Near field optical study of polaritons in two-dimensional van der Waals materials
Date
2022-12
Authors
Luan, Yilong
Major Professor
Advisor
Fei, Zhe
Shinar, Joseph
Wang, Jigang
Wang, Xuefeng
Lu, Meng
Committee Member
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Abstract
With the discovery of graphene, two dimensional (2D) van der Waals (vdW) materials have opened a new era and provided a new platform to the study of nano optics. vdW maerials can host various kinds of polaritons, which have the highest freedom of confinement. Thus, light can be trapped in subwavelength scale and lead to strong light-matter interaction. Traditional optical studies in this field are limited by their low spatial resolution due to the diffraction limit. To overcome this limit and achieve subwavelength resolution, near field optics study has been undergoing recently. In this thesis, we deploy scattering type scanning near-field optical microscope (s-SNOM) to study the polaritons behavior hosted by 2D vdW materials in nanoscale including both imaging and spectroscopy.
In chapter one, the concept of polaritons, the properties of vdW material and the background of near-field setup are introduced. In chapter two, we report a nano-optical imaging study of waveguide exciton polaritons (EPs) in tin sulfide (SnS) in the near-infrared (IR) region. The real space propagative EPs are mapped, which shows anisotropic optical response along a and b axis. In chapter three, a nano-infrared (IR) imaging study of trilayer graphene (TLG) with both ABA (Bernal) and ABC (rhombohedral) stacking orders is reported. The results indicate that the plasmon wavelength of ABA stack is hugely larger than that of ABC stack, which is directly linked to their electronic structures and carrier properties calculated with theory. In chapter four, a systematic plasmonic study of twisted bilayer graphene (tBLG) is performed. The plasmon propagation is showed to be sensitive to the twisted angle, which is a result of the renormalization of Fermi velocity, a direct consequence of interlayer electronic coupling. In chapter five, a quantitative model that is capable of computing accurately the s-SNOM signals of nanoscale samples is developed and used to demonstrate a novel method for ultra-sensitive infrared (IR) vibrational spectroscopy of molecules by combining the tip enhancement of the scattering-type scanning near-field optical microscope (s-SNOM) and the plasmon enhancement of the breathing-mode (BM) plasmon resonances of graphene nanodisks (GNDs).
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Type
dissertation