Field ion-scanning tunneling microscope investigation of sodium adsorption on the GaAs(110) 1 X 1 surface

A field ion-scanning tunneling microscope has been employed to study the geometry and the coverage-dependent growth structures formed by Na deposition on the GaAs(110) surface at room temperature. Our data showed that at the early absorption stage Na adatoms reside on bridge sites encompassing one Ga and two surface atoms to form linear chains along the [1 1 0] direction. The Na-Na nearest-neighbor distance in this low density chain structure is 8 A. At slightly increased coverage, a local 2 X 2 structure was observed. In contrast to the Cs/GaAs(110) surface, neither a two-dimensional ordered structure nor low-density zigzag chains were observed. Additional Na adsorption resulted in the formation of three-dimensional disordered clusters.