Mechanism of the short range ordering in a 2D binary alloy

Abstract Direct comparison of scanning tunneling microscopy (STM) and high-resolution core level photo-emission experiments provides a rationale for the mechanism of short range ordering in a two-dimensional (2D) binary alloy (1/3 monolayer (ML) Sn (1− x ) Si x /Si(1 1 1)-(√3×√3) R 30°). The host pure Sn metal surface ( x =0) results partitioned into two classes (2/9 and 1/9 ML) of ad-atoms occupying non-equivalent T 4 sites. Sn substitution with Si ad-atoms preferentially takes place at the majority type adsorption sites. This occurrence explains the atomic intermixing and the short range ordering directly observed with STM and typical of a wide class of 2D binary alloys.