Adsorption of Ba on Si(001)2 ×1 Surface

The initial adsorption of Ba on the Si(001)2 ×1 surface at 870°C has been studied by low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and angle-integrated ultraviolet photoelectron spectroscopy (AIUPS). The valence band, Si and Ba core level spectra and the work-function change (Δφ) were measured. The double domain (DD) (2 ×3)-, DD c(2×6)- and DD (2×1)-Ba surfaces appeared depending on the Ba coverage. AIUPS results show that both DD (2 ×3)-Ba and DD (2 ×1)-Ba surfaces are semiconducting in nature. The intensity ratio data of XPS core levels (Ba 3d/Si 2p) and the work-function change data reveal that the Ba coverages of the (2×3)-Ba and the DD (2×1)-Ba surfaces are 1/3 ML and 1/2 ML, respectively. The AIUPS spectra show that the structural models with Ba coverage of 1/3 ML and 1/2 ML, at the bridge sites between two Si dimers are reasonable for the (2 ×3)-Ba and the (2 ×1)-Ba surfaces, respectively.