Negative charge emission due to excimer laser bombardment of sodium trisilicate glass

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Abstract
We describe measurements of negative charge emission accompanying irradiation of sodium trisilicate glass (Na2O⋅3SiO2) with 248-nm excimer laser light at fluences on the order of 2 J/cm2 per pulse, i.e., at the threshold for ablative etching of the glass surface. The negative charge emission consists of a very prompt photoelectron burst coincident with the laser pulse, followed by a much slower plume of electrons and negative ions traveling with a high density cloud of positive ions, previously identified as primarily Na+. Using combinations of E and B fields in conjunction with time-of-flight methods, the negative ions were successfully separated from the plume and tentatively identified as O−, Si−, NaO−, and perhaps NaSi−. These negative species are probably formed by gas phase collisions in the near-surface region which result in electron attachment.