The thermal expansion coeffcient of monolayer, bilayer and trilayer graphene derived from the strain induced by cooling to cryogenic temperatures

This is the author accepted manuscript. The final version is available from the American Institute of Physics via the DOI in this recordData availability: The data that support the findings of this study are available from the corresponding author upon reasonable request.While thermally cycling monolayer, bilayer and trilayer graphene between 5 K and 300 K Raman spectroscopy has shown that cooling to 5 K induces a strain in these graphene flakes of −0.081 ± 0.003%. This strain was used to measure the graphene thermal expansion coefficient (TEC) which was found to be (−3.2±0.2)×10−6 K −1 for monolayers, (−3.4 ± 0.4) × 10−6 K −1 for bilayers and (−3.8 ± 0.6) × 10−6 K −1 for trilayers at room temperature. The TEC showed a similar temperature dependence across all graphene thicknesses and was found to be in good agreement with theoretical predictions. This study thus represents the first measurement of the TEC of bilayer and trilayer graphene. Modification of graphene flakes of all thicknesses with various electrical contact designs was found to have no significant impact on the resulting strain, and thus the TEC, compared to the pristine graphene.Engineering and Physical Sciences Research Council (EPSRC)Leverhulme Trus

Detection of anomalous Hall voltages in ultrahigh-mobility two-dimensional hole gases generated by optical spin orientation

By combining optical spin orientation and an externally applied longitudinal electric field, transverse charge accumulation has been detected in very high-mobility two-dimensional hole gases by measuring the transverse voltage drop across simple Hall devices. Our results indicate intrinsic band-structure (rather than extrinsic skew scattering) derived spin-orbit coupling as the underlying mechanism of this spin-polarized transport effect.This work was supported by the EPSRC.This is the author accepted manuscript. The final version was first published by APS at http://journals.aps.org/prb/abstract/10.1103/PhysRevB.91.201406

Exceptionally large migration length of carbon and topographically-facilitated self-limiting molecular beam epitaxial growth of graphene on hexagonal boron nitride

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Available online 18 December 2016We demonstrate growth of single-layer graphene (SLG) on hexagonal boron nitride (h-BN) by molecular beam epitaxy (MBE), only limited in area by the finite size of the h-BN flakes. Using atomic force microscopy and micro-Raman spectroscopy, we show that for growth over a wide range of temperatures (500◦C – 1000◦C) the deposited carbon atoms spill off the edge of the h-BN flakes. We attribute this spillage to the very high mobility of the carbon atoms on the BN basal plane, consistent with van der Waals MBE. The h-BN flakes vary in size from 30 µm to 100 µm, thus demonstrating that the migration length of carbon atoms on h-BN is greater than 100 µm. When sufficient carbon is supplied to compensate for this loss, which is largely due to this fast migration of the carbon atoms to and off the edges of the h-BN flake, we find that the best growth temperature for MBE SLG on h-BN is ∼950◦C. Self-limiting graphene growth appears to be facilitated by topographic h-BN surface features: We have thereby grown MBE self-limited SLG on an h-BN ridge. This opens up future avenues for precisely tailored fabrication of nano- and hetero-structures on pre-patterned h-BN surfaces for device applications.This work is supported by ONR (N000140610138 and Graphene MURI), AFOSR (FA9550-11-1-0010), EFRC Center for Re-Defining Photovoltaic Efficiency through Molecule Scale Control (award DE-SC0001085), NSF (CHE-0641523), NYSTAR and Spanish Government (AIC-B-2011-0806, MAT2014-54231, MAT2015-67021-R). S.W. and A.P. were supported by the US Department of Energy Office of Science, Division of Materials Science and Engineering (award DE-SC0010695)

Clinical Use and Therapeutic Potential of IVIG/SCIG, Plasma-Derived IgA or IgM, and Other Alternative Immunoglobulin Preparations

Intravenous and subcutaneous immunoglobulin preparations, consisting of IgG class antibodies, are increasingly used to treat a broad range of pathological conditions, including humoral immune deficiencies, as well as acute and chronic inflammatory or autoimmune disorders. A plethora of Fab- or Fc-mediated immune regulatory mechanisms has been described that might act separately or in concert, depending on pathogenesis or stage of clinical condition. Attempts have been undertaken to improve the efficacy of polyclonal IgG preparations, including the identification of relevant subfractions, mild chemical modification of molecules, or modification of carbohydrate side chains. Furthermore, plasma-derived IgA or IgM preparations may exhibit characteristics that might be exploited therapeutically. The need for improved treatment strategies without increase in plasma demand is a goal and might be achieved by more optimal use of plasma-derived proteins, including the IgA and the IgM fractions. This article provides an overview on the current knowledge and future strategies to improve the efficacy of regular IgG preparations and discusses the potential of human plasma-derived IgA, IgM, and preparations composed of mixtures of IgG, IgA, and IgM

The paradoxical role of meritocratic selection in the perpetuation of social inequalities at school

The school system is intended to offer all students the same opportunities, but most international surveys reveal an overall lower achievement for students from disadvantaged groups compared with more advantaged students. Recent experimental research in social psychology has demonstrated that schools as institutions contribute with their implicit cultural norms and structure to the production of inequalities. This chapter examines the role that a structural feature of school, namely meritocratic selection, plays in this reproduction of inequalities at school. First, we describe how meritocracy in the educational system can hold paradoxical effects by masking the virtuous/vicious cycles of opportunities created by educational institutions. Second, we present recent research suggesting that selection practices relying on a meritocratic principle—more than other practices—can lead to biased academic decisions hindering disadvantaged students. We propose that inequalities in school might not just result from isolated failures in an otherwise functional meritocratic system, but rather that merit-based selection itself contributes to the perpetuation of inequalities at school

The effect of optically-induced random anisotropic disorder on a two-dimensional electron system

We have studied the effect of optically-induced random, anisotropic disorder on the magnetoresistance of a Al0.3Ga0.7As/ GaAs two-dimensional electron system by exposing the heterojunction to an asymmetric laser speckle pattern. Changes in the amplitude of the Shubnikov-de Haas oscillations can be explained in terms of easy and hard conductivity paths parallel and perpendicular to the long axis of the oval speckle grains. We also observe corresponding changes in the electron scattering rates. © 2006 Elsevier Ltd. All rights reserved

The effect of controllable optically-induced random anisotropic disorder on the magnetotransport in a two-dimensional electron system

We have studied the effect of optically-induced random, anisotropic disorder on the magnetoresistance of a two-dimensional electron gas by exposing the sample to an anisotropic laser speckle pattern. Changes in the amplitude of the Shubnikov-de Haas oscillations can be explained in terms of easy and hard conductivity paths, parallel and perpendicular to the long axis of the oval speckle grains, respectively. © 2005 American Institute of Physics