Alignment of rod-shaped gold particles by electric fields

Abstract

The electro-optical response of colloidal dispersions of rod-shaped gold particles is studied for various aspect ratios (2.6 < L/d < 49; d = 15 nm) by monitoring the absorbance spectra in the visible wavelength regime. The absorbance spectra strongly depend on the degree of orientational order of the rods and the direction of the polarization of the incident light with respect to the applied electric field. From the change in absorbance of the transverse resonance the electro-optical effect is deduced: at low electric field strengths a linear dependence on the squared electric field strength is observed, and at sufficiently high electric field strengths saturation occurs. This is in agreement with electro-optical theory. With increasing length, the anisotropy in electric polarizability increases from 6.10-30 F.m2 to 12.10-30 F.2. It is found that the anisotropy in electric polarizability depends on the square root of the particle length.