Nanoparticle generation in ultrafast pulsed laser ablation of nickel

The process of particle generation during ultrafast pulsed laser ablation of nickel is investigated. Two types of particles with different sizes depending on the laser fluence are found, indicating different particle generation mechanisms. By limiting the laser fluence below a threshold of strong plasma formation, the large dropletlike particles can be eliminated. In addition, by supplying different background gases, various crystalline structures are obtained for the particles, including Ni∕NiO core/shell spheres and NiO cubes. This study provides evidence that ultrafast laser ablation can be a room temperature physical method for generating nanocrystals with a narrow particle size distribution.