140 results found
Mehonic A, Buckwell M, Montesi L, et al., 2016, Silica: Nanoscale Transformations in Metastable, Amorphous, Silicon-Rich Silica (Adv. Mater. 34/2016), Advanced Materials, Vol: 28, Pages: 7549-7549, ISSN: 0935-9648
Electrically biasing thin films of amorphous, substoichiometric silicon oxide drives surprisingly large structural changes, apparent as density variations, oxygen movement, and ultimately, emission of superoxide ions. Results from this fundamental study are directly relevant to materials that are increasingly used in a range of technologies, and demonstrate a surprising level of field-driven local reordering of a random oxide network.
Kien-Cuong P, Chang Y-H, McPhail DS, et al., 2016, Amorphous Molybdenum Sulfide on Graphene-Carbon Nanotube Hybrids as Highly Active Hydrogen Evolution Reaction Catalysts, ACS APPLIED MATERIALS & INTERFACES, Vol: 8, Pages: 5961-5971, ISSN: 1944-8244
Buckwell M, Montesi L, Mehonic A, et al., 2016, Structural investigation of resistance switching in silicon-rich silica films, IEEE-NANO 2015 - 15th International Conference on Nanotechnology, Publisher: IEEE, Pages: 489-492
Redox-based resistive RAM presents a development in non-volatile data storage, despite an incomplete understanding of switching mechanisms. However, in order to optimize and standardize device behavior it is necessary to have a better understanding of physical processes governing switching. Many oxide dielectrics have been studied in relation to switching, but silicon-based devices in particular offer a high capacity for integration into existing CMOS technologies at low cost. We present analyses of silicon-rich silica films to establish the chemical and structural processes underpinning electronic resistance switching behavior. Atomic force microscopy, x-ray photoelectron spectroscopy and secondary ion mass spectroscopy are used to characterize observed resistance changes. Reduction and structural reconfiguration of the oxide is seen to be concomitant with structural distortions and the appearance of conductive regions in otherwise-insulating material. Crucially, we demonstrate for the first time the correlation between resistance switching and the emission of oxygen from an electrically stressed dielectric film. These results confirm the current model of an oxygen-based mechanism and highlight the inherent limitations imposed by gradual oxygen depletion on device lifetime.
Pham KC, McPhail DS, Mattevi C, et al., 2016, Graphene-Carbon Nanotube Hybrids as Robust Catalyst Supports in Proton Exchange Membrane Fuel Cells, Journal of the Electrochemical Society, Vol: 163, Pages: F255-F263, ISSN: 0013-4651
Catalyst degradation is one major challenge preventing the worldwide commercialization of the Proton Exchange Membrane Fuel Cells. In this study, we investigate the development of a novel hierarchical carbonaceous support for the platinum catalysts, called graphene-carbon nanotube hybrids (GCNT), and its degradation behavior during an accelerated degradation test. The carbon support is fabricated by growing graphene directly onto carbon nanotubes to form a unique all-carbon nanostructure possessing both an ultra-high density of exposed graphitic edges of graphene and a porous structure of carbon nanotubes. The GCNT-supported platinum catalyst exhibits a higher intrinsic catalytic activity than a carbon black-supported platinum catalyst, and much higher than a CNT-supported platinum catalyst. The enhanced catalytic activity of the GCNT-supported platinum catalyst is explained by the high graphitic edge density which promotes the catalytic reactions on platinum catalyst. The GCNT-supported platinum catalyst also exhibits a superior electrochemical stability over that of the carbon black-supported platinum catalyst, explained by the high crystallinity of the GCNT support. The superior stability is expressed by a lower loss in polarization performance, a smaller increase in charge transfer resistance, a lower loss in the platinum electrochemical surface area, a lower rate of carbon corrosion, and a more stable catalyst microstructure.
Wang D, Romer F, Connell L, et al., 2015, Highly flexible silica/chitosan hybrid scaffolds with oriented pores for tissue regeneration, Journal of Materials Chemistry B, Vol: 3, Pages: 7560-7576, ISSN: 2050-7518
Inorganic/organic sol–gel hybrids have nanoscale co-networks of organic and inorganic components that give them the unique potential of tailored mechanical properties and controlled biodegradation in tissue engineering applications. Here, silica/chitosan hybrid scaffolds with oriented structures were fabricated through the sol–gel method with a unidirectional freeze casting process. 3-Glycidoxypropyl trimethoxysilane (GPTMS) was used to obtain covalent inorganic/organic coupling. Process variables were investigated such as cooling rate, GPTMS and inorganic content, which can be used to tailor the mechanical properties and hybrid chemical coupling. Structural characterization and dissolution tests confirmed the covalent cross-linking of the chitosan and the silica network in hybrids. The scaffolds had a directional lamellar structure along the freezing direction and a cellular morphology perpendicular to the freezing direction. Compression testing showed that the scaffolds with 60 wt% organic were flexible and elastomeric perpendicular to the freezing direction whilst behaving in an elastic-brittle fashion parallel to the freezing direction. The compressive strengths are about one order of magnitude higher in the latter direction reaching values of the order of 160 kPa. This behaviour provides potential for clinicians to be able to squeeze the materials to fit tissue defect sites while providing some mechanical support from the other direction.
Bundy JG, Liebeke M, Strittmatter N, et al., 2015, Unique metabolites protect earthworms against plant polyphenols, Nature Communications, Vol: 6, Pages: 1-7, ISSN: 2041-1723
All higher plants produce polyphenols, for defence against above-ground herbivory. These polyphenols also influence the soil micro- and macrofauna that break down plant leaf litter. Polyphenols therefore indirectly affect the fluxes of soil nutrients and, ultimately, carbon turnover and ecosystem functioning in soils. It is unknown how earthworms, the major component of animal biomass in many soils, cope with high-polyphenol diets. Here, we show that earthworms possess a class of unique surface-active metabolites in their gut, which we term ‘drilodefensins’. These compounds counteract the inhibitory effects of polyphenols on earthworm gut enzymes, and high polyphenol diets increase drilodefensin concentrations in both laboratory and field populations. This shows that drilodefensins protect earthworms from the harmful effects of ingested polyphenols. We have identified the key mechanism for adaptation to a dietary challenge in an animal group that has a major role in organic matter recycling in soils worldwide.
Thompson RB, Reffatto V, Bundy JG, et al., 2015, Correction: Identification of hydroxyapatite spherules provides new insight into subretinal pigment epithelial deposit formation in the aging eye (Proceedings of the National Academy of Sciences of the United States of America (2015) 112, 5, (1565-1570) DOI: 10.1073/pnas.1413347112), Proceedings of the National Academy of Sciences, Vol: 112, Pages: E3971-E3971, ISSN: 0027-8424
Pilgrim MG, Csincsik L, Fearn S, et al., 2015, High-resolution molecular imaging of hydroxyapatite associated with sub-RPE deposits, Annual Meeting of the Association-for-Research-in-Vision-and-Ophthalmology (ARVO), Publisher: ASSOC RESEARCH VISION OPHTHALMOLOGY INC, ISSN: 0146-0404
Mehonic A, Buckwell M, Montesi L, et al., 2015, Structural changes and conductance thresholds in metal-free intrinsic SiOx resistive random access memory, Journal of Applied Physics, Vol: 117, ISSN: 1089-7550
We present an investigation of structural changes in silicon-rich silicon oxide metal-insulator-metal resistive RAM devices. The observed unipolar switching, which is intrinsic to the bulk oxide material and does not involve movement of metal ions, correlates with changes in the structure of the oxide. We use atomic force microscopy, conductive atomic force microscopy, x-ray photoelectron spectroscopy, and secondary ion mass spectroscopy to examine the structural changes occurring as a result of switching. We confirm that protrusions formed at the surface of samples during switching are bubbles, which are likely to be related to the outdiffusion of oxygen. This supports existing models for valence-change based resistive switching in oxides. In addition, we describe parallel linear and nonlinear conduction pathways and suggest that the conductance quantum, G0, is a natural boundary between the high and low resistance states of our devices.
Thompson RB, Reffatto V, Bundy JG, et al., 2015, Identification of hydroxyapatite spherules provides new insight into subretinal pigment epithelial deposit formation in the aging eye, Proceedings of the National Academy of Sciences of the United States of America, Vol: 112, Pages: 1565-1570, ISSN: 1091-6490
Accumulation of protein- and lipid-containing deposits external to the retinal pigment epithelium (RPE) is common in the aging eye, and has long been viewed as the hallmark of age-related macular degeneration (AMD). The cause for the accumulation and retention of molecules in the sub-RPE space, however, remains an enigma. Here, we present fluorescence microscopy and X-ray diffraction evidence for the formation of small (0.5–20 μm in diameter), hollow, hydroxyapatite (HAP) spherules in Bruch’s membrane in human eyes. These spherules are distinct in form, placement, and staining from the well-known calcification of the elastin layer of the aging Bruch’s membrane. Secondary ion mass spectrometry (SIMS) imaging confirmed the presence of calcium phosphate in the spherules and identified cholesterol enrichment in their core. Using HAP-selective fluorescent dyes, we show that all types of sub-RPE deposits in the macula, as well as in the periphery, contain numerous HAP spherules. Immunohistochemical labeling for proteins characteristic of sub-RPE deposits, such as complement factor H, vitronectin, and amyloid beta, revealed that HAP spherules were coated with these proteins. HAP spherules were also found outside the sub-RPE deposits, ready to bind proteins at the RPE/choroid interface. Based on these results, we propose a novel mechanism for the growth, and possibly even the formation, of sub-RPE deposits, namely, that the deposit growth and formation begin with the deposition of insoluble HAP shells around naturally occurring, cholesterol-containing extracellular lipid droplets at the RPE/choroid interface; proteins and lipids then attach to these shells, initiating or supporting the growth of sub-RPE deposits.
Foss BJ, Hardy MC, Child DJ, et al., 2014, Oxidation of a Commercial Nickel-Based Superalloy under Static Loading, JOM, Vol: 66, Pages: 2516-2524, ISSN: 1047-4838
Druce J, Tellez H, Burriel M, et al., 2014, Surface termination and subsurface restructuring of perovskite-based solid oxide electrode materials, Energy and Environmental Science, Vol: 7, Pages: 3593-3599, ISSN: 1754-5692
We study the outer atomic surfaces of a series of perovskite-based ceramics using low energy ion scattering spectroscopy. After high temperature treatment, segregated A-site (or acceptor substituent) cations dominate the outer surfaces with no B-site cations detected. We also find evidence of an associated B-cation enriched region below the surface.
Chater RJ, Shollock BA, McPhail DS, et al., 2014, Differentially pumped quadrupole SIMS probe on FIB-based and two-beam microscopes, 19th International Conference on Secondary Ion Mass Spectrometry (SIMS), Publisher: WILEY-BLACKWELL, Pages: 372-374, ISSN: 0142-2421
Tellez H, Aguadero A, Druce J, et al., 2014, New perspectives in the surface analysis of energy materials by combined time-of-flight secondary ion mass spectrometry (ToF-SIMS) and high sensitivity low-energy ion scattering (HS-LEIS), Journal of Analytical Atomic Spectrometry, Vol: 29, Pages: 1361-1370, ISSN: 0267-9477
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and low-energy ion scattering (LEIS) are recently attracting great interest in energy materials research due to their capabilities in terms of surface sensitivity and specificity, spatial resolution and their ability to analyse the isotopic chemical composition. This work shows the synergy provided by this powerful combination to further our understanding of the surface chemistry and structure that ultimately determines the electrochemical performance in advanced electro-ceramic materials for energy storage and energy conversion applications. In particular, this novel approach has been applied to the analysis of (Li3xLa2/3−x□1/3−2x)TiO3 perovskite materials used as the electrolyte in lithium batteries and (La, Sr)2CoO4+δ epitaxial thin films used as oxygen electrodes in solid oxide fuel cells and solid oxide electrolysers. The analysis of these two promising materials requires the development and optimisation of new analytical approaches that take advantage of the recent instrumental developments in order to characterise the outermost and near-surfaces at the atomic scale.
Wang D, Nakamura J, Poologasundarampillai G, et al., 2014, ToF-SIMS evaluation of calcium-containing silica/gamma-PGA hybrid systems for bone regeneration., APPLIED SURFACE SCIENCE, Vol: 309, Pages: 231-239, ISSN: 0169-4332
Poologasundarampillai G, Yu B, Tsigkou O, et al., 2014, Poly(gamma-glutamic acid)/Silica Hybrids with Calcium Incorporated in the Silica Network by Use of a Calcium Alkoxide Precursor, Chemistry-A European Journal, Vol: 20, Pages: 8149-8160, ISSN: 1521-3765
Current materials used for bone regeneration are usually bioactive ceramics or glasses. Although they bond to bone, they are brittle. There is a need for new materials that can combine bioactivity with toughness and controlled biodegradation. Sol-gel hybrids have the potential to do this through their nanoscale interpenetrating networks (IPN) of inorganic and organic components. Poly(γ-glutamic acid) (γ-PGA) was introduced into the sol-gel process to produce a hybrid of γ-PGA and bioactive silica. Calcium is an important element for bone regeneration but calcium sources that are used traditionally in the sol-gel process, such as Ca salts, do not allow Ca incorporation into the silicate network during low-temperature processing. The hypothesis for this study was that using calcium methoxyethoxide (CME) as the Ca source would allow Ca incorporation into the silicate component of the hybrid at room temperature. The produced hybrids would have improved mechanical properties and controlled degradation compared with hybrids of calcium chloride (CaCl2), in which the Ca is not incorporated into the silicate network. Class II hybrids, with covalent bonds between the inorganic and organic species, were synthesised by using organosilane. Calcium incorporation in both the organic and inorganic IPNs of the hybrid was improved when CME was used. This was clearly observed by using FTIR and solid-state NMR spectroscopy, which showed ionic cross-linking of γ-PGA by Ca and a lower degree of condensation of the Si species compared with the hybrids made with CaCl2 as the Ca source. The ionic cross-linking of γ-PGA by Ca resulted in excellent compressive strength and reduced elastic modulus as measured by compressive testing and nanoindentation, respectively. All hybrids showed bioactivity as hydroxyapatite (HA) was formed after immersion in simulated body fluid (SBF).
Poologasundarampillai G, Wang D, Li S, et al., 2014, Cotton-wool-like bioactive glasses for bone regeneration, Acta Biomaterialia, Vol: 10, Pages: 3733-3746, ISSN: 1742-7061
Inorganic sol–gel solutions were electrospun to produce the first bioactive three-dimensional (3-D) scaffolds for bone tissue regeneration with a structure like cotton-wool (or cotton candy). This flexible 3-D fibrous structure is ideal for packing into complex defects. It also has large inter-fiber spaces to promote vascularization, penetration of cells and transport of nutrients throughout the scaffold. The 3-D fibrous structure was obtained by electrospinning, where the applied electric field and the instabilities exert tremendous force on the spinning jet, which is required to be viscoelastic to prevent jet break up. Previously, polymer binding agents were used with inorganic solutions to produce electrospun composite two-dimensional fibermats, requiring calcination to remove the polymer. This study presents novel reaction and processing conditions for producing a viscoelastic inorganic sol–gel solution that results in fibers by the entanglement of the intermolecularly overlapped nanosilica species in the solution, eliminating the need for a binder. Three-dimensional cotton-wool-like structures were only produced when solutions containing calcium nitrate were used, suggesting that the charge of the Ca2+ ions had a significant effect. The resulting bioactive silica fibers had a narrow diameter range of 0.5–2 μm and were nanoporous. A hydroxycarbonate apatite layer was formed on the fibers within the first 12 h of soaking in simulated body fluid. MC3T3-E1 preosteoblast cells cultured on the fibers showed no adverse cytotoxic effect and they were observed to attach to and spread in the material.
Wang D, Poologasundarampillai G, van den Bergh W, et al., 2014, Strategies for the chemical analysis of highly porous bone scaffolds using secondary ion mass spectrometry, BIOMEDICAL MATERIALS, Vol: 9, ISSN: 1748-6041
Pham K-C, Chua DHC, McPhail DS, et al., 2014, The Direct Growth of Graphene-Carbon Nanotube Hybrids as Catalyst Support for High-Performance PEM Fuel Cells, ECS ELECTROCHEMISTRY LETTERS, Vol: 3, Pages: F37-F40, ISSN: 2162-8726
Arora HS, Grewal HS, Singh H, et al., 2014, Microstructure-Property Relationship for Friction Stir Processed Magnesium Alloy, ADVANCED ENGINEERING MATERIALS, Vol: 16, Pages: 94-102, ISSN: 1438-1656
Fajardo S, Bastidas DM, Ryan MP, et al., 2014, Low energy SIMS characterization of passive oxide films formed on a low-nickel stainless steel in alkaline media., APPLIED SURFACE SCIENCE, Vol: 288, Pages: 423-429, ISSN: 0169-4332
Pham K-C, Chua DHC, McPhail DS, et al., 2013, Graphene nanoflakes carbon nanotubes hybrid as highly robust catalyst support in proton exchange membrane fuel cells, 246th National Meeting of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Leo BF, Chen S, Kyo Y, et al., 2013, The Stability of Silver Nanoparticles in a Model of Pulmonary Surfactant., Environ Sci Technol, Vol: 47, Pages: 11232-11240
The growing use of silver nanoparticles (AgNPs) in consumer products has raised concerns about their potential impact on the environment and human health. Whether AgNPs dissolve and release Ag+ ions, or coarsen to form large aggregates, is critical in determining their potential toxicity. In this work, the stability of AgNPs in dipalmitoylphosphatidylcholine (DPPC), the major component of pulmonary surfactant, was investigated as a function of pH. Spherical, citrate-capped AgNPs with average diameters of 14 ± 1.6 nm (n=200) were prepared by a chemical bath reduction. The kinetics of Ag+ ion release was strongly pH-dependent. After 14 days of incubation in sodium perchlorate (NaClO4) or perchloric acid (HClO4) solutions, the total fraction of AgNPs dissolved varied from ~10 % at pH 3, to ~2 % at pH 5, with negligible dissolution at pH 7. A decrease in pH from 7 to 3 also promoted particle aggregation and coarsening. DPPC (100 mg.L-1) delayed the release of Ag+ ions, but did not significantly alter the total amount of Ag+ released after two weeks. In addition, DPPC improved the dispersion of the AgNPs and inhibited aggregation and coarsening. TEM images revealed that the AgNPs were coated with a DPPC layer serving as a semi-permeable layer. Hence, lung lining fluid, particularly DPPC, can modify the aggregation state and kinetics of Ag+ ion release of inhaled AgNPs in the lung. These observations have important implications for predicting the potential reactivity of AgNPs in the lung and the environment.
Valliant EM, Romer F, Wang D, et al., 2013, Bioactivity in silica/poly(gamma-glutamic acid) sol-gel hybrids through calcium chelation, ACTA BIOMATERIALIA, Vol: 9, Pages: 7662-7671, ISSN: 1742-7061
Gholami F, Zein SHS, Gerhardt L-C, et al., 2013, Cytocompatibility, bioactivity and. mechanical strength of calcium phosphate cement reinforced with multi-walled carbon nanotubes and bovine serum albumin, CERAMICS INTERNATIONAL, Vol: 39, Pages: 4975-4983, ISSN: 0272-8842
Foss BJ, Gray S, Hardy MC, et al., 2013, Analysis of shot-peening and residual stress relaxation in the nickel-based superalloy RR1000, ACTA MATERIALIA, Vol: 61, Pages: 2548-2559, ISSN: 1359-6454
Chew K-K, Zein SHS, Ahmad AL, et al., 2013, The electrochemical studies of the corrosion resistance behaviour of hydroxyapatite coatings on stainless steel fabricated by electrophoretic deposition, Journal of Industrial and Engineering Chemistry, Vol: 19, Pages: 1123-1129, ISSN: 1226-086X
Westacott P, Tumbleston JR, Shoaee S, et al., 2013, On the role of intermixed phases in organic photovoltaic blends, Energy & Environmental Science, ISSN: 1754-5692
Kane DM, Chater RJ, Mcphail DS, 2012, Evaluation of imperfections in silica and chalcogenide glass microspheres using focussed ion beam milling and imaging, JOURNAL OF MICROSCOPY, Vol: 247, Pages: 186-195, ISSN: 0022-2720
Geier FM, Fearn S, Bundy JG, et al., 2012, ToF-SIMS analysis of biomolecules in the modelorganism Caenorhabditis elegans, Surface and Interface Analysis, Vol: 45, Pages: 234-236
C.elegans is a biomedical key model organism as it is a simple, easy to maintain eukaryote, which shares many gene homologueswith higher mammals. As each of its cells has been traced during development and characterized by light microscopy, massspectrometry-based time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging seems to promise exciting new insights.In this study, we have investigated simple but basic factors for ToF-SIMS-based imaging of C.elegans. By comparing chemicalstandards and two authentic C. elegans mutant extracts (N2 and Daf-2), we found that for our purposes, Bi3+ is better suiteddue to its higher mass and spatial resolution. We also investigated the use of light microscopy slides as imaging substrates andgold coating as standard for mass calibration in higher mass ranges. Our findings and preliminary imaging results show thatToF-SIMS is a well-suited platform for mass spectrometry imaging.
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