SURFACE CORE LEVELS OF IN ADSORPTION ON SI(001)2X1

The noble surface reconstructions of 2x2, 2x3, and 4x3 induced by In a dsorption on a Si(001) surface have been studied by high-resolution ph otoelectron spectroscopy using synchrotron radiation. The surface core -level shifts of Si 2p were resolved, for the first time, for group-II I adsorption on Si(001). It is shown that the Si dimers not bonded to In in the 2x3 phase are buckled and the Si dimers bonded to In are sym metric in both the 2x2 and 2x3 phases. In 4d spectra for all the three phases show a single component in agreement with the prevailing struc ture models of 2x3 and 2x2 phases but in contradiction to those of 4x3 .