Study of the electronic structure of Si(100)2x1 and Cs/Si(100)2x1 with MIES and UPS (HeI)

We report the MIES (He*1s2s) and UPS (HeI) spectra for clean Si(100)(2 x 1) and Cs/Si(100)(2 x 1). The cesium coverage is varied at room temperature between zero and saturation. The MIES results are compared with corresponding ones for Cs/Al(111) and Cs/W(110) (also presented here). Simulations of the MIES spectra for clean and cesiated Si(100)(2 x 1), based on presently available information on the electronic structure of the clean and cesiated surfaces, facilitate the interpretation of the spectra. The results obtained for small Cs coverages are compatible with ionic adsorption of Cs whereby the Cs 6s electron is transferred into the Si dangling bonds. For larger coverages the surface displays metallic character. We cannot decide however whether this is caused by the formation of a metallic-like Cs adlayer or by the filling of the Si dangling bonds leading to metallization of the Si substrate.