Electrochemical Formation of CdSe Monolayers on the Low Index Planes of Au

The electrochemical analog of atomic layer epitaxy (ALE) is being studied. ALE is a method for growing thin films of materials using a cycle of surface limited reactions. The surface limited reactions control the deposition by limiting the growth to an atomic layer at a time. In electrochemistry, a surface limited deposition is generally referred to as underpotential deposition (UPD), and UPD is used to form the atomic layers in electrochemical ALE (ECALE). The work presented here is an atomic level study of the deposition of the first few monolayers of CdSe via ECALE: by the alternated UPD of atomic layers of Se and Cd on the low index planes of Au. UPD of Se resulted in the formation of ordered structures on each of the low index planes of Au, as observed by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The subsequent UPD of Cd resulted in CdSe deposits which exhibited 1:1 stoichiometry, as determined by coulometry and Auger electron spectroscopy (AES). The following LEED patterns were observed for the CdSe monolayers: Au(111)(√7×√7)R19.1°, Au(111)(3×3), Au(110)(2×3), and the Au(100)(√2×2√2)R45°. Similar LEED patterns were observed on each surface for deposits formed using up to three ECALE cycles. In situ STM studies of Cd deposition on Se‐covered Au(111) indicated the formation of a (3×3) structure, consistent with LEED results, and with previous TEM studies. The same LEED patterns were also observed for CdSe monolayers where Cd was deposited as the first atomic layer. AES indicated that the element deposited first remained on the bottom, and that deposited second remained on top.