Site-Selective Reaction ofBr2with Second Layer Ga Atoms on the As-richGaAs(001)−2×4Surface

Abstract

The top layer of the $\mathrm{GaAs}(001)\ensuremath{-}(2\ifmmode\times\else\texttimes\fi{}4)$ surface consists of rows of As-As dimers. However, our scanning tunneling microscopy study shows that, in the initial adsorption stage, monoenergetic ${\mathrm{Br}}_{2}$ molecules (0.89 eV) react exclusively with the second layer Ga atoms exposed in trenches or at defects on the surface. A simple molecular orbital argument was used to explain the dynamics of forming gallium bromide species at various surface Ga sites.