CONSEQUENCES OF SIMULTANEOUS EXPOSURE OF INORGANIC SOLIDS TO EXCIMER LASER-LIGHT AND AN ELECTRON-BEAM

In previous work we examined the changes in surface topography of sodium trisilicate glass (Na2O·3SiO2) with exposure to pulsed 248-nm excimer laser light at fluences of 2.6-5 J/cm2 (per laser pulse), as well as the character of the products emitted from the glass surface (e.g., ± ions, electrons, ground state and excited neutral atoms and molecules). At fluences above a threshold, ablative etching occurs only after a number of preliminary laser pulses. In this work, we show a dramatic synergism in the ablation process by simultaneous bombardment of the glass surface with 0.5-2 keV electrons and laser pulses. Extensive etching can be initiated immediately and sustained indefinitely at subthreshold fluences. Reflection electron energy loss spectroscopy performed on electron-bombarded surfaces shows band gap states growing with exposure. We propose that surface and near-surface defects produced by inelastic scattering of the electron beam provide single-photon absorption centers, facilitating etching at subthreshold fluences. The potential for single-photon driven etching/ablation of other wide band gap dielectric materials is also discussed. These studies also support the hypothesis that etching and damage of such surfaces can occur after prolonged exposure to laser irradiation alone due to an accumulation of absorption centers.