| dc.description.abstract | A full picture of the growth mechanism of WS2 monolayers and bilayers through alkali-metal-halide-assisted thermal chemical vapor deposition (t-CVD) was unveiled in all aspects. Almost all types of WS2 flakes were demonstrated in the same system and considered almost all of the factors which may influence the synthesis, including the geometry of the system boundaries, the flow rate, the morphology and the properties of the growth substrate, the growth temperature, the vapor pressure, and the heating temperature of each precursor. We found that, among all parameters, the most important factors are the growth temperature, the vapor pressure, and the heating temperature of each precursor. Other parameters are just ways to alter these three main factors. A series of experiments were carried out and showed how these factors affect grain size, grain shape, and grain density. Moreover, not only the overall growth process was observed, analyzed, and quantified by an automatic program, but the grain evolution from a monolayer to a compact bilayer was also studied. This thesis provides detailed studies on the growth mechanism of WS2 and is a guide for the synthesis of any type of WS2. Once you get the first observable result in your system, no matter whether it is triangular or truncated monolayers, compact or concentric bilayers, flakes smaller than 10 µm or flakes larger than 200 µm, you can easily achieve successful synthesis by following the map in this thesis. Moreover, we developed a method for lithography without any photoresist, which is called “selective ion implantation.” The electronic structure of WS2 monolayers is manipulated through good control of defect type and defect density without any residues. We verified the achievement through optical measurements and further revealed the mechanism of their doping effect experimentally and theoretically. | en_US |