Correlations between embedded single gold nanoparticles in SiO2 thin film and nanoscale crater formation induced by pulsed-laser radiation

A model SiO2 thin-film system containing gold nanoparticles serving as nanoscale absorbing defects is investigated with the goal of unraveling the connection between the 351 nm pulsed-laser energy absorption process inside a single defect and the resulting film damage morphology. For this purpose, gold nanoparticles are lodged at a well-defined depth inside a SiO2 monolayer film. Particle sites, as well as nanoscale craters generated at these locations after 351 nm irradiation, are mapped by means of atomic force microscopy. The results of this mapping confirm a damage mechanism that involves initiation in the nanoscale defect followed by absorption spreading out to the surrounding matrix. At low laser fluences (below optically detected damage onset), the probability of crater formation and the amount of the material vaporized is, to within ±25% of the average value, almost independent of the particle size. Inhomogeneities in the particle environment are held responsible for variances in the laser-energy absorption process and, consequently, for the observed particle/crater correlation behavior. Investigation of the damage threshold as a function of particle size (2–19 nm range) showed that even few-nanometer-diameter particles can lead to a significant threshold reduction. The “nanoscale” damage threshold is introduced as a laser fluence causing localized melting without significant vaporization.