Dynamical Maxwell-Garnett optical modeling of nanogold-porous alumina composites: Mie and kappa influence on absorption maxima

Composites consisting of nanogold in porous alumina host membranes have been fabricated and characterized. Nanocluster size (11 nm to 60 nm radius) and shape (prolate to oblate) were varied experimentally. Two phenomena were responsible for the position of maximum absorption (λmax) of the composites. First, light scattering due to extrinsic electrodynamic effects became important as particle size was increased. This resulted in red shifts in λmax and is known as the Mie effect. Secondly, blue shifts were induced as particle aspect ratio was increased. We have designated shifts due to particle shape and orientation as the kappa effect. The two appeared to exert their influence independently. Simulations by means of the dynamical Maxwell-Garnett (DMG) expression resulted in good correlation with experimental λmax. We demonstrate again the versatility of the template method of synthesizing nanostructured materials. © 1997 Acta Metallurgica Inc.