Simultaneous bombardment of wide bandgap materials with UV excimer irradiation and keV electrons

Abstract

In previous works¹ we examined the changes in the 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, 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 these fluences, ablation readily occurs after a fixed number of preliminary laser pulses (an effect known as incubation). In the current study, we examine the precursors of this high fluence behavior at sub-threshold fluences < 2.6 J/cm2 and show that the effectiveness of laser bombardment in removing material is strongly dependent on defects produced either by high fluence 248 nm radiation or by electron radiation. 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. A model is discussed involving surface and near-surface defects created by the electron beam that provide single photon absorption centers and free electron--laser heating. We also show that similar results are obtained on single crystal NaCl, LiF, and UV grade fused silica. The potential for performing single photon driven etching/ablation on wide band gap dielectric materials is also discussed.