The diffusion and ordering of Cs over-layers, deposited at 90K onto GaAs(001), was observed by means of reflectance anisotropy spectroscopy after annealing to higher temperatures. At low coverages (less than 0.3 of a monolayer), an ordering of Cs was revealed by a narrowing of the Ga-dimer line in the reflectance anisotropy spectra. This occurred after annealing at temperatures above 200K. A possible reason for such ordering was suggested to be the diffusion of individual adatoms to preferential adsorption sites. At coverages greater than 0.5 of a monolayer, when most of the atoms were not isolated, diffusion-induced changes in the reflectance anisotropy spectra occurred at temperatures below 200K and were characterized by a broad spectrum. This suggested that there was a change in the surface macroscopic anisotropy.

V.L.Alperovich, D.Paget: Physical Review B, 1997, 56[24], R15565-8