Graphene, partially covered by h-BN protective layers, may displa

Graphene, partially covered by h-BN protective layers, may display promising electronic characteristics of graphene with much lower environmental sensitivity. Recently, chemical vapor deposition (CVD) synthesis of h-BN on Ni [14–16] or Cu [13, 17–19] substrates has been further investigated. For the following applications in graphene electronic devices, h-BN can be acquired by etching of the catalyst substrates and a transfer technique. Nevertheless, the transfer process brings

inevitable contamination or even destruction, and it is difficult to determine the position and the coverage ratio of h-BN on graphene. Considering this problem, we pay attention to the catalyst-free CVD growth of h-BN on graphene, which promises direct application in graphene electronic devices and may STA-9090 obviate the need for a transfer process. It has been AZD1480 chemical structure demonstrated that van der Waals epitaxy by catalyst-free CVD can be a promising route for the growth find more of topological heterostructures [20–22]. Moreover, the surface of graphene is atomically flat and without dangling bonds, which makes graphene a promising template for the van der Waals epitaxy of other two-dimensional

materials. Compounds with 1:1 B/N stoichiometry are often selected as h-BN precursors for CVD, and borazine (B3N3H6) could be a promising choice as it would produce BN and hydrogen, which are both environmentally friendly. In this research, the van der Waals epitaxy of h-BN nanosheets on mechanically exfoliated graphene by catalyst-free low-pressure CVD, using borazine as the precursor to h-BN, was demonstrated. The h-BN nanosheets preferred to grow on graphene rather

than on SiO2/Si and tended to exhibit a triangular morphology when grown on a narrow graphene belt. The h-BN nanosheets grown on graphene Montelukast Sodium were highly crystalline, albeit with various in-plane lattice orientations. Methods h-BN nanosheets were synthesized in a fused quartz tube with a diameter of 50 mm. Graphene was transferred onto silicon oxide/silicon (SiO2/Si) wafers by mechanical exfoliation from highly oriented pyrolytic graphite (HOPG, Alfa Asear, Ward Hill, MA, USA). The h-BN precursor (borazine) was synthesized by the reaction between NaBH4 and (NH4)2SO4 and purified according to our previous reports [23, 24]. The temperature for the CVD growth of h-BN nanosheets was set to 900°C. Before the growth of h-BN, with the tube heated to 900°C, graphene grown on SiO2/Si was first annealed for 60 min in an argon/hydrogen flow (Ar/H2, 5:1 by volume, both gases were of 99.999% purity from Pujiang Co., Ltd, Shanghai, China) of 180 sccm to remove pollutants remaining on the graphene after mechanical exfoliation. During the growth process, borazine, in a homemade bubbler, was introduced to the growth chamber by another Ar flow of 2 sccm, while the Ar/H2 flow remained unchanged. The typical growth time was 5 min, while the pressure was 10 to 100 Pa.

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