No 1, Vol. 5, 2003 


H. Amekura, Y. Takeda, K. Kono, H. Kitazawa and N. Kishimoto

Nanomaterials Laboratory, National Institute for Materials Science,
3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan


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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