Recently, hexagonal boron nitride (h-BN) has been shown to act as an ideal substrate to graphene by greatly improving the material transport properties thanks to its atomically flat surface, low interlayer electronic coupling and almost perfect reticular matching. Chemical vapour deposition (CVD) is presently considered the most scalable approach to grow graphene directly on h-BN. However, for the catalyst-free approach, poor control over the shape and crystallinity of the graphene grains and low growth rates are typically reported. In this work we investigate the crystallinity of differently shaped grains and identify a path towards a real van der Waals epitaxy of graphene on h-BN by adopting a catalyst-free CVD process. We demonstrate the polycrystalline nature of circular-shaped pads and attribute the stemming of different oriented grains to airborne contamination of the h-BN flakes. We show that single-crystal grains with six-fold symmetry can be obtained by adopting high hydrogen partial pressures during growth. Notably, growth rates as high as 100 nm/min are obtained by optimizing growth temperature and pressure. The possibility of synthesizing single-crystal graphene on h-BN with appreciable growth rates by adopting a simple CVD approach is a step towards an increased accessibility of this promising van der Waals heterostructure.
High mobility dry-transferred CVD bilayer graphene
我们报道了高质量化学气相沉积（CVD）双层石墨烯（BLG）的制备和表征。特别是，我们表明，CVD生长的BLG可以机械地从铜箔分离的六方氮化硼（hBN）晶体后，铜BLG接口的氧化。共焦拉曼光谱揭示了AB-堆叠顺序的BLG晶体和高的结构质量。从对完全封装的hBN/BLG/hBN霍尔棒器件的传输测量中，我们提取了在2 K下高达180，000 cm $^2$ /（Vs）和在300 K下高达40，000 cm $^2$ /（Vs）的电荷载流子迁移率，优于最先进的CVD双层石墨烯器件。此外，我们显示了一个开关比超过10,000和带隙开口的值高达15毫电子伏的位移场为0.2 V/nm，在这样的CVD生长的BLG。
Structures of iron and cobalt bimetallic clusters for optimized chemical vapor deposition growth of single-walled carbon nanotubes
The University of Tokyo（东京大学）；Center for Multidimensional Carbon Materials (CMCM), Institute for Basic Science (IBS)（基础科学研究院多维碳材料中心）；Dalian University of Technology（大连理工大学）；University of Antwerp（安特卫普大学）
High-quality electrical transport using scalable CVD graphene
在晶圆厂兼容的规模上生产和操纵石墨烯，同时保持其出色的载流子迁移率，是最终确定其技术应用的关键。我们表明，一个大规模的方法（化学气相沉积铜，然后由聚合物介导的半干转移）产生单层石墨烯晶体完全可比，在电子传输方面，微机械剥离的薄片。hBN用于封装石墨烯晶体$-$，而不参与它们从生长催化剂$-$的分离，并研究它们在场效应器件中的固有特性。在室温下，电子-声子耦合将迁移率设置为$\sim1.3 \times10^5$ cm $^2$ V $^{-1}$ s $^{-1}$在$\sim10^{11}$ cm $^{-2}$浓度下。在低温下，迁移率（$ > 6\times10^5$ cm $^2$ V $^{-1}$ s $^{-1}$ at $\sim10^{11}$ cm $^{-2}$）受到器件物理边缘的限制，并检测到电荷波动$ < 7\times10^9$ cm $^{-2}$。在垂直磁场下，我们观察到早期的朗道量子化（$B\sim50$ mT）和电子相关的签名，包括分数量子霍尔效应。
High-Yield Proximity-Induced Chemical Vapor Deposition of Graphene Over Millimeter-Sized Hexagonal Boron Nitride
我们提出了一种在六方氮化硼（h-BN）晶体上通过化学气相沉积石墨烯的无转移制备方法，该方法通过催化邻近效应，即通过Cu催化剂附近活化。我们证明了完全覆盖由单层石墨烯的半毫米大小的六方氮化硼晶体剥离在铜箔上生长之前。我们证明了铜催化剂的接近确保了高收率，生长速率估计在2μm/min至5μm/min之间。光学显微镜和电子显微镜以及共焦显微拉曼映射证实，石墨烯覆盖了h-BN晶体的顶表面，我们认为这是从支撑催化铜衬底的横向生长。原位生长的石墨烯的结构和电子输运表征呈现出约20，000 cm 2/（V.s）的电子迁移率。与通过将类似的CVD石墨烯手动转移到h-BN上获得的石墨烯/h-BN堆叠体的比较证实了自组装结构所达到的更好的中性。
