Abstract
Transition-metal Dichalcogenides (TMDCs) collectively name a series of two - dimensional materials, composed of transition metal groups and chalcogenides in the periodic table. These material have semiconducting properties, have shown atom-scale thickness, direct band gap, high transmittance and flexibility, etc. Besides these properties, TMDCs have shown outstanding performance in both flexible electronic device and optical electronic device. Very recently, it has been shown that synthesis of large film of polycrystalline monolayer TMDCs could be achieved using chemical vapor deposition (CVD). However, as compared to mechanically exfoliated samples, the CVD grown thin film typically have much lower carrier mobility, due to the growth process imperfections that induce various structural defects in the material. The first part of this thesis is inspecting the point defect in our CVD-synthesized WSe2, which exhibited PL intensity inhomogeneous. Synthetic 2D crystal films grown by chemical vapor deposition are typically polycrystalline, which contain many grain boundaries, these grain boundaries play an import role in the electron transport. The second part of this thesis is observing the grain boundary effects on electronic transport by fabricating WSe2 into back-gate structure field-effect transistors. Comparing the electron transport properties to the channel across the grain boundary and without the grain boundary, and using the continuous measurement to observe how the grain boundary effect with electrical transport properties in ambient condition.