Nitrogen controlled iron catalyst phase during carbon nanotube growth

Close control over the active catalyst phase and hence carbon nanotube structure remains challenging in catalytic chemical vapor deposition since multiple competing active catalyst phases typically co-exist under realistic synthesis conditions. Here, using in-situ X-ray diffractometry we show that the phase of supported iron catalyst particles can be reliably controlled via the addition of NH3 during nanotube synthesis. Unlike to polydisperse catalyst phase mixtures during H2 diluted nanotube growth, nitrogen addition controllably leads to phase-pure γ-Fe during pre-treatment and to phase-pure Fe3C during growth. We rationalize these findings in the context of ternary Fe-C-N phase diagram calculations and thus highlight the use of pretreatment- and add-gases as a key parameter towards controlled carbon nanotube growth.This is the author accepted manuscript. The final version is available from AIP via http://dx.doi.org/10.1063/1.489795

SUMO chain formation is required for response to replication arrest in S. pombe

SUMO is a ubiquitin-like protein that is post-translationally attached to one or more lysine residues on target proteins. Despite having only 18% sequence identity with ubiquitin, SUMO contains the conserved betabetaalphabetabetaalphabeta fold present in ubiquitin. However, SUMO differs from ubiquitin in having an extended N-terminus. In S. pombe the N-terminus of SUMO/Pmt3 is significantly longer than those of SUMO in S. cerevisiae, human and Drosophila. Here we investigate the role of this N-terminal region. We have used two dimensional gel electrophoresis to demonstrate that S. pombe SUMO/Pmt3 is phosphorylated, and that this occurs on serine residues at the extreme N-terminus of the protein. Mutation of these residues (in pmt3-1) results in a dramatic reduction in both the levels of high Mr SUMO-containing species and of total SUMO/Pmt3, indicating that phosphorylation of SUMO/Pmt3 is required for its stability. Despite the significant reduction in high Mr SUMO-containing species, pmt3-1 cells do not display an aberrant cell morphology or sensitivity to genotoxins or stress. Additionally, we demonstrate that two lysine residues in the N-terminus of S. pombe SUMO/Pmt3 (K14 and K30) can act as acceptor sites for SUMO chain formation in vitro. Inability to form SUMO chains results in aberrant cell and nuclear morphologies, including stretched and fragmented chromatin. SUMO chain mutants are sensitive to the DNA synthesis inhibitor, hydroxyurea (HU), but not to other genotoxins, such as UV, MMS or CPT. This implies a role for SUMO chains in the response to replication arrest in S. pomb

Introducing Overlapping Grain Boundaries in Chemical Vapor Deposited Hexagonal Boron Nitride Monolayer Films.

We demonstrate the growth of overlapping grain boundaries in continuous, polycrystalline hexagonal boron nitride (h-BN) monolayer films via scalable catalytic chemical vapor deposition. Unlike the commonly reported atomically stitched grain boundaries, these overlapping grain boundaries do not consist of defect lines within the monolayer films but are composed of self-sealing bilayer regions of limited width. We characterize this overlapping h-BN grain boundary structure in detail by complementary (scanning) transmission electron microscopy techniques and propose a catalytic growth mechanism linked to the subsurface/bulk of the process catalyst and its boron and nitrogen solubilities. Our data suggest that the overlapping grain boundaries are comparatively resilient against deleterious pinhole formation associated with grain boundary defect lines and thus may reduce detrimental breakdown effects when polycrystalline h-BN monolayer films are used as ultrathin dielectrics, barrier layers, or separation membranes

Reactive intercalation and oxidation at the buried graphene-germanium interface

We explore a number of different electrochemical, wet chemical, and gas phase approaches to study intercalation and oxidation at the buried graphene-Ge interface. While the previous literature focused on the passivation of the Ge surface by chemical vapor deposited graphene, we show that particularly via electrochemical intercalation in a 0.25 N solution of anhydrous sodium acetate in glacial acetic acid, this passivation can be overcome to grow GeO2 under graphene. Angle resolved photoemission spectroscopy, Raman spectroscopy, He ion microscopy, and time-of-flight secondary ion mass spectrometry show that the monolayer graphene remains undamaged and its intrinsic strain is released by the interface oxidation. Graphene acts as a protection layer for the as-grown Ge oxide, and we discuss how these insights can be utilized for new processing approaches.We acknowledge financial support from the EPSRC (EP/K016636/1, EP/P51021X/1) and the Future Photonics Hub - Innovation Partnership Fund (EPSRC EP/L00044X/1). P.B.W. acknowledges EPSRC Cambridge NanoDTC EP/G037221/1. R.S.W. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme through a EU Marie Skłodowska-Curie Individual Fellowship (Global) under grant ARTIST (no. 656870). R.W. acknowledges EPSRC Doctoral Training Award (EP/M506485/1)

In Situ Observations of Phase Transitions in Metastable Nickel (Carbide)/Carbon Nanocomposites.

Nanocomposite thin films comprised of metastable metal carbides in a carbon matrix have a wide variety of applications ranging from hard coatings to magnetics and energy storage and conversion. While their deposition using nonequilibrium techniques is established, the understanding of the dynamic evolution of such metastable nanocomposites under thermal equilibrium conditions at elevated temperatures during processing and during device operation remains limited. Here, we investigate sputter-deposited nanocomposites of metastable nickel carbide (Ni3C) nanocrystals in an amorphous carbon (a-C) matrix during thermal postdeposition processing via complementary in situ X-ray diffractometry, in situ Raman spectroscopy, and in situ X-ray photoelectron spectroscopy. At low annealing temperatures (300 °C) we observe isothermal Ni3C decomposition into face-centered-cubic Ni and amorphous carbon, however, without changes to the initial finely structured nanocomposite morphology. Only for higher temperatures (400-800 °C) Ni-catalyzed isothermal graphitization of the amorphous carbon matrix sets in, which we link to bulk-diffusion-mediated phase separation of the nanocomposite into coarser Ni and graphite grains. Upon natural cooling, only minimal precipitation of additional carbon from the Ni is observed, showing that even for highly carbon saturated systems precipitation upon cooling can be kinetically quenched. Our findings demonstrate that phase transformations of the filler and morphology modifications of the nanocomposite can be decoupled, which is advantageous from a manufacturing perspective. Our in situ study also identifies the high carbon content of the Ni filler crystallites at all stages of processing as the key hallmark feature of such metal-carbon nanocomposites that governs their entire thermal evolution. In a wider context, we also discuss our findings with regard to the much debated potential role of metastable Ni3C as a catalyst phase in graphene and carbon nanotube growth

Developing an award program for children's settings to support healthy eating and physical activity and reduce the risk of overweight and obesity

<p>Abstract</p> <p>Background</p> <p>This paper aimed to identify the best way to engage, motivate and support early childhood services (ECS) and primary schools (PS) to create policy and practise changes to promote healthy eating and physical activity. This information would be used to develop a suitable program to implement within these children's settings to reduce the risk of childhood overweight and obesity.</p> <p>Methods</p> <p>The Medical Research Council's (UK) framework for the design and evaluation of complex interventions was used to guide the development of the healthy eating and physical activity program suitable for ECS and PS. Within this framework a range of evaluation methods, including stakeholder planning, in-depth interviews with ECS and PS staff and acceptability and feasibility trials in one local government area, were used to ascertain the best way to engage and support positive changes in these children's settings.</p> <p>Results</p> <p>Both ECS and PS identified that they had a role to play to improve children's healthy eating and physical activity. ECS identified their role in promoting healthy eating and physical activity as important for children's health, and instilling healthy habits for life. PS felt that these were health issues, rather than educational issues; however, schools saw the link between healthy eating and physical activity and student learning outcomes. These settings identified that a program that provides a simple guide that recognises good practise in these settings, such as an award scheme using a health promoting schools approach, as a feasible and acceptable way for them to support children's healthy eating and physical activity.</p> <p>Conclusion</p> <p>Through the process of design and evaluation a program - <it>Kids - 'Go for your life'</it>, was developed to promote and support children's healthy eating and physical activity and reduce the risk of childhood overweight and obesity. <it>Kids - 'Go for your life' </it>used an award program, based on a health promoting schools approach, which was demonstrated to be a suitable model to engage ECS and PS and was acceptable and feasible to create policy and practise changes to support healthy eating and physical activity for children.</p

Graphene-based nanolaminates as ultra-high permeation barriers

Permeation barrier films are critical to a wide range of applications. In particular, for organic electronics and photovoltaics not only ultra-low permeation values are required but also optical transparency. A laminate structure thereby allows synergistic effects between different materials. Here, we report on a combination of chemical vapor deposition (CVD) and atomic layer deposition (ALD) to create in scalable fashion few-layer graphene/aluminium oxide-based nanolaminates. The resulting ~10 nm contiguous, flexible graphene-based films are >90% optically transparent and show water vapor transmission rates below 7 × 10¯³g/m²/day measured over areas of 5 × 5 cm². We deploy these films to provide effective encapsulation for organic light-emitting diodes (OLEDs) with measured half-life times of 880 h in ambient.We acknowledge funding via EPSRC-Innovate UK Grant (EP/M507751/1). B.C.B acknowledges funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreements 656214- 2DInterFOX. J.C.M. acknowledges support from the Austrian Science Fund (FWF, P25721-N20)

Sialic Acid Glycobiology Unveils Trypanosoma cruzi Trypomastigote Membrane Physiology.

Trypanosoma cruzi, the flagellate protozoan agent of Chagas disease or American trypanosomiasis, is unable to synthesize sialic acids de novo. Mucins and trans-sialidase (TS) are substrate and enzyme, respectively, of the glycobiological system that scavenges sialic acid from the host in a crucial interplay for T. cruzi life cycle. The acquisition of the sialyl residue allows the parasite to avoid lysis by serum factors and to interact with the host cell. A major drawback to studying the sialylation kinetics and turnover of the trypomastigote glycoconjugates is the difficulty to identify and follow the recently acquired sialyl residues. To tackle this issue, we followed an unnatural sugar approach as bioorthogonal chemical reporters, where the use of azidosialyl residues allowed identifying the acquired sugar. Advanced microscopy techniques, together with biochemical methods, were used to study the trypomastigote membrane from its glycobiological perspective. Main sialyl acceptors were identified as mucins by biochemical procedures and protein markers. Together with determining their shedding and turnover rates, we also report that several membrane proteins, including TS and its substrates, both glycosylphosphatidylinositol-anchored proteins, are separately distributed on parasite surface and contained in different and highly stable membrane microdomains. Notably, labeling for α(1,3)Galactosyl residues only partially colocalize with sialylated mucins, indicating that two species of glycosylated mucins do exist, which are segregated at the parasite surface. Moreover, sialylated mucins were included in lipid-raft-domains, whereas TS molecules are not. The location of the surface-anchored TS resulted too far off as to be capable to sialylate mucins, a role played by the shed TS instead. Phosphatidylinositol-phospholipase-C activity is actually not present in trypomastigotes. Therefore, shedding of TS occurs via microvesicles instead of as a fully soluble form

Interleukin-7 Influences FOXP3+CD4+ Regulatory T Cells Peripheral Homeostasis

Mechanisms governing peripheral CD4+ FOXP3+ regulatory T cells (Treg) survival and homeostasis are multiple suggesting tight and complex regulation of regulatory T cells homeostasis. Some specific factors, such as TGF-β, interleukin-2 (IL-2) and B7 costimulatory molecules have been identified as essentials for maintenance of the peripheral Treg compartment. Conversely, Treg dependency upon classical T cell homeostatic factors such as IL-7 is still unclear. In this work, we formally investigated the role of IL-7 in Treg homeostasis in vivo in murine models. We demonstrated that IL-7 availability regulated the size of peripheral Treg cell pool and thus paralleled the impact of IL-7 on conventional T cell pool. Moreover, we showed that IL-7 administration increased Treg cell numbers by inducing thymic-independent Treg peripheral expansion. Importantly the impact of IL-7 on Treg expansion was detected whether conventional T cells were present or absent as IL-7 directly participates to the peripheral expansion of Treg after adoptive transfer into lymphopenic hosts. Our results definitively identify IL-7 as a central factor contributing to Treg peripheral homeostasis, thus reassembling Treg to other T cell subsets in respect of their need for IL-7 for their peripheral maintenance