Attenuation, scattering, and depolarization of light by gold nanorods with silver shells

Gold nanoparticles with silver nanoshells are obtained by synthesizing gold nanorods in a growing solution containing cetyltrimethylammonium bromide, subsequent separation in a concentration gradient of glycerol, and reduction of silver nitrate by ascorbic acid under alkaline conditions in the presence of polyvinylpyrrolidone. The formation of silver nanoshells was monitored by the shift of plasmon resonances of extinction and differential light scattering, by the appearance of characteristics peaks of silver in the energy dispersive X-ray (EDX) spectra of samples, by the data of transmission electron microscopy, and by visual changes in the color of colloids. The spectrum of the intensity ratio of the co- and cross-polarized compo- nents of light scattered by gold-silver nanorods is measured for the first time, and it is observed that the maximum is shifted by 80–100 nm compared to previously published spectra of gold nanorods (Khlebtsov et al., J. Phys. Chem. C 112 , 12760 (2008)). The extinction and light scattering spectra are calculated by the method of separation of variables using the model of a confocal two-layer spheroid and these calculations are found to agree with spectral measurements. A method for determining the thickness of a silver nanolayer by the spectral shift of an extinction longitudinal resonance is described. The obtained data of optical spectroscopy and transmission electron microscopy and estimations of the mass of the deposited metal show that the aver-age thickness of the silver layer varies from 0.12 to 4 nm as the Ag/Au ratio changes from 2/80 to 90/80 μg/μg.