Correlating nanorod structure with experimentally measured and theoretically predicted surface plasmon resonance.

The extinction spectra of Au nanorods electrochemically synthesized using anodic aluminum oxide templates are reported. Homogeneous suspensions of nanorods with average diameters of 35, 55, 80, and 100 nm and varying lengths were synthesized, and their resultant surface plasmon resonances were probed by experimental and theoretical methods. Experimental extinction spectra of the nanoparticles exhibit good overall agreement with those calculated using the discrete dipole approximation. We determine the dependence of the dipole plasmon wavelength on both rod length and diameter, and we then utilize these results to derive an equation for predicting longitudinal dipole resonance wavelength for nanorod dimensions beyond the quasistatic limit. On average, the equation allows one to predict plasmon resonance maxima within 25 nm of the experimentally measured values. An analysis of factors that are important in determining the plasmon width is also provided. For long rods, the width decreases with increasing length in spite of increased radiative damping due to increased frequency dispersion in the real part of the metal dielectric function.