General model of sodium desorption and diffusion during electron bombardment of glass

A general model for alkali Auger signal decay during electron beam analysis has been developed. All previous models were based on diffusion into the bulk, but alkali ions were shown to be first converted to a new state in the solid by electron bombardment, then either diffusion or desorption could occur. Using an analytic mathematical description of these effects, the relative contribution of desorption and diffusion to decay of the Auger or desorbed ion signal were calculated. The desorption cross section of sodium was evaluated to be about 10−19 cm2 and electron stimulated desorption became important at beam current densities ≳10−3 A/cm2. Utilizing the concept of an electron‐induced surface complex, the experimental observation of an incubation time (during which the Auger signal remained constant) was explained and reasonable agreement between experimental data and model calculations was achieved.