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

Abstract

Thermal stability of nanoparticles, fabricated by high-current negative ions, has been studied focusing on optical applications. Negative Cu ions of 60 keV were irradiated to silica glasses at high dose rates up to 50 μA/cm2, to a total dose of 3×1016ions/cm2. The high-current implantation caused a bimodal distribution of Cu nanoparticles. Thermal annealing at 773–1273 K for 1 h was applied to the specimens. For each step, optical absorption 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 K gave no discernible changes in either nanoparticle morphology or absorption spectra. Above 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 indicates that the nanoparticle structure is thermally stable below about 873 K, and becomes unstable at higher temperatures.