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Publication
Journal of Applied Physics
Paper
Thermal activation in KrF laser ablation of CuCl
Abstract
248 nm excimer laser ablation of carefully prepared CuCl samples is reported, and shown to occur by a predominantly thermal mechanism. Using a quartz-crystal microbalance (QCM) to monitor ablation, a precise and detailed plot of single-pulse mass removal versus incident fluence was obtained for fluences up to 150 mJ/cm2. A two-parameter Arrhenius exponential function was found to fit the experimental ablation data. Calculations of laser-induced surface heating were carried out by use of a finite-difference heating code, formulated in terms of enthalpy. Ablation was observed to commence at a fluence of 25 mJ/cm2, where the calculated surface temperature is approximately 910 K - some 200 K above the melting point. Dynamic ablation was included in the finite-difference calculation by allowing the position of the CuCl surface ξ to vary in time. The best data fit is provided by the zeroth-order kinetic equation: dξ(t)/dt=(16 Å/ns)exp[(-38 kJ/mole)/RTξ], where Tξ is the surface temperature. A thermodynamic calculation shows the average heat of CuCl vaporization in the temperature range from 900 to 2000 K to be near the fit value of 38 kJ/mole. From plots of the ablation depth versus time, the CuCl surface was estimated to recede during the ablation at rates up to 10 cm/s.