FINITE-SIZED OBLATE AND ORTHO-PROLATE METAL NANOPARTICLES - OPTICAL THEORY AND POTENTIAL AS SURFACE-ENHANCED RAMAN-SPECTROSCOPIC SUBSTRATES

The relative absorption intensities of composites containing Au, Ag or Cu prolate (a>b=c), oblate (a<b=c), ortho-prolate (b>a=c) and ortho-o blate (b<a=c) nanoparticles have been modeled with the dynamical Maxwe ll-Garnett effective medium expression. The electric field of the ligh t was along the b-axis of the nanoparticles in simulations. The semi-r adii b for prolate-oblate particles and a for the ortho counterparts w ere equal to 26 nm. The results of simulations indicate that the absor ptive power of the composites increased as particle shape changed from ortho-oblate --> ortho-prolate and prolate --> oblate. We found that in simulations, ortho-prolate particles provided the greatest intensit y per unit volume fraction of metal. When considering particle shape o nly, the degree of enhancement expected from SERS substrates is approx imately proportional to the intensity of absorption. We also propose a simple means of fabricating SERS substrates by means of the template synthesis method. (C) 1997 Acta Metallurgica Inc.