| Author: | Lam, Ka Kin |
| Title: | Studies of indium tin oxide- and metal-base hyperbolic metamaterials |
| Advisors: | Mak, C. L. (AP) Leung, C. W. (AP) |
| Degree: | Ph.D. |
| Year: | 2023 |
| Subject: | Optical materials Metamaterials Thin films, Multilayered Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Physics |
| Pages: | 139 pages : color illustrations |
| Language: | English |
| Abstract: | IAI trilayer structure is a thin Au-spacer layer structure sandwiching with top and bottom ITO films (ITOt/Au/ITOb). It is an important component exhibiting various epsilon-near-zero (ENZ) surface plasmonic properties in near-infrared (NIR) range with wide range tunability. The effect of the top and bottom ITO thickness of this trilayer structure on its structural, electrical, optical and plasmonic properties is of paramount important to both scientists and engineers who need to understand the basic physics as well as apply this structure as optical devices. However, only few reports have been systematically studies on the effect of the relative position of the inserted gold layer among the two ITO layers. Five trilayers of constant 43 nm total thickness, but with various bottom and top ITO film thicknesses, are prepared by magnetron sputtering. Total internal reflection ellipsometry (TIRE) is used to study the optical reflectance changes caused by the surface plasmon resonance. The various plasmonic modes including the surface and bulk modes are confirmed by the reflectivity spectra obtained from experimental probed and numerically simulated by the Fresnel formalism. In the spectra, three reflectivity minima are observed. A low reflectivity dip has been observed at about 760 nm in the reflectivity spectra, while a Lorentzian-like transition on the real part of dielectric constant is observed. For the ITOt/Au/ITOb = 5/3/35 sample, where the Au layer is positioned closest to the sensing liquid, the above-mentioned reflectivity dip becomes most significant (based on the amplitude as well as half width) as compared to other samples, indicating that the closer ITOt/Au interface to the sensing liquid, the strongest observable plasmonic resonance effect. Furthermore, it is found that the reflectivity dip position is independent to the angle of incident but is sensitive to the refractive index of the sensing liquid below. Our results show that the dip position shifts to a shorter wavelength when refractive index of the transparent liquid increases. This phenomenon shows the potential application of this trilayer in improving the sensitivity of ellipsometer in finding unknown liquids' refractive index, based surface plasmon enhanced liquid sensing sensitivity. The study is extended by fabricating multilayer ITO/Au superlattices with 1-, 3- and 5- repeated IA units as the hyperbolic metamaterial (HMM). The surface plasmon mode is excited by the prism coupled ellipsometry and the reflectance dips from the spectra are observed. The surface modes are confirmed by the finite-difference time-domain (FDTD) simulation showing asymptotic mode migration properties to approximate 500 nm similar to the experimental results. Then Rhodamine6G (R6G) dye-doped PMMA film are spin-coated on top of the HMM structures. From the reflectance measurements, the original dip position disappears. Indeed, it is noticed that the original dip seems to be split into two dips. This observation is accounted by the Rabi splitting which is the evidence of the strong coupling between the SPP mode and excitonic modes. The promising results indicate that the resonance conditions are archived, and this opens a potential pathway for measuring the amplified emissions for the devices. |
| Rights: | All rights reserved |
| Access: | open access |
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