We have studied the influence of the surface roughness of copper foils on the sheet resistance of graphene sheets grown by chemical vapor deposition. The surface roughness of the copper foils was reproducibly controlled by electropolishing. We have found that the graphene sheet resistance monotonically decreases as the surface roughness of the copper foils decreases. We show that a pre-annealing treatment combined with an optimized electropolishing process of the Cu foils and a fast CVD growth prevents the evolution of the Cu surface roughness during graphene synthesis. This combination of fabrication conditions produces small grain polycrystalline graphene films with a sheet resistance of 210 Ω □(-1) and carrier mobility values as high as 5450 cm(2) V(-1) s(-1) after transfer onto SiO2/Si.

We present a detailed study on graphene-coated aluminum thin films for Li-ion battery anode applications. The best electrode ageing behavior is obtained for Al films encapsulated with four porous graphene layers. Graphene encapsulation prevents "crushed" Al nanoparticles from detaching from the anode, thus allowing prolonged charge-discharge cycling. Graphene also provides surface conduction paths for electrons as well as diffusion paths for Li atoms. For the first time, we report the electrochemical room temperature formation of phases such as LiAl and even LiAl, with a higher Li content than β-LiAl. More interestingly, we observe a progressive change of the composite thin film electrode, switching from a pure galvanic to a pseudocapacitive behavior as the size of the Al grains decreases from ∼100 to 5-10 nm due to repeated Li alloying-dealloying. The capacity values of ∼900 and 780 mAh/g are obtained after, respectively, 500 and 1000 charge-discharge cycles at 0.1C. Our results may refocus the interest of the battery community on Al-based thin film anodes, since they are potentially very simple to fabricate, particularly if porous graphene is replaced in the future by reduced graphite oxide.

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The successful mechanical exfoliation and chemical synthesis of graphene has attracted considerable attention for the synthesis of other twodimensional materials on graphene template. Chalcogenide materials such as Sb 2 Te 3 are of interest due to the rhombohedral lattice structure with twodimensional hexagonally closed-packed atomic layers along the c-axis. Here we synthesized c-axis-oriented Sb 2 Te 3 nanoplates (NPs) on graphene substrates by the microwave-assisted solvothermal method. The microwave irradiation resulted in a higher temperature of graphene, compared with the synthesis solution, which was revealed by the single-mode microwave experiments and an analytical model based on energy balance and convective heat transfer. Besides, the lattice mismatch between c-axis-oriented Sb 2 Te 3 and bridge sites of graphene was only 4%, which is also favorable for the graphene-templated Sb 2 Te 3 synthesis. c-Axis-oriented single-crystalline Sb 2 Te 3 NPs as large as 7 μm could be successfully synthesized on graphene with negligible damage of the graphene template. Larger surface coverage could be obtained by merging Sb 2 Te 3 NPs. The merged Sb 2 Te 3 NPs were polycrystalline with rotated grain boundaries. This work provides a facile, rapid, and low-cost synthesis route of c-axis-oriented Sb 2 Te 3 NPs on graphene templates, which may be extended for the synthesis of various two-dimensional materials with hexagonally closed-packed atomic layers along the c-axis. ■ INTRODUCTIONThe successful mechanical exfoliation and chemical synthesis of graphene, single atomic layer of sp 2 -hybridized carbon atoms, has initiated tremendous research activities in two-dimensional (2D) materials. 1,2 The layered materials such as boron nitrides, transition-metal dichalcogenides, and chalcogenides exhibited unique mechanical, electrical, and optical properties. 3,4 Among them, chalcogenide materials (Bi 2 Te 3 , Sb 2 Te 3 , Bi 2 Se 3 , etc.) have attracted considerable attention as near room temperature thermoelectric materials and topological insulators comprising only one Dirac cone. 5,6 High-quality chalcogenide thin films were typically synthesized by high-vacuum technologies such as molecular beam epitaxy (MBE), metal organic chemical vapor deposition, pulsed laser deposition, thermal evaporation, and sputtering. 7−18 Recently, chalcogenide thin films were also constructed on chemically inert graphene substrates using MBE as well as sputtering methods. 19−22 Especially, the simple sputtering method enabled the preferential c-axis orientation of Bi 2 Te 3 and Sb 2 Te 3 thin films on graphene templates possibly due to the hexagonal lattice structure, although the precise mechanism was not revealed. 19 Sb 2 Te 3 is a V 2 VI 3 pnictogen chalcogenide with a small band gap and belongs to the R3̅ m space group (rhombohedral structure) with 2D hexagonally closed-packed atomic layers along the c-axis. 23 One of the hurdles of these high-vacuum technologies is the scale-up synthesis at low cost. Besides, graphene was heavily damaged du...