Formation of the first monolayers of CdTe on Au(111) by electrochemical atomic layer epitaxy (EC-ALE): studied by LEED, Auger, XPS, and in-situ STM

The two-step alternated electrodeposition of Cd and Te atomic layers to form CdTe monolayers, electrochemical atomic layer epitaxy (EC-ALE), was studied on Au(111) using Auger electron spectroscopy (AES), low energy electron diffraction (LEED), in-situ scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS). Well ordered (√7×√7)R19.1°-CdTe and (3×3)-CdTe structures were formed using either Te or Cd as the first layer, and model structures are proposed for both. STM images suggest that previously proposed hexagonal structures based on a plane of zinc blende CdTe may be incorrect. A chain structure is suggested to account for the (√7×√7)R19.1°, based on 3/7 (0.43) ML each of Cd and Te. The (3×3)-CdTe structure results from the deposition of a CdTe sandwich: first an atomic layer of Cd on Au, followed by a layer of Te, and then a second Cd layer. Based on this three layer model for the (3×3), a three step deposit was formed, starting with Cd, then Te, and finally Cd. This resulted in an excellent quality LEED pattern, suggesting a well-ordered (3×3)-CdTe deposit and strongly supporting the proposed model. The importance of deposit stoichiometry was also investigated using STM, which indicated that too low a coverage in the first atomic layer resulted in cluster formation and the degradation of surface morphology.