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Defect Engineering of Two-Dimensional Electronically Functional Materials

Author
Zhang, Fu
Published
[University Park, Pennsylvania] : Pennsylvania State University, 2019.
Physical Description
1 electronic document
Additional Creators
Terrones, M. (Mauricio)
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Open Access.
Summary
In this thesis, we have carried out a systematic study on the material synthesis, state-of-the-art characterization and property investigations of transition metal dichalcogenides (TMDs) and their heterostructures by defect engineering. First, a defect-controlled approach for the nucleation and epitaxial growth of WSe2 on hBN is demonstrated. The results reveal an important nucleation mechanism for epitaxial growth of van der Waals heterostructures and indicate that hBN is a superior substrate for synthesizing single crystal TMD films, exhibiting a reduced density of inverted domain boundaries and improved optical and electronic properties. Second, we discuss the synthesis of high quality superconducting -phase molybdenum carbide (-Mo2C) flakes and 2D molybdenum carbide/disulfide heterostructures exhibiting higher superconducting transition temperatures, an insight into the formation mechanism and possible epitaxial-strained or moir configurations of MoS2/-MoC are discussed to explain the latter. Third, we have used a plasma-assisted method to introduce carbon-hydrogen (CH) units within monolayer WS2 for the first time. The carbon doping leads to reduction of the optical band gap, and the electronic transport gradually becomes entirely p-type behavior as the carbon doping level increases. Fourth, we have successfully used a single-step powder vaporization method to synthesis vanadium-doped WS2 (V-WS2) monolayers with a wide spectrum of vanadium concentrations. Interestingly, as-synthesized V-WS2 monolayers show a consistent reduction of the optical bandgap and the emergence of the p-type transport branch (reaching ambipolarity), as a function of vanadium concentration. In addition, ferromagnetic ordering is simultaneously induced in monolayer V-WS2 at room temperature and reaches optimal at ~2%at. vanadium concentrations. We have demonstrated that the electronic, optical and magnetic properties of TMDs could be tuned by defect engineering such as introducing foreign atoms into the lattice or by heterostacks formation. Mechanisms associated with these changes were also elucidated. The results summarized in this thesis could contribute to the fabrication of next-generation optoelectronic, magneto-optical and magneto-electronic devices, which is foreseen that 2D materials could have practical applications in the near future.
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Dissertation Note
Ph.D. Pennsylvania State University 2019.
Reproduction Note
Microfilm (positive). 1 reel ; 35 mm. (University Microfilms 29267545)
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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