Split ring resonators : flexible and tunable metamaterials, fano coupling and their applications in sensing
Date of Issue2016-02-01
School of Physical and Mathematical Sciences
Split ring resonators (SRRs) are widely used as plasmonics and metamaterials components because they have both electric and magnetic responses. The electric property arises from the dipole moment excited by the incident light while the magnetic mode emerges from the circulating current induced along the ring. In this dissertation, by utilizing the SRRs as the basic component, we developed transparent and flexible metamaterials by integrating the SRRs to the polymer. We also demonstrated the tunability of the optical response by combining the SRRs and the phase change material. In addition, the magnetic mode of SRRs was utilized to couple to the electric mode to generate the magnetic mode based Fano resonance, which is distinguished from the conventional electric mode based Fano resonance. Attributing metamaterials to a flexible substrate can provide the advantages such as transparency, deformability, light-weight and bio-compatibility. In this dissertation, free-standing and transparent metamaterials were fabricated by a nickel sacrificial layer assisted transfer method. The SRRs array can be transferred from a rigid substrate to polydimethylsiloxane (PDMS) without any damage. Both the structure and the optical properties of SRRs array can be maintained after transferring to the PDMS. A convenient surface enhanced Raman scattering (SERS) strategy was demonstrated by covering the PDMS-meta onto the surface with the analytes residing on, which can separate the SERS substrate from the analytes. More importantly, the free standing metamaterials were utilized to investigate the coupling between nano structures and metal film. Integration of SRR metamaterials to phase change materials can achieve the tunability of the optical response. The properties of metamaterials are fixed once the fabrication completed, it is desired to accomplish active metamaterials to satisfy various applications. By utilizing the phase change property of vanadium dioxide (VO2), we demonstrated that both the electric and magnetic responses of SRR can be tuned within near infrared range. We can control the resonance wavelength in real time by controlling the temperature of VO2. In addition, the tunable resonance of SRR was used to construct a tunable SERS device, which can engineer the SERS intensity by controlling the resonance wavelength. Another phase change material Ge2Sb2Te5 (GST) was utilized to couple to plasmonic structures to achieve tunable perfect absorber. In the conventional Fabry-Pérot (FP) cavity, the minimum thickness required to achieve interference condition should be a quarter wavelength. In this thesis, we demonstrated that an ultrathin lossy phase change film can sustain the interference effects and an unity absorption is attainable. The reflectivity difference of the amorphous and crystalline GST thin films can gave a high optical contrast ratio, highlighting the potential in the applications of optical switch and data storage. Furthermore, a plasmonic structure was added to make the absorption band broader. The coupling inside the split ring/disk cavity was investigated to reveal the magnetic mode based Fano resonance. Previously the Fano resonance mainly focused on the electric modes interaction. However, the interaction between a magnetic mode and an electric mode also can produce a Fano resonance. The magnetic mode based Fano resonance can generate high magnetism at the resonance wavelength. Herein, we revealed that the quadrupole and octupole magnetic modes of SRR can be coupled to electric dipole to generate a Fano resonance. In addition, the Fano spectra shape and resonance wavelength can be adjusted by changing the disk diameter and the split ring angle. The magnetic mode based Fano resonance was also demonstrated to be promising in the chemical and biological sensing.