Structure of domain walls in Al/Si(1 1 1) γ-phase

Using scanning tunneling microscopy (STM) and low energy electron diffraction, the structure of the Al/Si(1 1 1) γ-phase has been studied. The STM observations with atomic resolution in conjunction with the quantitative characterization of the γ-phase, including, determination of the Al coverage, top Si atom density, interatomic distances and superstructure mean period have allowed us to distinguish two types of the Al/Si(1 1 1) γ-phase. Both phases are built of triangular subunits, in which interior Al atoms substitute for the topmost Si atoms in the surface Si(1 1 1) double layer. The difference between the two γ-phases resides in the difference in the composition and structure of the domain walls. The Al/Si(1 1 1) γ-phase of the first type (labelled “heavy” γ-phase) contains light domain walls depleted of Al. The Al/Si(1 1 1) γ-phase of the second type (labelled “light” γ-phase) contains heavy Al-enriched domain walls. The possible structural models of the domain walls have been proposed.