Abstract
The influence of a three-dimensional (3D) photonic crystal (PC) on the plasmonic properties of gold nanorods (GNRs), which are placed on the surface of the PC, was investigated both numerically and experimentally. The 3D PC formed by closely packed polystyrene spheres was fabricated by using a pressure controlled isothermal heating vertical deposition technique. For a GNR whose longitudinal surface plasmon resonance (LSPR) is located at the bandgap edges of the PC, a dramatic narrowing of the absorption spectrum as well as an enhancement in electric field and thus the absorption was observed. It was suggested that the small group velocities at the bandgap edges of the PC are responsible for the slow decay of the plasmonic mode in the GNR. To confirm the enhancement in the absorption of the GNRs induced by the nearby PC, we examined the two-photon-induced luminescence (TPL) of an assembly of GNRs dispersed on the surface of the PC. Under the excitation of femtosecond laser pulses which was resonant with the LSPR of GNRs, it was found that the excitation intensity necessary for melting GNRs placed on the surface of the PC was nearly one order of magnitude smaller than that for GNRs placed on the surface of a glass slide, in good agreement with the results predicted by the numerical simulations. Our findings indicate the possibility of using PCs to modify the plasmonic and optical properties of GNRs which are quite useful for the practical applications of GNRs such as nanoscale sensors and optical data storage.
Highlights
A photonic crystal (PC) is a periodic arrangement of scatterers which forms a periodic modulation in dielectric constant or refractive index in space
We demonstrated that the melting energy for the gold nanorods (GNRs) placed on the surface of the PC formed by self-assembled PS spheres is reduced by nearly one order of magnitude as compared with that for the GNRs placed on the glass slide, in good agreement with the prediction of the numerical simulations based on the finite difference time domain (FDTD) technique
We have confirmed that the absorption of a GNR in the absence of the PC can be derived by calculating the electric field distribution inside the GNR
Summary
A photonic crystal (PC) is a periodic arrangement of scatterers which forms a periodic modulation in dielectric constant or refractive index in space. Barth et al proposed and demonstrated a hybrid cavity system in which metal nanoparticles are evanescently coupled to a dielectric PC cavity by using a nanoassembly method [37] They showed that the combined effect of plasmonic field enhancement and high quality factor (Q ≈900) opens new routes for the control of light-matter interaction at the nanoscale. Ganta et al described a method to coat fused-silica microresonators with high-aspect-ratio GNRs and observed that the microresonators maintained an optical quality factor greater than 107 after coating [40] Such microresonators combine the field enhancement of localized surface plasmon resonances with the cavity-enhanced evanescent components of high-Q whispering-gallery modes and they are useful for plasmonic sensing applications. A continuous wave instead of a short pulse was used to calculate the electric field distribution
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