Wafer-scale single-crystalline graphene monolayers are highly sought after as an ideal platform for electronic and other applications. At present, state-of-the-art growth methods based on chemical vapour deposition allow the synthesis of one-centimetre-sized single-crystalline graphene domains in ∼12 h, by suppressing nucleation events on the growth substrate. Here we demonstrate an efficient strategy for achieving large-area single-crystalline graphene by letting a single nucleus evolve into a monolayer at a fast rate. By locally feeding carbon precursors to a desired position of a substrate composed of an optimized Cu-Ni alloy, we synthesized an ∼1.5-inch-large graphene monolayer in 2.5 h. Localized feeding induces the formation of a single nucleus on the entire substrate, and the optimized alloy activates an isothermal segregation mechanism that greatly expedites the growth rate. This approach may also prove effective for the synthesis of wafer-scale single-crystalline monolayers of other two-dimensional materials.

Seamless stitching of graphene domains on polished copper (111) is proved clearly not only at atomic scale by scanning tunnelling microscopy (STM) and transmission electron micoscopy (TEM), but also at the macroscale by optical microscopy after UV-treatment. Using this concept of seamless stitching, synthesis of 6 cm × 3 cm monocrystalline graphene without grain boundaries on polished copper (111) foil is possible, which is only limited by the chamber size.

Hexagonal boron nitride (h-BN) has attracted significant attention because of its superior properties as well as its potential as an ideal dielectric layer for graphene-based devices. The h-BN films obtained via chemical vapour deposition in earlier reports are always polycrystalline with small grains because of high nucleation density on substrates. Here we report the successful synthesis of large single-crystal h-BN grains on rational designed Cu-Ni alloy foils. It is found that the nucleation density can be greatly reduced to 60 per mm 2 by optimizing Ni ratio in substrates. The strategy enables the growth of single-crystal h-BN grains up to 7,500 mm 2 , approximately two orders larger than that in previous reports. This work not only provides valuable information for understanding h-BN nucleation and growth mechanisms, but also gives an effective alternative to exfoliated h-BN as a high-quality dielectric layer for large-scale nanoelectronic applications.

Ground-state structures of supported C clusters, C(N) (N = 16, ..., 26), on four selected transition metal surfaces [Rh(111), Ru(0001), Ni(111), and Cu(111)] are systematically explored by ab initio calculations. It is found that the core-shell structured C(21), which is a fraction of C(60) possessing three isolated pentagons and C(3v) symmetry, is a very stable magic cluster on all these metal surfaces. Comparison with experimental scanning tunneling microscopy images, dI/dV curves, and cluster heights proves that C(21) is the experimentally observed dominating C precursor in graphene chemical vapor deposition (CVD) growth. The exceptional stability of the C(21) cluster is attributed to its high symmetry, core-shell geometry, and strong binding between edge C atoms and the metal surfaces. Besides, the high barrier of two C(21) clusters' dimerization explains its temperature-dependent behavior in graphene CVD growth.

b S Supporting Information N owadays, graphene is a superstar material in many fields including material science, physics, chemistry, electronics, and biology. 1À3 In addition to the high Young's modulus, strength and thermal conductivity that are comparable to those of carbon nanotubes (CNTs), 4À6 it possess a largely extended two-dimensional (2D) area and distinctive electronic properties. 7,8 Its superior mechanical, thermal, electronic, optical, and chemical properties ensure numerous applications in composites, renewable energy generation and storage, chemical sensors, catalysts, etc. In particular, graphene is believed to be the most promising candidate for replacing silicon in future electronic applications. 9À11

Thin film field‐effect phototransistors (FETs) can be developed from bandgap‐tunable, solution‐processed, few‐layer reduced graphene oxide (FRGO) films. Large‐area FRGO films with tunable bandgaps ranging from 2.2 eV to 0.5 eV can be achieved readily by solution‐processing technique such as spin‐coating. The electronic and optoelectronic properties of FRGO FETs are found to be closely related to their bandgap energy. The resulting phototransistor has great application potential in the field of photodetection.

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Paired, single-atom catalysts have been shown to demonstrate synergistic effects computationally and experimentally which enable them to outperform the benchmark catalyst, Pt/C, for electrochemical reactions. We explore the limit of these catalysts by screening different transition metal atoms (M = Co, Pt, Fe, Ni) in nitrogen-doped graphene for their ability to catalyze the oxygen reduction reaction (ORR). We employ density functional theory methods to explore the electronic factors affecting catalytic activity in an effort to rationalize trends in the performance of materials which are promising candidates for the next generation of electrocatalysts. It is found that CoPt@N8V4, composed of paired Co and Pt in a nitrogen-doped four-atom vacancy in graphene (N8V4), performs ideally for the ORR with an overpotential (η) of 0.30 V, followed closely by Co and Ni (η = 0.35 V) and paired Co (η = 0.37 V). The origin of activity is suggested to be the changing reduction potential of the active Co atom via the local distortion of the pore by the spectating metal partner. We utilize the ORR scaling relations and plot catalytic activity on a volcano plot, which we correlate with the degree of antibonding interactions with the O atom in the OH intermediate of the ORR. We establish that the local tuning of paired catalysts allows for the reactivity of metal atoms to be specifically modified for desirable reactivity.