Anomalous mobility of strongly bound surface species: Cl on GaAs(001)-c(8 x 2)

Although strongly bound chemisorbates at low coverage readily diffuse on me tal surfaces at 300 K, they generally do not diffuse on semiconductor surfa ces because of a large corrugation in the adsorbate-surface interaction pot ential. Chlorine chemisorbed on the Ga-rich GaAs(001)-c(8 x 2) surface has anomalously fast diffusion even though the chemisorption state is tightly b ound and highly specific. Simple Hartree-Fock total energy calculations sug gest that this diffusion of strongly bound adsorbates can occur at 300 K be cause there are multiple nearly degenerate adsorbate sites.