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Title: Wafer-scale single-crystalline AB-stacked bilayer graphene
Authors: Van Luan Nguyen, David J. Perello, Seunghun Lee, Chang Tai Nai, Bong Gyu Shin, Joong-Gyu Kim, Ho Yeol Park, Hu Young Jeong, Jiong Zhao, Quoc An Vu, Sang Hyub Lee, Kian Ping Loh, Se-Young Jeong, Young Hee Lee
Abstract: AB-stacked bilayer graphene (AB-BLG) is both a platform for developing fast switching devices and a promising high-mobility channel material for tunneling transistors. Numerous reports have attempted to synthesize AB-BLG directly on Cu or Ni-Cu alloy foils via chemical vapor deposition. However, grain size is still limited to micrometer scale, let alone controlling stacking order and uniform bilayer region. Here we report a wafer-scale formation of artificial single-crystalline AB-BLG via aligned transfer of two single-crystalline monolayers. The ultra-flat and faultless single-crystal Cu(111) film was prepared on 2 inch sapphire by magnetron sputter using a single-crystal Cu target, which allowed for high-quality layer-by-layer growth of Cu(111) film, a key step to synthesize wafer-scale single-crystalline monolayer graphene. The AB-stacking order is proven via angle-resolved photoemission spectroscopy, quantum Hall Effect (QHE), self-consistent effective mass characterization, and transmission electron microscopy. The artificial AB-BLG has no polymer residues, atomically sharp interface and electronically equivalent to exfoliated BLG. The alignment procedure is further utilized to fabricate twisted-BLG with near-AB misorientation ~1o. QHE and Shubnikov-de-Haas oscillations reveal significant Fermi velocity renormalization and indicate that individual layer properties are retained even in strong coupling regime6. Scalability and single-crystalline nature of the BLG films are confirmed by low energy electron diffraction pattern and further demonstrated by integrating 380 dual-gate field effect transistor devices on a 2×2 cm2 wafer. 96.5% devices show AB-stacking behavior, a displacement-field induced bandgap and median carrier mobility of 2200 (±200) cm2/Vs.