MODEL APPROACH TO THE CALCULATION OF THE SI(111)-7X7 OPTICAL-PROPERTIES

To understand the origin of the Si(111)-7 x 7 surface optical response , we have carried out microscopic calculations for model structures co ntaining all the DAS-model building elements: a Si(111)-2 x 2 adatom-r est-atom model and a Si(111)-3 x 3 adatom-dimer-stacking fault model. Based on these results, the optical properties of the Si(111)-7 x 7 su rface are extrapolated and the main optical peaks are interpreted in t erms of the surface band structure. A fair agreement with the experime ntal data for the Si(111)-7 x 7 reconstruction is obtained.