Confinement of laser-material interactions by metal film thickness for nanoparticle generation

Understanding the formation and evolution of nanoparticles generated during laser ablation is imperative in controlling the health risk associated with the ablated material, minimizing contamination and enhancing ablation rates. There is also a keen interest in undertaking a competitive analysis of nanoparticle generation compared with current synthesis techniques. Laser-material-ambient interactions are, however, complex due to the dynamic nature of the ablation environment and consequently it is difficult to characterize the process of nanoparticle formation and evolution. Al, Ni and Au films with thicknesses of 10, 25 and 75 nm were ablated by single nano- and femto-second laser pulses. Generated nanoparticles were collected and their height and diameter measured using AFM and SEM, respectively. Results identified that the thickness of the metal film is highly influential on the size and distribution of nanoparticles e.g., mean radius for Au nanoparticles generated during femtosecond laser ablation of 75, 25 and 10 nm thick films were 5.9 nm, 3.5 nm and 1.8 nm, respectively. The standard deviation (sigma) of radii of these nanoparticles generated from 75, 25 and 10 nm thick films also decreased from 8 nm, 6 nm to 1 nm, respectively.