Nickel nanoparticles generated by pulsed laser ablation in liquid CO₂

Nickel nanoparticles with various structures were synthesized by a pulsed laser ablation process in liquid CO₂ at 17 °C and 5.2 MPa. A nickel plate immersed in liquid CO₂ was used as a target. This was irradiated by a laser beam with a fundamental wavelength of 1064 nm at 2.46 mJ for 15 min. The generated particles were deposited on a silicon wafer after natural evaporation of the liquid CO₂, and analyzed by field emission scanning electron microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and transmission electron microscopy. Nickel and carbon particles with sphere-like structures or apple-shaped structures were observed. Furthermore, characteristic nickel/carbon particles with core/shell structures were also produced. The generated particles ranged in size between 5 and 350 nm in diameter, with dominant sizes under 50 nm.