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A family of materials similar to graphene are transition metal dichalcogenides (TMDs) which have emerged as an improved alternative. Importantly, each combination of TMD is unique, possessing different properties. Chemical vapor deposition (CVD) has become a popular method to grow TMDs at large scale and in reproducible fashion. Molybdenum disulfide (MoS2) has been intensely studied at the monolayer due the creation of an indirect band gap but little has been done to investigate few layered structures and as the number of layers change, so do the properties. In this work, CVD is utilized to grow uniform bilayer and trilayer MoS2 triangular islands and compare few layer islands to their monolayer counterpart. Another TMD, tungsten disulfide (WS2), also has an indirect band gap at the monolayer. The combination of different two-dimensional (2D) materials has become a new way to achieve different structures with tunable properties. Stacking of 2D materials using van der Waals interactions has already created a pathway to an almost limitless number of combinations. A common combination is graphene and boron nitride because boron nitride has the same structure as graphene and creates an insulated layer with very little charge trapping and surface defects. As a starting point for 2D heterostructures, graphene on top of boron nitride was investigated and found to indeed reduce charge trappings creating a Dirac point closer to zero than other dielectric substrates. With the previous work done using CVD to grow TMDs it was also thought possible to grow MoS2 on boron nitride to improve the quality and reduce charge trappings from the substrate. The quality of the MoS2 became improved due to similar lattice structures leading to epitaxial growth along the boron nitride. Finally, CVD combining the two TMDs studied above was used to create lateral heterostructures. The combination of these two materials creates a theoretically staggered band gap that could lead to controllable electronic or optical properties not yet explored due to the limitations of conventional stacked heterostructures.
Advisor: Alexander Sinitskii