Structure of Sulfur Adlayer on Cu(111) Electrode in Alkaline Solution

The structure of sulfur adlayer and the formation process of Cu 2 S layer on Cu(111) were investigated using in situ scanning tunneling microscopy (STM) in alkaline solution. In situ STM revealed two different structures of the sulfur adlayer, ( √ 3 × √ 3 ) R 30 ° and ( 19 × 19 ) , in the double-layer potential region. The ( √ 3 × √ 3 ) R 30 ° structure observed at negative potentials was transformed into ( 19 × 19 ) upon sweeping the potential in the positive direction. The ( 19 × 19 ) structure consisted of well-ordered triangular domains separated by boundaries running along the 〈110〉 direction. In each triangular domain of ( 19 × 19 ) , sulfur atoms were found to form a ( √ 3 × √ 3 ) R 30 ° structure. Characteristic hexagonal rings consisting of six sulfur atoms were observed at intersections of the domain boundaries of ( 19 × 19 ) . At anodic potentials, layers of Cu 2 S were epitaxially formed on Cu(111), on which a ( 7 × 7 ) R 19.1 ° structure was observed.