are not apparent in the maps due to insufficient data quality, The reliability of the maxi mum-entropy method is discussed, It is shown that the calculation proc edure must be continued to values of chi(2) < 1 in most cases, A metho d to estimate the uncertainty in the density values and to identify re liable features in the maps is presented. It is shown that the maximum -entropy method is a promising technique to obtain detailed structure information from a small number of accurate structure factors,