Electrochemical formation of Se atomic layers on Au(100)

Abstract

Studies of the electrodeposition of atomic layers of Se have been prompted by their importance in the formation of II–VI compound semiconductors by electrochemical atomic layer epitaxy (ECALE). ECALE is a method where a compound is formed by the sequential, alternated, electrodeposition of atomic layers of the constituent elements making up a compound. It has been shown that the structure of the first atomic layer is generally the most critical. The present article describes three different methods for forming that first atomic layer. Studies of the structures resulting from those methods have revealed four distinctly different Se structures, all of which can be considered atomic layers, as none is more than a single-Se atom thick. Graphs of coverage versus potential have been obtained for each of the methods, and show distinct plateaus over as much as 0.15 V, indicating the stability of some of the structures. The sequence of structures first involves the formation of a 1/4 coverage (2×2), followed by a (2×√10) at 1/3 coverage, and then a c(2×2) at 1/2 coverage. In addition, Se8 rings were observed to form, much the same as the S8 rings previously observed for S adsorbed on Au surfaces. At coverages near 0.7, these rings begin to coalesce into a nearly complete monolayer of Se atoms, but with systematic absences, which roughly correspond to the initial holes in the Se8 rings. This structure appears to have an average unit cell which can be described as a (3×√10).