Abstract
Plasmonic metamaterials have been positioned during the last decades as one of the most active research fields in nanophotonics, given the extended plasmonic responses, by design, to different frequency ranges in the optical spectrum, which have allowed their implementation in many relevant applications, such as biosensing and detection, solar energy conversion and photodetection, photochemistry, transformation optics and communications, to name some of them. However, the translation of these systems, to clinical and industrial applications, requires some improvements in the efficiency, selectivity, cost, reproducibility and control of the morphology at the nanoscale. This has motivated the exploration of alternative plasmonic materials, to the expensive and commonly used noble metals. Among the materials explored, aluminium has gained significant attention due to its excellent optical responses, which can be tuned from the deep ultraviolet to the near-infrared, allowing its applications in many different fields, particularly, the excellent optical response of Al in the UV range can be exploited for enhanced sensing and detection of biological compounds, such as cell free DNA, which has emerged as a molecular biomarker for cancer diagnosis, prognosis and monitoring, therefore, the integration of Al nanostructures as metamaterial systems can be implemented as point-of-care for cancer medical treatment. In addition, aluminium is an inexpensive, naturally abundant material, is compatible with complementary metal-oxide-semiconductor fabrication techniques, and presents high efficiency for generation of hot carriers after non-radiative plasmon decay, a feature that potentiates its application in new-generation electronic devices for photovoltaics and photodetection and photochemistry.Following those motivations, in this thesis, the development of two large-scale, subwave-length metamaterial systems based on aluminium, fabricated via cost-effective, self-assembled techniques, is presented. The first geometry consists of an array of aluminium nanorods, with fundamental plasmonic modes lying in the deep ultraviolet, and additional plasmonic resonances intrinsic to the metamaterial slab, spanning from the visible to the near-IR. The second geometry consists in an array of aluminium nanopores, with a strong plasmonic resonance in the ultraviolet region and a weaker mode in the near-IR. The tuning of such plasmonic resonances, when modifying the metamaterials’ dimensions, during the fabrication process, is demonstrated, and the results are supported by numerical simulations.
Finally, the successful evaluation of aluminium nanorod and nanopore metamaterial platforms for applications in biosensing, and resonant and non-resonant photodetection, respectively, are discussed. Al nanorod metamaterials show to perform extremely well as ultraviolet refractive index material sensor for B-DNA detection in water medium, reaching a limit of detection of ∼ 6ng/cm2, which corresponds to one strand of DNA deposited in every two rods, in the metamaterial array. On the other hand, Al nanopore metamaterial integrated in p-type silicon, showed excellent performance as resonant (ultraviolet) and non-resonant sub-bandgap photodetector (infrared), presenting hot carrier generation gain mechanism in the integrates Al-metamaterial-p-Si Schottky junction, which results in an enhanced photocurrent under illumination conditions of up to ∼160x and ∼14x, for the resonant and non-resonant case, under ±250 mV limiting bias, for both, hot holes and hot electron generation. A detailed description of the experimental techniques considered for the fabrication, characterisation and applications of the aluminium metamaterial platforms is given.
| Date of Award | 1 Sept 2021 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Wayne Dickson (Supervisor) & Anatoly Zayats (Supervisor) |