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Wafer scale single-crystalline AB-stacked bilayer graphene

Nguyen, Van Luan (SKKU, Suwon, KOR); Lee, Young Hee (SKKU, Suwon, KOR)

While a lot of efforts on preparing large area AB-BLG using Cu or Cu-Ni alloy substrate via chemical vapor deposition method have been reported, the obtained BLG is polycrystalline with the grain size still limit in micrometer-scale and bilayer region is partially achieved because the catalytic activity of the Cu surface is suppressed by the presence of monolayer. Because of these critical difficulties, we introduce a new concept to form wafer-scale single-crystalline AB-BLG. Firstly, wafer-scale single-crystalline monolayer graphene (MLG) was prepared on single crystal Cu(111) film via seamless stitching concept that we have reported (Adv. Mater. 27, 1376-1382, (2015)). The Cu(111) film was grown on 2” sapphire via conventional RF-magnetron sputtering which requires a narrow growth temperature zone and the use of single crystal Cu(111) target. The obtained Cu(111) film is ultra-flat (RMS of 1.8 Å) and stacking-faultless, a key issue to synthesize single-crystalline MLG. This MLG is then aligned transfer onto another MLG, while second MLG remains on the initial Cu(111) film. This process allows exact alignment and polymer-free interface between two layers, resulting in wafer-scale single-crystalline AB-BLG that is electronically equivalent to exfoliated BLG. Evidence of AB-BLG is supported via transmission electron microscopy, angle-resolved photoemission spectroscopy, quantum Hall Effect and self-consistent effective mass characterization. Clear plateaus and quantum steps following fourfold degenerate steps with well-defined Landau filling factors. From 2D mapping of Hall resistance vs. magnetic field and gate voltage, we observed a clear Landau fan for AB-BLG, consistent with those from exfoliated samples. The wafer-scale single-crystalline of artificial AB-BLG is confirmed by low energy electron diffraction pattern and further demonstrated by integrating 380 dual-gate FET devices on a 2 x 2 cm2 wafer. 96.5% devices show AB-stacking behaviour and median carrier mobility of 2200(±200) cm2/Vs.

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