Large-area graphene films are best synthesized via chemical vapour and/or solid deposition methods at elevated temperatures (~1,000 °C) on polycrystalline metal surfaces and later transferred onto other substrates for device applications. Here we report a new method for the synthesis of graphene films directly on sio 2 /si substrates, even plastics and glass at close to room temperature (25-160 °C). In contrast to other approaches, where graphene is deposited on top of a metal substrate, our method invokes diffusion of carbon through a diffusion couple made up of carbon-nickel/substrate to form graphene underneath the nickel film at the nickelsubstrate interface. The resulting graphene layers exhibit tunable structural and optoelectronic properties by nickel grain boundary engineering and show micrometre-sized grains on sio 2 surfaces and nanometre-sized grains on plastic and glass surfaces. The ability to synthesize graphene directly on non-conducting substrates at low temperatures opens up new possibilities for the fabrication of multiple nanoelectronic devices.

Crystalline TiO2 powders were prepared by the homogeneous precipitation method simply by heating and stirring an aqueous TiOCl2 solution with a Ti4+ concentration of 0.5M at room temperature to 100°C under a pressure of 1 atm. TiO2 precipitates with pure rutile phase having spherical shapes 200‐400 nm in diameter formed between room temperature and 65°C, whereas TiO2 precipitates with anatase phase started to form at temperatures >65°C. Precipitates with pure anatase phase having irregular shapes 2‐5 µm in size formed at 100°C. Possibly because of the crystallization of an unstable intermediate product, TiO(OH)2, to TiO2xH2O during precipitation, crystalline and ultrafine TiO2 precipitates were formed in aqueous TiOCl2 solution without hydrolyzing directly to Ti(OH)4. Also, formation of a stable TiO2 rutile phase between room temperature and 65°C was likely to occur slowly under these conditions, although TiO2 with rutile phase formed thermodynamically at higher temperatures.

The Poisson's ratio is a fundamental measure of the elastic-deformation behaviour of materials. Although negative Poisson's ratios are theoretically possible, they were believed to be rare in nature. In particular, while some studies have focused on finding or producing materials with a negative Poisson's ratio in bulk form, there has been no such study for nanoscale materials. Here we provide numerical and theoretical evidence that negative Poisson's ratios are found in several nanoscale metal plates under finite strains. Furthermore, under the same conditions of crystal orientation and loading direction, materials with a positive Poisson's ratio in bulk form can display a negative Poisson's ratio when the material's thickness approaches the nanometer scale. We show that this behaviour originates from a unique surface effect that induces a finite compressive stress inside the nanoplates, and from a phase transformation that causes the Poisson's ratio to depend strongly on the amount of stretch.

The development of ultrathin barrier films is vital to the advanced semiconductor industry. Graphene appears to hold promise as a protective coating; however, the polycrystalline and defective nature of engineered graphene hinders its practical applications. Here, we investigate the oxidation behavior of graphene-coated Cu foils at intrinsic graphene defects of different origins. Macro-scale information regarding the spatial distribution and oxidation resistance of various graphene defects is readily obtained using optical and electron microscopies after the hot-plate annealing. The controlled oxidation experiments reveal that the degree of structural deficiency is strongly dependent on the origins of the structural defects, the crystallographic orientations of the underlying Cu grains, the growth conditions of graphene, and the kinetics of the graphene growth. The obtained experimental and theoretical results show that oxygen radicals, decomposed from water molecules in ambient air, are effectively inverted at Stone–Wales defects into the graphene/Cu interface with the assistance of facilitators.

Control of a two-dimensional (2D) structure of assembled graphene oxide (GO) sheets is highly desirable for fundamental research and potential applications of graphene devices. We show that an alkylamine surfactant, i.e., octadecylamine (ODA), Langmuir monolayer can be utilized as a template for adsorbing highly hydrophilic GO sheets in an aqueous subphase at the liquid-gas interface. The densely packed 2-D monolayer of such complex films was obtained on arbitrary substrates by applying Langmuir-Schaefer or Langmuir-Blodgett technique. Morphology control of GO sheets was also achieved upon compression by tuning the amount of spread ODA molecules. We found that ODA surfactant monolayers prevent GO sheets from sliding, resulting in formation of wrinkling rather than overlapping at the liquid-gas interface during the compression. The morphology structures did not change after a graphitization procedure of chemical hydrazine reduction and thermal annealing treatments. Since morphologies of graphene films are closely correlated to the performance of graphene-based materials, the technique employed in this study can provide a route for applications requiring wrinkled graphenes, ranging from nanoelectronic devices to energy storage materials, such as supercapacitors and fuel cell electrodes.