A WSe2 -based vertical graphene-transition metal dichalcogenide heterojunction barristor shows an unprecedented on-current increase with decreasing temperature and an extremely high on/off-current ratio of 5 × 10(7) at 180 K (3 × 10(4) at room temperature). These features originate from a trap-assisted tunneling process involving WSe2 defect states aligned near the graphene Dirac point.

A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability.

We describe the successful in situ chemical vapor deposition synthesis of a graphene-based heterostructure in which a graphene monolayer is protected by top and bottom boron nitride films. The boron nitride film/graphene monolayer/boron nitride film (BGB) was found to be a mechanically robust and chemically inert heterostructure, from which the deleterious effects of mechanical transfer processes and unwanted chemical doping under air exposure were eliminated. The chemical compositions of each film layer were monitored ex situ using UV-visible absorption spectroscopy and X-ray photoelectron spectroscopy, and the crystalline structures were confirmed using transmission electron microscopy and selected-area electron diffraction measurements. The performance of the devices fabricated using the BGB film was monitored over six months and did not display large changes in the mobility or the Dirac point, unlike the conventional graphene devices prepared on a SiO2 substrate. The in situ-grown BGB film properties suggest a novel approach to the fabrication of commercial-grade graphene-based electronic devices.

We report the selective growth of large-area bilayered graphene film and multilayered graphene film on copper. This growth was achieved by introducing a reciprocal chemical vapor deposition (CVD) process that took advantage of an intermediate h-BN layer as a sacrificial template for graphene growth. A thin h-BN film, initially grown on the copper substrate using CVD methods, was locally etched away during the subsequent graphene growth under residual H2 and CH4 gas flows. Etching of the h-BN layer formed a channel that permitted the growth of additional graphene adlayers below the existing graphene layer. Bilayered graphene typically covers an entire Cu foil with domain sizes of 10-50 μm, whereas multilayered graphene can be epitaxially grown to form islands a few hundreds of microns in size. This new mechanism, in which graphene growth proceeded simultaneously with h-BN etching, suggests a potential approach to control graphene layers for engineering the band structures of large-area graphene for electronic device applications.