ION-BEAM-ASSISTED DEPOSITION OF AU NANOCLUSTER NB2O5 THIN-FILMS WITH NONLINEAR-OPTICAL PROPERTIES/

Gold nanocluster thin films (similar to 200 nm thickness) consisting o f metal clusters similar to 5 nm in size embedded in a matrix of Nb2O5 were deposited by ion beam-assisted deposition (IBAD) by coevaporatio n of Au and Nb with O-2(+) ion bombardment. The microstructure and opt ical characteristics of these films were examined as-deposited and aft er annealing at 600 degrees C. Annealing crystallized the amorphous ox ide matrix and ripened the nanoclusters. A strong linear absorption at the wavelength of the surface plasmon resonance for Au developed as a result of annealing. The linear optical behavior was modeled using Mi e scattering theory. Good agreement was found between the nanocluster sizes predicted by the theory and the particle sizes observed experime ntally using transmission electron microscopy (TEM). The nonlinear opt ical (NLO) properties of the nanocluster films were probed experimenta lly using degenerate four wave mixing and nonlinear transmission. The wavelength was near the peak of the surface plasmon resonance as measu red by VIS/UV spectroscopy. Values of \chi(xxxx)((3))\ were 7.3 x 10(- 8) and 3.0 x 10(-10) esu for annealed and unannealed samples, respecti vely. The dominant mechanism for the nonlinear response was change in dielectric constant due to the generation of a distribution of hot, ph otoexcited electrons.