Optical properties of aligned rod-shaped gold particles dispersed in poly(vinyl alcohol) films

The polarization spectra of template-synthesized colloidal gold rods with aspect ratios ranging from L/d = 1.8 to 49 (and a diameter d = 15 nm) embedded in poly(vinyl alcohol) (PVA) films are studied as a function of the film elongation. Orientation of the colloidal gold rods is obtained by stretching the PVA films. The polarization absorbance spectra of aligned systems show only one resonance band instead of two absorbance bands as found for randomly distributed gold rods. The visible and near-infrared spectra reveal that the rods are completely oriented when the film is stretched 4-6 times its original length. No significant effect of the aspect ratio is observed on the film elongation required for complete alignment. The alignment of gold rods by the stretched-film method is visualized by reflection confocal scanning laser microscopy (CSLM). The CSLM micrographs also demonstrate the distribution of single gold rods in the film.