Local atomic arrangement of Pb and Sn on the Si(111)√3×√3-(Pb,Sn) surface

A √3×√3-(Pb,Sn) surface was studied by means of scanning tunneling microscopy (STM) and core-level photoelectron spectroscopy (PES) to identify its local atomic arrangement. Observed spots in STM were classified into three types, which were white and gray (α), gray and white (β), and black and gray (γ) spots in the filled- and empty-state images, respectively. The STM images also showed a local 3×3-(Pb,Sn) arrangement in the √3×√3-(Pb,Sn) surface. Both Pb 5d and Sn 4d core-levels spectra indicated that there were two components on the √3×√3-(Pb,Sn) surface, and the peak positions and shapes of Pb 5d and Sn 4d core-levels of the √3×√3-(Pb,Sn) surface were almost the same as those of the √3×√3-Pb and √3×√3-Sn surfaces. Comparison between the heights of the STM spots on the single and binary adsorbate surfaces and their core-levels spectra suggested that Sn and Pb were located at α and β positions, respectively. The nominal coverage of the local 3×3-(Pb,Sn) arrangement was determined to be 1/9 and 2/9 ml for Sn and Pb, respectively.