A scanning tunneling microscopy and X-ray photoelectron spectroscopy study of electrochemically grown ZnS monolayers on Au(111)

The structure and chemical composition of electrosynthesized ZnS thin films on Au(111) substrates was studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The films mere grown by alternating underpotential deposition and oxidative adsorption cycles of S and Zn from solution precursors (electrochemical atomic layer epitaxy, EC-ALE). Oxidative adsorption of the first layer of S results in a (root 3 x root 3)R30 degrees adlattice on Au(111). In the initial Zn monolayer, XPS indicates the presence of SO42- derived from the supporting electrolyte. The coadsorbed SO42- can be chemically or electrochemically displaced by H2S(aq) or HS(aq)-, leading to the formation of ZnS. Atomically resolved STM images show the ZnS/Au(lll) monolayer to be 6-fold symmetric with an interatomic spacing of 0.37 +/- 0.01 nm. The structure of the deposit on the micrometer scale was also investigated by STM. The first complete EC-ALE cycle results in the formation of nanocrystallites of ZnS randomly distributed across Au(111) terraces. The average diameter of the crystallites is 10 +/- 5 nm, and the apparent coverage of ZnS is 0.38.