Reaction dynamics of the As-rich GaAs(001)-2 * 4 surface with monoenergetic Br_2 molecules: A scanning tunneling microscopy study

摘要

The adsorption of 0.15-eV and 0.89-eV Br_2 onto the As-rich GaAs(001)-2 * 4 surface at 300 K has been investigated on the atomic scale over a wide range of total Br coverage using scanning tunneling microscopy (STM). It is found that the strained As-As dimer bonds and the As-Ga back bonds are significantly weakened and chemically activated by the Br atoms site-selectively adsorbed onto the second-layer Ga atoms. Consequently, at higher Br coverages, incident Br_2 will preferentially react with these As-As and As-Ga Bonds, removing (etching) As-As dimers and forming AsBr((s)) or AsBr_(2(s)) species, GaBr_((s)) chains, and etching pit islands. The incident energy of Br_2 has a strong effect on the adsorption mechanisms.