FORMATION OF THE FIRST MONOLAYER OF CDSE ON AU(111) BY ELECTROCHEMICAL ALE

Electrochemical ALE (ECALE), the electrochemical analog of atomic laye r epitaxy (ALE), is being developed. Central to ALE is the formation o f atomic layers of the elements using surface limited reactions, in a cycle. In electrochemistry another name for a surface limited electrod eposition reaction is underpotential deposition (UPD). In ECALE, compo und thin films are formed an atomic layer at a time by using UPD, in a cycle. In the study presented here the formation of the first monolay er of CdSe on Au(lll) is described. The first step in the ECALE cycle is the formation of an atomic layer of Se via UPD. UPD of Se resulted in a surface composed of domains of two structures: a (root 3 x root 3 )R30 degrees structure at 1/3 coverage, and a close packed layer of sq uare eight membered Se rings. The ring structure consists of three dom ains, each rotated by 120 degrees. Formation of a single structure, ho mogeneously covering the whole surface proved difficult due to the kin etics of the UPD process. Subsequent deposition of a Cd atomic layer r esulted in formation of a CdSe structure with a (3 x 3) unit cell, and 4/9 coverage of both Cd and Se. A structure proposed to account for t he unit cell and coverages, consists of a slice out of the bulk wurtzi te structure for CdSe laid onto the Au(Ill) substrate, where twice the surface lattice constant for CdSe matches up with three times the Au interatomic spacing.