SURFACE SITE DEPENDENCE TO NEGATIVE-ION FORMATION

The processes of electron transfer and dissociative scattering are explored for collisions of hyperthermal NO+ on GaAs(110). The experiments reveal a marked angular dependence to O- emergence. A strong correlation between the O(-)scattering angle and the final atom-surface interaction site provides a map of the lateral dependence to reactivity. The results are modeled by sequential neutralization, dissociation, and electron attachment steps. Classical trajectory calculations, in conjunction with an empirical opacity function, accurately reproduce the experimental results. The opacity function is interpreted as the probability that an electron will attach to a departing O fragment as a function of the last surface site the atom impacts. The experiments indicate that O- emergence occurs predominantly for oxygen atoms which come in close contact with the localized dangling bond states of GaAs(110).