Electronic properties of metal-covered silicon surfaces: Cs and Ba overlayers on the Si(100)2x1 and Si(111)7x7 surfaces

A comparative study of Cs and Ba adsorption on the metal-like-Si(111)7 x 7 and semiconducting-like Si(100)2 x 1 surfaces has been performed sing the t hreshold photoemission spectroscopy. Electronic band structure and ionizati on energy have been studied as a function of submonolayer coverage. The ele ctronic structures of the Cs/Si(100)2 x 1 and Ba/Si(100)2 x 1 interfaces ar e found; to be similar and consist of two adsorbate-induced bands correspon ding to two inequivalent adsorption sites. The interfaces are semiconductor -like. Results indicate dominant role of the substrate under interface form ation and support the double-layer model. In the Case of the Si(111)7 x 7 s urface effect of Cs adsorption leads to metal-like interface. Upon Ba adsor ption, suppression of metallicity of the Si(111)7 x 7 surface is revealed.: The Ba/Si(111)7 x 7 interface is identified as being semiconducting. One,C s-induced band for the Cs/Si(111)7 x 7 interface and four Ba-induced bands for the Ba/Si(111)7 x 7 interface are found. Experimental data provide dire ct evidence that the electronic properties of the metal-covered Si(111)7 x 7 surface depend strongly on the adsorbate.