van der Waals substrate mediated heteroepitaxy of germanium and vanadium disulfide films

Authors
Littlejohn, Aaron James
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Other Contributors
Wang, G.-C. (Gwo-Ching), 1946-
Lu, T.-M. (Toh-Ming), 1943-
Yamaguchi, Masashi
Gall, Daniel
Issue Date
2018-05
Keywords
Physics
Degree
PhD
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This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
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Abstract
Atmospheric pressure chemical vapor deposition was employed for the synthesis of layered transition metal dichalcogenide vanadium disulfide. By tuning several key growth parameters, we achieved VS2 flakes with diameters over 100 μm, larger than those reported in the literature. In addition, ultrathin flakes with thicknesses of several atomic layers are achieved without the use of an exfoliation method as is typically required. X-ray diffraction and high-resolution transmission electron microscopy confirm the flakes’ monocrystalline quality. Raman spectra are collected which, for the first time, agree with the vibrational modes for the trigonal phase of VS2 as determined by density functional theory calculations. Through electron backscatter diffraction pole figure analysis, transmission electron microscopy and optical microscopy a complex epitaxial relationship with nine preferred in-plane orientations is observed in some regions of the VS2/mica samples. Remarkably, this is qualitatively in agreement with a superlattice area mismatch model, providing further evidence of the ability of electrostatic interactions to dictate the nucleation of film atoms in van der Waals heterostructures. Finally, magnetic force microscopy demonstrates room temperature ferromagnetic signal in ultrathin flakes in agreement with several density functional theory calculations. The discovery of an ultrathin ferromagnetic metal such as VS2 may have dramatic impact on emerging fields such as spintronics and quantum computing.
Description
May 2018
School of Science
Department
Dept. of Physics, Applied Physics, and Astronomy
Publisher
Rensselaer Polytechnic Institute, Troy, NY
Relationships
Rensselaer Theses and Dissertations Online Collection
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