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PUBLISHED ; Export Date: 15 September 2016 ; Advances in lithium ion batteries would facilitate technological developments in areas from electrical vehicles to mobile communications. While 2-dimensional systems like MoS2 are promising electrode materials due to their potentially high capacity, their poor rate-capability and low cycle-stability are severe handicaps. Here we study the electrical, mechanical and lithium storage properties of solution-processed MoS2/carbon nanotube anodes. Nanotube addition gives up to ?1010 and ?40 increases in electrical conductivity and mechanical toughness respectively. The increased conductivity results in up to a ?100 capacity enhancement to ~1200 mAh/g (~3000 mAh/cm3) at 0.1 A/g, while the improved toughness significantly boosts cycle stability. Composites with 20 wt% nanotubes combined high reversible capacity with excellent cycling stability (e.g. ~950 mAh/g after 500 cycles at 2 A/g) and high-rate capability (~600 mAh/g at 20 A/g). The conductivity, toughness and capacity scaled with nanotube content according to percolation theory while the stability increased sharply at the mechanical percolation threshold. We believe the improvements in conductivity and toughness obtained after addition of nanotubes can be transferred to other electrode materials such as silicon nanoparticles. ; Acknowledgements: We thank Science Foundation Ireland (11/PI/1087), the European Research Council (SEMANTICS), the European Union Seventh Framework Program under grant agreement n?604391 (Graphene Flagship), the Shanghai Science and Technology Commission, China (Grant No. 13DZ2260900), the National Natural Science Foundation of China (51472173 and 51522208), and the Natural Science Foundation of Jiangsu Province (BK20140302 and SBK2015010320) for financial support. We acknowledge support from the SFI-funded AMBER research centre (SFI/12/RC/2278) and the Collaborative Innovation Centre of Suzhou Nano Science and Technology.

PUBLISHED ; Cited By :1 Export Date: 15 September 2016 ; Although many electrochemical properties of 2D materials depend sensitively on the nanosheet dimensions, there are no systematic, quantitative studies which analyse the effect of nanosheet size and thickness on electrochemical parameters. Here we use size-selected WS2 nanosheets as a model system to determine the effect of nanosheet dimensions in two representative areas ? hydrogen evolution electrocatalytic electrodes and electrochemical double layer capacitor electrodes. We chose these applications as they depend on the interaction of ions with the nanosheet edge and basal plane, respectively, and so would be expected to be nanosheet-size-dependent. The data shows the catalytic current density to scale inversely with mean nanosheet length while the volumetric double layer capacitance scales inversely with mean nanosheet thickness. Both of these results are consistent with simple models allowing use to extract intrinsic quantities, namely the turnover frequency and the double layer thickness respectively. ; The research leading to these results was funded by Science Foundation Ireland grant number (11/PI/1087) and European Research Council (SEMANTICS). We have also received funding from the European Union Seventh Framework Program under grant agreement n?604391 Graphene Flagship and from the Science Foundation Ireland (SFI) funded centre AMBER (SFI/12/RC/2278).

The concentration of nanosheet suspensions is an important technological parameter which is commonly measured by optical spectroscopy, using the absorption coefficient to transform absorbance into concentration. However, for all 2D materials, the absorption coefficient is poorly known, resulting in potentially large errors in measured concentration. Here we derive an expression relating the optical absorption coefficient of an isotropic dispersion of nanosheets to the intrinsic monolayer absorption. This has allowed us to calculate the absorption coefficients for suspensions of graphene, MoS2 and other 2D materials, and to estimate the monolayer absorption for new materials from careful measurement of the suspension absorption coefficient. ; The research leading to these results has received funding from the European Union Seventh Framework Program under grant agreement n?604391 Graphene Flagship. We have also received support from the Science Foundation Ireland (SFI) funded centre AMBER (SFI/12/RC/2278). In addition, JNC acknowledges the European Research Council (SEMANTICS) and SFI (11/PI/1087) for financial support

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We acknowledge funding from Science Foundation Ireland via the AMBER research centre (SFI/12/RC/2278) and a PI award (11/PI/1087). We are grateful for financial support from the European research Council (SEMANTICS) and the European Union Seventh Framework Programme under grant agreements n?604391 and n?696656 Graphene Flagship.

PUBLISHED ; Cited By :5 Export Date: 15 September 2016 ; While liquid phase exfoliation can be used to produce nanosheets stabilized in polymer solutions, very little is known about the resultant nanosheet size, thickness or monolayer content. Here we use semi-quantitative spectroscopic metrics based on extinction, Raman and photoluminescence (PL) spectroscopy to investigate these parameters for WS2 nanosheets exfoliated in aqueous polyvinylalcohol (PVA) solutions. By measuring Raman and PL simultaneously, we can track the monolayer content via the PL/Raman intensity ratio while varying processing conditions. We find the monolayer population to be maximized for a stabilizing polymer concentration of 2 g/L. In addition, the monolayer content can be controlled via the centrifugation conditions, exceeding 5% by mass in some cases. These techniques have allowed us to track the ratio of PL/Raman in a droplet of polymer-stabilized WS2 nanosheets as the water evaporates during composite formation. We find no evidence of nanosheet aggregation under these conditions although the PL becomes dominated by trion emission as drying proceeds and the balance of doping from PVA/water changes. Finally, we have produced bulk PVA/WS2 composites by freeze drying where >50% of the monolayers remain unaggregated, even at WS2 volume fractions as high as 10%. ; The research leading to these results has received funding from the European Union Seventh Framework Program under grant agreement n?604391 Graphene Flagship. We have also received support from the Science Foundation Ireland (SFI) funded centre AMBER (SFI/12/RC/2278). In addition, JNC acknowledges the European Research Council (SEMANTICS) and SFI (11/PI/1087) for financial support. VV-M and CG acknowledge Marie Curie ITN network ?MoWSeS? (grant no. 317451). CB acknowledges the German research foundation DFG (BA 4856/1-1). M.O. acknowledges an Irish Research Council scholarship via the Enterprise Partnership Scheme, Project 201517, Award 12508. G.S.D. acknowledges support from the SFI (PI_10/IN.1/I3030).

PUBLISHED ; This work was primarily supported by an SFI PYRA grant as well as the SFI-funded AMBER research centre (SFI/12/RC/2278) as part of the platform projects program. In addition, we 20 acknowledge the European Union Seventh Framework Program under grant agreement n?604391 Graphene Flagship.

PUBLISHED ; Layered inorganic materials, such as the transition metal dichalcogenides (TMDs), have attracted much attention due to their exceptional electronic and optical properties. Reliable synthesis and characterization of these materials must be developed if these properties are to be exploited. Herein, we present low-frequency Raman analysis of MoS2, MoSe2, WSe2 and WS2 grown by chemical vapour deposition (CVD). Raman spectra are acquired over large areas allowing changes in the position and intensity of the shear and layer-breathing modes to be visualized in maps. This allows detailed characterization of mono- and few-layered TMDs which is complementary to well-established (high-frequency) Raman and photoluminescence spectroscopy. This study presents a major stepping stone in fundamental understanding of layered materials as mapping the low-frequency modes allows the quality, symmetry, stacking configuration and layer number of 2D materials to be probed over large areas. In addition, we report on anomalous resonance effects in the low-frequency region of the WS2 Raman spectrum. ; This work is supported by the SFI under Contract No. 12/RC/2278 and PI_10/IN.1/I3030. M.O.B. acknowledges an Irish Research Council scholarship via the Enterprise Partnership Scheme, Project 201517, Award 12508. N.M. acknowledges SFI (14/TIDA/2329). D.H. and J.N.C. acknowledge the European Union Seventh Framework Programme under grant agreement n?604391 Graphene Flagship. The authors thank Christian Wirtz for illustrations as well as Riley Gatensby and Kangho Lee for assistance with CVD.

PUBLISHED ; In this work we have used melt-processing to mix liquid-exfoliated boron?nitride nanosheets with PET to produce composites for gas barrier applications. Sonication of h-BN powder, followed by centrifugation-based size-selection, was used to prepare suspensions of nanosheets with aspect ratio >1000. The solvent was removed to give a weakly aggregated powder which could easily be mixed into PET, giving a composite containing well-dispersed nanosheets. These composites showed very good barrier performance with oxygen permeability reductions of 42% by adding just 0.017 vol% nanosheets. At low loading levels the composites were almost completely transparent. At higher loading levels, while some haze was introduced, the permeability fell by [similar]70% on addition of 3 vol% nanosheets. ; We thank SAB Miller for funding this research project. We also acknowledge funding from the European Union Seventh Framework Programme under grant agreement no 604391 Graphene Flagship. We have also received support from the Science Foundation Ireland (SFI) funded centre AMBER (SFI/ 12/RC/2278). In addition, JNC acknowledges the European Research Council (SEMANTICS). We also thank the Advanced Microscopy Lab for help with microscopic analysis

PUBLISHED ; Cited By :4 Export Date: 15 September 2016 ; Liquid phase exfoliation is a powerful and scalable technique to produce defect-free mono- and few-layer graphene. However, samples are typically polydisperse and control over size and thickness is challenging. Notably, high throughput techniques to measure size and thickness are lacking. In this work, we have measured the extinction, absorption, scattering and Raman spectra for liquid phase exfoliated graphene nanosheets of various lateral sizes (90 ≤ 〈L〉 ≤ 810 nm) and thicknesses (2.7 ≤ 〈N〉 ≤ 10.4). We found all spectra to show well-defined dependences on nanosheet dimensions. Measurements of extinction and absorption spectra of nanosheet dispersions showed both peak position and spectral shape to vary with nanosheet thickness in a manner consistent with theoretical calculations. This allows the development of empirical metrics to extract the mean thickness of liquid dispersed nanosheets from an extinction (or absorption) spectrum. While the scattering spectra depended on nanosheet length, poor signal to noise ratios made the resultant length metric unreliable. By analyzing Raman spectra measured on graphene nanosheet networks, we found both the D/G intensity ratio and the width of the G-band to scale with mean nanosheet length allowing us to establish quantitative relationships. In addition, we elucidate the variation of 2D/G band intensities and 2D-band shape with the mean nanosheet thickness, allowing us to establish quantitative metrics for mean nanosheet thickness from Raman spectr ; The research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement no 604391 Graphene Flagship. In addition, we acknowledge Science Foundation Ireland (11/PI/ 1087), the European Research Council (SEMANTICS and POC grant UP2DM) and Thomas Swan & Co. Ltd for financial support. CB acknowledges the German research foundation DFG (BA 4856/1-1). We thank Asbury Carbons and Imerys Graphite and Carbon for suppling parent graphite materials free of ch