John A. Stride

Gram-scale production of graphene based on solvothermal synthesis and sonication

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.

Muons Probe Strong Hydrogen Interactions with Defective Graphene

Here, we present the first muon spectroscopy investigation of graphene, focused on chemically produced, gram-scale samples, appropriate to the large muon penetration depth. We have observed an evident muon spin precession, usually the fingerprint of magnetic order, but here demonstrated to originate from muon-hydrogen nuclear dipolar interactions. This is attributed to the formation of CHMu (analogous to CH(2)) groups, stable up to 1250 K where the signal still persists. The relatively large signal amplitude demonstrates an extraordinary hydrogen capture cross section of CH units. These results also rule out the formation of ferromagnetic or antiferromagnetic order in chemically synthesized graphene samples.

Graphene doping to enhance the flux pinning and supercurrent carrying ability of a magnesium diboride superconductor

The effect of graphene doping on the electromagnetic properties of MgB2 has been examined, in comparison with the case for undoped MgB2. It was found that graphene doping is more efficient than other forms of carbon doping for effecting improvement in the critical current density?field performance (Jc(B)), with little change in the transition temperature of MgB2. An?optimal enhancement of Jc(B) was achieved for 3.7?at.% graphene doped MgB2, by a factor of 30 at 5?K and 10?T, as compared to undoped MgB2. It is found that spatial fluctuation in Tc is responsible for the flux pinning mechanism of graphene doped MgB2.

Kesterite Cu2ZnSnS4 thin film solar cells by a facile DMF-based solution coating process

Kesterite Cu2ZnSnS4 (CZTS) thin films were fabricated using a low-cost and environmentally friendly route from a dimethylformamide (DMF) solution of a metal–thiourea complex. Thermal gravimetric analysis (TGA) has been performed to reveal the thermal decomposition behavior of the CZTS precursors for drying and sulfurization process design. A facile solution method of in situ introducing sodium dopant by adding NaOH into the precursor solution is presented. The sodium dopant improves the open circuit voltage (Voc) and fill factor (FF) and thereby enhances the power conversion efficiency from 4.47% to 5.68%. The enhanced performance is related to the increased grain size and increased minority carrier lifetime. A large number of large voids observed in the bulk absorber and at the absorber/back contact interface are considered to be the main reason for the low short circuit current density (Jsc).

Exchange interactions in trinuclear basic chromium(III) clusters : direct observation of the magnetic spectrum by inelastic neutron scattering

Incoherent inelastic neutron scattering spectra are reported for salts of the complex [Cr3O(OOCCH3)6(OH2)3]+. The data are consistent with predominantly antiferromagnetic coupling between pairs of chromium ions. The complete spectrum of transitions between successive states with total spin S=1/2, 3/2, 5/2, 7/2, and 9/2 has been observed for the first time. Splittings of the ground state S=1/2 have been observed directly and attributed to lowering of symmetry of the triangular cluster. For the chloride salt the data confirm that two sets of complex cations with different degrees of symmetry lowering are present in the crystal, at least at the lowest temperatures used (T=1.4 to 50 K). In principle, the relationship of J values for the symmetry‐lowered case could be described as ‘‘isosceles,’’ with Jab≳Jbc=Jac or Jab<Jbc=Jac; or as ‘‘scalene,’’ with all three J values different. We find that, for at least one of the two sets of metal ion clusters, the scalene case applies, with J values of −11.5±0.2, −10.5±0...

Exploring the application of metastable wurtzite nanocrystals in pure-sulfide Cu2ZnSnS4 solar cells by forming nearly micron-sized large grains

An innovative approach to overcome the main challenge of solution-based pure-sulfide Cu2ZnSnS4 thin film solar cells by sulfurizing quaternary Cu2ZnSnS4 nanocrystals into nearly micron-sized large grains in a few minutes is presented. We developed an efficient phase-transition-driven grain growth strategy to explore the application of metastable wurtzite Cu2ZnSnS4 nano-materials in the photovoltaic field. The obtained Cu2ZnSnS4 thin film has a typical bilayer microstructure containing large grains on the top and fine grains at the bottom. Clear variations of phase, morphology, and component redistribution of the Cu2ZnSnS4 thin film were identified after the sulfurization process, which is critical to get a dense large-grained Cu2ZnSnS4 layer from quaternary nanocrystals. By tuning the composition of the wurtzite Cu2ZnSnS4 nanocrystals, annealing conditions, and sodium-containing compound, laboratory-scale photovoltaic cells with 4.83% efficiency were demonstrated without anti-reflection coatings. These results suggest the potential application of metastable wurtzite nanocrystals in pure-sulfide Cu2ZnSnS4 solar cells. This unique approach may also open up new opportunities to other optoelectronic devices, such as CuIn(S,Se)2, Cu2(In,Ga)Se4, CdTe, and Cu2ZnGe(S,Se)4 solar cells.

Magneto-structural correlations of a three-dimensional Mn based metal–organic framework

A 3D metal-organic framework, [Na{Mn(3)(Hbtc)(2)(btc)}.5H(2)O](n) () (H(3)btc = 1,3,5-benzene tricarboxylic acid), was synthesized under hydrothermal conditions. The structure of was established by single crystal X-ray diffraction analysis; crystallizes in the monoclinic space group P2/c, a = 9.753(3) A, b = 12.751(2) A, c = 14.174(4) A, beta = 109.41(1) degrees . The complex is isostructural to previously reported MIL-45 and consists of one dimensional wave like chains of carboxylate bridged hexa-coordinated Mn(ii) ions. Variable temperature magnetic susceptibility measurements revealed dominant antiferromagnetic exchange interactions and the intra-chain exchange constants J(1) = -2.4 cm(-1) and J(2) = -0.6 cm(-1) compare well with literature values for similar materials. Inter-chain interactions are expected to be very small in this compound and there is no indication of magnetic ordering phenomena in the temperature range from 300-2 K.

Switchable magnetism: neutron diffraction studies of the desolvated coordination polymer Co3(OH)2(C4O4)2.

We report the magnetic structure of the two magnetically ordered phases of Co3(OH)2(C4O4)2, a coordination polymer that consists of a triangular framework decorated with anisotropic Co(II) ions. Neutron diffraction experiments allow us to confirm that the magnetic behavior changes upon dehydration and reveal the complex phase behavior of this system, relative to the hydrated compound Co3(OH)2(C4O4)2·3H2O. One phase is shown to display spin idle behavior, where only a fraction of the moments order at intermediate temperatures, while at the lowest temperatures the system orders fully, in this case with a net magnetic moment. This novel magnetic behavior is discussed within the framework of a simple Hamiltonian and representational analysis and rationalizes this multiphase behavior by considering the combination of frustration and anisotropy. The change in behavior on dehydration is also rationalized with respect to the changes in the single-ion anisotropy of the cobalt.

Two stage magnetic ordering and spin idle behavior of the coordination polymer Co3(OH)2(C4O4)2·3H2O determined using neutron diffraction.

We report the magnetic structure of two of the magnetically ordered phases of Co(3)(OH)(2)(C(4)O(4))(2)·3H(2)O, a coordination polymer that consists of a triangular framework decorated with anisotropic Co(II) ions. The combination of neutron diffraction experiments and magnetic susceptibility data allows us to identify one phase as displaying spin idle behavior, where only a fraction of the moments order at intermediate temperatures, while at the lowest temperatures the system orders fully. This novel magnetic behavior is discussed within the framework of a simple Hamiltonian and representational analysis and rationalizes this multiphase behavior by considering the combination of frustration and anisotropy.

The Central Atom Size Effect on the Structure of Group 14 Tetratolyls

The tetraphenyl derivatives of the Group 14 elements are of great potential interest as supramolecular constructs in extended porous networks. The tetratolyl derivatives are particularly important precursors to usable constructs, courtesy of the ease of functionalisation at the site of the paramethyl group. The methyl groups constitute the outer contact sphere of individual tetratolyl molecules, making them particularly sensitive to the nature of the intermolecular interactions. Upon variation of the central atom, the methyl group dynamics allow a direct probe of these contact potentials across the complete series of materials. Due to the similar electronic properties of the different central atoms, the tolyl groups are chemically similar throughout the series meaning that the dominant effect is simply that of molecular size, which is dictated by the central atom. Methyl tunnelling spectroscopy is an extremely sensitive probe of intermolecular potentials and molecular interactions about torsional rotor units such a methyl groups, with high-resolution inelastic neutron scattering (hr-INS) spectroscopy being the most direct method to measure these small energy splittings. This is most clearly manifested at low temperatures, with the internal molecular vibrations restricted primarily to the ground state. So-called methyl tunnelling transitions due to quantum interactions, or quantum tunnelling, of the wavefunctions of ground state rotors thermally trapped in the torsional potential energy minima and the equivalent positions about the torsional axis, result in observable transitions in hr-INS spectra. Distinct peaks are obtained in the meV spectral region for each distinct methyl environment. In this respect, the tunnelling spectra can be related directly to the crystal structure. The heavier analogues, having tin and lead as the central atoms, are known to be isomorphic, in the space group I4̄, with the silicon and germanium tetratolyl derivatives being reported under the Pc space group. This is in stark contrast to the tetraphenyl species that are isomorphic throughout the Group 14 elements, indicating that the methyl groups at the molecular periphery have profound effects on the extent of molecular packing interactions upon variation of the size of the central atom. The implication of existing structural data is that a symmetry break occurs at a central atom radius of about 1.3 (lying between the reported radii for germanium and tin atoms), presumably due to steric hindrance in the methyl group environments. However, the structure of the carbon analogue, obtained herein for the first time, indicates that it is of the same structure as the heavier tin and lead centred materials. The tetratolyl Group 14 compounds were synthesised by using a general reaction scheme involving the nucleophilic addition of an organometallic reagent to the electrophilic centre of the Group 14 element. The tetrachloride derivatives were used for the synthesis of the silane, germane and stannane compounds (see Scheme 1 in the Supporting Information). However the synthesis of the carbon analogue proceeded through the corresponding tetraphenyl derivative (see Scheme 2 in the Supporting Information). Crystal datasets were collected for all of the compounds and were found to be consistent with published data where available. The carbon analogue C ACHTUNGTRENNUNG(Tol)4 was found to belong to the tetragonal space group I4̄ and with a cell volume of 1143.89 , which should be compared to 1223.32 and 1215.58 3 for Sn ACHTUNGTRENNUNG(Tol)4 and Pb ACHTUNGTRENNUNG(Tol)4, respectively (Figure 1). hr-INS data for the carbon, silicon, germanium and tin analogues were recorded on the IN16 backscattering spectrometer at ILL, Grenoble, France over a range of temperatures, 2 T [a] M. C. C. Ng, Dr. D. J. Craig, Dr. J. B. Harper, Dr. J. A. Stride School of Chemistry, University of New South Wales Sydney 2052 (Australia) E-mail : j.stride@unsw.edu.au [b] Dr. L. v. van-Eijck Institute Laue-Langevin, 6 rue Jules Horowitz BP156 38042 Grenoble Cedex 9, (France) [c] Dr. J. A. Stride Bragg Institute, Australian Nuclear Science and Technology Organisation, PMB 1 Menai, NSW 2234 (Australia) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200900360.