EXCIMER-LASER ABLATION OF THIN GOLD-FILMS ON A QUARTZ-CRYSTAL MICROBALANCE AT VARIOUS ARGON BACKGROUND PRESSURES

Excimer laser ablation of gold films deposited on a quartz crystal mic robalance is investigated. The ablation rate is directly obtained from the frequency shift of the microbalance. The measured single-shot abl ation rate is found to be at least two orders of magnitude higher than the numerical predictions based on a surface vaporization model. Surf ace morphology studies indicate that hydrodynamic ablation plays a lea ding role in excimer laser ablation of thin gold films. In situ reflec tivity and scattering measurements of the gold-film surface during the transient heating and melting upon excimer laser irradiation show tha t the melting duration is of microsecond order, which is much longer t han the nanosecond melting duration in the case of a bulk target. This longer duration of melting may promote liquid motion, which leads to hydrodynamic ablation at a much higher rate compared with that of atom ic vaporization from the surface. Experiments show that the ablation r ate is also a strong function of the background gas pressure, which ma y be the result of the interactions between the gold vapor evaporated from the surface and the hydrodynamic motion in the molten gold.