Diffusion and ordering of Cs adatoms on GaAs(001) studied by reflectance anisotropy spectroscopy

Abstract

Diffusion and ordering of Cs overlayers deposited at a low temperature of 90 K on GaAs(001) are observed by reflectance anisotropy (RA) spectroscopy after annealing to higher temperatures. At low coverages $(<~0.3$ monolayer), the ordering of cesium is revealed as a narrowing of the Ga-dimer line in the RA spectra, which occurs after annealing at $T>~200$ K. A possible reason for such ordering is the diffusion of individual adatoms to preferential adsorption sites. At coverages larger than 0.5 monolayer, for which the majority of adatoms are not isolated, the diffusion-induced changes of RA spectra occur at a temperature lower than 200 K and are characterized by a broad spectrum, which suggest a change of the surface macroscopic anisotropy.