RECONSTRUCTIONS FORMED BY PB ON GE(111) SURFACES REEXAMINED BY STM

The dense 2D structures of Pb on Ge(111) formed at above one monolayer coverage have been reexamined at room temperature with scanning tunne ling microscopy. It was found that the square-root 3 - beta phase, des pite its structural simplicity has a very complex appearance; dependin g on the tunneling parameters, structures with either one, three, or f our protrusions per square-root 3 unit cell were observed. Remarkably it is not possible to associate any of the observed patterns of protru sions directly with the location of individual atoms. However, by comp aring the results on the commensurate square-root 3 - beta phase and t he closely related striped incommensurate phase it was possible to dis tinguish between features induced by the substrate and the adsorbate.