Scanning tunneling microscopy identification of surface species on the As-rich GaAs(001)-2 x 4:Br surface

The reaction of 0.89 eV Br-2 with a 300 K As-rich GaAs(001)-2 x 4 surface at high coverage has been probed with scanning tunneling microscopy (STM). Although the surface topology is very heterogeneous, our STM images show that most reaction products are arranged along the original dimer rows of the clean surface. Height and lateral registry analysis of the reaction products show that, in some areas of the surface where basic surface bromide species are spatially well-resolved, STM can be used to identify the primary reaction products even at high coverage. These surface bromide species include gallium monobromide (GaBr), arsenic monobromide (AsBr) bridge-bonded to two Ga atoms or two As atoms, and arsenic dibromide (AsBr2) bonded to an As atom or a Ga atom. The characteristic heights and lateral registries associated with these surface bromides, as well as the persistence of the long-range row structure, indicate that the nearly tetrahedral sp(3)-hybridized bonding geometry still dominates at high coverage and no amorphous halogenation layer is formed. (C) 1999 Published by Elsevier Science B.V. All rights reserved.