A decade of intense research on two-dimensional (2D) atomic crystals has revealed that their properties can differ greatly from those of the parent compound1,2. These differences are governed by changes in the band structure due to quantum confinement and are most profound if the underlying lattice symmetry changes3,4. Here we report a high-quality 2D electron gas in few-layer InSe encapsulated in hexagonal boron nitride under an inert atmosphere. Carrier mobilities are found to exceed 103 cm2 V−1 s−1 and 104 cm2 V−1 s−1 at room and liquid-helium temperatures, respectively, allowing the observation of the fully developed quantum Hall effect. The conduction electrons occupy a single 2D subband and have a small effective mass. Photoluminescence spectroscopy reveals that the bandgap increases by more than 0.5 eV with decreasing the thickness from bulk to bilayer InSe. The band-edge optical response vanishes in monolayer InSe, which is attributed to the monolayer's mirror-plane symmetry. Encapsulated 2D InSe expands the family of graphene-like semiconductors and, in terms of quality, is competitive with atomically thin dichalcogenides5,6,7 and black phosphorus8,9,10,11.
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This work was supported by the European Research Council, the Graphene Flagship, the Engineering and Physical Sciences Research Council (EPSRC, UK) and The Royal Society. D.A.B. and I.V.G. acknowledge support from the Marie Curie programme SPINOGRAPH (Spintronics in Graphene). A.M. acknowledges support of the EPSRC Early Career Fellowship EP/N007131/1. S.V.M. was supported by the NUST MISiS (grant K1-2015-046) and the Russian Foundation for Basic Research (RFBR15-02-01221 and RFBR14-02-00792). V.F. acknowledges support from the ERC Synergy Grant Hetero2D, the EPSRC grant EP/N010345/1 and the Lloyd Register Foundation Nanotechnology grant, and V.Z. from the European Graphene Flagship Project. Measurements in high magnetic field were supported by the High Field Magnet Laboratory–Radboud University/Foundation for Fundamental Research on Matter, member of the European Magnetic Field Laboratory, and by the EPSRC via its membership to the EMFL (grant EP/N01085X/1). We thank M. Mohammed for assisting with UV PL measurements.
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Facile synthesis of thin black TiO2 − x nanosheets with enhanced lithium-storage capacity and visible light photocatalytic hydrogen production
Journal of Solid State Electrochemistry (2019)