Formation of and phase transitions in electrodeposited tellurium atomic layers on Au(111)

Detailed studies of the structures formed by the electrodeposition of atomi c layers of Te on Au(1 1 1) surfaces from aqueous solutions were performed using in situ scanning tunneling microscopy (STM), as well as by UHV-EC tec hniques such as low energy electron diffraction and Auger electron spectros copy. There are two features in the voltammetry that may be considered unde rpotential deposition (UPD). However. from the voltammetry, it is clear tha t the deposition process is kinetically slow, and from this study it appear s that several atomic layer structures are actually formed at overpotential s. Prior to deposition, a surface excess of a tellurium oxide species coats the surface. This layer is then converted to a Au(1 1 1)(root3 x root3)R30 degrees -Te structure with an array of domain walls, at similar to1/3 ML. The initial structure appears to have a symmetric array of walls, resulting in a (13 x 13) periodicity, which then converts to a less symmetric struct ure where the domain walls form rhombi, with a larger periodicity. During t he second UPD feature, the coverage increases, forming a (root7 x root 13) unit cell at 0.36 ML and then a (3 x 3) at 0.44 ML. Commensurate with the f ormation of these higher coverage structures, a roughening transition takes place, where the surface becomes pitted, resulting in about 40% of the sur face being covered with single atom deep pits. This process appears to be r elated to the pits formed in the surfaces of self-assembled monolayers (SAM ) of thiols on Au surfaces, and layers of Se and S on Au surfaces. Several theories have been suggested to account for these pits. The model that appe ars to best explain the pits is based on shrinking of the size of the under lying Au atoms, reconstructing the underlying Au. There also appears to be a high coverage structure, near 0.9 ML, that forms at potentials near where the (3 x 3) forms, but only by holding the potential for an extended perio d of time. Subsequent dissolution of this high coverage structure produces domains of disordered Te atoms, which gradually decrease in coverage until the (3 x 3) is again formed at 0.44 ML. (C) 2001 Elsevier Science B.V. All rights reserved.