Facile synthesis routes, directed assembly, and biological applications of two-dimensional transition metal dichalcogenides
- Restrictions on Access:
- Open Access.
- This thesis focuses on two-dimensional (2D) transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2). The controlled synthesis, directed assembly, and biological applications of 2D TMDs are investigated. Chapter 1 introduces the fundamentals of 2D TMDs, and reviews defect engineering of these atomic layers. Synthesis of single-phased MoS2 and WS2 monolayers has been reported previously. Chapter 2 reports synthesis of MoxW1-xS2 monolayer alloys by chemical vapor deposition. The as grown MoxW1-xS2 single crystals show gradual concentration profiles of transition metal atoms. The in-plane compositional gradient results in continuously tunable bandgaps. Transition metals form one-dimensional stripes in central regions of triangular-shaped crystals. Two types of synthetic defects, i.e. metal dopants and chalcogen vacancies, are observed to couple with each other in the alloys. The non-random and anisotropic alloys provide a rich setting to study 2D growth kinetics and nanoscale defect engineering. Chemical vapor deposition of TMDs generally requires a high growth temperature, which limits its applications in certain areas such as flexible electronics. In Chapter 3, the synthesis temperature is reduced by introducing tellurium powders into the growth precursors. The addition of tellurium does not affect the phase purity or crystallinity of the as-synthesized MoS2 and WS2 monolayers. These materials show optical and electrical performance comparable to those synthesized at higher temperatures. Established transfer methods of 2D TMDs include wet transfer and deterministic transfer. Chapter 4 demonstrates controlled and scalable transfer of monolayer WS2 triangles on a substrate using electric-field-assisted assembly. WS2 monolayers are selectively positioned on a guiding electrode structure using the dielectrophoretic force and its torque acting on the monolayers. Triangular sheets assemble with a preferential orientation relative to the electrodes. The assembly process neither deforms monolayer sheets, nor introduces structural defects to the materials, as confirmed by optical spectroscopies. The assembly method offers an alternative to conventional transfer methods in 2D monolayer integrations.The extraordinary photoluminescence of semiconducting TMDs makes them attractive for cellular imaging. Chapter 5 studies how cells interact with 2D TMDs. It is observed that certain cells digest monolayer WS2, become light-emitting afterwards, and are able to pass this light-emitting characteristic to their progeny cells. The residual WS2 monolayers, after interaction with cells, become structurally defective. This work may trigger further studies on 2D/bio interfaces.
- Dissertation Note:
- Ph.D. Pennsylvania State University 2018.
- Reproduction Note:
- Microfilm (positive). 1 reel ; 35 mm. (University Microfilms 13871872)
- Technical Details:
- The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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