Graduation Year

2019

Document Type

Thesis

Degree

M.S.M.S.E.

Degree Name

MS in Materials Science and Engineering (M.S.M.S.E)

Degree Granting Department

Chemical Engineering

Major Professor

Dmitri Voronine, Ph.D.

Committee Member

Denis Karaiskaj, Ph.D.

Committee Member

Yusuf Emirov, Ph.D.

Keywords

enhancement, microscopy, photoluminescence, Raman scattering, transition metal dichalcogenides

Abstract

Nanoscale optical characterization of two-dimensional (2D) materials and heterostructures is important for the design of novel optoelectronic flexible nano-devices. Nano-optical photoluminescence (PL) and Raman imaging of bilayer 2D materials has been a challenging problem due to weak signals. The exciton-dominated light emission of two-dimensional (2D) transition metal dichalcogenide (TMDC) materials is affected by the formation of defects and doping states. Previous studies have shown that chemical treatment modifies the defect and doping states of chemical vapor deposition (CVD)-grown monolayers of MoS2 and WS2, which provides a promising possibility for engineering the optoelectronic properties of these 2D TMDCs. Here, near-field spectroscopy and imaging were used to study the effect of superacid treatment to improve the optical properties of bilayer MoS2-WS2 lateral heterostructures. CVD-grown bilayer MoS2-WS2 lateral heterostructures were treated with bis-(trifluoromethane)-sulfonamide (TFSI), and photoluminescence (PL)/Raman signals of the non-treated and chemically treated samples were obtained with 20 nm resolution. The enhancement factors of the PL/Raman signals were obtained, revealing the synergistic effect of the TFSI and tip enhancement.

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