N. Umeda

Fabrication of nickel oxide nanoparticles in SiO2 by metal-ion implantation combined with thermal oxidation

A method is proposed to synthesize oxide nanoparticles in insulators, using metal-ion implantation and following thermal oxidation, which introduces less damage compared to the sequential implantation of metal ions and oxygen ions. Ni-oxide nanoparticles are formed in O2 gas flow at ∼800°C for 1h, through thermal oxidation of Ni metal nanoparticles, which were introduced in SiO2 by charging-free negative ion implantation of 60keV. After the oxidation, optical absorption in the visible region, which is due to Ni metal nanoparticles in the specimen, disappears, and a steep absorption edge of insulator NiO appears around ∼4eV. Simultaneously, the large magnetization of Ni metal nanoparticles changes to a weak magnetization of antiferromagnetic NiO nanoparticles. The nanoparticle formation is confirmed by transmission electron microscopy observation.

Embedment of ZnO nanoparticles in SiO2 by ion implantation and low-temperature oxidation

Samples of silica glass (SiO2) implanted with 60keV Zn ions to a fluence of 1.0×1017ions∕cm2 were annealed in oxygen gas to form ZnO nanoparticles (NPs). Although the ZnO NPs were formed mainly on the SiO2 surface after oxidation at 700°C for 1h, they were formed inside the SiO2 substrate after lower temperature and long-duration oxidation at 500°C for ∼70h, i.e., the embedment of ZnO NPs in SiO2 was attained. The embedded NPs show a slightly stronger exciton peak and much weaker defect luminescence than the NPs formed on the surface.

Optical transitions of Cu2O nanocrystals in SiO2 fabricated by ion implantation and two-step annealing

Nanocrystals (NCs) of cuprous oxide (Cu2O), cupric oxide (CuO), and copper metal (Cu) are fabricated in silica glasses (SiO2) by implantation of 60keV Cu− ions at different annealing conditions. At room temperature, Cu2O NCs show two sharp absorption peaks at 2.58 and 2.71eV due to autoionized exciton states, and Cu NCs show a broad peak at ∼2.2eV due to the surface plasmon resonance (SPR). With decreasing temperature down to 2.8K, the peaks of Cu2O NCs become much narrower, while the SPR peak of Cu NCs keeps almost the same peak width.