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 \nratios (2.6 < L/d < 49; d = 15 nm) by monitoring the absorbance spectra in the visible wavelength regime. \nThe absorbance spectra strongly depend on the degree of orientational order of the rods and the direction of \nthe polarization of the incident light with respect to the applied electric field. From the change in absorbance \nof the transverse resonance the electro-optical effect is deduced: at low electric field strengths a linear \ndependence on the squared electric field strength is observed, and at sufficiently high electric field strengths \nsaturation occurs. This is in agreement with electro-optical theory. With increasing length, the anisotropy in \nelectric polarizability increases from 6.10-30 F.m2 to 12.10-30 F.2. It is found that the anisotropy in electric \npolarizability depends on the square root of the particle length.