Browsing by Author "Thomsen, L"
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- ItemDeuterium retention and near-surface modification of ion-irradiated diamond exposed to fusion-relevant plasma(IOP Science, 2014-04-01) Deslandes, A; Guenette, MC; Corr, CS; Karatchevtseva, I; Thomsen, L; Lumpkin, GR; Riley, DPChemical vapour deposited diamond was irradiated with 5 MeV carbon ions to simulate the damage caused by collision cascades from neutron irradiation in a fusion environment. Ion-irradiated samples were then exposed to a deuterium plasma in MAGPIE with ion flux of ~1.3 × 1021 ions m−2 s−1. Raman and near edge x-ray absorption fine structure (NEXAFS) spectroscopy were used to characterize the degree of disorder and sp2-bonding induced by the ion irradiation. The signals of sp2-bonded and disordered carbon were observed to decrease after exposure to the deuterium plasma, although sharp Raman peaks indicative of vacancy and interstitial defects induced by the MeV ions were less affected. Recovery of a diamond-like surface after plasma exposure was evident in the NEXAFS spectra. Elastic recoil detection analysis showed that the ion-damaged diamond retained more deuterium than diamond exposed only to deuterium plasma. For the case of unirradiated samples, diamond retained more deuterium than graphite. However, for the case of the ion-irradiated samples, diamond exhibited less deuterium retention than graphite. © 2014, IAEA Vienna.
- ItemDiamond structure recovery during ion irradiation at elevated temperatures(Elsevier, 2015-12-15) Deslandes, A; Guenette, MC; Belay, K; Elliman, RG; Karatchevtseva, I; Thomsen, L; Riley, DP; Lumpkin, GRCVD diamond is irradiated by 5 MeV carbon ions, with each sample held at a different temperature (300–873 K) during irradiations. The defect structures resulting from the irradiations are evident as vacancy, interstitial and amorphous carbon signals in Raman spectra. The observed variation of the full width at half maximum (FWHM) and peak position of the diamond peak suggests that disorder in the diamond lattice is reduced for high temperature irradiations. The dumbbell interstitial signal is reduced for irradiations at 873 K, which suggests this defect is unstable at these temperatures and that interstitials have migrated to crystal surfaces. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy results indicate that damage to the diamond structure at the surface has occurred for room temperature irradiations, however, this structure is at least partially recovered for irradiations performed at 473 K and above. The results suggest that, in a high temperature irradiation environment such as a nuclear fusion device, in situ annealing of radiation-created defects can maintain the diamond structure and prolong the lifetime of diamond components. © 2015 Elsevier B.V.
- ItemEnhanced high voltage stability of spinel‐type structured LiNi0.5Mn1.5O4 electrodes: targeted octahedral crystal site modification(Wiley, 2024-05-01) Zou, JS; Liang, G; Zhang, SH; Thomsen, L; Fan, Y; Pang, WK; Guo, ZP; Peterson, VKHigh‐voltage spinel‐type structured LiNi0.5Mn1.5O4 (LNMO) shows promise as a next‐generation high‐energy‐density lithium‐ion battery cathode material, however, capacity decay on extended cycling hinders its widespread adoption, underscoring an urgent need for further development. In this work, we introduce Zn at octahedral 16c crystal sites in LNMO with Fdm space group to improve rate capability and reduce the rapid capacity decay otherwise experienced during extended cycling. The current work resolves the detailed influence of isolated modification at octahedral 16c crystal sites, unveiling the mechanism for these performance improvements. We show that occupation of Zn at previously empty 16c sites prevents the migration of Ni/Mn to adjacent 16c sites, eliminating transformation to a rock‐salt type structured Ni0.25Mn0.75O2 phase above 4.8 V, preventing structure degradation and suppressing voltage polarization. This study provides insights into the fundamental structure‐function relationship of the LNMO battery cathode, pointing to pathways for the crystal structure engineering of materials with superior performance. © 2024 The Authors. Batteries & Supercaps published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
- ItemInfluence of plasma impurities on the effective performance of fusion relevant materials(Australian Institute of Physics, 2014-02-04) Riley, RP; Guenette, MC; Deslandes, A; Middleburgh, SC; Lumpkin, GR; Thomsen, L; Corr, CSThe development of a sustainable source of power derived from fusion energy is presently constrained by the limited number of materials capable of operating under such extreme conditions. Plasma facing components within magnetically confined fusion reactors must withstand extremes of temperature and loads, while maintaining a high tolerance to radiation damage from energetic particles or neutrons. More specifically, factors of sputtering yield, thermal conduction, electrical conduction and retention of fuel can all degrade the performance of the reactor and hence detrimentally lower the efficiency. In aiming to improve our understanding of materials capable of operating within the fusion environment, it is essential to establish how present generation materials become degraded. Use of ion beam accelerators and linear plasma devices simulate the respective impact of energetic neutron damage (14.1 MeV) and plasma erosion (H+, D+, He+) within a magnetically confined fusion environment. Methods of characterising changes in the local structure and chemistry of surface and near surface regions of fusion relevant materials quantify material degradation resulting from the uptake of plasma impurities. While complementary density functional theory (DFT) simulations have identified possible mechanisms for degradation of material performance. An overview of material evaluation methods will also be presented.
- ItemIntroducing 4s–2p orbital hybridization to stabilize spinel oxide cathodes for lithium-ion batteries(Wiley-VCH GmbH, 2022-04-25) Liang, GM; Olsson, E; Zou, JS; Wu, ZB; Li, JX; Lu, CZ; D'Angelo, AM; Johannessen, B; Thomsen, L; Cowie, BCC; Peterson, VK; Cai, Q; Pang, WK; Guo, ZPOxides composed of an oxygen framework and interstitial cations are promising cathode materials for lithium-ion batteries. However, the instability of the oxygen framework under harsh operating conditions results in fast battery capacity decay, due to the weak orbital interactions between cations and oxygen (mainly 3d–2p interaction). Here, a robust and endurable oxygen framework is created by introducing strong 4s–2p orbital hybridization into the structure using LiNi0.5Mn1.5O4 oxide as an example. The modified oxide delivers extraordinarily stable battery performance, achieving 71.4 % capacity retention after 2000 cycles at 1 C. This work shows that an orbital-level understanding can be leveraged to engineer high structural stability of the anion oxygen framework of oxides. Moreover, the similarity of the oxygen lattice between oxide electrodes makes this approach extendable to other electrodes, with orbital-focused engineering a new avenue for the fundamental modification of battery materials. © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH - Open access.
- ItemInvestigating the order-disorder phase transition in Nd2-xYxZr2O7via diffraction and spectroscopy(Royal Society of Chemistry, 2013-01-01) Blanchard, PER; Liu, S; Kennedy, BJ; Ling, CD; Zhang, Z; Avdeev, M; Cowie, BCC; Thomsen, L; Jang, LYThe pyrochlore-defect fluorite phase transition in the mixed-metal zirconate Nd2-xYxZr2O7 (0 <= x <= 2) solid solution was investigated using synchrotron X-ray and neutron diffraction, as well as X-ray absorption spectroscopy. Diffraction analysis revealed a two-phase region between 1.0 <= x <= 1.2. In the pyrochlore phase, Zr L-3-edge XANES analysis demonstrated a gradual change in the local coordination environment of the B site with increasing Y content that was consistent with an increase in disorder. Although Y L-3-edge XANES analysis suggested that the Y cations remained in an ordered coordination environment in the pyrochlore phase, disorder did gradually increase once the fluorite phase formed. It was found that Y cations prefer an ordered coordination environment near the phase boundary whereas Zr cations prefer a disordered coordination environment. © 2013, Royal Society of Chemistry
- ItemIon irradiated graphite exposed to fusion-relevant deuterium plasma(Elsevier, 2014-12-01) Deslandes, A; Guenette, MC; Corr, CS; Karatchevtseva, I; Thomsen, L; Ionescu, M; Lumpkin, GR; Riley, DPGraphite samples were irradiated with 5 MeV carbon ions to simulate the damage caused by collision cascades from neutron irradiation in a fusion environment. The ion irradiated graphite samples were then exposed to a deuterium plasma in the linear plasma device, MAGPIE, for a total ion fluence of ∼1 × 1024 ions m−2. Raman and near edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to characterize modifications to the graphitic structure. Ion irradiation was observed to decrease the graphitic content and induce disorder in the graphite. Subsequent plasma exposure decreased the graphitic content further. Structural and surface chemistry changes were observed to be greatest for the sample irradiated with the greatest fluence of MeV ions. D retention was measured using elastic recoil detection analysis and showed that ion irradiation increased the amount of retained deuterium in graphite by a factor of four. © 2014, Elsevier B.V.
- ItemA long cycle-life high-voltage spinel lithium-ion battery electrode achieved by site-selective doping(John Wiley & Sons, Inc, 2020-03-23) Liang, GM; Wu, ZB; Didier, C; Zhang, WC; Cuan, J; Li, BH; Ko, KY; Hung, PY; Lu, CZ; Chen, YZ; Leniec, G; Kaczmarek, SM; Johannessen, B; Thomsen, L; Peterson, VK; Pang, WK; Guo, ZPSpinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode candidate for the next-generation high energy-density lithium-ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site-selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fdurn:x-wiley:14337851:media:anie202001454:anie202001454-math-0001 m structure. This site-selective doping not only suppresses unfavorable two-phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg-doped LNMOs exhibit extraordinarily stable electrochemical performance in both half-cells and prototype full-batteries with novel TiNb2O7 counter-electrodes. This work pioneers an atomic-doping engineering strategy for electrode materials that could be extended to other energy materials to create high-performance devices. © 2020 Wiley-VCH Verlag GmbH & Co
- ItemA multilayered approach to polyfluorene water-based organic photovoltaics(Elsevier Science BV, 2012-07-01) Stapleton, A; Vaughan, B; Xue, BF; Sesa, E; Burke, K; Zhou, XJ; Bryant, G; Werzer, O; Nelson, A; Kilcoyne, ALD; Thomsen, L; Wanless, E; Belcher, W; Dastoor, PWater-based polymer nanoparticle dispersions offer the prospect of addressing two of the main challenges associated with printing large area organic photovoltaic (OPV) devices; namely how to control the nanoscale architecture of the active layer and eliminate the need for hazardous organic solvents during device fabrication. However, to date, the efficiencies of nanoparticulate-based devices have been inferior to that of the corresponding bulk-heterojunction devices. Here we present an approach for producing optimised OPV devices from polymer nanoparticles via the fabrication of multilayered device architectures. We show that by controlling both nanoparticle morphology and inter-particle interactions it is now possible to build polyfluorene OPV devices from aqueous dispersions of nanoparticles that are more efficient than the corresponding bulk heterojunction devices. In particular we show that: (1) the polyfluorene nanoparticle morphology is suited to effective charge separation, (2) thermal treatment of the deposited layers results in improved interparticle connectivity and effective charge transport, and (3) the optimal device thickness is a delicate balance between the repair of layer defects and the creation of stress cracking in the nanoparticulate film. As such, this work offers insights for the development of printable photovoltaic devices based on water-dispersed nanoparticulate formulations. © 2012, Elsevier Ltd.
- ItemNEXAFS spectroscopy of CVD diamond films exposed to fusion, relevant hydrogen plasma(Elsevier, 2013-04-01) Guenette, MC; Deslandes, A; Samuell, CM; Tadich, A; Thomsen, L; Cowie, BCC; Corr, CS; Riley, DPA series of CVD diamond films have been exposed to hydrogen plasma in the linear magnetized plasma device, MAGPIE, with various applied sample stage biases between 0 V (no applied bias) to − 500 V. The plasma-induced damage to the surface structure of the diamond films has been investigated by Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy in both the Auger electron yield (AEY) and total fluorescence yield (TFY) modes. The key diamond NEXAFS spectral features (diamond core exciton and second absolute band gap) are found to be diminished following plasma exposure as measured in the surface sensitive, AEY spectra, whilst these features remain unchanged relative to an unexposed diamond reference film as measured using the bulk sensitive, TFY spectra. These results, in conjunction with SRIM simulations, show definitively that the damage to the surface of the diamond films is restricted to the scale of the penetration depth of the H ions and no damage is induced at greater depths. The power and sensitivity of NEXAFS spectroscopy in assessing damage to the surface of diamond from fusion-relevant plasma-surface interactions are demonstrated. © 2013, Elsevier B.V.
- ItemReconstructing Cu nanoparticle supported on vertical graphene surfaces via electrochemical treatment to tune the selectivity of CO2 reduction toward valuable products(ACS Publications, 2022-04-07) Ma, ZP; Tsounis, C; Toe, CY; Kumar, PV; Subhash, B; Xi, SB; Yang, HY; Zhou, SJ; Lin, ZH; Wu, KH; Wong, RJ; Thomsen, L; Bedford, NM; Ng, YH; Han, ZJ; Amal, RReconstructing a catalyst with tunable properties is essential for achieving selective electrochemical CO2 reduction reaction (CO2RR). Here, a reduction–oxidation–reduction (ROR) electrochemical treatment is devised to advisedly reconstruct copper nanoparticles on vertical graphene. Undercoordinated sites and oxygen vacancies constructed on the Cu active sites during the ROR treatment enhance the CO2RR activity. Moreover, by varying the oxidation potential while maintaining the reduction potential during the ROR treatment, CO2RR selectivity can be tuned between *COOH- and *OCHO-derived products. Specifically, rich grain boundaries are formed on the ROR catalyst with a high oxidation potential (+1.2 VRHE), favoring the *COOH/*OCCO adsorption and leading C–C coupling to *COOH-derived products, while the catalyst undergoing ROR at a low oxidation potential (+0.8 VRHE) lacks grain boundaries, resulting in highly selective formate (*OCHO-derived) production. Our findings are evidenced by combined in situ and ex situ characterizations and theoretical calculations. © 2022 American Chemical Society
- ItemRetention and damage in 3C-β SiC irradiated with He and H ions(Elsevier B.V., 2016-02-01) Deslandes, A; Guenette, MC; Thomsen, L; Ionescu, M; Karatchevtseva, I; Lumpkin, GR3C-β SiC was implanted with He and H ions using plasma immersion ion implantation (PIII). Regions of damage were created at various depths by applying a sample stage bias of 5 kV, 10 kV, 20 kV or 30 kV. Raman spectroscopy results indicate that He irradiation leads to more damage compared to H irradiation, as observed via increased disordered C and Si signals, as well as broadening of the SiC peaks. X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) results indicate significant change to the SiC structure and that surface oxidation has occurred following irradiation, with the degree of change varying dependent on impinging He fluence. The distributions of implanted species were measured using elastic recoil detection analysis. Despite the varying degree and depth of damage created in the SiC by the He ion irradiations, the retained H distribution was observed to not be affected by preceding He implantation. © 2015 Elsevier B.V.
- ItemTowards better understanding of atomically precise gold clusters and titania made using surface modifying agents(Australian Institute of Physics, 2014-02-04) Golovko, VB; Ruzicka, JY; Abu Bakar, A; Anderson, DP; Adnan, R; Donoeva, B; Ovoshchnikov, D; Metha, GF; Andersson, GG; Thomsen, L; Cowie, B; McNicoll, C; Ingham, B; Kemmitt, T; Fang, V; Kennedy, JControlled synthesis of titania nanoparticles using recently perfected sol-gel methodology, synthesis of atomically precise metal clusters, their deposition and activation on oxide supports and studies of properties of the resulting materials as promising catalysts and sensors will be briefly discussed. Our work on synthesis of titania nanoparticles is focused on careful tuning of the reaction conditions and use of selected surface modifying agents capable of directing and controlling growth of nanoparticles with specific size, phase and even population of Ti+3 sites at the surface. Promising performance of titania made using our methodology as near-IR reflective coating will be briefly highlighted. From pre-historic times gold was known as a chemically inert, “noble” metal until, in 1987, Haruta et al. proved that gold nanoparticles can be catalytically active. Results of research focused on the use of size-controlled, chemically pre-synthesised nanoparticles (colloids and clusters) with core sizes ranging from classical 1.5 nm “Au55” systems to atomically precise, uniquely small clusters (Au9 etc.) including a range of mixed-metal clusters will be presented. Immobilization of such clusters on a variety of supports had been pursued in an attempt to fabricate a family of site-isolated catalysts, where properties of the active site are defined by the nature of the precursor with great precision. Catalytic performance in selected reactions will be highlighted. New insights in the nature of our precisely defined precursors (pure and immobilised onto supports) obtained using relevant materials characterization techniques, such as Synchrotron X-ray Photoelectron Spectroscopy will be presented.
- ItemAn unconventional method for measuring the Tc L3-edge of technetium compounds(Journal of Synchrotron Radiation, 2014-01-01) Blanchard, PER; Reynolds, EM; Kennedy, BJ; Ling, CD; Zhang, Z; Thorogood, GJ; Cowie, BCC; Thomsen, LTc L3-edge XANES spectra have been collected on powder samples of SrTcO3 (octahedral Tc4+) and NH4TcO4 (tetrahedral Tc7+) immobilized in an epoxy resin. Features in the Tc L3-edge XANES spectra are compared with the pre-edge feature of the Tc K-edge as well as other 4d transition metal L3-edges. Evidence of crystal field splitting is obvious in the Tc L3-edge, which is sensitive to the coordination number and oxidation state of the Tc cation. The Tc L3 absorption edge energy difference between SrTcO3 (Tc4+) and NH4TcO4 (Tc7+) shows that the energy shift at the Tc L3-edge is an effective tool for studying changes in the oxidation states of technetium compounds. The Tc L3-edge spectra are compared with those obtained from Mo and Ru oxide standards with various oxidation states and coordination environments. Most importantly, fitting the Tc L3-edge to component peaks can provide direct evidence of crystal field splitting that cannot be obtained from the Tc K-edge. © International Union of Crystallography.
- ItemXPS and NEXAFS study of fluorine modified TiO2 nano-ovoids reveals dependence of Ti3+ surface population on the modifying agent(Royal Society of Chemistry, 2014-04-04) Ruzicka, JY; Bakar, FA; Thomsen, L; Cowie, BCC; McNicoll, C; Kemmitt, T; Brand, HEA; Ingham, B; Andersson, GG; Golovko, VBCrystalline titanium dioxide was synthesised under mild conditions by the thermal degradation of peroxotitanic acid in the presence of a number of fluoride-containing surface modifying agents (NH4F, NH4BF4, NH4PF6, NBu4F, NBu4BF4, NBu4PF6). The resulting materials were characterised by PXRD, SEM, HRTEM, XPS and NEXAFS. Particle phase, size, and surface area were noticeably affected by the choice of surface modifying agent. Both the cation and anion comprising the modifying agent affect the surface Ti3+ population of the materials, with two apparent trends observed: F− > BF4− > PF6− and NBu4+ > NH4+. All materials displayed evidence of fluorine doping on their surfaces, although no evidence of bulk doping was observed. © 2014 The Royal Society of Chemistry (Open Access)