Nickel nanoparticles with various structures were synthesized by a pulsed laser ablation process in liquid CO 2 at 17°C and 5.2 MPa. A nickel plate immersed in liquid CO 2 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 CO 2 , 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.

Pulsed laser ablation is known to be a promising method for synthesizing metal nanoparticles. Here, Au–carbon nanoparticles were synthesized by pulsed laser ablation under pressurized carbon dioxide. Au plate was ablated using a Nd:YAG laser with a wavelength of 532 nm and energy of 0.83 mJ in a high‐pressure chamber. The experiments were performed at temperatures and pressures of 21–25 °C and 7–15 MPa, corresponding to carbon dioxide densities of 0.75–0.89 g/cm3, respectively. The synthesized products were collected on a silicon wafer and analyzed using field emission scanning electron microscopy, transmission electron microscopy, and a scanning transmission electron microscopy system equipped with energy‐dispersive X‐ray spectroscopy. The results showed that the generated metal nanoparticles exhibited spherical and nanocluster structures. Au, C, and O were clearly found on the nanoparticle products.

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