Investigation of silver - glass nanocomposites by positron lifetime spectroscopy

Nanocrystalline silver particles were grown in a glass medium by ion-exchange and reduction techniques and studied by positron lifetime spectroscopy. The particle sizes varied from 5 to about 25 nm as observed by transmission electron microscopy. The positron lifetime spectra of all the samples could be decomposed into three components having lifetimes of around 160 ps, 400 ps and 1500 ps. The first is ascribed to positron annihilation at the interfaces of the nanocrystalline silver and the glass matrix, and it decreases and stabilizes as the silver grain size increases. The second component is explained as arising from positrons trapped and annihilated at the free-volume defects in the glass matrix. The third component arises because of the annihilation of orthopositronium at large free-volume defects. The effects of temperature on the interfacial defects and the processes leading to the formation of additional positron trapping centres are discussed.