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 first time for a two-dimensional surface structure using X-ray and electron-diffraction data. The maps clearly resolve all the 102 atoms of the Takayanagi dimer-adatom-stacking-fault model. The atomic positions determined from the map are in good agreement with those from a least-squares refinement, Electron bondings between atoms are not apparent in the maps due to insufficient data quality, The reliability of the maximum-entropy method is discussed, It is shown that the calculation procedure must be continued to values of chi(2) < 1 in most cases, A method to estimate the uncertainty in the density values and to identify reliable 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,