Browsing by Author "James, M"

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    40th Annual Condensed Matter and Materials Meeting, Charles Sturt University, Wagga Wagga, NSW, 2nd February – 5th February, 2016
    (Australian Institute of Physics, 2016-02-02) Tadich, A; Brand, HEA; Appadoo, D; Finlayson, TR; James, M
    The 40th Annual Condensed Matter and Materials Meeting was held at Charles Sturt University, Wagga Wagga, NSW from 2 - 5 February, 2016. There were 116 attendees, including international visitors from Scotland, China, Taiwan and New Zealand. A total of 10 invited and 29 contributed oral papers were presented during the two and one half days of scientific sessions. There were also two sessions with a total of 70 poster presentations. All presenters were invited to submit a manuscript (six pages for invited papers and four for contributed papers) for publication in the conference proceedings. Each manuscript was refereed by at least two anonymous reviewers who worked to a set of guidelines made available by the editor. Each accepted publication therefore satisfies the requirements for classification as a refereed conference publication (E1). The organizers would like to thank the reviewers for their time and effort in reviewing manuscripts, which resulted in 10 papers being accepted for publication.
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    Ab initio structure determinations of high-performance radioactive waste forms
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Carter, ML; Wallwork, KS; James, M; Withers, RL
    Immobilisation of high-level radioactive wastes in stable matrices for long-term storage or geological disposal is a key step in closing the nuclear fuel cycle. Titanate minerals have shown much promise in their capacity to take up radioactive elements into their crystal structures at regular lattice sites in pyrochlore and brannerite phases. Previously unreported uranyl titanates BaUTiO6 and Na2U3Ti2O11 have been synthesised under argon at 1400 and 1250 deg. C, respectively and their structures determined by ab initio techniques using a combination of electron, synchrotron and neutron powder diffraction. BaUTiO6 crystallises with a carnotite-type structure (P21/c; a=6.4463(1) A, b=8.5999(1) A, c=10.2532(1) A; >=75.936(1)o and V=551.36(1) A3); while Na2U3Ti2O11 forms an orthorhombic structure (Pnma; a=31.0421(8) A, b=7.2774(2) A, c=7.6111(2) A and V=1719.4(1) A3). Due to their potential value as a radioactive waste forms, the leach rates of uranium, barium and sodium were determined. Normalised uranium leach rates from BaUTiO6 and Na2U3Ti2O11, averaged over 7 days were orders of magnitude less than those for brannerite and for U-containing pyrochlore waste forms. © The Authors
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    Ab initio structure determinations of high-performance radioactive waste forms
    (Elsevier B. V., 2006-11-15) Carter, ML; Wallwork, KS; James, M; Withers, RL
    Immobilisation of high-level radioactive wastes in stable matrices for long-term storage or geological disposal is a key step in closing the nuclear fuel cycle. Titanate minerals have shown much promise in their capacity to take up radioactive elements into their crystal structures at regular lattice sites in pyrochlore and brannerite phases. Previously unreported uranyl titanates BaUTiO6 and Na2U3Ti2O11 have been synthesised under argon at 1400 and 1250 deg. C, respectively and their structures determined by ab initio techniques using a combination of electron, synchrotron and neutron powder diffraction. BaUTiO6 crystallises with a carnotite-type structure (P21/c; a=6.4463(1) A, b=8.5999(1) A, c=10.2532(1) A; >=75.936(1)o and V=551.36(1) A3); while Na2U3Ti2O11 forms an orthorhombic structure (Pnma; a=31.0421(8) A, b=7.2774(2) A, c=7.6111(2) A and V=1719.4(1) A3). Due to their potential value as a radioactive waste forms, the leach rates of uranium, barium and sodium were determined. Normalised uranium leach rates from BaUTiO6 and Na2U3Ti2O11, averaged over 7 days were orders of magnitude less than those for brannerite and for U-containing pyrochlore waste forms. Crown Copyright © 2006 Published by Elsevier B.V
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    An AC susceptibility study of strontium cobaltates, Ln1-xSrxCoO3-δ where Ln = Y, Ho and Dy
    (Australian Institute of Physics, 2003-02-04) Wilson, KF; Goossens, DJ; Cochrane, JM; James, M
    We discuss the AC susceptibility of members of the Ln1-xSrxCoO3-δ family of materials where 0.66 ≤ x ≤ 0.9 and Ln = Y, Dy and Ho. The materials exhibit ferro- or ferrimagnetic ordering below room temperature. Despite the disorder introduced by mixed Co valence states, no glassiness is apparent in the imaginary part of the AC susceptibility or in the frequency dependence of the transition temperature. In addition, in the Dy and Ho materials it is found that the rare earth moments do not couple to the Co magnetic lattice.
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    Anionic phospholipid interactions of the prion protein N terminus are minimally perturbing and not driven solely by the octapeptide repeat domain
    (American Society for Biochemistry and Molecular Biology, 2010-10-15) Boland, MP; Hatty, CR; Separovic, F; Hill, AF; Tew, DJ; Barnham, KJ; Haigh, CL; James, M; Masters, CL; Collins, SJ
    Although the N terminus of the prion protein (PrPC) has been shown to directly associate with lipid membranes, the precise determinants, biophysical basis, and functional implications of such binding, particularly in relation to endogenously occurring fragments, are unresolved. To better understand these issues, we studied a range of synthetic peptides: specifically those equating to the N1 (residues 23–110) and N2 (23–89) fragments derived from constitutive processing of PrPC and including those representing arbitrarily defined component domains of the N terminus of mouse prion protein. Utilizing more physiologically relevant large unilamellar vesicles, fluorescence studies at synaptosomal pH (7.4) showed absent binding of all peptides to lipids containing the zwitterionic headgroup phosphatidylcholine and mixtures containing the anionic headgroups phosphatidylglycerol or phosphatidylserine. At pH 5, typical of early endosomes, quartz crystal microbalance with dissipation showed the highest affinity binding occurred with N1 and N2, selective for anionic lipid species. Of particular note, the absence of binding by individual peptides representing component domains underscored the importance of the combination of the octapeptide repeat and the N-terminal polybasic regions for effective membrane interaction. In addition, using quartz crystal microbalance with dissipation and solid-state NMR, we characterized for the first time that both N1 and N2 deeply insert into the lipid bilayer with minimal disruption. Potential functional implications related to cellular stress responses are discussed. © 2010, American Society for Biochemistry and Molecular Biology
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    The antimicrobial peptide aurein 1.2 disrupts model membranes via the carpet mechanism
    (Royal Society of Chemistry, 2012-01-01) Fernandez, DI; Le Brun, AP; Whitwell, TC; Sani, MA; James, M; Separovic, F
    The membrane interactions of the antimicrobial peptide aurein 1.2 were studied using a range of biophysical techniques to determine the location and the mechanism of action in DMPC (dimyristoylphosphatidylcholine) and DMPC/DMPG (dimyristoylphosphatidylglycerol) model membranes that mimic characteristics of eukaryotic and prokaryotic membranes, respectively. Neutron reflectometry and solid-state NMR revealed subtle changes in membrane structure caused by the peptide. Quartz crystal microbalance with dissipation, vesicle dye leakage and atomic force microscopy measurements were used to investigate the global mode of peptide interaction. Aurein 1.2 displayed an enhanced interaction with the anionic DMPC/DMPG membrane while exhibiting primarily a surface interaction with both types of model membranes, which led to bilayer disruption and membrane lysis. The antimicrobial peptide interaction is consistent with the carpet mechanism for aurein 1.2 with discrete structural changes depending on the type of phospholipid membrane. © 2012, Royal Society of Chemistry
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    The Australian Synchrotron in 2015 – turning bright ideas into brilliant outcomes
    (Australian Institute of Physics, 2016-02-03) James, M
    When VIP visitors come to the Australian Synchrotron (Commonwealth Ministers & their minders, Directors of national and international laboratories & research institutes; VCs & DVCRs; my Mother-in-Law…) we like to play a little game to try and impress them and to demonstrate the impact of our efforts. It goes a little like this: Mike: “Pick a topic, any topic, and I will tell you how we make a difference to that, by research carried-out at the Australian Synchrotron” (It helps a little if they have an interest in a specific disease or medical condition, but this is not essential). VIP: “Well…, How about…” And so on... A strange way to try and achieve the much-needed financial security that our facility so needs I hear you say; and yes, when we face some of our more imaginative foes, the link to their topic can be more than a little tenuous. (Ok sometimes, we crash and burn). However, for the most part, with about 1000 experiments per year to choose from, we walk away with our heads held high. My talk will give a brief overview of the Australian Synchrotron, as well as its status and future as one of the most substantial pieces of research infrastructure in the country. I will present some recent research highlights, particularly pertaining to condensed matter research, and challenge you to challenge us to see how the Australian Synchrotron can make a difference to your research. Pick a topic, any topic…
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    The Australian Synchrotron in the international Year of Crystallography
    (Australian Institute of Physics, 2014-09-01) James, M; Brand, HEA; Panjikar, S
    The Australian Synchrotron has been providing world quality X-ray diffraction instrumentation and expertise to the scientific community via the Powder Diffraction and two Macromolecular Crystallography beamlines since 2007. These capabilities reach across the scientific landscape from studies of advanced materials for applications such as electronics displays and new energy technologies, to development of new pharmaceuticals, studies of disease and other fundamental biological processes. © 2014 Australian Institute of Physics Inc.
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    The binding and fluorescence quenching efficiency of nitroaromatic (explosive) vapors in fluorescent carbazole dendrimer thin films
    (Royal Society of Chemistry, 2013-01-01) Shaw, PE; Cavaye, H; Chen, SSY; James, M; Gentle, IR; Burn, PL
    We present a study on three generations of fluorescent carbazole dendrimers that exhibit strong binding with nitroaromatic compounds accompanied by photoluminescence (PL) quenching, making them attractive sensing materials for the detection of explosives such as 2,4,6-trinitrotoluene (TNT). The absorption and release of vapors of the (deuterated) TNT analogue 4-nitrotoluene (pNT) from thin films of the dendrimers were studied with a combination of time-correlated neutron reflectometry and PL spectroscopy. When saturated with pNT the PL of the films was fully quenched and could not be recovered with flowing nitrogen at room temperature but only upon heating to 40-80 [degree]C. Although the majority of the absorbed pNT could be removed with this method the recovered films were found to still contain a residual pNT concentration of [similar]0.1 molecules per cubic nanometer. However, the proportion of the PL recovered increased with generation with the third generation dendrimer exhibiting close to full recovery despite the presence of residual pNT. This result is attributed to a combination of two effects. First, the dendrimer films present a range of binding sites for nitroaromatic molecules with the stronger binding sites surviving the thermal recovery process. Second, there is a large decrease of the exciton diffusion coefficient with dendrimer generation, preventing migration of the excitation to the remaining bound pNT.© 2013, Royal Society of Chemistry
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    Characterisation of alkyl-functionalised Si(111) using reflectometry and AC impedance spectroscopy
    (Elsevier, 2007-12-15) Wong, ELS; James, M; Chilcott, TC; Coster, HGL
    The past few years have seen a dramatic increase in the study of organic thin-film systems that are based on silicon–carbon covalent bonds for bio-passivation or bio-sensing applications. This approach to functionalizing Si wafers is in contrast to gold-thiol or siloxane chemistries and has been shown to lead to densely packed alkyl monolayers. In this study, a series of alkyl monolayers [CH³(CH²)nCH=CH²; n=7, 9, 11, 13, 15] were directly covalent-linked to Si(111) wafers. The structures of these monolayers were studied using X-ray reflectometry (XRR) and AC impedance spectroscopy. Both techniques are sensitive to the variation in thickness with each addition of a CH2 unit and thus provide a useful means for monitoring molecular-scale events. The combination of these techniques is able to probe not only the thickness, but also the interfacial roughness and capacitance of the layer at the immobilized surface with atomic resolution. Fundamental physical properties of these films such as chain canting angles were also determined. © 2007, Elsevier Ltd.
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    Characterization of thin films for X-ray and neutron waveguiding by x-ray reflectivity and atomic force microscopy
    (Wiley-VCH Verlag GMBH, 2013-11-01) Pelliccia, D; Kandasamy, S; James, M
    X-ray and neutron guiding in thin-film waveguides are finding numerous applications, such as sub-micron beam production for X-ray microscopy, and applications in neutron interferometric devices and polarizers. Thin-film waveguides are composed of a three-layer stack where the central layer, displaying low absorption for X-rays/neutrons, act as a guiding film. The utilization of such systems with low brilliance X-rays and neutron sources, requires the thickness of the guiding film to be increased. The efficiency of the waveguides critically depends on the thickness of the guiding layer and its surface roughness. In this paper we address the problem of producing relatively thick and smooth guiding layers for a high efficiency, thin-film neutron waveguide. We have produced a Ni/Al/Ni tri-layer structure with a 500 nm thick Al layer optimized for neutron waveguiding. The characterization is performed by complementary X-ray reflectometry and atomic force microscopy. The surface roughness estimation by mean of the two methods is presented and discussed. We show that a combination of sputtering/evaporation processes is beneficial in reducing the roughness of the Al film. © 2013, Wiley-VCH Verlag GmbH & Co. KGaA
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    Characterizing the photoinduced switching process of a nitrospiropyran self-assembled monolayer using in situ sum frequency generation spectroscopy
    (American Chemical Society, 2012-10-02) Darwish, TA; Tong, YJ; James, M; Hanley, TL; Peng, QL; Ye, S
    Sum frequency generation (SFG) vibrational spectroscopy is employed to investigate the reversible, photoinduced spiro -> merocyanine isomerization of a self-assembled monolayer, the result of attachment of nitrospiropyran to a gold surface using a dithiolane anchoring group. The attachment of these molecular "alligator clips" to spiropyran molecules provide an easily accessible method to self-assemble a robust monolayer of spiropyran on a gold surface, which allows photoswitching of the spiropyran units. Probing the symmetric and antisymmetric stretching modes of the nitro group allows the determination of the structural orientation of the charged moiety with respect to the surface normal as well as the isomerization rates under photoinduced switching conditions. The photoisomerization of the spiropyran SAM on the gold surface is much faster than the rates of switching spiropyrans in a solid crystalline form, and the rate of thermal relaxation of the opened to closed form in this study is found to be on the same time scale as the relaxation of spiropyran when present in solutions with polar solvents. © 2012, American Chemical Society.
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    CO2 triggering and controlling orthogonally multiresponsive photochromic systems
    (American Chemical Society, 2010-08-11) Darwish, TA; Evans, RA; James, M; Malic, N; Triani, G; Hanley, TL
    We report a new generic method of reversibly controlling the photochromism of spiropyrans. It was found that the photochromic effect of spiropyrans can be reversibly switched on and off by addition and removal of carbon dioxide (CO2) to spiropyran in alcohol solutions containing an amidine (i.e., DBU) that acts as a CO2 sensitizer. Spiropyrans are not photochromic in the presence of DBU but photochromic when CO2 is subsequently added to the solution. The CO2 is readily removed by inert gas bubbling, thus allowing facile activation and deactivation of the photochromic effect. Carbon dioxide, without the presence of the sensitizing amidine, had no effect on photochromism of the spiropyrans. Other photochromic dyes classes such as spirooxazines and chromenes are not affected by this CO2/DBU stimulus. As a result, orthogonal activation of mixtures of spirooxazines and spiropyrans was achieved to provide four color states (clear, yellow, green, and blue) by varying the combinations of the stimuli of UV, visible light, CO2, and CO2 depleted. This finding now permits the many applications using spiropyrans to be CO2 responsive. © 2010, American Chemical Society
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    Comparative study of neutron reflectometry, x-ray reflectometry and electrical impedance spectroscopy of organic films on silicon
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Wong, ELS; James, M; Coster, HGL; Chilcott, TC
    A comparative study has been made of the substructure and properties of functionalized organic layers on silicon substrates, using neutron reflectivity, X-Ray reflectivity and low frequency electrical impedance spectroscopy (EIS). All three techniques have similar spatial structural resolution. X-Ray reflectometry provides information on the electron density of substructural layers whilst EIS provides data on the electric polarizability and electrical conductance properties of individual substructural layers. Neutron reflectivity likewise provides data on the atomic mass density of the layers. With organic films the contrast in neutron scattering for the elements of interest such as C, O, N is not very large. However, replacement of H2O with D2O allows a much enhanced contrast to be obtained and provides information in particular of the interdigitation of water molecules into film. This impinges on the polarizability and electrical conductance as as measured by EIS. © 2005 The Authors
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    Comparing the reactivity of alkynes and alkenes on silicon (100) surfaces
    (American Chemical Society, 2009-12-15) Ng, A; Ciampi, S; James, M; Harper, JB; Gooding, JJ
    The relative reactivities of alkynes to alkenes on hydrogen-terminated silicon (100) surfaces, under conditions where a monolayer will be produced via hydrosilylation, were measured using two different approaches. The first approach was to form monolayers from a series of solutions containing different mole fractions of an alkyne, with a trifluorothioacetate distal moiety and an alkene with a terminal carboxylic acid functional. X-ray photoelectron spectroscopic analysis of the resultant surfaces showed that the mole fraction of alkyne on the surface was larger than that in the respective alkyne/alkene mixture. By filling the XPS data, we estimated that the reactivity ratio of alkynec to alkene was approximately 1.7 +/- 0.2 when monolayers were formed at 120 degrees C. The second approach was using a molecule containing both an alkyne at one end and an alkene at the other, non-1-yne-8-ene, as the hydrosilylation reagent such that either end Could attach to the silicon surface. The relative orientation of this molecule, once reacted with it hydrogen-terminated Si(100) surface, was determined by coupling ail additional reagent to the distal end of the monolayer. The reagent used was azidoferrocene, which could attach onto free alkyne moieties on the surface only via the 1,3-Huisgen cycloaddition "click" reaction. Electrochemical analysis was then used to determine how many ferrocene moieties were attached to the SAM surface. In this way, it was shown that the alkyne end reacted preferentially with the silicon surface compared with the alkene end. The reactivity ratio of the alkyne end to the alkene end was increased front 2.0 +/- 0.2 to 9 +/- 1 when the temperature was decreased from 120 to 65 degrees C. © 2009, American Chemical Society
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    Competition between dewetting and cross-linking in poly(N-vinylpyrrolidone)/polystyrene bilayer films
    (American Chemical Society, 2011-12-06) Telford, AM; Thickett, SC; James, M; Neto, C
    We investigated the dewetting of metastable poly(N-vinylpyrrolidone) (PNVP) thin films (45 nm) on top of polystyrene (PS) thin films (58 nm) as a function of annealing temperature and molecular weight of PS (96 and 6850 kg/mol). We focused on the competition between dewetting, occurring as a result of unfavorable intermolecular interactions at the PNVP/PS interface, and spontaneous cross-linking of PNVP, occurring during thermal annealing, as we recently reported (Telford, A. M.; James, M.; Meagher, L.; Neto, C. ACS Appl. Mater. Interfaces2010, 2, 2399?2408). Using optical microscopy, we studied how the dewetting morphology and dynamics at different temperatures depended on the relative viscosity of the top PNVP film, which increased with cross-linking time, and of the bottom PS film. In the PNVP/PS96K system, cross-linking dominated over dewetting at temperatures below 180 °C, reducing drastically nucleated hole density and their maximum size, while above 180 °C the two processes reversed, with complete dewetting occurring at 200 °C. On the other hand, the PNVP/PS6850K system never achieved advanced dewetting stages as the dewetting was slower than cross-linking in the investigated temperature range. In both systems, dewetting of the PNVP films could be avoided altogether by thermally annealing the bilayers at temperatures where cross-linking dominated. The cross-linking was characterized quantitatively using neutron reflectometry, which indicated shrinkage and densification of the PNVP film, and qualitatively through selective removal of the bottom PS film. A simple model accounting for progressive cross-linking during the dewetting process predicted well the observed hole growth profiles and produced estimates of the PNVP cross-linking rate coefficients and of the activation energy of the process, in good agreement with literature values for similar systems.© 2011, American Chemical Society
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    Comprehensive study of carbon dioxide adsorption in the metal–organic frameworks M2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn)
    (Royal Society of Chemistry, 2014-08-28) Queen, WL; Hudson, MR; Bloch, ED; Mason, JA; Gonzalez, MI; Lee, JS; Gygi, D; Howe, JD; Lee, K; Darwish, TA; James, M; Peterson, VK; Teat, SJ; Smit, B; Neaton, JB; Long, JR; Brown, CM
    Analysis of the CO2 adsorption properties of a well-known series of metal–organic frameworks M2(dobdc) (dobdc4− = 2,5-dioxido-1,4-benzenedicarboxylate; M = Mg, Mn, Fe, Co, Ni, Cu, and Zn) is carried out in tandem with in situ structural studies to identify the host–guest interactions that lead to significant differences in isosteric heats of CO2 adsorption. Neutron and X-ray powder diffraction and single crystal X-ray diffraction experiments are used to unveil the site-specific binding properties of CO2 within many of these materials while systematically varying both the amount of CO2 and the temperature. Unlike previous studies, we show that CO2 adsorbed at the metal cations exhibits intramolecular angles with minimal deviations from 180°, a finding that indicates a strongly electrostatic and physisorptive interaction with the framework surface and sheds more light on the ongoing discussion regarding whether CO2 adsorbs in a linear or nonlinear geometry. This has important implications for proposals that have been made to utilize these materials for the activation and chemical conversion of CO2. For the weaker CO2 adsorbents, significant elongation of the metal–O(CO2) distances are observed and diffraction experiments additionally reveal that secondary CO2 adsorption sites, while likely stabilized by the population of the primary adsorption sites, significantly contribute to adsorption behavior at ambient temperature. Density functional theory calculations including van der Waals dispersion quantitatively corroborate and rationalize observations regarding intramolecular CO2 angles and trends in relative geometric properties and heats of adsorption in the M2(dobdc)–CO2 adducts. © 2014, The Royal Society of Chemistry.
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    Controlling hierarchy in solution-processed polymer solar cells based on crosslinked P3HT
    (Wiley-VCH Verlag GmbH & Co. KGaA, 2013-01-01) Tao, C; Aljada, M; Shaw, PE; Lee, KH; Cavaye, H; Balfour, MN; Borthwick, RJ; James, M; Burn, PL; Gentle, IR; Meredith, P
    Understanding and controlling the morphology of donor/acceptor blends is critical for the development of solution processable organic solar cells. By crosslinking a poly(3-n-hexylthiophene-2,5-diyl) (P3HT) film we have been able to spin-coat [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) onto the film to form a structure that is close to a bilayer, thus creating an ideal platform for investigating interdiffusion in this model system. Neutron reflectometry (NR) demonstrates that without any thermal treatment a smaller amount of PCBM percolates throughout the crosslinked P3HT when compared to a non-crosslinked P3HT film. Using time-resolved NR we also show thermal annealing increases the rate of diffusion, resulting in a near-uniform distribution of PCBM throughout the polymer film. XPS measurements confirm the presence of both P3HT and PCBM at the annealed film's surface indicating that the two components are intermixed. Photovoltaic devices fabricated using this bilayer approach and suitable annealing conditions yielded comparable power conversion efficiencies to bulk heterojunction devices made from the same materials. The crosslinking procedure has also enabled the formation of patterned P3HT films by photolithography. Pillars with feature sizes down to 2 μm were produced and after subsequent deposition of PCBM and thermal annealing devices with efficiencies of up to 1.4% were produced.© 2013, Wiley-VCH Verlag GmbH & Co. KGaA
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    Correlation of diffusion and performance in sequentially processed P3HT/PCBM heterojunction films by time-resolved neutron reflectometry
    (Royal Society of Chemistry, 2013-01-01) Lee, KH; Zhang, YL; Burn, PL; Gentle, IR; James, M; Nelson, A; Meredith, P
    Control over the structure of donor/acceptor blends is essential for the development of solution processable organic solar cells (OSCs). We have used time-resolved neutron reflectometry (NR) and in situ annealing to investigate the nanoscale structure and interdiffusion of sequentially spin-coated thin films of poly(3-n-hexylthiophene-2,5-diyl) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and correlated the evolving structure with the device performance. While the as-prepared film shows a clear two-layer structure it is evident that (19 wt%) PCBM has percolated throughout the lower P3HT layer. Upon heating, analysis of time-resolved NR data shows that the diffusion process is dependent on the annealing temperature. At temperatures up to 110 [degree]C, the two-layer structure is retained and only a small amount of PCBM diffuses from the interface into the lower layer, increasing the total PCBM content throughout the P3HT layer to 26 wt%. Significantly, this small change in acceptor content leads to a profound increase in device performance; with the power conversion efficiency (PCE) of the OSCs increasing from 0.47% (unannealed, 19 wt% PCBM) to 3.23% (annealed, 26 wt% PCBM) with the latter showing a similar efficiency to devices prepared from a blend containing 50 wt% PCBM. Further annealing at 120 and 130 [degree]C sees rapid interdiffusion between the two layers, along with an overall expansion in the thickness of the bilayer film. Despite the complete intermixing of the PCBM and P3HT to form a structure resembling a bulk heterojunction, essentially no improvement in device performance was observed for annealing at temperatures above 110 [degree]C. © 2013, Royal Society of Chemistry
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    Crystal chemistry and structures of (Ca,U) titanate pyrochlores
    (Wiley-Blackwell, 2010-10-01) James, M; Carter, ML; Zhang, ZM; Zhang, YJ; Wallwork, KS; Avdeev, M; Vance, ER
    Analysis of multiphase (Ca,U) titanate pyrochlore samples produced under argon or in air, using laboratory X-ray powder diffraction (XRD) and electron microscopy revealed discrete pyrochlore phase compositions, together with either perovskite or rutile impurities. Investigations of these samples using diffuse reflectance and X-ray photoelectron spectroscopies revealed mixed U4+/U5+ oxidation states for argon-annealed samples and U5+/U6+ oxidation states for air-annealed samples. Single-phase (Ca1.25U4+0.25U5+0.50)Ti2O7 (argon) and (Ca1.40U5+0.60)(Ti1.90U6+0.10)O7 (air) compositions were synthesized and characterized using a combination of synchrotron X-ray and neutron powder diffraction. Severe intensity reduction of hkl odd XRD peaks from the sample produced in air was found to be the result of U6+ sharing the Ti site. The refined crystal structures for both single-phase samples were found to be consistent with the compositions and mixed oxidation states observed by the above spectroscopic measurements. Although the normalized uranium leach rate of the argon-annealed sample was found to be approximately twice that of the air-annealed sample, in 7-day Product Consistency Test the durability of both compounds with respect to leaching by water was found to be excellent. Ca releases were in the range of 0.01–0.03 g/L and U releases were <3 × 10−5 g/L. © 2010, Wiley-Blackwell.