Formation mechanism of silver nanocrystals made by ion irradiation of Na+ « Ag+ ion-exchanged sodalime silicate glass

Sodalime silicate glass surface layers were doped with up to 7.0 at.% Ag⁺ ions by ion-exchange in a AgNO₃/NaNO₃ solution at 330-355^oC. Ion irradiation using either 400 and 500 keV He, 1 MeV Ne or 2 MeV Xe was then used to induce the growth of metallic nanocrystals in the ion-exchanged region. The ion fluences ranged from 1.3 x 10¹⁴ ions/cm² to 1.1 x 10¹⁷ ions/cm². X-ray and electron diffraction show small Ag nanocrystals with a broad size distribution, up to a diameter of 10-15 nm, after irradiation. Optical transmission measurements show the characteristic surface plasmon resonance of metallic Ag around 420 nm. The absorption resonance sharpens and increases in strength with increasing ion irradiation fluence, indicating that both nanocrystal size and volume fraction increase with irradiation fluence. Depending on ion fluence, up to ~15% of the ion-exchanged Ag⁺ ions is incorporated in nanocrystals. From a systematic comparison of the degree of nanocrystal formation as a function of ion species, fluence and energy, it is concluded that nanocrystal formation is mainly caused by the atomic displacement energy loss component of the incoming ion beam; the electronic energy deposition component is less efficient.