Browsing by Author "Prince, KE"

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    Application of secondary ion mass spectrometry in studies of niobium segregation in niobium-doped titanium dioxide
    (The Australian Ceramic Society, 2007) Sheppard, LR; Atanacio, AJ; Bak, T; Nowotny, J; Prince, KE
    Secondary ion mass spectrometry (SIMS) is a powerful technique in the study of materials that demonstrate compositional changes as a function of depth from the surface. This is due to the high chemical sensitivity of SIMS (sensitive to ppb) and potential for high depth resolution. However, as a semi-quantitative technique, the application of SIMS to quantitative studies can be problematic without knowledge of the appropriate calibration information, which must be obtained through the use of carefully prepared reference specimens. In the present work, SIMS is used in the investigation of surface segregation in niobium doped polycrystalline TiO2. This material has demonstrated important photo-catalytic properties with implications for alternative energy generation and environmentally-friendly water purification, but requires investigation in relation to surface versus bulk processing. The present paper demonstrates the use of SIMS in the quantitatively assessment of segregation in TiO2 and the development of a calibration curve. © 2007, The Australian Ceramic Society
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    Boron enhanced H diffusion in amorphous Si formed by in implantation
    (Cambridge University Press, 2008-03-25) Johnson, BC; Atanacio, AJ; Prince, KE; McCallum, JC
    Boron enhanced H diffusion in amorphous Si (a-Si) layers formed by ion implantation is observed using secondary ion mass spectroscopy (SIMS). Constant concentrations of B were achieved using multiple energy B implantations into thick a-Si layers. The evolution of single H implanted profiles centered on the uniformly B-implanted regions was studied for partial anneals at temperatures in the range 380 – 640 °C. Boron enhanced diffusion is observed and the enhanced diffusion coefficient shows trends with temperature typically associated with a Fermi level shifting dependence. A modified form of the generalized Fermi level shifting model is considered in light of these results. © Materials Research Society 2008
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    Bulk diffusion of niobium in single-crystal titanium dioxide
    (American Chemical Society, 2007-07-19) Sheppard, LR; Atanacio, AJ; Bak, T; Nowotny, J; Prince, KE
    The present work reports the tracer diffusion coefficient for Nb-93 in rutile TiO2 single crystals using secondary ion mass spectrometry (SIMS). The determined tracer diffusion coefficient exhibited the following temperature dependence in air (p(O-2) = 21 kPa) over the range 1073-1573 K: D-93Nb= (4.7 m(2) s(-1)) x 10(-7 +/- 0.4) exp ((-244 +/- 9 kJ mol(-1))/RT) Through comparison to the self-diffusion of Ti-44 in rutile TiO2, Nb-93 is interpreted to diffuse via the interstitialcy mechanism. The obtained tracer diffusion data are useful for ensuring compositional control during the processing of Nb-doped TiO2-based semiconductors using solid-state reactions between Nb2O5 and TiO2. © 2007, American Chemical Society
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    Characterisation of alumina–silica films deposited by ALD
    (John Wiley & Sons, 2006-11-29) Prince, KE; Evans, PJ; Triani, G; Zhang, ZM; Bartlett, JR
    Atomic layer deposition (ALD) is a surface mediated chemical vapour deposition method that is capable of producing uniform films over large areas. In addition, the technique has been used to deposit highly conformal films on high aspect ratio structures. The applicability of any film deposition technique is dependent upon the properties of the final product. Many applications, such as optical coatings, require films of constant composition, low levels of impurities, and adherent interfaces. The latter may derive its strength from some form of interfacial mixing but this should not have an adverse effect on film performance. Dynamic SIMS (D-SIMS) offers a versatile tool for monitoring film and interface compositions as a function of depth. Sputtering the surface with Cs+ primary ions and detecting MCs+ secondary ions was found to offer the best analytical conditions for ALD films. In the present study, D-SIMS has been used to characterise films grown with silicon-containing precursors at temperatures between 200 and 300 °C. The D-SIMS results have been complemented with data obtained from XPS and an in situ quartz crystal microbalance (QCM). This combination of analytical techniques enabled the effects of different ALD process conditions to be evaluated. With this approach, it was possible to compare the relative amounts of Si in the films, determined by SIMS and XPS, with the mass gains measured for different pulsing sequences with the QCM. © 2006 John Wiley & Sons, Ltd.
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    Characterisation of arsenic doped HgCdTe grown by molecular beam epitaxy
    (IEEE, 2006-12-06) Tsen, GK; Sewell, RH; Atanacio, AJ; Prince, KE; Musca, CA; Dell, JM; Antoszewski, J; Faraone, L
    Extrinsic p-type doping of Mercury Cadmium Tel-luride (HgCdTe) epilayers grown by Molecular Beam Epitaxy (MBE) was carried out with an arsenic (As) cracker cell. As-grown samples were characterised via Fourier Transform Infrared Transmission Spectrometry (FTIR), Secondary Ion Mass Spectrometry (SIMS) as well as variable field magneto-transport measurements coupled with the quantitative mobility spectrum analysis (QMSA) to study the Hall effect characteristics. Arsenic activation annealing of the samples were performed and magneto-transport measurements repeated. Results indicate that as-grown samples show n-type behaviour indicating that arsenic incorporate as donors in the material with annealed samples showing p-type characteristics with heavy compensation. © Copyright 2006 IEEE
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    Characterisation of phase relations and properties in air-oxidised Ti3SiC2
    (Elsevier, 2007-09-25) Low, IM; Wren, E; Prince, KE; Atanacio, AJ
    The oxidation of Ti3SiC2 in air from 25 to 1450 degrees C is characterised by differential thermal and gravimetric analysis (DTA/TGA), X-ray diffraction (XRD), grazing-incidence synchrotron radiation diffraction (GISRD), neutron diffraction (ND), transmission electron microscopy (TEM), secondary ions mass spectroscopy (SIMS) and Vickers indentation. The diffraction results show that rutile formed at a temperature of similar to 750 degrees C. A glassy phase - formed at > 1000 degrees C - devitrified upon cooling to room temperature to form tridymite but crystallised to cristobalite at temperatures >= 1300 degrees C. Composition depth-profiling of the surface layer oxides by XRD, GISRD and SIMS revealed a graded distribution of phases (TiO2, SiO2 and Ti3SiC2) both at the nanoscale (<= 1100 degrees C) and microscale level (1200 degrees C), which is particularly distinct at the interfaces. The oxide layers also exhibit a graded variation in microhardness. © 2007, Elsevier Ltd.
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    Depth-profiling of surface composition in air-oxidised Ti{sub 3}SiC{sub 2}
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2005-11-20) Low, IM; Wren, E; Oo, Z; Prince, KE; Atanacio, AJ
    Titanium silicon carbide (Ti3SiC2) is a remarkable ternary compound that defies many of the expected properties of a ceramic. It has better thermal and electrical conductivity than titanium metal, is resistant to thermal shock, and is relatively light. Its hardness is exceptionally low for a carbide, and like graphite, it is readily machinable. Hitherto, mixed and confusing results have been reported for the oxidation resistance and behaviour of Ti3SiC2 in air. For instance, the oxidation resistance of Ti3SiC2 was reported to be excellent at temperatures below 1100 degrees C due to the formation of a protective SiO2 surface layer. However, oxidation of Ti3SiC2 was detected to commence as low as 400 degrees C through the formation of an anatase-like TiO2 film that eventually transformed to rutile at 1050 degrees C. In addition, although the existence of the protective TiO2 (rutile) has been confirmed by all the researchers, the presence of the protective SiO2 film is much more elusive. In a recent study, the oxidized layers were reported to exhibit a duplex microstructure in the temperature range 1000-1500 degrees C with an outer layer of TiO2 (rutile) and an inner layer consisting of SiO2 and TiO2. In a similar study, researchers also found the protective oxide scales that formed to be layered with the inner layer composed of silica (∼1200 degrees C) and titania and the outer layer comprised of pure rutile (∼900 degrees C). The growth of these oxide layers is both temperature and time-dependent and was thought to occur by the outward diffusion of titanium and carbon and the inward diffusion of oxygen through surface pores or cracks. However, the nature and precise composition of the oxide layers formed during oxidation remain controversial, especially in relation to the presence of SiO2 and the graded nature of the oxides formed. In this paper, the surface composition depth-profiles of air-oxidized Ti3SiC2 have been investigated by secondary ion mass spectroscopy (SIMS) in the temperature range 500-1400 degrees C. Line scan and near-surface depth profiling by SIMS have revealed a distinct gradation in phase composition within the surface oxide layers.
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    Determination of niobium diffusion in titania and zirconia using secondary ion mass spectrometry
    (Taylor & Francis (Informa UK), 2007-01-01) Sheppard, LR; Zhou, MF; Atanacio, AJ; Bak, T; Nowotny, J; Prince, KE
    This paper provides an outline for the use of secondary ion mass spectrometry (SIMS) in the determination of diffusion data in metal oxides. The focus is on the determination of Nb bulk and grain boundary diffusion coefficients in TiO2 and zirconia. Specifically, the diffusion of Nb in TiO2 and yttria doped (10 mol.-%) ZrO2 (10YSZ) has been assessed. The following bulk diffusion coefficients D 93Nb were obtained D 93Nb =(1·03±0·051) × 10−18 m2 s−1 10YSZ(1273K) D 93Nb =(1·91±0·096) × 10−16 m2 s−1 TiO2(1273K) The grain boundary diffusion parameter for Nb grain boundary diffusion in 10YSZ was also determined D 93Nb δα =(7·48 ± 0·37) × 10−25 m2 s−1 10YSZ(1273K) The Nb grain boundary diffusion coefficient D′93Nb was determined to be D′93Nb =(3·99 ± 0·20) × 10−16 m2 s−1 10YSZ(1273K) © 2007 Informa UK Limited
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    Diffusion kinetics of indium in TiO2 (rutile)
    (John Wiley & Sons, Inc, 2013-03-22) Atanacio, AJ; Bak, T; Nowotny, J; Prince, KE
    This work determines the self-diffusion coefficients of indium in TiO 2 single crystal (rutile). Diffusion concentration profiles were imposed by deposition of a thin surface layer of InCl3 on the TiO2 single crystal and subsequent annealing in the temperature range 1073-1573 K. The diffusion-induced concentration profiles of indium as a function of depth were determined using secondary ion mass spectrometry (SIMS). These diffusion profiles were used to calculate the self-diffusion coefficients of indium in the polycrystalline In2TiO5 surface layer and the TiO2 single crystal. The temperature dependence of the respective diffusion coefficients, in the range 1073-1573 K, can be expressed by the following formulas: DIn-In2TiO5=1. 9×10-13exp(-142kJ/mol/RT)[m2s-1] and DIn-TiO2=7.4×10-4exp(-316kJ/mol/RT) [m2s-1] The obtained activation energy for bulk diffusion of indium in rutile (316 kJ/mol) is similar to that of zirconium in rutile (325 kJ/mol). The determined diffusion data can be used in selection of optimal processing conditions for TiO2-In2O3 solid solutions. © 2013 The American Ceramic Society.
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    Diffusion kinetics of indium ion TiO2 single crystal
    (John Wiley & Sons, 2013-05-11) Atanacio, AJ; Bak, T; Nowotny, J; Prince, KE
    This work determines the self-diffusion coefficients of indium in TiO2 single crystal (rutile). Diffusion concentration profiles were imposed by deposition of a thin surface layer of InCl3 on the TiO2 single crystal and subsequent annealing in the temperature range 10731573K. The diffusion-induced concentration profiles of indium as a function of depth were determined using secondary ion mass spectrometry (SIMS). These diffusion profiles were used to calculate the self-diffusion coefficients of indium in the polycrystalline In2TiO5 surface layer and the TiO2 single crystal. The temperature dependence of the respective diffusion coefficients, in the range 10731573K, can be expressed by the following formulas: DInIn2TiO5=1.9x1013exp(142kJ/molRT)[m2s1] and DInTiO2=7.4x104exp(316kJ/molRT)[m2s1] The obtained activation energy for bulk diffusion of indium in rutile (316kJ/mol) is similar to that of zirconium in rutile (325kJ/mol). The determined diffusion data can be used in selection of optimal processing conditions for TiO2In2O3 solid solutions.© 2013 The American Ceramic Society
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    Dissolution of Synroc in deionised water at 150°C
    (Materials Research Society (MRS)/Cambridge University Press/Springer Nature, 1996-02-15) Smith, KL; Colella, M; Thorogood, GJ; Blackford, MG; Lumpkin, GR; Hart, KP; Prince, KE; Loi, E; Jostsons, A
    Synroc containing 20 wt% simulated high level waste (HLW) was subjected to two sets of leach tests at 150°C where the leachant was and was not replaced during the test (replacement and non-replacement testing). The leachant was a KH-phthalate buffered solution (pH 4.2). Samples were characterised before and after leach testing using SEM, AEM and SIMS. Elemental concentrations in leachates were measured using ICP-MS. In concert with the findings of i) a dissolution study of perovskite in a flowing leachant and ii) a previous Synroc dissolution study (wherein Synroc containing 10 wt% simulated HLW was subjected to periodic replacement, leach testing in deionised water at 150°C), the results of this study show that when the leachant replacement frequency is varied from 7 d to the duration of the test, there is no effect on leach rate or leaching mechanisms. © Materials Research Society 1997
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    Durability of a cementitious wasteform for intermediate level waste
    (Springer Nature, 2008-12-01) McGlinn, PJ; Brew, DRM; Aldridge, LP; Payne, TE; Olufson, KP; Prince, KE; Kelly, IJ
    Cementitious material is the most commonly used encapsulation medium for low and intermediate level radioactive waste. This paper focuses on the aqueous durability of a Materials Testing Reactor (MTR) cementitious wasteform – a possible candidate for the proposed intermediate level waste management facility in Australia. A series of medium term (up to 92 months) durability tests, without leachate replacement, were conducted on samples of this wasteform. The wasteform was made from cement, ground granulated blast furnace slag and a simulated waste liquor. The compressive strength (39 MPa) was typical of MTR cement wasteforms and well above that required for handling or storage. The wasteform was an inhomogeneous mixture containing calcite, a calcium silicate hydrate phase, hydrotalcite and unreacted slag particles. After leaching for 92 months the crystallinity of the calcium silicate hydrate phase increased. The majority of the releases of Ca, Si, Al, Sr, S, Na and K was reached within 4 days of leaching, with the maxima ie. the highest concentrations in the leachates, occurring at 3 months for Ca, Al, Sr, S, Na and K, and at 1 month for Si. For the longer leach periods (6 months and 3 months respectively) there was a slight reduction in concentration in the leachates, and these levels were similar to those for the longest period of 92 months, suggesting steady-state conditions prevailing after 3 to 6 months of leaching. The highest releases of matrix elements were for Na (37%), K (40%) and S (16%). Releases for elements such as Ca, Na, Al and Sr were similar in magnitude to those reported by the UKAEA in earlier MTR studies. After leaching for 92 months there was an alteration layer about 80 ∞m deep where calcium has been depleted. Na, K and Sr showed signs of diffusion towards the outer part of the cement samples. © 2008 Materials Research Society
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    Effect of niobium segregation on surface properties of titanium dioxide
    (Society of Photo-Optical Instrumentation Engineers (SPIE), 2006-09-08) Sheppard, LR; Atanacio, AJ; Bak, T; Nowotny, J; Prince, KE
    The present paper considers the effect of segregation on the performance of photo-electrode materials for photo-electrochemical water splitting. This phenomenon, which alters the surface composition of a material during processing at elevated temperatures, has the capacity to dominate interfacial charge transfer between the photo-electrode and the electrolyte. As the present understanding of segregation in metal oxides is limited, this paper aims at addressing the need to collect empirical data which can be used for the development of novel materials. In the present investigation, Nb surface segregation was investigated at 1273 K under high and low oxygen activity using secondary ion mass spectrometry (SIMS). A calibration procedure was used to enable quantifiable data and Nb was observed to segregate strongly, especially at high oxygen activity. While this was attributed to the defect disorder, it remained unclear whether gas/solid equilibrium was achieved, and consequently whether the observed behaviour represents equilibrium segregation. Irrespectively, the observed behaviour clearly illustrates how the surface composition of a metal oxide can be altered through the control of segregation. This must be considered in the pursuit of high performance photo-electrode materials for water splitting under sunlight. © (2006) Society of Photo-Optical Instrumentation Engineers (SPIE).
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    Effect of oxygen activity on surface composition of in-doped TiO2 at elevated temperatures
    (American Chemical Society, 2012-09-13) Atanacio, AJ; Nowotny, J; Prince, KE
    The present work reports the effect of oxygen activity on the segregation-induced surface concentration of indium for In-doped TiO2 at different time intervals (5-120 h) of annealing at 1273 K. It is shown that equilibrium segregation of indium in oxidizing conditions, p(O-2) = 21 kPa, is established within 20 h. However, annealing in reducing conditions, p(O-2) = 10(-10) Pa, does not lead to equilibrium segregation due to indium evaporation, which becomes substantial at p(O-2) < 10(2) Pa. In these conditions, annealing results in an initial rise of surface concentration due to segregation and subsequent decrease due to evaporation. These data may be used for the modification of surface vs bulk composition of In-doped TiO2 in a controlled manner. © 2012, American Chemical Society.
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    Effect of vacuum annealing on the phase stability of Ti3SiC2
    (Wiley-Blackwell, 2007-08) Low, IM; Oo, Z; Prince, KE
    The effect of vacuum annealing on the thermal stability and phase transition of Ti3SiC2 has been investigated by X-ray diffraction (XRD), neutron diffraction, synchrotron radiation diffraction, and secondary ion mass spectroscopy (SIMS). In the presence of vacuum or a controlled atmosphere of low oxygen partial pressure, Ti3SiC2 undergoes a surface dissociation to form nonstoichiometric TiC and/or Ti5Si3Cx that commences at ~1200°C and becomes very pronounced at ≥ 1500°C. Composition depth profiling at the near surface of vacuum-annealed Ti3SiC2 by XRD and SIMS revealed a distinct gradation in the phase distribution of TiC and Ti5Si3Cx with depth. © 2007, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
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    Effective gel for gold nanoparticle formation, support and metal oxide templating
    (Royal Society of Chemistry, 2007-08-07) Wang, XD; Egan, CE; Zhou, MF; Prince, KE; Mitchell, DRG; Caruso, RA
    Gold nanoparticles were synthesized using agarose as a reducing agent, which gelled to support the gold nanoparticles, then readily functioned as a template to produce a porous, evenly-distributed Au/TiO2 nano-hybrid. © 2007, Royal Society of Chemistry
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    Electron and ion microprobe analysis of calcium distribution and transport in coral tissues
    (Company of Biologists, 2007-07-15) Marshall, AT; Clode, PL; Russell, RA; Prince, KE; Stern, R
    It is shown by x-ray microanalysis that a gradient of total intracellular Ca concentration exists from the outer oral ectoderm to the inner skeletogenic calicoblastic ectoderm in the coral Galaxea fascicularis. This suggests an increase in intracellular Ca stores in relation to calcification. Furthermore, Ca concentration in the fluid-filled space of the extrathecal coelenteron is approximately twice as high as in the surrounding seawater and higher than in the mucus-containing seawater layer on the exterior of the oral ectoderm. This is indicative of active Ca2+ transport across the oral epithelium. Polyps were incubated in artificial seawater in which all 40Ca was replaced by 44Ca. Imaging Ca2+ transport across the epithelia by secondary ion mass spectroscopy (SIMS) using 44Ca as a tracer showed that Ca2+ rapidly entered the cells of the oral epithelium and that 44Ca reached higher concentrations in the mesogloea and extrathecal coelenteron than in the external seawater layer. Very little Ca2+ was exchanged in the mucocytes, cnidocytes or zooxanthellae. These observations again suggest that Ca2+ transport is active and transcellular and also indicate a hitherto unsuspected role in Ca2+ transport for the mesogloea. © 2007, Company of Biologists
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    Elimination of undesirable water layers in solid-contact polymeric ion-selective electrodes
    (American Chemical Society, 2008-09-01) Veder, JP; De Marco, R; Clarke, G; Chester, R; Nelson, A; Prince, KE; Pretsch, E; Bakker, E
    This study aimed to develop a novel approach for the production of analytically robust and miniaturized polymeric ion sensors that are vitally important in modem analytical chemistry (e.g., clinical chemistry using single blood droplets, modem biosensors measuring clouds of ions released from nanoparticle-tagged biomolecules, laboratory-on-a-chip applications, etc.). This research has shown that the use of a water-repellent poly(methyl methacrylate)/poly(decyl methacrylate) (PMMA/PDMA) copolymer as the ion-sensing membrane, along with a hydrophobic poly(3-octylthiophene 2,5-diyl) (POT) solid contact as the ion-to-electron transducer, is an excellent strategy for avoiding the detrimental water layer formed at the buried interface of solid-contact ion-selective electrodes (ISEs). Accordingly, it has been necessary to implement a rigorous surface analysis scheme employing electrochemical impedance spectroscopy (EIS), in situ neutron reflectometry/EIS (NR/EIS), secondary ion mass spectrometry (SIMS), and small-angle neutron scattering (SANS) to probe structurally the solid-contact/membrane interface, so as to identify the conditions that eliminate the undesirable water layer in all solid-state polymeric ion sensors. In this work, we provide the first experimental evidence that the PMMA/PDMA copolymer system is susceptible to water "pooling" at the interface in areas surrounding physical imperfections in the solid contact, with the exposure time for such an event in a PMMA/PDMA copolymer ISE taking nearly 20 times longer than that for a plasticized poly(vinyl chloride) (PVC) ISE, and the simultaneous use of a hydrophobic POT solid contact with a PMMA/PDMA membrane can eliminate totally this water layer problem. © 2008, American Chemical Society
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    Evidence of a water layer in solid-contact polymeric ion sensors
    (Royal Society of Chemistry, 2008-01-01) De Marco, R; Veder, JP; Clarke, G; Nelson, A; Prince, KE; Pretsch, E; Bakker, E
    This paper presents the very first direct structural evidence for the formation of a 100 +/- 10 angstrom water layer in coated-wire polymeric-membrane ion-selective electrodes (ISEs). © 2008, Royal Society of Chemistry
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    Fabrication, structural characterization and testing of a nanostructured tin oxide gas sensor
    (Institute of Electrical and Electronics Engineers (IEEE), 2009-04-07) Partridge, JG; Field, MR; Sadek, AZ; Kalantar-Zadeh, K; Du Plessis, J; Taylor, MB; Atanacio, AJ; Prince, KE; McCulloch, DG
    A nanostructured SnO 2 conductometric gas sensor was produced from thermally evaporated Sn clusters using a thermal oxidation process. SnO 2 clusters were simultaneously formed in an identical process on a Si 3 N 4 membrane featuring an aperture created by a focused ion beam (FIB). Clusters attached to the vertical edges of the aperture were imaged using a transmission electron microscope. The original morphology of the Sn cluster film was largely preserved after the thermal oxidation process and the thermally oxidized clusters were found to be polycrystalline and rutile in structure. NO 2 gas sensing measurements were performed with the sensor operating at various temperatures between 25degC and 290degC. At an operating temperature of 210degC, the sensor demonstrated a normalized change in resistance of 3.1 upon exposure to 510 ppb of NO 2 gas. The minimum response and recovery times for this exposure were 45 s and 30 s at an operating temperature of 265degC. The performance of the SnO 2 sensor compared favorably with previously published results. Finally, secondary ion mass spectrometry and X-ray photoelectron spectroscopy were used to establish the levels of nitrogen present in the films following exposure to NO 2 gas. © Copyright 2009 IEEE