Pressure effects during excimer laser ablation of magnesium diboride targets

Abstract

The expansion dynamics and kinetics of the plasma produced by excimer laser irradiation of MgB 2 in Ar background gas has been studied by space- and time-resolved optical emission spectroscopy. The experimental results show that there is a distance-related pressure threshold above which the expansion dynamics changes from a free expansion to a shock wave regime, causing both a considerable increase of the fraction of excited Mg atoms and a simultaneous reduction of their kinetic flux energy. The analysis of the results within the framework of a model describing the plume expansion into an ambient gas indicates that the shock wave formation leads to plume heating, thus, influencing its excitation/ionisation kinetics. The production of a plume whose particles are characterised by a lower flux kinetic energy and a higher degree of internal energy can be particularly useful for MgB 2 thin film deposition at lower substrate temperature, due to the high volatility of Mg.