Near-infrared active metamaterials and their applications in tunable surface-enhanced Raman scattering.

By utilizing the phase change properties of vanadium dioxide (VO2), we have demonstrated the tuning of the electric and magnetic modes of split ring resonators (SRRs) simultaneously within the near IR range. The electric resonance wavelength is blue-shift about 73 nm while the magnetic resonance mode is red-shifted about 126 nm during the phase transition from insulating to metallic phases. Due to the hysteresis phenomenon of VO2 phase transition, both the electric and magnetic modes shifts are hysteretic. In addition to the frequency shift, the magnetic mode has a trend to vanish due to the fact that the metallic phase VO2 has the tendency to short the gap of SRR. We have also demonstrated the application of this active metamaterials in tunable surface-enhanced Raman scattering (SERS), for a fixed excitation laser wavelength, the Raman intensity can be altered significantly by tuning the electric mode frequency of SRR, which is accomplished by controlling the phase of VO2 with an accurate temperature control.