Browsing by Author "Wang, Zixing"
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Item Novel Synthesis and Modification Methods of 2-dimensional Materials(2019-04-19) Wang, Zixing; Ajayan, Pulickel M.2-dimensional transition metal dichalcogenides (2D TMDCs) has gained increasing interest for their versatile and unique electrical, optical, chemical and mechanical properties, giving them wide applications in electrocatalysts, photocatalysts, energy storage, and optoelectronics. This thesis discusses three novel ways to synthesize and modify 2D TMDCs. The novel synthesis methods are based on chemical vapor deposition (CVD) and surfactant assisted colloidal wet synthesis. The modification method is based on chem-mechanical etching of the 2D monolayer TMDC materials on Si substrate. To be specific, 2-dimensional transition metal carbide (TMC), boride (TMB), and nitride (TMN) have been grown through two chemical vapor deposition methods. The 2D TMC, TMN and TMB grown using transition metal-copper immiscible system show superior mechanical hardness, scratch resistance, and oxidation resistivity. 2D MoxBy grown from molybdenum oxide power is larger in size and can be used to test various properties, including electrical conductivity and chemical catalytic activity. The preparation of 2D TMDC nanoribbons is through a reducing agent aqueous solution. This is a simple and tunable way for generating TMDC (MoS2 and MoSe2) nanoribbons from CVD grown 2D TMDCs on Si/SiO2. The reducing agents convert Mo(IV) from the defect sites to a lower oxidation state, thus disturbing the structure and expanding the defects. H2O acts as a detaching and tearing medium that pulls the TMDC flake into nanoribbons. The area of conversion, density, and thickness of the nanoribbons can be tuned by concentration and potency of the reducing agents. The 2D nanoribbons possess high structural integrity, zigzag edges with chalcogenide termination, and a consistent bandgap of 1.82 eV that is independent of ribbon width.Item Substitution of copper atoms into defect-rich molybdenum sulfides and their electrocatalytic activity(Royal Society of Chemistry, 2021) Wang, Zixing; Kannan, Harikishan; Su, Tonghui; Swaminathan, Jayashree; Shirodkar, Sharmila N.; Hernandez, Francisco C. Robles; Benavides, Hector Calderon; Vajtai, Robert; Yakobson, Boris I.; Meiyazhagan, Ashokkumar; Ajayan, Pulickel M.Studies on intercalation or substitution of atoms into layered two-dimensional (2D) materials are rapidly expanding and gaining significant consideration due to their importance in electronics, catalysts, batteries, sensors, etc. In this manuscript, we report a straightforward method to create sulphur (S) deficient molybdenum (Mo) sulfide (MoS2−x) structures and substitute them with zerovalent copper (Cu) atoms using a colloidal synthesis method. The synthesized materials were studied using several techniques to understand the proportion and position of copper atoms and the effect of copper functionalization. Specifically, the impact of change in the ratio of Cu : S and the hydrogen evolution reaction (HER) activity of the derived materials were evaluated. This technique paves the way for the synthesis of various functionalized 2D materials with a significant impact on their physical and chemical behavior making them potential candidates for catalysis and several other applications such as energy storage and the development of numerous functional devices.