Wavelength tuning of surface plasmon resonance by annealing silver-copper nanoparticles

Utilizing a pulsed laser deposition method, silver-copper (Ag–Cu) nanoparticles have been synthesized by irradiating the laser light of $λ=248nm$ on Ag and Cu plates under the pressure below $1×10−4Pa$⁠. The peak absorption attributed to surface plasmon resonance (SPR) of the Ag–Cu nanoparticles appeared at $763nm$⁠, which was approximately $200nm$ higher wavelength than that of Ag nanoparticles. With increase in the annealing temperature from $300to548K$⁠, the peak absorption attributed to SPR of the Ag–Cu nanoparticles shifted continuously from $763to437nm$⁠. This fact proved that the peak absorption attributed to SPR can be tuned in the whole visible region by changing the annealing temperature only. Moreover, from the results of atomic force microscopy and grazing angle x-ray diffraction, the SPR wavelength tuning is conjectured due not to the change in the surface morphology of the Ag–Cu nanoparticles but to the increase in the electric conductivity of the nanoparticles induced by the precipitation of Cu atoms.