X-ray photoemission study of the Ba/Si(100) interface and the oxidation of Si promoted by Ba overlayers

The interaction of barium overlayers with the Si(100) surface and the subsequent interface formation have been studied by x-ray photoelectron spectroscopy. Also studied, were the effects of Ba overlayers and the Ba/Si interface on the oxidation of Si at different Ba coverage (0≤θ≤2.4 ML) and different oxygen exposures. It is found that the Ba/Si interface formation follows a two-step mechanism. At low Ba coverage (θ≤2 ML), Ba deposits on top of, and strongly interacts with, silicon. This interaction is associated with charge transfer from the overlayer Ba atoms to silicon. Between 2 and 4 ML Ba coverage, the Ba/Si interface is unstable and silicon diffuses through the Ba overlayer. In addition, Ba overlayers on the Si(100) surface are found to significantly enhance the oxidation of silicon. At θ=2.4 ML Ba coverage, the obtained SiO2 oxides are found to be a factor of 5 thicker than those obtained for the clean unpromoted Si(100) surface.