Composition-Dependent plasmon shift in Au-Ag alloy nanotubes: Effect of local field distribution

The composition-controlled shift of the transverse surface plasmon resonance (SPR) in Au-Ag alloy nanotubes was theoretically studied by using the Drude model and quasi-static approximation. Increasing the gold composition leads to the red shift of both low- and high-energy SPR. The antisymmetric plasmon mode is more sensitive to the change in gold composition. The physical origin based on local electric field distribution in the transverse section plane was investigated to illuminate the effect of gold composition on the shift of the SPR. The local field corresponding to antisymmetric coupling is polarized parallel to the incident polarization. Thus, the thin shell enhances the electron scattering and lowers the plasmon energy, which in turn results in an intense red shift of the SPR.