Effects of controlled doping and defects on the physical properties of Group-VI transition metal dichalcogenides

Group-VI transition metal dichalcogenides (TMDCs) are promising atomically thin semiconductors for nanoelectronic and nanophotonic devices. Intrinsic defects in these materials are well known to have profound influence on the electronic and optical properties. We have successfully synthesized high quality group-VI TMDCs materials by using the chemical vapor transport (CVT) method and have characterized these TMDCs samples at both atomic and macroscopic scales. Raman spectroscopy revealed a linear dependence of thickness with the growth time. X-ray photoelectron spectroscopy revealed a metal/chalcogenides atom ratio to be (1/2) for all thicknesses. Combining the ultraviolet photoemission spectra and scanning tunneling spectra, we successfully constructed the band diagram of these TMDCs materials. Additionally, by introducing controlled concentrations of point-like defects via 2.5MeV electron irradiation, the effects of irradiation on various physical properties of TMDCs can be understood systematically. We performed Raman spectroscopic studies to examine the disorder effects on phonon modes, and magneto-opto Kerr effect (MOKE) measurements to understand point defect-induced magnetism in TMDCs.