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Circular dichroism in semiconducting-plasmomic hybrid chiral nanostructures

Sarkar, Sumant (2021) Circular dichroism in semiconducting-plasmomic hybrid chiral nanostructures. Doctoral thesis, Northern Arizona University.

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Chiral metamaterials have become an active area of research due to the rich possibilities of discovering new fundamental light-matter interactions as well as a multitude of potential applications, including greatly enhanced molecular sensing among many others. The ability to improve, control and fine tune the chiro-optical activity is critical to expanding these areas of cutting-edge research. However, the ability to control and “tune” the chiro-optical activity remains a serious practical challenge. In this dissertation, four different methods for achieving such control are developed and described in detail. By choosing a large bandgap semiconducting material (TiO2) for a periodic array of chiral nanostructures, “giant” chiro-optical activity was achieved at ultraviolet wavelengths for the first time. This is important because the signature frequencies of biomolecules often lie in this region. By only slightly varying the morphology of the semiconducting chiral nanostructures, a high level of tunability over the chiro-optical activity was established. Most impactful, a broadband and tunable CD across UV and visible wavelengths was achieved with heterogeneous nanohelices made from a combination of semiconducting and plasmonic materials. Critically, the optical activity of these hybrid nanostructures was found not to be a simple algebraic sum of the CD of the underlying materials, but a strong synergistic enhancement arising from the hybrid nature of the metamaterial was instead observed. We ascribe this effect to the strongly modified electronic band structure induced by the interface between the disparate materials. The highly enhanced optical activity, i.e., CD, opens the door to targeted engineering of chiral metamaterials for a multitude of novel applications.

Item Type: Thesis (Doctoral)
Publisher’s Statement: © Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords: chirality; circular dichroism; molecular sensing; nanostructures; plasmonics; TiO2
Subjects: Q Science > QC Physics
NAU Depositing Author Academic Status: Student
Department/Unit: Graduate College > Theses and Dissertations
College of the Environment, Forestry, and Natural Sciences > Physics and Astronomy
Date Deposited: 04 Feb 2022 21:30
Last Modified: 28 Dec 2022 08:30
URI: https://openknowledge.nau.edu/id/eprint/5660

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