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We propose a method to synthesize oxide nanoparticles in insulators by oxidizing
metal nanoparticles which introduces less damage comparing with commonly used sequential
implantation of metal ions and oxygen ions. Nanoparticles of Ni and Cu were fabricated in
SiO2 by the negative ion implantation, and were oxidized in O2 gas flow at 600 - 1000 °C for
1 hr. The oxidized nanoparticles were evaluated using optical absorption spectroscopy, SQUID
magnetometry and Rutherford backscattering spectrometry (RBS), in comparison with annealed
samples in vacuum at the same temperatures. Whereas the vacuum-annealed Ni nanoparticles
show a broad absorption over visible and ultraviolet regions, the O2-annealed Ni
nanoparticles, i.e., oxidized ones, become transparent in the visible region and show a
steep absorption edge around ~4 eV. A strong ferromagnetic signal of Ni nanoparticles
disappears after the oxidation. These results strongly indicate formation of NiO. In the
case of Cu nanoparticles, the absorption spectra do not significantly change, except
disappearance of a surface plasmon resonance (SPR) peak after oxidation. The oxidation
drastically improves thermal stability against high-temperature diffusion.
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