Nonlinear optical properties of MeV and keV ion beam synthesized Ag nanoclusters

Ag nanoclusters embedded in silica glass matrix have been synthesized by high fluence ion implantation using both keV and MeV ion beams. In keV implantation case, optical absorption shows an intense surface plasmon resonance (SPR) peak corresponding to the Ag clusters formed in the matrix. Transmission electron microscopy (TEM) measurements carried out on identically implanted SiO₂ thin films on a TEM catcher grid shows the presence of Ag nanoclusters of size around 4 nm in the matrix. However, for the MeV implantation case, the SPR peak appears in the optical absorption spectra only after air annealing the sample at 500 °C for one hour. For the annealed samples, TEM measurements show the presence of 6 nm sized Ag nanoclusters. On the other hand the as-implanted sample shows smaller nanoclusters with a lower particle density in the matrix. Interestingly, open aperture z-scan measurements carried out on keV implanted samples did not show any nonlinear absorption, while the MeV as-implanted as well as annealed samples showed nonlinear absorption. The nonlinear absorption coefficient of the MeV annealed sample is extracted from a fit to the z-scan data considering a three photon like absorption process.