Core-level photoelectron study of Si( [formula omitted]) √7×√3-( [formula omitted]) surface

Abstract

The Sn 4 d and Pb 5 d core-level photoelectron spectra have been studied in order to clarify their bonding properties and atomic arrangement on a Si(1 1 1) √7×√3-(Pb, Sn) surface, which is formed by the coadsorption of 0.4 ML Pb and 0.4 ML Sn and shows two kinds of bright spots in the scanning tunneling microscopic (STM) images: (A) those aligned zigzag on the T 1 site and (B) those on the T 1 and H 3 sites along the [1 1 −2] direction. The Pb 5 d spectrum shows a single spin–orbit-split feature with weak tailing towards the high binding energy side, while the Sn 4 d spectrum exhibits shoulder structures at the high binding energy side of the main peaks. This definitely indicates at least two different Sn–Si bonds or inequivalent Sn adsorbing sites and single bond or site for Pb. Thus the spots A at the T 1 site and those B at the T 1 and H 3 sites in the STM images are ascribed to Pb and Sn adatoms, respectively. The formation process of this surface will be also discussed in terms of the core-level spectra.