SURFACE AND BULK CORE-LEVEL SHIFTS OF THE SI(111)3X1-NA AND SI(111)DELTA-7X7-NA SURFACES

By means of surface sensitive photoelectron spectroscopy using synchro tron radiation, we have measured the Si 2p surface and bulk core level shifts for the Si(111)3 X 1-Na and Si(111)delta 7 X 7-Na surfaces, an d obtained new information about these surface structures. As for the 3 X 1-Na, we found that there are two kinds of surface Si atoms which are differently charged. The number of surface Si atoms is estimated t o be about 4 in the surface unit cell. We also estimated the coverage of this surface as similar to 1/3 ML in contrast to 2/3 ML so far beli eved from the STM images. This result removes the discrepancy between the semiconductor character and the odd number of electrons in the uni t cell of the 3 X 1-Na so far reported in the literature. From these r esults we have proposed some possible models for the Si(111)3 X 1-Na s urface.