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Core-shell nanoparticles composed of ferromagnetic cobalt platinum cores covered by non-magnetic silica shells were synthesized by laser ablating a composite target in a helium background gas. The average diameter of the CoPt core was controlled by adjusting the CoPt/SiO2 ratio of the ablation target. The particles were also classified in the gas phase using an electrical mobility classifier. The present method successfully synthesized nearly monodispersed nanoparticles with an average core diameter of 2.5nm. This article describes the synthesis of the core-shell nanoparticles and investigates their magnetic properties.

The formation of 10 nm scale Si pillars using deposited metal clusters of various kinds (Au, Ag etc) as nuclei for the creation of etch masks has been investigated via microwave plasma etching at about . Experiments using size-selected Ag clusters indicate that the cluster size affects the efficiency of pillar formation but has little effect on the diameter of the fabricated pillars. The average diameter of pillars fabricated with Au clusters is 9 nm, while that with Ag clusters is 19 nm. This is attributed to the difference in chemical reactivity of the clusters with S or F, the components of the etching gas, which results in a different ability to form etch masks by condensation of species.

We recently developed a rapid single-step calcium phosphate (CaP) precipitation technique on several substrates using a laser-assisted biomimetic process (LAB process). In this process, ultraviolet (UV, λ = 355 nm) pulsed laser irradiation has been applied to a substrate that is immersed in a supersaturated CaP solution. In the present study, the LAB process for CaP precipitation on a titanium substrate was successfully expanded to include not only UV but also visible (VIS, λ = 532 nm) and near infrared (NIR, λ = 1064 nm) lasers. Surface heating and plasma-mediated surface reactions (micro-deformation, oxidization, photoexcitation, and wetting) generated by UV, VIS, or NIR lasers are considered to be involved in the CaP precipitation on the titanium surface in the LAB process. The kinetics of these reactions and consequently of CaP precipitation were dependent on the laser wavelength and fluence. The higher laser fluence did not always accelerate CaP precipitation on the substrate; rather, it was found that an optimal range of fluence exists for each laser wavelength. These results suggest that for efficient CaP precipitation, a suitable laser wavelength should be selected according to the optical absorption properties of the substrate material and the laser fluence should also be adjusted to induce surface heating and plasma-mediated surface reactions that are favorable for CaP precipitation.

The thermal oxidation of alloy nanoparticles (NPs) composed of nickel and a noble metal was investigated by high-resolution electron microscopic observations of the NPs oxidized in a gas phase under different oxidation conditions. When Ni0.8Au0.2 NPs were heated with oxygen from room temperature, oxidation progressed to form Au–NiO core–shell structures, however, the Au core spilled out by breaking the NiO shell at high temperatures. In contrast, when the alloy NPs were subjected to rapid thermal oxidation, which was enabled by heating the NPs at high temperatures (≥500 °C) and then abruptly exposed to oxygen, oxidation advanced anisotropically such that a NiO island protruded and built up to form a NiO nanorod. This resulted in the formation of Au-tipped NiO nanorods in which a hemispherical Au tip bonded to a NiO nanorod via a Au {111}/NiO{100} interface. We found that the relative sizes of Au and NiO in Au-tipped NiO nanorods were easily and widely controlled by changing the Au mole fraction (0.05–0.8) of the alloy NPs. Similarly, rapid thermal oxidation of Ni–Pt NPs generated Pt-tipped NiO nanorods in which a spherical Pt tip was half-embedded in a NiO nanorod. The present gas-phase approach has great potential for fabricating functional asymmetric hybrid nanostructures in clean conditions.

Cluster size distribution was found to be largely varied by altering the gas flow conditions in the gas evaporation method, where clusters are generated in one chamber and carried into the other chamber through a nozzle with a helium gas stream. Mean and mode diameters of clusters were found to be inversely proportional to the pressure difference between the two chambers, indicating that the gas flow condition influences the coalescence growth of the clusters in free space.