Metal nanocrystal formation in magnesium aluminate spinel and silicon dioxide with high-flux Cu- ions

Intense Cu- ions of 60 keV spontaneously grow nanospheres embedded within a shallow depth in insulators, which exhibit optical nonlinearity. The in-beam growth of nanoparticles is preferred but subjected to phase instability. Spinel oxides may be a candidate substrate to realize the phase stability, because of good radiation resistance and sufficient transparency. Spinel of MgAl2O4 and amorphous(a-) SiO2 were irradiated with Cu- at dose rates up to 100 mu A/cm(2), at a total dose of 3.0 x 10(16) ions/cm(2). Nanocrystal morphology and optical absorption (hv = 0.5 5 eV) varied depending on dose rate. At high dose rates, a-SiO2 showed a strong tendency of depth-dependent rearrangement and particle coarsening. The MgAl2O4 also showed spontaneous precipitation of nanoparticles but, in contrast, neither long-range rearrangement of implants nor particle coarsening, up to high dose rates. Therefore, the MgAl2O4 spinel is a promising substrate to realize fine and stable nanostructures. (C) 2000 Elsevier Science B.V. All rights reserved.