Chemically selective adsorption of molecular oxygen on GaAs(100)c(2x8)

The chemisorption sites of molecular oxygen on the technologically importan t As-rich GaAs(100)c(2x8) surface were imaged with scanning tunneling micro scopy (STM). The oxygen atoms insert into the arsenic-gallium backbonds and , subsequently, replace the arsenic atoms in the dimer rows. The displaced arsenic atoms aggregate in clusters of increasing size forming metallic ars enic. The strongly electronegative oxygen atoms are initially attracted by the larger electron density at the arsenic atoms, but the reaction of the o xygen atoms with the gallium atoms is thermodynamically favored. This leads to a 100% chemical selectivity for oxygen insertion into the As-Ga backbon ds and subsequent chemisorption of the oxygen atoms into the arsenic sites. (C) 2000 American Institute of Physics. [S0021-9606(00)71142-1].