Surface structures of thallium on Ge(111)

The surface structures of thallium on Ge(I 1 I)c(2 x 8) have been investiga ted by scanning tunneling microscopy (STM), LEED, and Auger electron spectr oscopy. The surface phase diagram of TI on Ge(I 1 1) contains two ordered o verlayers, a pseudomorphic (I x I)-Tl monolayer surface, obtained by TI dep osition at room temperature, and a Tl-induced (3 x 1) reconstruction; the l atter forms at elevated temperature (300-350 degreesC). The pseudomorphic ( I x I)-Tl structure is interpreted in terms of TI adatoms replacing the Ge adatoms and adsorbed in on-top T-1-type surface sites of the unreconstructe d Ge(I 1 1) surface. The STM data of the (3 x 1) reconstruction are consist ent with a modified version of the honeycomb chain-channel model of this st ructure as proposed in the literature. The TI induced surface reconstructio ns on Ge(I 1 1) are discussed in relation to the monovalent chemical charac ter of Tl adatoms. At high coverages the growth of the TI adlayer is charac terised by a Stranski-Krastanov mode with highly mobile adatoms on the firs t wetting layer. The three-dimensional Tl islands grow epitaxially ordered and rotationally aligned with the substrate. (C) 2001 Elsevier Science B.V. All rights reserved.