ULTRAFAST ELECTRON DYNAMICS IN GOLD NANOSHELLS

We present ultrafast optical studies on nanoshells, which consist of a nanoscale Au2S dielectric core surrounded by an ultrathin Au shell. T he plasmon frequency of these nanoparticles can be controlled by varyi ng the ratio of the core diameter to shell thickness. By tuning this p lasmon peak, we have observed both transient bleaching and transient a bsorption for Au nanoshells embedded in polyvinyl alcohol. We relate t he induced change in transmission of gold nanoshell films to the elect ron dynamics in the thin gold shell. Our results indicate that even wh en the plasmon frequency is shifted below the onset of interband trans itions, interband effects are still of primary importance in determini ng the nonlinear optical response. An electron relaxation time of 1.65 +/-0.10 ps is measured that corresponds to an electron-phonon coupling constant of 2.2 x 10(16) W/(m(3) K), smaller than that observed in bu lk Au films. [S0163-1829(98)50740-0].