Relative reactivity of arsenic and gallium dimers and backbonds during the adsorption of molecular oxygen on GaAs(100)(6×6)

The chemisorption sites of molecular oxygen on the mixed GaAs(100)(6×6) surface were imaged at room temperature using scanning tunneling microscopy (STM). This surface is terminated by both gallium dimers and arsenic dimers, neither of which react with oxygen. Instead, the As–Ga backbonds are shown to react with O2 with 100% chemical selectivity. The reason for this selectivity is found in the interaction of the highly electronegative oxygen atoms with the higher electron density at the arsenic atoms. One oxygen atom displaces the attacked arsenic atom while the other oxygen atom bonds to two nearby gallium atoms, resulting in the thermodynamically most stable reaction products: metallic arsenic clusters and gallium oxide.