Carbon nanostructures have emerged as likely candidates for a wide range of applications, driving research into novel synthetic techniques to produce nanotubes, graphene and other carbon-based materials. Single sheets of pristine graphene have been isolated from bulk graphite in small amounts by micromechanical cleavage, and larger amounts of chemically modified graphene sheets have been produced by a number of approaches. Both of these techniques make use of highly oriented pyrolitic graphite as a starting material and involve labour-intensive preparations. Here, we report the direct chemical synthesis of carbon nanosheets in gram-scale quantities in a bottom-up approach based on the common laboratory reagents ethanol and sodium, which are reacted to give an intermediate solid that is then pyrolized, yielding a fused array of graphene sheets that are dispersed by mild sonication. The ability to produce bulk graphene samples from non-graphitic precursors with a scalable, low-cost approach should take us a step closer to real-world applications of graphene.

No abstract

No abstract

No abstract

It has been shown that graphene doping is sufficient to lead to an improvement in the critical current density -field performance (J c (B)), with little change in the transition temperature in MgB 2 . At 3.7 at% graphene doping of MgB 2 an optimal enhancement in J c (B) was reached by a factor of 30 at 5 K and 10 T, compared to the un-doped sample.The results suggested that effective carbon substitutions by grapheme, 2D nature of grapheme and the strain effect induced by difference thermal coefficient between single grapheme sheet and MgB 2 superconductor may play an important role in flux pinning enhancement.Correspondence and requests for materials should be addressed to S. X. Dou (shi_dou@uow.edu.au) . 2 Substitutional chemistry can modify, in a controlled way, the electronic structures of superconductors and their superconducting properties, such as the transition temperature (T c ), critical current density (J c ), upper critical field (H c2 ), and irreversibility field (H irr ). In particular, carbon containing dopants, including nano-meter sized carbon (nano-C), silicon carbide (SiC), carbon nanotubes (CNTs), hydrocarbons/carbohydrates, and graphite are effective means to enhance the J c -field dependence and H c2 1-11 . In this work, it will be seen the graphene as one kind of caborn source dopant, how it is useful to incorporation into MgB 2 and it is expected that H c2 and the flux pinning properties should be improved.However, until now there has been no report on the effects of graphene doping on the superconductivity of MgB 2 , partly due to the unavailability of graphene on a suitable scale. Recently, high-throughput solution processing of large-scale graphene has been reported by a number of groups 12-17 . Based on the works of Choucair et al. 18 , sufficient quantities of graphene were obtained for doping the bulk MgB 2 samples via a diffusion process. The crystalline Boron powder (0.2 to 2.4 µm) 99.999%without and with graphene 18 was prepared by ball milling with toluene medium. Then the powders were dried in a vacuum oven to evaporate the medium. These powders were mixed and pressed into pellets.The pellets were then put into an iron tube filled with Mg powder (-325mesh 99%). The samples were sintered at 850°C for 10 hrs in a quartz tube; the heating rate was 5 o Cmin -1 under high purity argon (Ar 99.9%) gas. The phase and crystal structure of all the samples were investigated by X-ray diffraction (XRD). T c was defined as the onset temperature at which diamagnetic properties were observed. The magnetic J c was derived from the width of the magnetization loop using Bean's model by a Physical Properties Measurement System (PPMS). Transport measurements for resistivity (ρ) were done using a standard AC four probe method. In addition, H c2 (T) and H irr (T) were defined as the fields where the temperature dependent resistance at constant magnetic field R(H c2 , T) = 0.9R ns and R(H irr , T) = 0.1R ns with R ns being the normal state resistance near 40 K.The common format Mg(B 1-x C x ), x=0, 0.03...