Positive ion emission from oxidized aluminum during ultraviolet excimer laser irradiation

Abstract

We report quadrupole mass-selected time-of-flight measurements of positive ions from oxidized aluminum metal (and for comparison, single-crystal sapphire) during pulsed excimer laser irradiation at 193 and 248 nm. This work focuses on laser fluences well below onset of rapid etching or optical breakdown. By far the most intense emissions are due to Al+. On previously unexposed material, the ion kinetic energies are initially well above the photon energy, consistent with the ejection of Al+ sorbed at surface electron traps. During prolonged irradiation, the emission intensities and kinetic energies gradually fall. Emission from patches of oxide would account for previous reports of laser-induced Al+ emission from metallic aluminum surfaces cleaned by ion etching if patches of thin oxide were to survive the etching treatment.