Nickel nanoparticles generated by pulsed laser ablation in liquid CO2

Abstract

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.

Formation ofAu–carbon nanoparticles by laser ablation under pressurizedCO2

“…These results are similar to those of a work previously reported on PLA in liquid CO 2 using a Nd:YAG laser with a laser energy of 2.46 mJ. 16 Au nanoparticles prepared by PLA in pressurized CO 2 were well dispersed and exhibited a broad size distribution, as shown in Figure 4. At an identical laser power of 0.83 mJ, the average size of nanoparticles decreased from 16.0 to 8.9 nm with the density of CO 2 increasing from 0.75 to 0.89 g/cm 3 .…”

“…The Au nanosphere‐like structure generated at 0.89 g/cm 3 in Figure appears smaller than those generated under other conditions. Similar to the generation of metal nanoparticles by PLA in aqueous media, the production of Au nanoparticles by PLA under high‐density CO 2 was affected by several parameters such as laser fluence, irradiation time, excitation wavelength, pulse width, and the CO 2 phase . Generally, the PLA plasma plume evolution in a confining liquid leads to cluster formation, nucleation, and crystal growth during the ablation process.…”

“…Similar to the SEM images, the TEM images in Figure (a–c) indicate that the particles generated under each set of conditions are spherical. These results are similar to those of a work previously reported on PLA in liquid CO 2 using a Nd:YAG laser with a laser energy of 2.46 mJ …”

“…Similar to the generation of metal nanoparticles by PLA in aqueous media, the production of Au nanoparticles by PLA under high-density CO 2 was affected by several parameters such as laser fluence, irradiation time, excitation wavelength, pulse width, and the CO 2 phase. 9,14,16 Generally, the PLA plasma plume evolution in a confining liquid leads to cluster formation, nucleation, and crystal growth during the ablation process. Hence, the PLA plasma plume in high-density CO 2 will also rapidly quench in the confining liquid-like CO 2 .…”

“…STEM-EDS was performed to analyze the presence of carbon on the generated nanoparticles. Several reports 9,16,[20][21][22] have concluded that the PLA reaction medium and ablated matter can react during the formation of particles. However, the alloy nanoparticle formation mechanism during PLA and the process mechanisms are still not well understood.…”