Title: Control and Synthesis of Moiré and Fully Commensurate Structures in van der Waals Heterostructures
When: Friday, June 28, 2024, 15:30
Place: Department of Condensed Matter Physics, Faculty of Sciences, Module 3, Seminar Room (5th Floor)
Speaker: Prof. Gwan-Hyoung Lee/Department of Materials Science and Engineering, Seoul National University. CEO / S-Graphene co., South Korea
The exploration of two-dimensional (2D) materials, particularly transition metal dichalcogenides (TMDs), has opened new avenues for advancing electronic device technologies beyond conventional silicon-based systems. Our recent research focuses on the fabrication and characterization of van der Waals (vdW) heterostructures, highlighting significant progress in the atomic reconstruction of TMD layers and the elucidation of their intrinsic ferroelectric properties. We demonstrate a novel process whereby strong interlayer interactions within TMD layers induce an atomic reconstruction from a twisted heterostructure into a fully commensurate (FC) phase by hexagonal boron nitride (hBN)-encapsulation annealing. This transformation enables the fabrication of perfectly aligned, zero-twisted stacked bilayers. The resultant FC structures exhibit pronounced ferroelectric properties, including a high Curie temperature and an abrupt polarization transition. Simultaneously, we address the challenges associated with the synthesis and scalability of high-quality TMDs by introducing the hypotaxial growth method. This technique facilitates the wafer-scale synthesis of single-crystal TMD films on amorphous or lattice-mismatched substrates, preserving interlayer crystalline alignment with an overlying 2D template. Through the strategic sulfurization of a pre-deposited Mo film covered by graphene, we achieve controlled growth of TMDs through nanopores in the graphene, resulting in a continuous wafer-scale crystalline film and the simultaneous removal of the top graphene layer. This process allows for the precise control of TMD thickness on a variety of substrates and enables the growth of large-scale single-crystal TMDs with exceptional thermal conductivity and carrier mobility. Our findings not only shed light on the atomic-scale mechanisms governing the ferroelectric behavior of TMD vdW heterostructures but also introduce a scalable approach for the fabrication of high-quality, single-crystal TMDs on arbitrary substrates.
