OPTICAL-ABSORPTION BY COLLOIDAL PRECIPITATES IN BISMUTH-IMPLANTED FUSED-SILICA - ANNEALING BEHAVIOR

The near-surface regions of high-purity fused silica disks (Corning 7940) were modified by implantation with Bi2+ ions at 160 keV and at room temperature. The glasses implanted with a nominal dose of 6×10 16 Bi2+ ions/cm2 at ∼5 μA/cm2 were subsequently annealed in oxidizing and inert atmospheres. The annealing temperature ranged from 500 to 1100 °C. The doses retained before and after the anneals were determined from Rutherford backscattering. A broad optical-absorption band at ∼5 eV (248 nm) was resolved and attributed to surface plasmon resonance from colloidal bismuth metal particles precipitated after implantation and observed by transmission electron microscopy. After annealing in oxygen for 60 min at temperatures ≥1000 °C the bismuth in the sample decreased by ∼70%. Annealing in an oxidizing atmosphere oxidized the metallic precipitates, and oxidation changed the optical absorption of the samples. For samples annealed in argon, a relatively small decrease in retained dose by ∼12% was observed for temperatures ≥1000 °C. Based on the difference in the effects of annealing in oxygen and in argon, the bismuth atoms in the samples annealed in argon are not oxidized and remain in the particles. The small changes in the distribution of bismuth after annealing in argon are due to diffusion of bismuth atoms from colloidal particles to larger particles, i.e., Ostwald ripening, as well as evaporation from the surface of the fused silica. © 1995 American Institute of Physics.