Time dependence of the surface plasmon resonance of copper nanorods

Abstract

Copper nanorods have been synthesized by electrodeposition with different lengths in porous polycarbonate (PCT) membranes with a pore diameter of 50 nm and a thickness of 4 µm. The PCT membranes were dissolved in dichloromethane (CH2Cl2) and the solvent was replaced by methanol solutions. Extinction peaks at 587, 581 and 574 nm were observed for the Cu nanorods with aspect ratio R = 6,8 and 10 in methanol, respectively. Polarization of the molecules of the medium around the wires changes the dielectric constant of the medium. Hence, the wavelength of the extinction peaks does not shows good agreement with calculations that were done on basis of Gans' theory with nominal dielectric constant of the medium. In this study, the effective medium dielectric constant for Cu nanorods in methanol was obtained by comparing the experimental data and calculation results. The effective medium dielectric constant (εmeff) for the Cu nanorods in methanol was decreased by increasing the aspect ratio of the nanorods. After one week, CuO or Cu2O shells with about 20 nm radius were observed around the copper nanorods and so the contemporary peak wavelength was shifted to red. In this case, variation of the shell's diameter with time caused the change in value of εmeff. It was found for the Cu nanorods that the value of εmeff increased with time.