STUDIES OF THE STRUCTURES FORMED BY THE ALTERNATED ELECTRODEPOSITION OF ATOMIC LAYERS OF CD AND TE ON THE LOW-INDEX PLANES OF AU .1. LEED AND AUGER STUDIES

We present here a low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) study of the surface chemistry resulting from electrodeposition of two monolayers of CdTe on the low-index planes of Au by electrochemical atomic layer epitaxy (ECALE). ECALE is the electrochemical analog of atomic layer epitaxy (ALE). In the present study, well-ordered monolayers of CdTe were formed by the alternated electrodeposition of atomic layers of Cd and Te, at underpotential, on all three Au planes. Deposition of the first monolayer of CdTe was performed by depositing Te either oxidatively at underpotential or reductively at underpotential, followed by reductive Cd underpotential deposition (UPD). The structures formed were the same in both cases: Au(100)(square-root 2 x square-root 2)R45-degrees-CdTe, Au(110)(2 x 3)-CdTe, and Au(111)(square-root 7 x square-root 7)R19.1-degrees-CdTe. Varying the initial cover-age of Te did not change the resulting CdTe structure, although the higher coverages of Te showed sharper LEED patterns and no emersed oxygen. Deposition of Cd as the first atomic layer followed by oxidative Te UPD resulted in the same structures as those found when Te was used for the first atomic layer. Optimal CdTe monolayers were formed on surfaces where the first atomic layer deposited was homogeneously distributed and of the correct coverage. The correct initial coverage is determined by the coverage needed to complete the subsequently formed CdTe monolayer. On Au(100), an initial coverage of 0.5 appears to be optimal in order to form the Au(100)(square-root 2 x square-root 2)R45-degrees-CdTe. Deposition of a second CdTe monolayer onto the first resulted in structures similar to the first monolayer, but with increased diffuse intensity in the resulting LEED patterns under the conditions used.