Optical Absorption Spectra of Coinage Metals (Cu, Ag, Au) Nanorods: A Theoretical Study

Gold nanorods of average aspect ratio 3.1 have been synthesized. The nanorod solution has been characterized with UV-visible absorption spectra and TEM. UV-visible spectra of gold nanorods solution exhibit two plasmon modes, called transverse and longitudinal modes. Transverse and longitudinal plasmon modes of Cu, Ag and Au nanorods have been simulated on the basis of Gan's model for different aspect ratio keeping medium dielectric constant fixed and for different medium dielectric constant keeping aspect ratio fixed. Simulated result shows that the absorption maximum of longitudinal mode depends linearly on aspect ratio of nanorods, medium dielectric constant and type of metals. Empirical relations to obtain peak longitudinal plasmon frequency in terms of aspect ratio and medium dielectric constant for Cu, Ag and Au have been suggested. Vibrational dephasing time of Cu, Ag and Au for different resonance energy is also calculated.