TEMPLATE-SYNTHESIZED NANOSCOPIC GOLD PARTICLES - OPTICAL-SPECTRA AND THE EFFECTS OF PARTICLE-SIZE AND SHAPE

We have prepared nanoscopic gold cylinders of controlled radius and as pect ratio via electrodeposition of the metal within the pores of anod ically-grown porous aluminum oxide membranes. The nanocylinder radii a re determined by the pore dimensions of the host alumina which, in tur n, depend on anodization conditions. The particle aspect ratios were c ontrolled by varying the amount of Au deposited within the pores. The optical spectra of the gold nanocylinder/alumina composites exhibit st rong absorption bands in the visible spectrum. The extinction maxima ( lambda(max)) values for gold particles approaching spherelike geometry agree well with Mie theory calculations. The blue shift of lambda(max ) as the particle aspect ratio is increased is in qualitative agreemen t with Maxwell-Garnett theory. We propose a simple modification of Max well-Garnett theory that addresses both size and shape effects.