Aggregation and migration of ion-implanted silver in lithia-alumina-silica glass

The near-surface nucleation and crystallization behavior of Ag+ ion-implanted lithia-alumina-silica glasses has been studied. For room-temperature Ag implants, crystallization of the glass ceramic phase was prevented by dissolution of Ag precipitates and migration of Ag atoms at temperatures below that necessary for formation of the glass ceramic phase. Crystallization was demonstrated after low-temperature or low-dose-rate implantations. Optical spectroscopy was used to monitor the size of colloidal Ag particles and to detect the presence of the crystalline phase. Rutherford backscattering spectroscopy (RBS) was used to obtain the depth distribution of Ag atoms in the glass and thus monitor Ag migration. For samples implanted at room temperature and at relatively high dose rates (∼1 μA/cm2), aggregation of the Ag atoms into colloids occurred during implantation and also during subsequent annealing to temperatures ?350 °C. The RBS spectra indicate some migration of the Ag to the surface at these temperatures. For annealing temperatures ≳350 °C, both optical and RBS measurements show that Ag is lost from the glass surface. The initial spatial distribution of the Ag for these high-dose-rate room-temperature implantations was distorted by interactions with the associated damage and possibly by local electric fields caused by neutralization of the implanted ions. It was possible to obtain dispersed Ag nuclei by implanting at low sample temperatures (80 K) or at low beam current (∼200 nA/cm2) to reduce ion-beam heating. Although some migration to the surface was seen in these samples, it occurred at higher temperatures and crystalline precipitation was achieved by annealing at 500 °C.