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Heterostructure engineering in 2D van der Waals Materials: Unveiling magnetism and strain effects

thesis
posted on 2023-12-09, 22:18 authored by Andres E Llacsahuanga AllccaAndres E Llacsahuanga Allcca

Since the discovery of graphene in 2004, numerous other materials with intriguing electronic, optical, and magnetic properties have been found to be layered and exfoliatable down to atomic thickness. Owing to their weak interlayer coupling, mediated only by van der Waals forces, this new class of 2-dimensional materials, also known as van der Waals (vdW) materials, allows layer-by-layer stacking, overcoming some of the limitations of growth techniques. In particular, the growing inventory of vdW materials has expanded to include magnetic materials, further broadening the possibilities of novel devices based on stacked heterostructures. These magnetic heterostructures can find applications in spintronics and memory devices and may be combined with other vdW materials with optical properties for applications in optoelectronics. In this thesis, we assembled heterostructures via mechanical transfer or growth to modify the magnetism in these vdW materials. We used various optical and electrical techniques to probe the modified magnetism or its effects on the novel heterostructure. Thus, we observed the emergence of the magnetic proximity effect on the topological insulator BiSbTeSe2 after dry transferring a thin flake of Cr2Ge2Te6 on top, taking steps towards the observation of novel topological phases, such as the quantum Hall insulator. Additionally, we demonstrated an increased Curie temperature and magnetic anisotropy, effectively enhancing the magnetism, in thin flakes of Cr2Ge2Te6 and Cr2Si2Te6 after sputtering NiO or MgO. Finally, noting that the effect of modified magnetism in Cr2Ge2Te6 after sputtering NiO or MgO is induced due to wrinkle formation and strain, we further reproduce similar wrinkle formation on other 2D materials such as hBN, graphite, and 2D antiferromagnets (XPS3, (X= Mn, Fe, Ni), CrSBr, RuCl3). We used polarized Raman spectroscopy to characterize the induced biaxial strain in hBN and showed that such wrinkle formation can lead to moderately (up to 1.4% strain) spatially inhomogeneous and anisotropic strain profiles. These efforts demonstrate the versatility of tailoring the properties of these vdW materials.

History

Degree Type

  • Doctor of Philosophy

Department

  • Physics and Astronomy

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Yong P. Chen

Additional Committee Member 2

Leonid Rokhinson

Additional Committee Member 3

Tongcang Li

Additional Committee Member 4

Luis M. Kruczenski