Manipulation and Enhancement of Excitonic Optical Spectroscopy in Two-Dimensional Semiconductors
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Authors
Tyson, Kurt Henry
Date
2024-05-02
Type
thesis
Language
eng
Keyword
2D Material Semiconductors , Exciton-Plasmon Coupling , Plexcitons , Darkfield Scattering , Photoluminescence , Photoenhancement , Ultrafast Lifetime Dynamics
Alternative Title
Abstract
Two-dimensional materials present a promising foundation for developing next-generation ultrathin, flexible, and durable optoelectronic devices. Amongst the family of 2D materials, semiconducting monolayer MoS2 has garnered immense attention due to its direct bandgap with emissions in the visible light spectrum. Not only does this pave the way towards atomically thin photodetectors, emitters, and switches, but the high excitonic binding energies at room temperature provide a promising platform to explore novel physical phenomena such as exciton-plasmon polaritons. Unfortunately, MoS2 suffers from low photoluminescence quantum yield (PLQY), where non-radiative recombination pathways compete with the radiative recombination of excitons. This leads to an extensive reduction in light emission efficiency (0.01-0.6%). Inherent defect sites, vacancies, and charge carrier density contribute to decreased PLQY, but the underlying mechanisms are heavily debated. In this work, we investigate factors that affect the photoluminescence (PL) of MoS2 and the accompanying fabrication challenges. We first apply a superacid treatment to MoS2, which is known to increase PLQY to near unity. We demonstrate a photoinduced PL enhancement up to 74x in intensity from laser light exposure over hours. Using a high vacuum chamber, we verify that exposure to air is necessary for PL enhancement to occur. We attribute PL intensity and peak wavelength changes to a reduction in non-radiative pathways using single photon lifetime counting.
We also explore metallic nanostructure decoration to MoS2 as a means to further enhance PL and investigate exciton-plasmon coupling mechanisms. We couple the resulting excitonic photoluminescence in MoS2 to lithographically defined plasmonic gold nanodisk arrays. We study how the placement of the 2D membrane and superacid treatment affect the coupling strength of the system. This creates light-matter hybrid particles known as exciton-plasmon polaritons, defined by observed spectral splitting at the exciton resonance. We achieve a Rabi splitting of 86meV in untreated MoS2 with nanodisks on top and 113meV after TFSI treatment. We also contribute new fabrication processes to obtain clean large-area monolayer MoS2 on both polymer and silicon substrates. The presented work is an important step in manipulating 2D semiconductor light emission and detection for future optoelectronic devices.
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Attribution 4.0 International
Queen's University's Thesis/Dissertation Non-Exclusive License for Deposit to QSpace and Library and Archives Canada
ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Queen's University's Thesis/Dissertation Non-Exclusive License for Deposit to QSpace and Library and Archives Canada
ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.