Browsing by Author "Evans, PJ"

Now showing 1 - 20 of 25
  • No Thumbnail Available
    Item
    Atomic layer deposition of SIO2 on porous alumina membranes: controlling the pore size and transport properties
    (SPIE, 2008-12-30) Velleman, L; Triani, G; Evans, PJ; Atanacio, AJ; Shapter, JG; Losic, D
    Atomic layer deposition (ALD) of SiO2 onto nanoporous alumina (PA) membranes was investigated with the aim of adjusting the pore size and transport properties. PA membranes from commercial sources with a range of pore diameters (20 nm, 100 nm and 200 nm) were used and modified by atomic layer deposition using tris(tert-butoxy)silanol and water as the precursor couple. By adjusting the number of deposition cycles, the thickness of the conformal silica coating was controlled, reducing the effective pore diameter, and subsequently changing the transport properties of the PA membrane. Silica coated PA membranes with desired pore diameters from <5 nm to 100 nm were fabricated. In addition to the pore size, the transport properties and selectivity of fabricated silica coated PA membranes were controlled by chemical functionalisation using a silane with hydrophobic properties. Structural and chemical properties of modified membranes were studied by dynamic secondary ion mass spectrometry (DSIMS) and scanning electron microscopy (SEM). Spectrophotometric methods were used to evaluate the transport properties and selectivity of silica coated membranes by permeation studies of hydrophobic and hydrophilic organic molecules. The resultant silica/PA membranes with specific surface chemistry and controlled pore size are applicable for molecular separation, cell culture, bioreactors, biosensing and drug delivery. © 2008 Society of Photo-Optical Instrumentation Engineers (SPIE)
  • Thumbnail Image
    Item
    Characterisation and properties of low temperature ALD TiO2 films
    (Pielaszek Research, 2007-09-18) Triani, G; Evans, PJ; Campbell, JA; Latella, BA; Atanacio, AJ; Attard, DJ; Burford, RP
    The atomic layer deposition of films under conditions outside the ALD window involves additional processes that have to be accounted for in order to achieve good quality films. [1] In the present study, the growth of ALD TiO2 films on silicon and polycarbonate in the temperature range 80 - 120°C has been investigated in detail for two combinations of pulsing times. Furthermore, both substrate materials were exposed to a low-pressure water plasma to investigate the effect of pre-treatment on the deposited films. A suite of characterisation techniques including XRD, SIMS, RBS, AFM, XTEM and spectroscopic ellipsometry was used to probe the physical and chemical properties of the films. In addition, microtensile testing of the films enable the interface energy and toughness to be determined. These measurements showed water plasma treatment prior to deposition increased the interface energy and interface toughness from 11 to 26 Jm-2 and 1.24 to 1.96 MPa.m1/2 respectively. The contact angle of the TiO2 films was measured to assess their wettability. These tests involved subjecting the films to single and cumulative exposures of UV radiation followed by measurement of the contact angle. For an 85 nm film on polycarbonate, the contact angle decreased from 60° for the as-deposited surface to 10° following a 15 minute exposure. A 25 nm film yielded a similar decrease though this was only achieved after a 50 minute exposure. 1.M. Ritala and M. Leskelä, in Handbook of Thin Film Materials, Volume 1: Deposition and Processing of Thin Films, H.S. Halwa (ed.), Chap. 2, Academic, NY, 2002. © 2007 Pielaszek Research
  • No Thumbnail Available
    Item
    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.
  • No Thumbnail Available
    Item
    Comparison of implantation and diffusion behavior of Ti, Sb and N in ion-implanted single crystal and polycrystalline ZnO: a SIMS study
    (Elsevier, 2010-01-15) Lee, J; Metson, J; Evans, PJ; Pal, U; Bhattacharyya, D
    Implantation and diffusion behavior of Sb, Ti and N in ZnO single crystal and sputter deposited thin films were studied through secondary ion mass spectrometric studies on ion-implanted and thermally annealed samples. Sb was implanted and Ti and N were co-implanted into ZnO single crystals and polycrystalline thin films on Si substrates at room temperature. The implanted samples were then annealed at 800°C. Depth profiles of implant distributions before and after annealing were examined by Secondary Ion Mass Spectrometry (SIMS). As expected, implant range is sensitive to the mass of the dopants; and the dopant distribution is broadened as implanted elements migrate deeper into the film on thermal annealing. While diffusion of N in the ZnO thin film is not significant, Ti tends to diffuse deeper into the sample during annealing. For Ti and N co-implanted single crystal, annealing induced diffusion causes more redistribution of the lighter N than Ti. In general, implanted dopants diffuse more easily in thin films compared to the single crystal due to the presence of grain boundaries in the latter. © 2010, Elsevier Ltd.
  • No Thumbnail Available
    Item
    Comparisons of alumina barrier films deposited by thermal and plasma atomic layer deposition
    (Elsevier, 2019-03) Jarvis, KL; Evans, PJ; Nelson, A; Triani, G
    Barrier films are commonly deposited onto flexible substrates by atomic layer deposition (ALD) to protect organic electronics from degradation due to the ingress of moisture. Both thermal ALD and plasma-enhanced ALD (PEALD) have been used for this purpose, but few comparisons have been made as to which technique produces superior barrier films. In this study, alumina (Al2O3) barrier films have been deposited by thermal ALD and PEALD to investigate the effect of the deposition technique on the water vapor transmission rate (WVTR). Al2O3 films with thicknesses of approximately 10 or 20 nm were deposited at 100 or 120°C. The chemistry, morphology, and density of the films were investigated with X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray reflectometry respectively. The WVTRs of the films were measured using tritiated water (HTO) permeation at 25°C and 95% relative humidity. Both the thermal and PEALD films had similar Al:O ratios, whereas the PEALD films were slightly smoother than the thermal ALD films. No significant difference in the film densities was observed. All PEALD films had lower WVTRs than their thermally deposited counterparts. The lowest WVTR measured was 4.2 × 10−2 g m−2/day for a 17-nm-thick PEALD Al2O3 film deposited at 120°C. These results indicate the importance of optimizing deposition parameters to enable production of the most effective barrier films, which are essential in applications such as organic electronics. © 2018 Elsevier Ltd.
  • No Thumbnail Available
    Item
    Controlled pore structure modification of diatoms by atomic layer deposition of TiO2
    (Royal Society of Chemistry, 2006-09-04) Losic, D; Triani, G; Evans, PJ; Atanacio, AJ; Mitchell, JG; Voelcker, NH
    Diatoms produce diverse three-dimensional, regular silica structures with nanometer to micrometer dimensions and hold considerable promise for biological or biomimetic fabrication of nanostructured materials and devices. The unique hierarchical porous structure of diatom frustules is in particular attractive for membrane applications in microfluidic systems. In this paper, a procedure for pore size modifications of two centric diatom species, Coscinodiscus sp. and Thalassiosira eccentrica (T. eccentrica) using the atomic layer deposition (ALD) of ultrathin films of titanium oxide (TiO2) is described. TiO2 is deposited by sequential exposures to titanium chloride (TiCl4) and water. The modified diatom membranes were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDAX), and secondary ion mass spectrometry (SIMS). These techniques confirmed the controlled reduction of pore sizes while preserving the shape of the diatom membrane pores. Pore diameters of diatom membranes can be further tailored for specific applications by varying the number of cycles and by changing their surface functionality.© The Royal Society of Chemistry 2006
  • Thumbnail Image
    Item
    Creating thin magnetic layers at the surface of Sb2Te3 topological insulators using a low-energy chromium ion beam
    (AIP Publishing, 2020-05-11) Cortie, DL; Zhao, WY; Yue, Z; Li, Z; Bake, A; Marenych, O; Pastuovic, Z; Nancarrow, M; Zhang, ZM; Qi, DC; Evans, PJ; Mitchell, DRG; Wang, XL
    The surfaces of Sb2Te3 topological insulator crystals were implanted using a 40 keV chromium ion beam. To facilitate uniform doping, the Sb2Te3 was passivated with a thin TiO2 film before the implantation step. The resulting chemical structure was studied using atomic-resolution transmission electron microscopy. A fluence of 7 × 1015 ions/cm2 at 40 keV lead to amorphization of the Sb2Te3 surface, with chromium predominantly incorporated in the amorphous layer. Heating to 200 °C caused the amorphous region to recrystallize and led to the formation of a thin chromium-rich interfacial layer. Near-edge x-ray absorption spectroscopy indicates a uniform valence state of Cr3+ throughout, with no evidence of metallic clustering. High-temperature superparamagnetic behavior was detected up to 300 K, with an increased magnetic moment below 50 K. © 2020 Author(s).
  • No Thumbnail Available
    Item
    Dye⋯TiO2 interfacial structure of dye-sensitised solar cell working electrodes buried under a solution of I−/I3− redox electrolyte
    (Royal Society of Chemistry, 2017-07-27) McCree-Grey, J; Cole, JM; Holt, SA; Evans, PJ; Gong, Y
    Dye-sensitised solar cells (DSCs) have niche prospects for electricity-generating windows that could equip buildings for energy-sustainable future cities. However, this ‘smart window’ technology is being held back by a lack of understanding in how the dye interacts with its device environment at the molecular level. A better appreciation of the dye⋯TiO2 interfacial structure of the DSC working electrodes would be particularly valuable since associated structure–function relationships could be established; these rules would provide a ‘toolkit’ for the molecular engineering of more suitable DSC dyes via rational design. Previous materials characterisation efforts have been limited to determining this interfacial structure within an environment exposed to air or situated in a solvent medium. This study is the first to reveal the structure of this buried interface within the functional device environment, and represents the first application of in situ neutron reflectometry to DSC research. By incorporating the electrolyte into the structural model of this buried interface, we reveal how lithium cations from the electrolyte constituents influence the dye⋯TiO2 binding configuration of an organic sensitiser, MK-44, via Li+ complexation to the cyanoacrylate group. This dye is the molecular congener of the high-performance MK-2 DSC dye, whose hexa-alkyl chains appear to stabilise it from Li+ complexation. Our in situ neutron reflectometry findings are built up from auxiliary structural models derived from ex situ X-ray reflectometry and corroborated via density functional theory and UV/vis absorption spectroscopy. Significant differences between the in situ and ex situ dye⋯TiO2 interfacial structures are found, highlighting the need to characterise the molecular structure of DSC working electrodes while in a fully assembled device. © Royal Society of Chemistry 2020
  • No Thumbnail Available
    Item
    Engineering titanium and aluminum oxide composites using atomic layer deposition
    (AIP Publishing, 2011-12-23) Biluš Abaffy, N; McCulloch, DG; Partridge, JG; Evans, PJ; Triani, G
    Mixed metal oxides provide a convenient means to produce coatings with tailored physical properties. We investigate the possibility of synthesizing novel coatings of mixed titanium and aluminum oxide using atomic layer deposition (ALD). Results show that ALD films were prepared with compositions ranging between Al2O3 and TiO2 having refractive indices between 1.6 and 2.4 (at λ = 550 nm) at low temperature. The microstructure and bonding environment within the films was investigated using electron microscopy and x-ray absorption spectroscopy. The films were amorphous, and the Ti and Al atoms were mixed at the atomic scale. The electrical breakdown characteristics of the films were measured and showed that films with intermediate compositions had poor leakage current properties, believed to be caused by the presence of distorted bonding configurations. This study shows that ALD can be used to deposit high quality thin films with tailored optical properties, particularly suitable for applications in which complex topographies are required. © 2011 American Institute of Physics
  • No Thumbnail Available
    Item
    Fabrication of titania nanotube membranes by atomic layer deposition using nanoporous alumina as a template
    (Engineers Australia, 2011-09-18) Evans, PJ; Triani, G; Nambiar, M; Shapter, JG; Losic, D
    Conformal TiO2 films have been deposited onto highly oriented porous alumina arrays to characterise membranes with controlled pore modification. A suite of tools have been used to probe the evolution of these coated porous structures. Depth profiling by secondary ion mass spectroscopy revealed the distribution of elements Ti and O deposited throughout the coated porous alumina. High resolution imaging using scanning electron microscopy confirmed the reduction in pore-size as a function of deposition cycles. Following the removal of the porous alumina template, free-standing titania nanotubes were prepared which show the pore geometry of the alumina template was preserved. ©2011 Engineers Australia
  • No Thumbnail Available
    Item
    Identifying gold losses through application of SIMS technology
    (Maney Publishing, 2010-12-01) Chapman, N; Prince, KE; Evans, PJ; Radke, F; Hayward, P; Lester, N
    Mining companies are continuously searching for new technologies that can improve plant efficiency, by reducing operating costs and maximising metal recovery. Identification of how gold losses occur within an operating plant is crucial for determining appropriate operating strategies for improved metallurgical performance. Classical mineralogical and metallurgical techniques enable the operator to identify where losses occur in terms of particle size and mineral associations, however, how the gold is hosted within the mineral grains (for example, as solid solution or as fine microinclusions) is more difficult to determine. Secondary ion mass spectrometry (SIMS), a surface analytical technique is capable of detecting elements from ppm to ppb concentrations. Further, SIMS can be used to quantify gold in sulphide minerals, through comparison with implanted reference samples. Analysis of feed and tailing samples, from the processing circuit of the Kanowna Belle Gold Mine, in Western Australia using a combination of mineralogical, metallurgical and SIMS techniques was able to provide detailed information regarding the deportment of gold within this circuit. This analysis will be used to design and test process changes to improve gold recovery at a bench scale with possible implementation in the full scale plant. This paper provides details of the testwork methodology, and resultant laboratory study to improve gold recovery. © 2010, Maney Publishing
  • No Thumbnail Available
    Item
    Influence of the polymeric substrate on the water permeation of alumina barrier films deposited by atomic layer deposition
    (Elsevier, 2018-03-15) Jarvis, KL; Evans, PJ; Triani, G
    Atomic layer deposited (ALD) barrier films have been deposited onto a wide variety of flexible polymeric substrates to determine their effectiveness as moisture barriers for organic electronics. Little research has however been conducted on the contribution of the substrate to the barrier properties. In this study, alumina (Al2O3) barrier films have been deposited onto different polymeric substrates by ALD to investigate the effect of the substrate type and thickness on the water vapour transmission rate (WVTR). 24 nm Al2O3 films were deposited via plasma enhanced ALD onto 75 and 125 μm thick polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) substrates. Half of the substrates were also O2 plasma pre-treated prior to Al2O3 film deposition to determine its effect on the WVTR. The WVTR of the substrates prior to barrier film deposition was measured using tritiated water (HTO) permeation. Prior to barrier film deposition, it was shown that the WVTR decreased as the substrate thickness increased while PEN had a lower WVTR than PET. After Al2O3 barrier film deposition, the WVTR followed the previously observed trend with lower WVTR for thicker substrates and for PEN over PET. The substrates O2 plasma pre-treated prior to barrier film deposition also showed lower WVTRs, which were attributed to surface cleaning and improved film adhesion. The lowest WVTR measured was 3.1 × 10− 3 g·m− 2/day for a 24 nm Al2O3 film deposited onto O2 plasma pre-treated 125 μm PEN. These results demonstrate that the properties of the polymer substrate influence the WVTR even after barrier film deposition and can therefore be used to improve the barrier properties. © 2018 Elsevier B.V.
  • No Thumbnail Available
    Item
    Low temperature atomic layer deposition of titania thin films
    (Elsevier, 2010-04-02) Triani, G; Campbell, JA; Evans, PJ; Davis, J; Latella, BA; Burford, RP
    This paper presents a comprehensive study of atomic layer deposition of TiO2 films on silicon and polycarbonate substrates using TiCl4 and H2O as precursors at temperatures in the range 80–120°C. An in-situ quartz crystal microbalance was used to monitor different processing conditions and the resultant films were characterised ex-situ using a suite of surface analytical tools. In addition, the contact angle and wettability of as-deposited and UV irradiated films were assessed. The latter was found to reduce the contact angle from ≥ 80° to < 10°. Finally, the effect of surface pre-treatment on film toughness and adhesion was investigated and the results show a significant improvement for the pre-treated films. © 2010, Elsevier Ltd.
  • No Thumbnail Available
    Item
    A medium-energy photoemission and ab-initio investigation of cubic yttria-stabilised zirconia
    (AIP Scitation, 2014-03-01) Cousland, GP; Cui, XY; Smith, AE; Stampfl, CM; Wong, L; Tayebjee, M; Yu, DH; Triani, G; Evans, PJ; Ruppender, HJ; Jang, LY; Stampfl, APJ
    Experimental and theoretical investigations into the electronic properties and structure of cubic yttria-stabilized zirconia are presented. Medium-energy x-ray photoemission spectroscopy measurements have been carried out for material with a concentration of 8-9 mol. % yttria. Resonant photoemission spectra are obtained for a range of photon energies that traverse the L2 absorption edge for both zirconium and yttrium. Through correlation with results from density-functional theory (DFT) calculations, based on structural models proposed in the literature, we assign photoemission peaks appearing in the spectra to core lines and Auger transitions. An analysis of the core level features enables the identification of shifts in the core level energies due to different local chemical environments of the constituent atoms. In general, each core line feature can be decomposed into three contributions, with associated energy shifts. Their identification with results of DFT calculations carried out for proposed atomic structures, lends support to these structural models. The experimental results indicate a multi-atom resonant photoemission effect between nearest-neighbour oxygen and yttrium atoms. Near-edge x-ray absorption fine structure spectra for zirconium and yttrium are also presented, which correlate well with calculated Zr- and Y-4d electron partial density-of-states and with Auger electron peak area versus photon energy curve. © 2014, AIP Publishing LLC.
  • Thumbnail Image
    Item
    Modification of surface and barrier properties of polyethylene terepthalate and polycarbonate plastics by ion implantation
    (Australian Institute of Physics, 2005-02-04) Doolan, KR; Evans, PJ; Short, KT
    PET is used to produce a wide range of packaging for foods and beverages. Because oxygen can diffuse through it[1, 2, 3], PET is not suitable for fabrication of bottles for the storage of beer and red wine which are both degraded by oxygen. To store oxygen degradable foods for extended periods of time in PET packaging, oxygen diffusion through the PET must be prevented by incorporating a barrier layer or barrier polymer[1] into the PET matrix. We have begun a study of diffusion of light gases through samples of PET film that have been ion-implanted with aluminium and silicon ions to determine how dose level of these ions affects diffusion rate of helium and other gases through PET film. Polycarbonate (PC) is used to produce plastic products that have high toughness, high optical clarity and good resistance to UV degradation. However, PC sheet scratches easily because it is relatively soft. If PC sheet can be surface hardened to achieve scratch resistance similar to that of Perspex, it could be used to replace products, such as aircraft windows, currently fabricated from Perspex with tougher products fabricated from PC. Ion-implantation is one method that can be used to increase surface hardness and decrease surface wear rate [4]. © 2005 Australian Institute of Physics.
  • Thumbnail Image
    Item
    Properties of ALD Al2O3 protective coatings
    (American Vacuum Society, 2010-10-21) Evans, PJ; Murai, Y; Lindsay, MJ; Davis, J; Triani, G
    In recent years, atomic layer deposition (ALD) has emerged as a technology platform for nanofabrication [1]. This interest has evolved from its intrinsic advantages; inherent thickness control, the ability to prepare highly conformal pin-hole free films, low temperature film growth and its large area uniformity. These redeeming characteristics have broadened the application of ALD films in such diverse areas as encapsulation of nanoparticles [2], templating of complex structures [3] and the modification of membranes [4]. The deposition of atomic layer protective coatings on flexible polymers and metals is another target application to improve the lifetime performance of functional materials that may be susceptible to degradation [5]. In particular, the ingress of moisture and atmospheric gases as well as the effects of abrasion and thermal cycling can significantly diminish a material’s suitability in cases where its bulk properties meet all other requirements. Inorganic barrier coatings on flexible substrates are subject to additional constraints where the mechanical strength and adhesion of the protective coating are particularly important. In this study, ALD alumina coatings were deposited on flexible substrates including polycarbonate, polyethylene naphthalate (PEN), copper and titanium, to investigate their toughness and adhesion under tensile load. In addition, the effect of deposition conditions on the performance of these protective coatings will be presented. References H. Kim, H.B.R. Lee, and W.J. Maeng, Thin Solid Films, 517 (2009) 2563-2580. J.R. Scheffe, A. Frances, D.M. King, X. Liang, B.A. Branch, A.S. Cavanagh, S.M. George, and A.W. Weimer, Thin Solid Films, 517 (2009) 1874-1879. G. Triani, P.J. Evans, D.J. Attard, K.E. Prince, J Bartlett, S. Tan, and R.P. Burford, J. Mater. Chem., 16 (2006) 1355-1359. L.Velleman, G. Triani, P.J. Evans, J. G. Shapter, and D. Losic, Micropor. Mesopor. Mater. 126 (2009) 87-94. T. Hirkikorpi, M. Vaha-Nissi, T. Mustonen, E.Iiskola and M. Karppinen, Thin Solid Films, 518 (2010) 2654-2658
  • Thumbnail Image
    Item
    A quadrupole mass spectrometer system for nuclear safeguards applications.
    (Australian Nuclear Science and Technology Organisation, 1987-12) Evans, PJ
    An on-line enrichment monitor for nuclear safeguards-related surveillance of a pilot-scale gas centrifuge plant is described. This monitor utilises a quadrupole mass spectrometer to measure the isotopic composition of UF6 in the feed and product gas streams. Details of the design and construction are given and several difficulties are identified and discussed. Finally the performance of this system is illustrated with typical results.
  • No Thumbnail Available
    Item
    Sol-gel tungsten oxide/titanium oxide multilayer nanoheterostructured thin films: structural and photoelectrochemical properties
    (American Chemical Society, 2007-12-20) Luca, V; Blackford, MG; Finnie, KS; Evans, PJ; James, M; Lindsay, MJ; Skyllas-Kazacos, M; Barnes, PRF
    Multilayer structures of alternating thin titanium and tungsten oxide layers having dimensions of similar to 20 nm have been fabricated from titanium alkoxide and various tungstate precursor solutions using the dip coating technique. Single, double, and triple layer titanate and tungstate thin films were deposited on silicon substrates, and these films were initially annealed at 400°C. Structural and microstructural aspects of the films were investigated using a variety of techniques, including X-ray reflectometry, grazing incidence X-ray absorption spectroscopy (GIXAS), cross-sectional transmission electron microscopy (TEM), and secondary ion mass spectrometry. The dimensions of the films and the character of the interfaces were principally gauged by cross-sectional TEM and X-ray reflectometery. All films were continuous on a local scale and had relatively low surface roughness. At the treatment temperature of 400°C, only the tungsten oxide component showed appreciable crystallinity. The multilayer films had relatively diffuse interfaces, even after annealing in air at this temperature. At these temperatures, easily measurable diffusion of tungsten into the titanium oxide component was observed, whereas the diffusion of titanium into the tungsten oxide component occurred to a lesser degree. At higher temperatures, interdiffusion of components was found to be significant. TEM, X-ray diffraction, and Ti K-edge GIXAS measurements indicated that annealing at 400°C generated films in which the titanate component remained amorphous while the tungstate component crystallized in the tetragonal modification Of WO3, which is normally stable only at high temperatures. Grazing incidence X-ray absorption spectroscopy allowed the degree of distortion of the tungsten oxygen polyhedra to be monitored as a function of depth into the film. The photoelectrochernical activity of the multilayer film electrodes was investigated, and the activity for water photo-oxidation was assessed. The photoelectrochernical response was greatest when crystalline WO3 was bounded on both sides by amorphous TiO2 layers. In this bounded state, WO3 had unique structural characteristics. © 2007, American Chemical Society
  • No Thumbnail Available
    Item
    Structural and chemical modification of porous alumina membranes
    (Elsevier, 2009-11) Velleman, L; Triani, G; Evans, PJ; Shapter, JG; Losic, D
    Structural and chemical modification of porous anodic alumina (AAO) membranes was investigated with the aim of fine-tuning pore diameters and chemical selectivity. AAO membranes from commercial sources with pore diameters (20, 100 and 200 nm) were used as the substrate. Atomic layer deposition (ALD) of silica (SiO2) has been used for membrane structural modification using tris(tert-butoxy)silanol and trimethylaluminium as the precursor couple. By adjusting the number of ALD deposition cycles (3–20), the effective pore diameter of AAO membranes was significantly reduced to desired values (<10 nm) improving the separation properties of commercial membranes. The chemical functionalization of silica coated AAO membranes with a perfluorodecyldimethylchlorosilane (PFDS) shows that the transport and selectivity properties of silica composite AAO membranes can be varied by functionalization using silane chemistry. The hydrophobic PFDS-modified membranes showed enhanced sensitivity (flux ratio 5.52) to the transport of hydrophobic molecules (tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy), over hydrophilic molecules (rose bengal (RB)). Structural and chemical properties of modified membranes were confirmed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), dynamic secondary ion mass spectrometry (DSIMS), and contact angle measurements. The resultant silica coated commercial AAO membranes with specific surface chemistry and controlled pore size are applicable for advanced molecular separation, cell culture, tissue engineering, biosensing and drug delivery. © 2009, Elsevier Ltd.
  • Thumbnail Image
    Item
    Structure and magnetism of ultra-small cobalt particles assembled at titania surfaces by ion beam synthesis
    (Elsevier, 2021-12) Bake, A; Rezoanur Rahman, M; Evans, PJ; Cortie, MB; Nancarrow, M; Abrudan, R; Radu, F; Khaydukov, Y; Causer, GL; Callori, SJ; Livesey, KL; Mitchell, DRG; Pastuovic, Z; Wang, XL; Cortie, DL
    Metallic cobalt nanoparticles offer attractive magnetic properties but are vulnerable to oxidation, which suppresses their magnetization. In this article, we report the use of ion beam synthesis to produce ultra-small, oxidation-resistant, cobalt nanoparticles embedded within substoichiometric TiO2-δ thin films. Using high fluence implantation of cobalt at 20–60 keV, the particles were assembled with an average size of 1.5 ± 1 nm. The geometry and structure of the nanoparticles were studied using scanning transmission electron microscopy. Near-edge X-ray fluorescence spectroscopy on the L2,3 Co edges confirms that the majority of the particles beneath the surface are metallic, unoxidised cobalt. Further evidence of the metallic nature of the small particles is provided via their high magnetization and superparamagnetic response between 3 and 300 K with a low blocking temperature of 4.5 K. The magnetic properties were studied using a combination of vibrating sample magnetometry, element-resolved X-ray magnetic circular dichroism, and depth-resolved polarised neutron reflectometry. These techniques provide a unified picture of the magnetic metallic Co particles. We argue, based on these experimental observations and thermodynamic calculations, that the cobalt is protected against oxidation beneath the surface of titania owing to the enthalpic stability of TiO2 over CoO which inhibits solid state reactions. Crown Copyright © 2021 Published by Elsevier B.V.