Surface plasmon resonance of two-segmented Au-Cu nanorods

Two-segmented gold-copper nanorods were electrodeposited inside the pores of polycarbonate track-etched membranes from two separate solutions. The PCT membranes were dissolved in dichloromethane (CH(2)Cl(2)) and the solvent was replaced by methanol solution. Optical absorption spectra of two-segmented Au-Cu nanorods dispersed in methanol showed two peaks which were related to the transverse mode of copper and the longitudinal mode of gold. By increasing the length of the gold segment, when the total length of both metals was fixed at 1 µm, the copper and gold peaks shifted to the blue and red wavelengths, respectively. We observed that the wavelengths of the extinction peaks are not in good agreement with the expected value obtained from calculations using the nominal dielectric constant of the medium. Therefore, we suggest the effective medium dielectric constant (ε(m)(eff)) for Cu and Au segments by comparing the experimental data and calculation results. The values of ε(m)(eff) decrease by increasing the gold length.