Thermal stability of nanoparticles in silica glass implanted with high-flux Cu- ions

Thermal stability of nanoparticles, fabricated by high-current negative ion s, has been studied focusing on optical applications. Negative Cu ions of 6 0 keV were irradiated to silica glasses at high dose rates up to 50 mu A/cm (2), to a total dose of 3 x 10(16) ions/cm(2). The high-current implantatio n caused a bimodal distribution of Cu nanoparticles. Thermal annealing at 7 73-1273 K for 1 h was applied to the specimens. For each step, optical abso rption was measured in an energy range from 0.5 to 6.5 eV and nanoparticle morphology was evaluated by cross-sectional TEM. Depth profiles of Cu atoms were compared to those by RBS. Thermal annealing below 873 It gave no disc ernible changes in either nanoparticle morphology or absorption spectra. Ab ove 1073 K, pronounced coarsening of Cu particles occurred, with enhancing the bimodal distribution. Around 1273 K, all the Cu particles disappeared, suggesting evaporation of Cu implants from the surface. The result indicate s that the nanoparticle structure is thermally stable below about 873 K, an d becomes unstable at higher temperatures. (C) 2000 Published by Elsevier S cience B.V. All rights reserved.