Construction of moke microscope for magnetic studies of vanadium disulfide flakes

Valdman, Lukas
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Wang, G.-C. (Gwo-Ching), 1946-
Shi, Jian
Ullal, Chaitanya
Sundararaman, Ravishankar
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Materials engineering
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Vanadium disulfide (VS2) is a transition metal dichalcogenide predicted by density functional theory to possess magnetic behaviour at room temperature. The intrinsic magnetic ordering is thickness dependent, when the ultrathin VS2 is ferromagnetic and the bulk VS2 is paramagnetic. The ultrathin H-phase VS2 is a direct band gap semiconductor, making it a potential candidate in the field of spintronics. The second part of this thesis describes the synthesis and characterization of vanadium disulfide ultrathin flakes. Chemical vapor deposition-based growth recipe was developed producing ultrathin flakes with aspect ratio in the range of ~ 6×10^3, one of the largest reported in the literature. The thinnest flakes were two single layers thick and less than 2 μm large, as detected with atomic force microscopy. The (001) out-of- plane orientation was confirmed by X-ray diffraction. The chemical composition of our samples was investigated by energy dispersive spectroscopy and the V to S ratio was determined to be 1.28 to 2, indicating a vanadium rich phase. Finally, the MOKE microscope was employed to study the predicted room temperature ferromagnetism. While the microscope was able to locate particular VS2 ultrathin flakes, overcoming the major bottleneck of previous magnetic studies, no hysteresis loops were recorded. This may be caused by the incorrect stoichiometry, inability to grow large coverage of one to few monolayers thick VS2 and atmosphere contamination.
August 2020
School of Engineering
Dept. of Materials Science and Engineering
Rensselaer Polytechnic Institute, Troy, NY
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