Absolute coverage determination in the K/Si(111):B- 2√3×2√3R30 surface

Abstract

In this paper, we report on the experimental determination of alkali absolute coverage in the K/Si(111):B-2√3×2√3R30°surface. To this end, we carried out a comparative study with the closest system, namely, K/Si(111)-3×1, for which potassium coverage has been widely demonstrated to be 1/3 of a monolayer. We used x-ray photoemission spectroscopy to count and compare the number of potassium atoms in both surfaces, together with a scanning tunneling microscopy in order to check the completion of these ultrathin layers. The analysis leads to a 1/2 monolayer coverage in the 2√3×2√3R30°surface, that is six potassium atoms per unit cell. Assuming this coverage, we can propose a simple model structure with potassium atoms arranged in trimers; we discuss the effect of such a reconstruction in terms of two distinct "up" and "down" Si adatom sites as well as the resulting surface electronic properties. © 2011 American Physical Society.