Formation of ordered B structure on W(100)

Adsorption of a metalloid, boron (B) on W(100) was investigated using low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) in ultra-high vacuum (UHV) condition. W(100)-c(2 x 2)-B superstructure was formed by annealing at high temperature (1200 K). The best fit structure obtained from LEED analysis and STM observation manifested that B atom positioned at four-fold hollow site with the coverage of 0.5 ML, forming low B concentrated tungsten boride compound, W2B, on W (100) surface. The W atoms beneath B atoms moved downward to form B-W bonds for stabilizing the surface atoms. XPS confirmed B 1s peak shifting towards lower binding energy compared to pure B 1s, which indicated the charge transfer from W to B. No ordered structures other than c(2 x 2) have been observed with the increase of B, which indicates that B atoms diffuse into bulk, not forming ordered B sheets, due to the low diffusion barrier into bulk by annealing.