Subwavelength multilayer metal-insulator nanostructures with tuneable resonances have been widely used for various applications in optoelectronics and photonics, due to their unique dispersion relation of the dielectric permittivity. In this thesis, we firstly studied the optical properties and the resonance modes of the metal/insulator/metal (MIM) metamaterial system by spectroscopic ellipsometry and COMSOL Multiphysics calculations based on finite element methods. Our calculation results show that MIM systems with vertical or lateral gratings can both support the multiple cavity modes that form the epsilon-near-zero (ENZ) resonance with an effective dielectric constant close to zero. Their large local density states are beneficial to the Purcell effect enhancement of the spontaneous emission. Moreover, the low-energy multi-cavity modes can be adjusted in the visible range via tuning the insulator thickness. The difference is that the MIM system with lateral grating leads to uncoupled multiple ENZ resonance, while the vertical grating MIM structure owns strongly coupled modes which form ENZ bands. To demonstrate the usefulness of the emission enhancement of MIM structures in practical applications, multilayer metal-insulator nanostructures are adopted to improve the spontaneous emission of the emitter. Herein, we explored the effects of interface modifications on the overall performance in perovskite LEDs. Firstly, we designed and optimized the flat perovskite LED (PeLED) through systematic analysis of the power loss channels based on the optical mode. All the theoretical analysis is carried out through finite element simulations. Under the assumption of efficient photon generation in the emitting layer with an internal quantum yield of 0.9, the effect of the dipole orientation is analyzed and then thickness of the charge injection and emitter layer was optimized. Finally, we tuned the transparent electrode thickness to get the maximum value of the external quantum efficiency. Moreover, we further studied the influence of interface modifications happening at the electron-transport interface on the whole performance of perovskite-based flat PeLEDs. Particularly, we explored the integrating of photonic structure, while keeping the optical property of the emitting material. Interesting, our calculations reveal that the specially designed nanopatterning can promote to improve the Purcell factor and the outcoupling efficiency, thereby enhance the external quantum efficiency, related to the nanopattern-free PeLED configuration. In particular, an average enhancement around 100% for the external quantum efficiency was achieved, and thus improving the radiative emission of the PeLED devices. These findings indicated that using morphological patterning to enhance LED performance is realistic method, similar to other light emission technologies. Finally, a nanoscale optical pressure/temperature nano sensor based on gap-plasmonic nanostructure, composing of the MIM nanopillar arrays covered by a metallic film, is proposed. The gap plasmon frequency is highly sensitive to the distance of the pillars to the Ag film, which allows optical sensing of pressure/ambient temperature/ refractive-index by variation in the colour of the device.
|Titolo della tesi:||Plasmonics in Metal Insulator Cavities|
|Data di discussione:||24-mar-2022|
|Appare nelle tipologie:||Tesi di dottorato|