The family of 2D van der Waals (vdW) layered materials has attracted immense interest because of continuous discoveries of unique and intriguing physical phenomena in new members and stacked heterostructures. [1][2][3] However, a few issues regarding scalability and integration have to be resolved prior to practical applications. Among them is control of the crystal orientation of 2D vdW films, which is still elusive. One immediate benefit of single-orientation growth is the elimination of The ability to control the crystal orientation of 2D van der Waals (vdW) layered materials grown on large-scale substrates is crucial for tailoring their electrical properties, as well as for integration of functional 2D devices. In general, multiple orientations, i.e., two or four orientations, appear through the crystal rotational symmetry matching between the material and its substrate. (1 0 1) surface. Moreover, thanks to the high interfacial strength with the underlying Cu, the single-orientation h-BN is free of thermal wrinkles, and exhibits a spatially homogeneous morphology and tunnel conductance. The findings point to a feasible approach to direct growth of singleorientation, wrinkle-free h-BN thin film for high-performance 2D electrical devices, and will be of benefit for controllable synthesis of other vdW materials. Here, it is reported that hexagonal boron nitride (h-BN), an ideal electric barrier in the family of 2D materials, has a single orientation on inclined Cu (1 0 1) surfaces, where the Cu planes are tilted from the (1 0 1) facet around specific in-plane axes. Density functional theory (DFT) calculation indicates that this is a manifestation of only one favored h-BN orientation with the minimum vdW energy on the inclined Cu

We show millimeter-scale graphene single crystals synthesized on commercial Cu foils by the atmospheric pressure chemical vapor deposition (CVD) method, which does not involve the routine use of a specially designed CVD reactor or long-term processes. Upon the designed annealing step in the Ar environment, the natural oxide layer covering on Cu catalysts is to a large extent maintained and is further used to protect the surface passivation and restrict the graphene nucleation. Moreover, for Cu foils placing on certain solid supports, we found that the graphene deposition is highly related to the environments proximate to each surface (referred to as open or confined space, respectively). For instance, the domain size of as-grown graphene is larger (smaller), while the nucleation density is higher (lower) on the back (top) surface. The possible mechanism to interpret the discrepancy on either side is discussed in the frame of the graphene nucleation and growth kinetics. At the nucleation stage, the thermal decomposition of the oxide layer leads to oxygen (O) desorption at high temperature on the open side and dominates the temperature dependence of nucleation density. On the confined side, the O desorption is suppressed due to the collision rebound effect, but highly concentrated active carbon species will be trapped in the vicinity of the back surface, which may promote the threshold of nucleation on the O-containing Cu surface. The following growth of graphene islands is edge-attachment limited on both sides of the Cu foil but with different enlargement rates. The roughness of support substrates also affects the deposition of graphene. With an optimized annealing condition and a polished quartz support, ∼3 mm isolated graphene islands with an average growth rate of ∼25 μm/min were obtained. The as-grown hexagonal domains were further confirmed to be uniform, monolayer, single-crystalline graphene with a field-effect mobility of ∼4900 cm2 V–1 s–1 at room temperature.

A heating treatment is often used in graphene research to remove adsorbates and resist materials from graphene. Heating graphene followed by air exposure is also known to result in heavy hole doping in graphene, although the role of heating has been unclear. Here, we demonstrate that a practical graphene sample fabricated using the commonly used growth and transfer techniques is unstable against heating in a high vacuum. Structural disorder likely due to defect formation is induced by heating, and the disorder is accompanied by hole doping. Our analysis shows that the main cause of the defect formation is graphene reacting with O2 and H2O molecules inserted between graphene and the substrate. The hole doping caused by air exposure after heating is explained by gas adsorption at the defect sites.

Three-dimensional (3D) graphene architectures are of great interest as applications in flexible electronics and biointerfaces. In this study, we demonstrate the facile formation of predetermined 3D polymeric microstructures simply by transferring monolayer graphene. The graphene adheres to the surface of polymeric films via noncovalent π−π stacking bonding and induces a sloped internal strain, leading to the self-rolling of 3D microscale architectures. Micropatterns and varied thicknesses of the 2D films prior to the self-rolling allows for control over the resulting 3D geometries. The strain then present on the hexagonal unit cell of the graphene produces a nonlinear electrical conductivity across the device. The driving force behind the self-folding process arises from the reconfiguration of the molecules within the crystalline materials. We believe that this effective and versatile way of realizing a 3D graphene structure is potentially applicable to alternative 2D layered materials as well as other flexible polymeric templates.

The doping and scattering effect of substrate on the electronic properties of chemical vapor deposition (CVD)-grown graphene are revealed. Wet etching the underlying SiO2 of graphene and depositing self-assembled monolayers (SAMs) of organosilane between graphene and SiO2 are used to modify various substrates for CVD graphene transistors. Comparing with the bare SiO2 substrate, the carrier mobility of CVD graphene on modified substrate is enhanced by almost 5-fold; consistently the residual carrier concentration is reduced down to 1011 cm−2. Moreover, scalable and reliable p- and n-type graphene and graphene p-n junction are achieved on various silane SAMs with different functional groups.