Investigation Of The Optical Functional Hybridplasmonic Nanostructures

Plasmonic materials, metallic nanostructures that support surface plasmon resonances（SPR）, have attracted increasing attention due to a wide range of applications as lasers, sensors, optical filters, imaging, enhanced fluorescence based devices, surface enhanced Raman scattering, etc. To acquire certain optical properties, many efforts have been made to fabricate novel nanostructures. With further extension of research, it was realized that diverse geometrical metal nanostructures could excite distinct resonance modes. For instance, individual metallic nanoparticles and their ensembles can support localized surface plasmon resonances, and the optical properties of nanoparticles depend sensitively on the particle size, shape, and composition, etc. Unlike solid metallic nanoparticles, the metallic nanoshells consisted of a dielectric core surrounded by a concentric metal shell, and the excited plasmon resonances in metallic nanoshells can be engineered through controlling the inner core and outer shell dimensions. If the thickness of the metallic shell layer is exceedingly thin, outer shell and void plasmons couple to each other, which lead to the splitting of the plasmon resonances into interesting hybrid modes. Novel optical properties in metallic shells could be observed by carefully designing.Recently, metallic nanoshells composed of a dielectric core and a thin metallic shell layer have been extensively investigated. Novel optical properties have been observed by introducing different geometrical confinement of light inside the voids. Spherical nanoshells with symmetry-breaking have been systemic studied, and hybrid plasmonic-photonic resonances or Fano resonances could be supported through controlling structure parameters. Columnar nanoshells have also been investigated, and by manipulating the thickness of metallic layer and the diameters of the inner core and out shell, dark plasmonic resonances are directly excited. And these innovative optical properties may be used to enhance and localize the SPR energy or achieve a high-quality factor for improving sensing performance. Hence, there is a strong demand to explore the possibility of low-cost and efficient techniques in fabricating plasmonic materials possessing distinct geometrical nanoshells, which may show innovative optical properties.In chapter 2, Ag hollow frustum array films were fabricated to support hybrid plasmon modes by a versatile colloidal lithography. The arrays possess structural features of a frustum-like void core surrounded by a concentric metal shell, whose shape just like a cup. The unique structure with a cavity element provides hybrid plasmonic resonances coupling between frustum-like mode and void-like surface plasmon（SP） mode. The transmission spectra of hollow frustum arrays with different structural parameters reveal a blue-shift because of a reduction of the effective volume of the nanocavity. The resonance modes of structured films are also investigated, indicating the dominance of the interface and the great influence on the spectra. The fabricated films provide a hollow element as well as a strongly enhanced field which result in high sensing performance and a variety of other potential applications. The structured films also show a sensitive response to surrounding environment changes, yet with excellent linearity. Moreover, the Ag hollow frustum array film could also be applied to detect p-ATP with a concentration as low as 10^-9 M.In chapter 3, because the Ag hollow frustum array films possess good transfer properties, making use of this advantage, the samples can be transferred to arbitrary substrates and fabricated into new structures during transfer. Just using a simple transfer process, a novel obverse nanocup array film was prepared. The fabrication processes are versatile and low-cost. The designed nanocup array film could support a hybrid plasmonic resonance coupling between frustum-like mode and void-like surface plasmon mode as well as Fano resonance. Simulated electric field distribution and charge distribution are investigated to explain the hybrid mechanism. The unique structure with a cavity element provides a hybridization of frustum-like mode and void-like SP plasmons, leading to greatly enhanced surface plasmon（SP） energy, which largely improves plasmonic sensing and surface enhanced Raman scattering performance. Numerical simulations show good agreement with the experimental results, enabling a rational fabrication of structures with defined optical properties. Moreover, the fabricated nanostructures are highly sensitive to the surrounding environment with strictly linear and strong dependence on refractive index, revealing great potential application as plasmonic sensors and the highest relative sensitivities could reach up to 71 % per refractive index unit（RIU）. Furthermore, the existence of hybrid modes induces distinct electric field distributions inside and outside of the nanocup, may allowing the structured film to be utilized as a spatial selective sensor.