On the magnitude of adsorption enhancement by electron beam excitation of molecules in the gas phase

Abstract

On semiconductor surfaces adsorption enhancement due to the influence of an electron beam is often observed. This effect has usually been ascribed to the excitation or dissociation of adsorbed species; some evidence has, however, been brought to show that ionisation of molecules in the gas phase is responsible. The magnitude of the latter effect is calculated and it is shown that under the normal experimental conditions of Auger spectroscopy it only plays a role when the sticking coefficient for adsorption under normal conditions is lower than approximately 10^-6. For electron-beam-stimulated oxidation of GaAs it is further shown that excitation in the gas phase cannot be responsible for the enhancement. Only effects associated with adsorbed oxygen such as dissociation provide an explanation.