STRUCTURE AND THERMAL-STABILITY OF NANOCRYSTALLINE SILVER STUDIED BY TRANSMISSION ELECTRON-MICROSCOPY AND POSITRON-ANNIHILATION SPECTROSCOPY

Positron annihilation spectroscopy was carried out on nanocrystalline silver. Both lifetime and Doppler broadening were measured. High-resol ution electron microscopy observations were also performed. Diffuse va cancy clusters, the sizes of which correspond to two to four vacancies , and voids of 1-5 nm diameter, were found to reduce the average atomi c density of the grain boundary. Some grains grew to a diameter larger than about 70 nm during annealing the specimen from 50 to 100-degrees -C. A large fraction of the diffuse vacancy clusters and voids in the boundaries remained after annealing at 400-degrees-C. They were stabil ized during annealing probably by gaseous atoms.