Korea Research Institute of Standards and Science , Daejeon 34113, Korea.
Center for Theoretical Physics of Complex Systems, Institute for Basic Science , Daejeon 34051, Korea.
Nano Lett. 2017 Jan 11;17(1):206-213. doi: 10.1021/acs.nanolett.6b03821. Epub 2016 Dec 27.
The chemical and mechanical stability of hexagonal boron nitride (h-BN) thin films and their compatibility with other free-standing two-dimensional (2D) crystals to form van der Waals heterostructures make the h-BN-2D tunnel junction an intriguing experimental platform not only for the engineering of specific device functionalities but also for the promotion of quantum measurement capabilities. Here, we exploit the h-BN-graphene tunnel junction to directly probe the electronic structures of single-layer and bilayer graphene in the presence and the absence of external magnetic fields with unprecedented high signal-to-noise ratios. At a zero magnetic field, we identify the tunneling spectra related to the charge neutrality point and the opening of the electric-field-induced bilayer energy gap. In the quantum Hall regime, the quantization of 2D electron gas into Landau levels (LL) is seen as early as 0.2 T, and as many as 30 well-separated LL tunneling conductance oscillations are observed for both electron- and hole-doped regions. Our device simulations successfully reproduce the experimental observations. Additionally, we extract the relative permittivity of three-to-five layer h-BN and find that the screening capability of thin h-BN films is as much as 60% weaker than bulk h-BN.
六方氮化硼（h-BN）薄膜具有化学和机械稳定性，并且与其他独立二维（2D）晶体兼容，可形成范德华异质结，这使得 h-BN-2D 隧道结成为一个有趣的实验平台，不仅可用于设计特定的器件功能，还可提高量子测量能力。在这里，我们利用 h-BN-石墨烯隧道结，在存在和不存在外部磁场的情况下，以空前的高信噪比直接探测单层和双层石墨烯的电子结构。在零磁场下，我们确定了与电荷中性点和电场诱导双层能隙打开相关的隧道谱。在量子霍尔区，二维电子气最早在 0.2 T 时量子化到 Landau 能级（LL），并且在电子和空穴掺杂区都观察到多达 30 个分离良好的 LL 隧道电导振荡。我们的器件模拟成功再现了实验观测结果。此外，我们还提取了三到五层 h-BN 的相对介电常数，并发现薄膜 h-BN 的屏蔽能力比体相 h-BN 弱 60%。
