Surface structures of thallium on Ge(1 1 1)

The surface structures of thallium on Ge(1 1 1)c(2×8) have been investigated by scanning tunneling microscopy (STM), LEED, and Auger electron spectroscopy. The surface phase diagram of Tl on Ge(1 1 1) contains two ordered overlayers, a pseudomorphic (1×1)-Tl monolayer surface, obtained by Tl deposition at room temperature, and a Tl-induced (3×1) reconstruction; the latter forms at elevated temperature (300–350°C). The pseudomorphic (1×1)-Tl structure is interpreted in terms of Tl adatoms replacing the Ge adatoms and adsorbed in on-top T1-type surface sites of the unreconstructed Ge(1 1 1) surface. The STM data of the (3×1) reconstruction are consistent with a modified version of the honeycomb chain-channel model of this structure as proposed in the literature. The Tl induced surface reconstructions on Ge(1 1 1) are discussed in relation to the monovalent chemical character of Tl adatoms. At high coverages the growth of the Tl adlayer is characterised by a Stranski–Krastanov mode with highly mobile adatoms on the first wetting layer. The three-dimensional Tl islands grow epitaxially ordered and rotationally aligned with the substrate.