A comparative study of KrF laser ablation of aluminum and alumina in oxygen ambiance

Abstract

This paper is dedicated to a comparative study of aluminum and alumina plasmas, induced under the same conditions of laser fluence and oxygen gas pressure in the range of 0.02 to 5 mbar. In this comparative analysis, measurements of ablated mass versus laser fluence and optical emission spectroscopy diagnostic of the plasmas are studied. The results from ablated mass measurements reveal the existence of two regimes of ablation according to a laser fluence threshold for phase explosion mechanism. This laser fluence threshold was found different for Al and Al2O3. A difference in the amount of ablated mass/pulse is also observed and is assigned to the optical (reflectivity and absorption) and thermodynamical properties (evaporation temperature) of the targets. Below a certain laser fluence threshold, thermal and non-thermal processes are involved. Above this laser fluence threshold, the mechanism of ablation is assigned to phase explosion. For plasma diagnostic by optical emission spectroscopy, two species were followed; the neutral Al (396.15 nm) for its persistence in time and distance and the AlO (the band head emission at 484.21 nm) molecule that is probably the precursor in alumina thin films formation. The spectra revealed a disparity in the intensity emission of neutral Al and AlO molecules, which were, related to the target's properties. The origin of AlO molecules recorded in aluminum and alumina plasma under oxygen ambiance is discussed. Their translational temperature for neutral Al, molecular vibrational temperature, and free linear velocities, are also compared.