PET web samples have been treated by magnetically enhanced glow discharges powered using either medium frequency pulse direct current (p-DC) or low frequency high power pulse (HIPIMS) sources. The plasma pre-treatment processes were carried out in an Ar?O2 atmosphere using either Cu or Ti sputter targets. XPS, AFM and sessile drop water contact angle measurements have been employed to examine changes in surface chemistry and morphology for different pre-treatment process parameters. Deposition of metal oxide onto the PET surface is observed as a result of the sputter magnetron-based glow discharge web treatment. Using the Cu target, both the p-DC and HIPIMS processes result in the formation of a thin CuO layer (with a thickness between 1 and 11 nm) being deposited onto the PET surface. Employing the Ti target, both p-DC and HIPIMS processes give rise to a much lower concentration of Ti (
Gravani S, Polychronopoulou K, Stolojan V, Cui Q, Gibson PN, Hinder SJ, Gu Z, Doumanidis CC, Baker MA, Rebholz C (2010) Growth and characterization of ceria thin films and Ce-doped gamma-Al2O3 nanowires using sol-gel techniques, NANOTECHNOLOGY 21 (46) 465606 pp. ---
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³-Al2O3 is a well known catalyst support. The addition of Ce to ³-Al2O3 is known to beneficially retard the phase transformation of ³-Al2O3 to ±-Al2O3 and stabilize the ³-pore structure. In this work, Ce-doped ³-Al2O3 nanowires have been prepared by a novel method employing an anodic aluminium oxide (AAO) template in a 0.01 M cerium nitrate solution, assisted by urea hydrolysis. Calcination at 500 °C for 6 h resulted in the crystallization of the Ce-doped AlOOH gel to form Ce-doped ³-Al2O3 nanowires. Ce3 + ions within the nanowires were present at a concentration of
Scheuerlein C, Taborelli M, Hilleret N, Brown A, Baker MA (2002) An AES study of the room temperature conditioning of technological metal surfaces by electron irradiation, APPLIED SURFACE SCIENCE 202 (1-2) PII S0169-4332(02)00868-1 pp. 57-67 ELSEVIER SCIENCE BV
Lamb DA, Irvine SJC, Clayton AJ, Kartopu G, Barrioz V, Hodgson SD, Baker MA, Grilli R, Hall J, Underwood CI, Kimber R (2016) Characterization of MOCVD Thin-Film CdTe Photovoltaics on Space-Qualified Cover Glass, IEEE Journal of Photovoltaics 6 (2) pp. 557-561
This paper details the AM0 conversion efficiency of a metal-organic chemical vapor phase deposition thin-film cadmium telluride (CdTe) solar cell deposited onto a cerium-doped cover glass (100 ¼m). An AM0 best cell conversion efficiency of 12.4% (0.25-cm2 contact area) is reported. An AM0 mean efficiency of 12.1% over eight cells demonstrated good spatial uniformity. Excellent adhesion of the cell structure to the cover glass was observed with an adhesive strength of 38 MPa being measured before cohesive failure of the test adhesive. The device structure on cover glass was also subject to severe thermal shock cycling of +80 °C to -196 °C, showing no signs of delamination and no deterioration of the photovoltaic (PV) performance.
UPADHYAYA D, BAKER MA, WARDCLOSE CM, TSAKIROPOULOS P, FROES FH (1993) INTERFACE STUDIES IN A TI-6AL-4V-SIGMA FIBER-COMPOSITE, JOURNAL DE PHYSIQUE IV 3 (C7) pp. 1717-1722 EDITIONS PHYSIQUE
Goller R, Torri P, Baker MA, Gilmore R, Gissler W (1999) The deposition of low-friction TiN-MoSx hard coatings by a combined are evaporation and magnetron sputter process, SURFACE & COATINGS TECHNOLOGY 120 pp. 453-457 ELSEVIER SCIENCE SA
Lenardi C, Baker MA, Briois V, Nobili L, Piseri P, Gissler W (1999) Properties of amorphous a-CH(: N) films synthesized by direct ion beam deposition and plasma-assisted chemical vapour deposition, DIAMOND AND RELATED MATERIALS 8 (2-5) pp. 595-600 ELSEVIER SCIENCE SA
Brown HL, Thornley SA, Wakeham SJ, Thwaites MJ, Curry RJ, Baker MA (2015) The impact of substrate bias on a remote plasma sputter coating process for conformal coverage of trenches and 3D structures, JOURNAL OF PHYSICS D-APPLIED PHYSICS 48 (33) ARTN 335303 IOP PUBLISHING LTD
Duarte DD, Bell SJ, Lipp J, Schneider A, Seller P, Veale MC, Wilson MD, Baker MA, Sellin PJ, Kachkanov V, Sawhney KJS (2013) Edge effects in a small pixel CdTe for X-ray imaging, JOURNAL OF INSTRUMENTATION 8 ARTN P10018
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Large area detectors capable of operating with high detection efficiency at energies
above 30 keV are required in many contemporary X-ray imaging applications. The properties of
high Z compound semiconductors, such as CdTe, make them ideally suitable to these applications.
The STFC Rutherford Appleton Laboratory has developed a small pixel CdTe detector with 80×80
pixels on a 250 µm pitch. Historically, these detectors have included a 200 µm wide guard band
around the pixelated anode to reduce the effect of defects in the crystal edge. The latest version of
the detector ASIC is capable of four-side butting that allows the tiling of N×N flat panel arrays. To
limit the dead space between modules to the width of one pixel, edgeless detector geometries have
been developed where the active volume of the detector extends to the physical edge of the crystal.
The spectroscopic performance of an edgeless CdTe detector bump bonded to the HEXITEC ASIC
was tested with sealed radiation sources and compared with a monochromatic X-ray micro-beam
mapping measurements made at the Diamond Light Source, U.K. The average energy resolution
at 59.54 keV of bulk and edge pixels was 1.23 keV and 1.58 keV, respectively. 87% of the edge
pixels present fully spectroscopic performance demonstrating that edgeless CdTe detectors are a
promising technology for the production of large panel radiation detectors for X-ray imaging
HAUPT J, BAKER MA, STROOSNIJDER MF, GISSLER W (1994) AUGER-ELECTRON SPECTROSCOPY STUDIES ON TINX, SURFACE AND INTERFACE ANALYSIS 22 (1-12) pp. 167-170 JOHN WILEY & SONS LTD
Joseph MC, Tsotsos C, Baker MA, Kench PJ, Rebholz C, Matthews A, Leyland A (2005) Characterisation and tribological evaluation of nitrogen-containing molybdenum-copper PVD metallic nanocomposite films, SURFACE & COATINGS TECHNOLOGY 190 (2-3) pp. 345-356 ELSEVIER SCIENCE SA
TiAlBN coatings have been deposited by electron beam (EB) evaporation from a single TiAlBN material source onto AISI 316 stainless steel substrates at a temperature of 450 °C and substrate bias of ? 100 V. The stoichiometry and nanostructure have been studied by X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. The hardness and elastic modulus were determined by nanoindentation. Five coatings have been deposited, three from hot-pressed TiAlBN material and two from hot isostatically pressed (HIPped) material. The coatings deposited from the hot-pressed material exhibited a nanocomposite nc-(Ti,Al)N/a-BN/a-(Ti,Al)B2 structure, the relative phase fraction being consistent with that predicted by the equilibrium Ti?B?N phase diagram. Nanoindentation hardness values were in the range of 22 to 32 GPa. Using the HIPped material, coating (Ti,Al)B0.29N0.46 was found to have a phase composition of 72?79 mol.% nc-(Ti,Al)(N,B)1 ? x+ 21?28 mol.% amorphous titanium boride and a hardness of 32 GPa. The second coating, (Ti,Al)B0.66N0.25, was X-ray amorphous with a nitride+boride multiphase composition and a hardness of 26 GPa. The nanostructure and structure?property relationships of all coatings are discussed in detail. Comparisons are made between the single-EB coatings deposited in this work and previously deposited twin-EB coatings. Twin-EB deposition gives rise to lower adatom mobilities, leading to (111) (Ti,Al)N preferential orientation, smaller grain sizes, less dense coatings and lower hardnesses.
© 2015 Elsevier B.V.Membrane filtration is employed for water treatment and wastewater reclamation purposes, but membranes alone are unable to remove pollutant molecules and certain pathogens. Photocatalytically active N-doped TiO2 coatings have been deposited by sol-gel onto 200 nm pore size alumina membranes for water treatment applications using two different methods, via pipette droplets or spiral bar applicator. The uncoated and coated membranes were characterised by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectrometry (EDX). Both coatings showed the presence of N-doped anatase, with a surface coverage between 84 and 92%, and nitrogen concentration (predominantly interstitial) of 0.9 at.%. The spiral bar applicator deposited coatings exhibit a thicker mud-cracked surface layer with limited penetration of the porous membrane, whilst the pipette deposited coatings have mostly penetrated into the bulk of the membrane and a thinner layer is present at the surface. The photocatalytic activity (PCA), measured through the degradation of carbamazepine (CBZ), under irradiation of a solar simulator was 58.6% for the pipette coating and 63.3% for the spiral bar coating. These photocatalytically active N-doped sol-gel coated membranes offer strong potential in forming the fundamental basis of a sunlight based water treatment system.
Bell SJ, Schneider A, Seller P, Veale MC, Wilson MD, Baker MA, Perumal V, Sellin PJ, Chen H, Marthandam P (2013) A multi-technique characterization of electroless gold contacts on single crystal CdZnTe radiation detectors, Journal of Physics D: Applied Physics 46 (45)
Cadmium zinc telluride (CdZnTe) is now established as a popular choice of sensor for the detection of ³-rays and hard x-rays, leading to its adoption in security, medical and scientific applications. There are still many technical challenges involving the deposition of high-quality, uniform metal contacts on CdZnTe. A detailed understanding of the interface between the bulk CdZnTe and the metal contacts is required for improvements to be made. To understand these complex interfaces, a range of complementary materials characterization techniques have been employed, including x-ray photoelectron spectroscopy depth profiling, focused ion beam cross section imaging and energy dispersive x-ray spectroscopy. In this paper a number of Redlen CdZnTe detectors with asymmetric anode/cathode contacts have been investigated. The structures of the contacts were imaged and their compositions identified. It was found that the two stage electroless indium/electroless gold deposition process on 'polished only' surfaces formed a complex heterojunction on the cathode, incorporating compounds of gold, gold-tellurium, tellurium oxide (of varying stoichiometry) and cadmium chloride up to depths of several 100 nm. Trace amounts of indium were found, in the form of an indium-gold compound, or possibly indium oxide. At the surface of the CdZnTe bulk, a thin Cd depleted layer was observed. The anode heterojunction, formed by a single stage electroless gold deposition, was thinner and exhibited a simpler structure of gold and tellurium oxide. The differing (asymmetric) nature of the anode/cathode contacts gave rise to asymmetric current-voltage (I-V) behaviour and spectroscopy. © 2013 IOP Publishing Ltd.
Protective coatings have been deposited on electrogalvanized steel by immersion in solutions containing 2-Butyne-1.4-diol propoxylate (C7H11O3), cerium nitrate, sodium nitrate and sodium sulphate for different immersion periods. The surface morphology and chemical composition of the coatings formed on the electrogalvanized steel were studied using field emission gun scanning electron microscopy, X-ray photoelectron spectroscopy and Fourier Transform Infrared Spectroscopy. The corrosion resistance of the electrogalvanized steel prior to and after surface treatment was investigated by electrochemical impedance spectroscopy in 0.1 mol L-1 NaCl solution. The results were compared to the performance of a chromate conversion coating in the same solution. The coatings formed on the electrogalvanized steel surface showed the presence of a mixed organic/inorganic layer containing Ce2O3 and CeO2 which improved the corrosion resistance of the substrate and showed a superior corrosion resistance to that provided by a chromate conversion coating.
Baker MA, Gissler W, Klose S, Trampert M, Weber F (2000) Morphologies and corrosion properties of PVD Zn-Al coatings, SURFACE & COATINGS TECHNOLOGY 125 (1-3) pp. 207-211 ELSEVIER SCIENCE SA
© 2015 IOP Publishing Ltd.Fully spectroscopic x/³-ray imaging is now possible thanks to advances in the growth of wide-bandgap semiconductors. One of the most promising materials is cadmium zinc telluride (CdZnTe or CZT), which has been demonstrated in homeland security, medical imaging, astrophysics and industrial analysis applications. These applications have demanding energy and spatial resolution requirements that are not always met by the metal contacts deposited on the CdZnTe. To improve the contacts, the interface formed between metal and semiconductor during contact deposition must be better understood. Gold has a work function closely matching that of high resistivity CdZnTe and is a popular choice of contact metal. Gold contacts are often formed by electroless deposition however this forms a complex interface. The prior CdZnTe surface preparation, such as mechanical or chemo-mechanical polishing, and electroless deposition parameters, such as gold chloride solution temperature, play important roles in the formation of the interface and are the subject of the presented work. Techniques such as focused ion beam (FIB) cross section imaging, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS) and current - voltage (I-V) analysis have been used to characterize the interface. It has been found that the electroless reaction depends on the surface preparation and for chemo-mechanically polished (1 1 1) CdZnTe, it also depends on the A/B face identity. Where the deposition occurred at elevated temperature, the deposited contacts were found to produce a greater leakage current and suffered from increased subsurface voiding due to the formation of cadmium chloride.
Baker MA, Greaves SJ, Wendler E, Fox V (2000) A comparison of in situ polishing and ion beam sputtering as surface preparation methods for XPS analysis of PVD coatings, THIN SOLID FILMS 377 pp. 473-477 ELSEVIER SCIENCE SA
Grilli R, Simpson R, Mallinson CF, Baker MA (2014) Comparison of Ar+ monoatomic and cluster ion sputtering of Ta2O5 at different ion energies, by XPS: Part 1 - Monoatomic ions, Surface Science Spectra 21 (1) pp. 50-67
© 2014 American Vacuum Society.A standard 30 nm thick Ta2O5 oxide layer grown on Ta was examined by XPS after Ar+ ion bombardment at ion energies of 200 eV, 500 eV, and 3 keV. The reduction of Ta2O5, resulting from the preferential sputtering of oxygen after ion beam bombardment at different energies has been investigated. Survey spectra, C 1s, Ta 4f and O 1s spectra are presented for each profile at three stages: native surface, after reaching the steady-state oxide composition, and from the underlying metal substrate. Reducing the Ar+ energy from 3 keV to 200 eV makes no substantial difference in the degree of Ta2O5 reduction observed following ion bombardment.
Saliba-Silva A, Faria RN, Baker MA, Costa I (2004) Improving the corrosion resistance of NdFeB magnets: an electrochemical and surface analytical study, SURFACE & COATINGS TECHNOLOGY 185 (2-3) pp. 321-328 ELSEVIER SCIENCE SA
BAKER MA (1993) THE APPLICATION OF SURFACE IMAGING TECHNIQUES TO THE STUDY OF PITTING CORROSION INITIATION IN STAINLESS-STEELS, SURFACE AND INTERFACE ANALYSIS 20 (6) pp. 535-& JOHN WILEY & SONS LTD
X-ray photoelectron spectroscopy (XPS) was carried out to analyse a commercially available butanenedioic acid (succinic acid) powder. XPS spectra were obtained using incident monochromatic Al Ka radiation at 1486.6 eV. A survey spectrum together with O 1s and C 1s core level spectra are presented. The presence of characteristic carbon and oxygen photoelectrons peaks allows the use these results as a reference for dicarboxylic acids.
Horovitz I, Avisar D, Baker MA, Grilli R, Lozzi L, Di Camillo D, Mamane H (2016) Carbamazepine degradation using a N-doped TiO2 coated photocatalytic membrane reactor: Influence of physical parameters, JOURNAL OF HAZARDOUS MATERIALS 310 pp. 98-107 ELSEVIER SCIENCE BV
Tsotsos C, Kanakis K, Davison A, Baker MA, Matthews A, Leyland A (2006) Mechanical and tribological properties of CrTiCu(B,N) glassy-metal coatings deposited by reactive magnetron sputtering, SURFACE & COATINGS TECHNOLOGY 200 (14-15) pp. 4601-4611 ELSEVIER SCIENCE SA
Polychronopoulou K, Baker MA, Rebholz C, Neidhardt J, O'Sullivan M, Reiter AE, Kanakis K, Leyland A, Matthews A, Mitterer C (2009) The nanostructure, wear and corrosion performance of arc-evaporated CrBxNy nanocomposite coatings, SURFACE & COATINGS TECHNOLOGY 204 (3) pp. 246-255
ELSEVIER SCIENCE SA
Colpo P, Ceccone G, Sauvageot P, Baker M, Rossi F (2000) Characterization of zirconia coatings deposited by inductively coupled plasma assisted chemical vapor deposition, JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 18 (4) pp. 1096-1101 AMER INST PHYSICS
BAKER MA, CASTLE JE (1992) THE INITIATION OF PITTING CORROSION OF STAINLESS-STEELS AT OXIDE INCLUSIONS, CORROSION SCIENCE 33 (8) pp. 1295-1312 PERGAMON-ELSEVIER SCIENCE LTD
Saliba-Silva AM, de Melo HG, Baker MA, Brown AM, Costa I (2003) Characterization of sintered NdFeB magnets after phosphating in alkaline and acidic environments, ADVANCED POWDER TECHNOLOGY III 416-4 pp. 54-59 TRANS TECH PUBLICATIONS LTD
Baker MA (1995) Encyclopedia of Analytical Science: Sam-Sur, In: Townshend A (eds.), Encyclopedia of Analytical Science: Sam-Sur
Saliba-Silva AM, Baker MA, De Melo HG, Costa I (2001) Corrosion protection of sintered NdFeB magnets by phosphating, Computational and Experimental Methods 6 pp. 65-74
Phosphating of sintered NdFeB magnets has been studied by immersion in a solution of 0.15 M NaH 2PO 4 acidified to pH 3.7 under polarization. Cyclic polarization experiments indicated that phosphating could be assisted by polarization, with the current density decreasing as the number of polarization cycles increased. Auger electron spectroscopy (AES) and Energy Dispersive X-ray Analysis (EDX) of magnets exposed to the phosphating treatment confirmed the formation of the phosphate layer over both main phases of the specimen, namely, the magnetic (¦) and the Nd-rich phase. Electrochemical impedance spectroscopy (EIS) measurements performed on treated and untreated magnets immersed in synthetic saliva showed the phosphate conversion layer to improve the corrosion resistance and provided evidence of its porous nature. The phosphating procedure adopted in the present investigation is a promising surface treatment for improving the corrosion resistance of sintered NdFeB magnets.
Grilli R, Simpson R, Mallinson CF, Baker MA (2014) Comparison of Ar+ monoatomic and cluster ion sputtering of Ta2O5 at different ion energies, by XPS: Part 2 - Cluster ions, Surface Science Spectra 21 (1) pp. 68-83
© 2014 American Vacuum Society.A standard 30 nm thick Ta2O5 oxide layer grown on Ta was examined by XPS after Arn+ cluster ion bombardment at ion energies of 4 keV, 5 keV and 6 keV, with a cluster size of 1000 atoms. The reduction of Ta2O5, resulting from the preferential sputtering of oxygen after ion beam bombardment at different energies has been investigated. Survey spectra, C 1s, Ta 4f and O 1s spectra are presented for each profile at three stages: native surface, after reaching the steady-state oxide composition, and from the underlying metal substrate. It is necessary to reach a voltage of 6 keV to obtain a good sputter rate. The use of the cluster source seems to be promising to reduce the preferential sputtering phenomenon.
Rebholz C, Monclus MA, Baker MA, Mayrhofer PH, Gibson PN, Leyland A, Matthews A (2007) Hard and superhard TiAlBN coatings deposited by twin electron-beam evaporation, SURFACE & COATINGS TECHNOLOGY 201 (13) pp. 6078-6083 ELSEVIER SCIENCE SA
Thin films of TiN were prepared via RF magnetron reactive sputtering at various deposition pressures. The characteristics of the plasmas were measured by optical emission spectroscopy to optimize the conditions for the deposition of TiN coatings. After deposition, the thin films were annealed in a closed furnace at several different temperatures, and revealed the formation of different phases of TiO 2. The resulting TiN/TiO 2 thin films showed drastic changes in their crystal structure, optical properties, and photoelectrochemical performance. By examining how the deposition pressure and postdeposition annealing conditions affected the TiN film structure and performance, samples were prepared to optimize visible light absorption and activity. A model for the oxidation process was proposed which described the structural change from TiN to TiO 2 through optical, morphological, and crystalline characterization. This study has systematically shown the ability to tailor the optical, crystalline, and photoactive properties of TiO 2 by tailoring the intrinsic properties of TiN thin films and subsequent annealing. These results can be utilized for many solar driven optoelectronic devices. © 2012 American Chemical Society.
Jimenez O, Audronis M, Baker MA, Matthews A, Leyland A (2008) Structure and mechanical properties of nitrogen-containing Zr-Cu based thin films deposited by pulsed magnetron sputtering, JOURNAL OF PHYSICS D-APPLIED PHYSICS 41 (15) ARTN 155301 IOP PUBLISHING LTD
Gibson PN, Baker MA, Ozsan ME (2002) Investigation of sulphur diffusion at the CdS/CdTe interface of thin-film solar cells, SURFACE AND INTERFACE ANALYSIS 33 (10-11) pp. 825-829 JOHN WILEY & SONS LTD
Baker MA, Gilmore R, Gibson PN, Gissler W (1997) The microstructure and properties of Ti-B-C coatings for tribological applications, ECASIA 97: 7TH EUROPEAN CONFERENCE ON APPLICATIONS OF SURFACE AND INTERFACE ANALYSIS pp. 1127-1130 JOHN WILEY & SONS LTD
Baker MA, Rebholz C, Leyland A, Matthews A (2002) Electron spectroscopic studies of nanocomposite PVD TiAlBN coatings, VACUUM 67 (3-4) pp. 471-476 PERGAMON-ELSEVIER SCIENCE LTD
Gissler W, Baker MA, Haupt J, Gibson PN, Gilmore R, Mollart TP (1997) Phase composition and tribological behavior of titanium boron nitride coatings, DIAMOND FILMS AND TECHNOLOGY 7 (3) pp. 165-180 MYU K K
Lamb DA, Irvine SJC, Clayton AJ, Barrioz V, Kartopu G, Baker MA, Underwood CI, Grilli R, Kimber R, Hall J (2015) Lightweight and low-cost thin film photovoltaics for large area extra-terrestrial applications, IET Renewable Power Generation 9 (5) pp. 420-423
This work describes progress towards achieving a flexible, high specific power and low-cost photovoltaic (PV) for emerging large area space applications. The study reports the highest conversion efficiency of 15.3% AM1.5G for a CdTe device on ultra-thin cerium-doped cover glass, the standard protective material for extra-terrestrial PVs. The deposition technique used for all of the semiconductor layers comprising the device structure was atmospheric pressure metal organic chemical vapour deposition. Improvements to the device structure over those previously reported led to a Voc of 788 mV and a relatively low series resistance of 3.3 ©·cm2. These were largely achieved by the introduction of a post-growth air anneal and a refinement of the front contact bus bars, respectively. The aluminium-doped zinc oxide transparent conductive oxide, being the first layer applied to the cover glass, was subject to thermal shock cycling +80 to (-) 196°C to test the adhesion under the extreme conditions likely to be encountered for space application. Scotch Tape testing and sheet resistance measurements before and after the thermal shock testing demonstrated that the aluminium-doped zinc oxide remained well adhered to the cover glass and its electrical performance unchanged.
Clayton AJ, Baker MA, Babar S, Gibson PN, Irvine SJC, Kartopu G, Lamb DA, Barrioz V (2015) Influence of CdCl2 activation treatment on ultra-thin Cd1-xZnxS/CdTe solar cells, THIN SOLID FILMS 590 pp. 241-247 ELSEVIER SCIENCE SA
BAKER MA, UPADHYAYA D (1994) AN INTERFACIAL STUDY OF A SIGMA FIBER TI-6AL-4V COMPOSITE USING SCANNING AUGER EDX MICROSCOPY, SURFACE AND INTERFACE ANALYSIS 22 (1-12) pp. 308-313 JOHN WILEY & SONS LTD
Baker MA (1994) Materials Science and Technology, Characterization of Materials, In: Lifshin E, Cahn RW, Haasen P, Kramer EJ (eds.), Materials Science and Technology, Characterization of Materials Wiley-VCH
This is the second of two volumes focusing on the principal analytical techniques forcharacterizing metal alloys, semiconductors, polymers, and ceramics.
Hinder SJ, Grilli R, Rustame M, Santos WIA, Baker MA, Costa I (2014) A surface analytical investigation of cerium-based conversion coatings deposited onto an AA2024-T3 aluminium alloy cladding layer, Surface and Interface Analysis 46 (10-11) pp. 735-739
Copyright © 2014 John Wiley & Sons, Ltd.Cerium-based conversion coatings are being investigated as alternatives to chromating treatments for the corrosion protection of aluminium and its alloys because of the environmentally unfriendly nature of the chromating process. This study investigates the surface film composition, structure and corrosion performance following a two-step surface treatment for an AA2024-T3 clad aluminium alloy. The two-step treatment comprised of an initial cerium conversion process involving immersion in an aqueous solution containing Ce3+ ions at 75°C followed by immersion in a propylene glycol solution at 75°C. The coating surface morphology, composition and structure have been studied using SEM, XPS, Auger spectroscopy and Fourier transform infrared spectroscopy, while corrosion resistance was evaluated using electrochemical impedance spectroscopy. The coating formed by the two-step treatment is an interconnecting fibrous (pseudo) boehmite layer with the incorporation of Ce3+ in the film. This two step treatment coating exhibits high impedance compared with the coatings formed through exposure to just stage 1 or stage 2 of the two-step treatment and shows good potential for improved corrosion protection.
X-ray photoelectron spectroscopy (XPS) was carried out to analyse a commercially available propanedioic acid (malonic acid) powder. XPS spectra were obtained using incident monochromatic Al Ka radiation at 1486.6 eV. A survey spectrum together with O 1s and C 1s core level spectra are presented. The presence of characteristic carbon and oxygen photoelectrons peaks allows the use these results as a reference for dicarboxylic acids.
Space photovoltaics is dominated by multi-junction (III-V) technology. However, emerging
applications will require solar arrays with; high specific power (kW/kg), flexibility in
stowage and deployment and a significantly lower cost than the current III-V technology
offers. This research demonstrates direct deposition of thin film CdTe onto the radiation-hard
cover glass that is normally laminated to any solar cell deployed in space. Four CdTe
samples, with 9 defined contact device areas of 0.25 cm2, were irradiated with protons of 0.5
MeV energy and varying fluences. At the lowest fluence, 1×1012 cm-2, the relative efficiency
of the solar cells was 95%. Increasing the proton fluence to 1×1013 cm-2 and then 1×1014 cm-2
decreased the solar cell efficiency to 82% and 4% respectively. At the fluence of 1×1013 cm-2,
carrier concentration was reduced by an order of magnitude. Solar Cell Capacitance
Simulator (SCAPS) modelling obtained a good fit from a reduction in shallow acceptor
concentration with no change in the deep trap defect concentration. The more highly
irradiated devices resulted in a buried junction characteristic of the external quantum
efficiency, indicating further deterioration of the acceptor doping. This is explained by
compensation from interstitial H+ formed by the proton absorption. An anneal of the 1×1014
cm-2 fluence devices gave an efficiency increase from 4% to 73% of the pre-irradiated levels,
indicating that the compensation was reversible. CdTe with its rapid recovery through
annealing, demonstrates a radiation hardness to protons that is far superior to conventional
multi-junction III-V solar cells.
CeO2 and CexSm1-xO2 nanoparticle mixed oxides have been synthesized by microwave assisted sol-gel (MW sol-gel) and conventional sol-gel (C sol-gel) synthesis carried out at 60oC (typical sol-gel) and 100oC (approaching the MW temperature). Different characterization techniques, namely, XRD, BET, Raman, SEM, FTIR, TEM, XPS, H2-TPR, CO2-TPD, and XPS have been employed to understand the process-structure-properties relationship of the catalysts. The CO oxidation performance has been determined both in the absence and in the presence of H2 in the feed gas stream. Microwave heating yields a more thermally stable precursor material, which preserves 75% of its mass up to 600oC, attributable to the different chemical nature of the precursor, compared to the typical sol-gel material with the same composition. Varying the synthesis method has no profound effect on the surface area of the materials, which is in the range 4-35m2/g. Conventional sol-gel synthesis performed at 60 and 100oC yields CeO2 particles with a crystallite size of 29 nm and 24 nm compared to 21-27 nm for MW sol-gel synthesis (at different power values). The MW sol-gel CexSm1-xO2 catalysts exhibit a smaller crystallite size (12-18 nm). The pure ceria nanoparticles were shown to have a stoichiometry of approximately CeO1.95. The presence of Ce3+ and Sm3+ in the mixed oxide particles facilitates the presence of oxygen vacant sites, confirmed by Raman. Oxygen mobile species have been traced using H2-TPR studies and a compressive lattice strain in the 0.45-1.9% range of the cubic CexSm1-xO2 lattice were found to be strongly correlated with the CO oxidation performance in the presence and absence of H2 in the oxidation feed stream. MW sol-gel synthesis led to more active CeO2 and Ce0.5Sm0.5O2 catalysts, demonstrated by T50 (temperature where 50% CO conversion is achieved), being reduced by 131 oC and 47 oC, respectively, compared to typical sol-gel catalysts. Conventional synthesis performed at 100oC leads to a CeO2 catalyst of initially higher activity at a certain temperature window (220-420oC), though with a slower increase of XCO with temperature compared to the MW one. MW sol-gel synthesized Ce0.8Sm0.2O2 exhibited a high performance (~90%) for CO oxidation over a period of more than 20 h in stream. In addition the effect of reaction temperature and contact time (W/F) on the activity of the CeO2-based materials for CO oxidation kinetics were investigated. The activation energy of the reaction was found to be in the 36-43 kJ/mole range depending on the catalyst composition.
Most current analysis of nano-indentation test data assumes the sample to behave as an isotropic, homogeneous body. In practice, engineering materials such as structural steels, titanium alloys and high strength aluminium alloys are multi-phase metals with microstructural length scales that can be the same order of magnitude as the maximum achievable nano-indentation depth. This heterogeneity results in considerable scatter in the indentation load-displacement traces and complicates inverse analysis of this data. To address this problem, an improved and optimised inverse analysis procedure to estimate bulk tensile properties of heterogeneous materials using a new ?multi-objective? function has been developed which considers nano-indentation data obtained from several indentation sites. The technique was applied to S355 structural steel bulk samples as well as an autogenously electron beam welded sample where there is a local variation of material properties. Using the new inverse analysis approach on the S355 bulk material resulted in an error within 3% of the experimental yield strength and strain hardening exponent data, which compares to an approximate 9% error in the yield strength and an 8% error in the strain hardening exponent using a more conventional approach to the inverse analysis method. Applying the new method to indentation data from different regions of an S355 steel weld and using this data as an input into an FE model of the cross-weld, tensile data from the FE model resulted matching the experimentally measured properties to within 5%, confirming the efficacy of the new inverse analysis approach.
Ultra-thin CdTe:As/Cd1-xZnxS photovoltaic solar cells with an absorber thickness of 0.5 µm were deposited by metal-organic chemical vapour deposition on indium tin oxide coated boro-aluminosilicate substrates. The Zn precursor concentration was varied to compensate for Zn leaching effects after CdCl2 activation treatment. Analysis of the solar cell composition and structure by X-ray photoelectron spectroscopy depth profiling and X-ray diffraction showed that higher concentrations of Zn in the Cd1-xZnxS window layer resulted in suppression of S diffusion across the CdTe/Cd1-xZnxS interface after CdCl2 activation treatment. Excessive Zn content in the Cd1-xZnxS alloy preserved the spectral response in the blue region of the solar spectrum, but increased series resistance for the solar cells. A modest increase in the Zn content of the Cd1-xZnxS alloy together with a post-deposition air anneal resulted in an improved blue response and an enhanced open circuit voltage and fill factor. This device yielded a mean efficiency of 8.3% over 8 cells (0.25 cm2 cell area) and best cell efficiency of 8.8%.
To investigate the role of intermetallic particles in the localised corrosion of AA7075-T6, three particles were monitored over 16 hours immersion in 3.5 wt.% KCl solution. These were examined using Auger electron spectroscopy, energy dispersive x-ray spectroscopy, scanning Kelvin probe force microscopy and focused ion beam-scanning electron microscopy. Despite similar Volta potential measurements, the corrosion microchemistry varied significantly with composition. A Al7Cu2Fe intermetallic resulted in trenching while a (Al,Cu)6(Fe,Cu) intermetallic showed crevice corrosion and sub-surface intergranular corrosion and a Al12Fe3Si intermetallic appeared to be galvanically inactive but showed crevice formation at the matrix interface and sub-surface intergranular corrosion.
Polychronopoulou K, Rebholz C, Baker MA, Theodorou L, Demas N, Hinder SJ, Polycarpou A, Doumanidis C, Boebel K (2008) Nanostructure, mechanical and tribological properties of reactive magnetron sputtered TiCx coatings, DIAMOND AND RELATED MATERIALS 17 (12) pp. 2054-2061
ELSEVIER SCIENCE SA
Charisiou N, Papageridis K, Siakavelas G, Tzounis L, Kousi K, Baker M, Hinder S, Cabeza V, Polychronopoulou K, Goula M (2017) Glycerol Steam Reforming for Hydrogen Production over Nickel Supported on Alumina, Zirconia and Silica Catalysts, Topics in Catalysis 60 (15-16) pp. 1226-1250
The aim of the work was to investigate the influence of support on the catalytic performance of Ni catalysts for the glycerol steam reforming reaction. Nickel catalysts (8 wt%) supported on Al2O3, ZrO2, SiO2 were prepared by the wet impregnation technique. The catalysts? surface and bulk properties, at their calcined, reduced and used forms, were determined by ICP, BET, XRD, NH3-TPD, CO2-TPD, TPR, XPS, TEM, TPO, Raman, SEM techniques. The Ni/Si sample, even if it was less active for T
Space photovoltaics is dominated by multi?junction (III?V) technology. However, emerging applications
will require solar arrays with high specific power (kW/kg), flexibility in stowage and
deployment, and a significantly lower cost than the current III?V technology offers. This research
demonstrates direct deposition of thin film CdTe onto the radiation?hard cover glass that is normally
laminated to any solar cell deployed in space. Four CdTe samples, with 9 defined contact
device areas of 0.25 cm2, were irradiated with protons of 0.5?MeV energy and varying fluences.
At the lowest fluence, 1 × 1012 cm?2, the relative efficiency of the solar cells was 95%. Increasing
the proton fluence to 1 × 1013 cm?2 and then 1 × 1014 cm?2 decreased the solar cell efficiency to
82% and 4%, respectively. At the fluence of 1 × 1013 cm?2, carrier concentration was reduced by
an order of magnitude. Solar Cell Capacitance Simulator (SCAPS) modelling obtained a good fit
from a reduction in shallow acceptor concentration with no change in the deep trap defect concentration.
The more highly irradiated devices resulted in a buried junction characteristic of the
external quantum efficiency, indicating further deterioration of the acceptor doping. This is
explained by compensation from interstitial H+ formed by the proton absorption. An anneal of
the 1 × 1014 cm?2 fluence devices gave an efficiency increase from 4% to 73% of the pre?irradiated
levels, indicating that the compensation was reversible. CdTe with its rapid recovery through
annealing demonstrates a radiation hardness to protons that is far superior to conventional multijunction
III?V solar cells.
Inverse analysis of nanoindentation data has attracted increasing interest in industry due to its ability to estimate the bulk tensile properties of materials and potentially offers an alternative technique to conventional characterisation methods. Inverse analysis of nanoindentation data is particularly valuable in applications where conventional techniques are not suitable due to either the scale of characterisation (very small regions) or because the testing is expensive and time consuming. Despite using best practices to minimise sources of error in the experimental data, given the scale of the indentations, the heterogeneity of material microstructure can create significant variability in the data, ultimately affecting the reliability of the inverse analysis solution. This thesis proposes and discusses pragmatic approaches to mitigate the effects of material heterogeneity on the accuracy of the inverse problem solution as well as of nanoindentation data in general. The work has involved finite element analysis modelling, nanoindentation and tensile testing.
One mitigation approach consisted in the implementation and verification of a new ?multi-objective? function inverse analysis methodology where the bias of selecting only one experimental nanoindentation curve as representative of the homogenised response of the material is overcome. The new approach uses all the experimental curves generated from a grid of nanoindentations and employs a weighted averaging procedure. This methodology was applied to S355 steel samples through recording nanoindentation and tensile test data. Despite the variation present in the experimental nanoindentation load-depth curves, this being in the order of 13%, the ?multi-objective? function approach was found to estimate the tensile parameters with an error margin as low as 3-6% compared to an error margin of 9-20% for the conventional method.
A framework of activities was also undertaken to monitor the variation of the measured nanoindentation properties (e.g. hardness) as function of the indentation depth, in relation to the average grain size of the material. Commercial purity aluminium 1050 samples (with varying average grain sizes) and S355 steel were employed as test materials. These results in addition to those from other materials were used to construct a look-up plot of the hardness COV values as function of the normalised nanoindentation depths (normalised with respect to the average grain diameter). The plot
With the progression towards higher aspect ratios and finer topographical dimensions in many micro- and nano-systems, it is of technological importance to be able to conformally deposit thin films onto such structures. Sputtering techniques have been developed to provide such conformal coverage through a combination of coating re-sputtering and ionised physical vapour deposition (IPVD), the latter by use of a secondary plasma source or a pulsed high target power (HiPIMS). This paper reports on the use of an alternate remote plasma sputtering technique in which a high density (>1013 cm-3) magnetised plasma is used for sputter deposition, and additionally is shown to provide IPVD and a re-sputtering capability. From the substrate I-V characteristics and optical emission spectroscopy (OES) data, it is shown that remote plasma sputtering is an inherently continuous IPVD process (without the need of a secondary discharge). Through the reactive deposition of Al2O3 onto complex structures, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) results demonstrate that applying a negative substrate bias during film growth can result in re-sputtering of deposited material and film growth on surfaces obscured from the initial sputter flux. Using 5:1 (height:width) aspect ratio trenches, the substrate bias was set to 0, -245 and -334 V. At 0 V substrate bias, the alumina coating is predominantly deposited on the horizontal surfaces; at -344 V, it is predominantly deposited onto the side walls and at -245 V a more uniform layer thickness is obtained over the trench. The process was optimised further by alternating the substrate bias between -222 and -267 V, with a 50 % residence time at each voltage, yielding a more uniform conformal coverage of the 5:1 aspect ratio structures over large areas.
Cadmium zinc telluride (CdZnTe) is a leading sensor material for spectroscopic X/g-ray
imaging in the fields of homeland security, medical imaging, industrial analysis and
astrophysics. The metal-semiconductor interface formed during contact deposition is of
fundamental importance to the spectroscopic performance of the detector and is primarily
determined by the deposition method. A multi-technique analysis of the metalsemiconductor
interface formed by sputter and electroless deposition of gold onto (111)
aligned CdZnTe is presented. Focused ion beam (FIB) cross section imaging, X-ray
photoelectron spectroscopy (XPS) depth profiling and current-voltage (IV) analysis have
been applied to determine the structural, chemical and electronic properties of the gold
contacts. In a novel approach, principal component analysis has been employed on the XPS
depth profiles to extract detailed chemical state information from different depths within
the profile. It was found that electroless deposition forms a complicated, graded interface
comprised of tellurium oxide, gold/gold telluride particulates, and cadmium chloride. This
compared with a sharp transition from surface gold to bulk CdZnTe observed for the
interface formed by sputter deposition. The electronic (IV) response for the detector with
electroless deposited contacts was symmetric, but was asymmetric for the detector with
sputtered gold contacts. This is due to the electroless deposition degrading the difference
between the Cd- and Te-faces of the CdZnTe (111) crystal, whilst these differences are
maintained for the sputter deposited gold contacts. This work represents an important step
in the optimisation of the metal-semiconductor interface which currently is a limiting factor
in the development of high resolution CdZnTe detectors.
X-ray photoelectron spectroscopy (XPS) was carried out to analyse a commercially available pentanedioic acid powder. XPS spectra were obtained using incident monochromatic Al Ka radiation at 1486.6 eV. A survey spectrum together with O 1s and C 1s core level spectra are presented.
Linear saturated dicarboxylic acids are a class of organic chemical compounds with two carboxyl functional groups (-COOH) at the extremities of their aliphatic chains. This class of organic acids can be represented by the general molecular formula HOOC-(CH2)n-COOH. The most common values for n with their respective acid names are present in Table I. The general chemical behavior and reactivity of these compounds are similar to monocarboxylic acids, and they are all widely used in the production of copolymers, such as polyamides and polyesters (Refs. 1?3). The easy conversion of carboxyl groups to esters has industrial importance since many esters are used as taste and odor enhancers. Carboxylic acids are also used as catalysts, replacing ecologically unfavorable organic halides (Ref. 4). Over the last three decades, interest in such acids has increased, specifically regarding their application to improve the corrosion resistance of metallic substrates such as zinc, copper, iron, and aluminum (Refs. 5?12). Research has also shown that carboxylic acids can be used as additives for the electro synthesis of polymeric protective coatings. Such coatings promote passivation of different metallic substrates, allowing the oxidation of the carboxylic acid monomers without concomitant reactions (Refs. 10?13). More recently, carboxylic acids have been used to generate hydrophobic surfaces on various metallic substrates (Fe, Al, Cu, Mg, Zn, Ti, etc.) forming self-assembled layers by adsorption, via carboxyl groups, to the positively charged metal surfaces (Refs. 14?18).
This thesis contains work on three topics, the commissioning of an integrated surface science instrument, the ageing of LiH and the surface reactivity of U. The integrated system contains a variety of surface science techniques which have been used extensively in the investigations presented here. These techniques are: scanning electron microscopy (SEM), Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), secondary ion mass spectrometry (SIMS), temperature programmed decomposition (TPD), low energy electron diffraction (LEED) and molecular beam scattering (MBS).
LiH ageing has been split into two regimes, wet and dry ageing. Wet ageing explicitly requires the presence of an external source of H2O, while dry ageing does not. This work has primarily looked at dry ageing, in which reactions are thermally driven, on both bulk and thin film LiH. Thin films of lithium were deposited in-situ on Ni(100) and were converted to LiH through exposure to H2 at 1mbar. Four reactions were found to occur in the dry ageing process. The rate-limiting mechanisms were found to be different in thin films compared to bulk. The rate-limiting mechanism for the decomposition of LiOH was found to be the rate of nucleation in bulk samples, whereas it was the rate of growth of nuclei in thin films. For the solid state reaction (LiH + LiOH -> Li2O + H2), the same mechanism was found to be rate limiting in both cases (i.e. 3D diffusion). However, the activation energy was determined to be significantly higher in a thin film, thought to be a result of a decrease in defect concentration and the number of grain boundaries in the thin film. The Li2O layer formed through the solid state reaction exhibited a high defect concentration and poor crystallinity, attributed to the large lattice mismatch between itself and LiH. This was shown to impact on its subsequent reactivity. On exposure of a LiH thin film to H2O, a chemisorbed H2O state was observed.
High purity polycrystalline uranium metal sample was prepared in-situ by ambient temperature Ar+ sputtering. Annealing of the clean uranium sample caused segregation of UO2-x and UOxCy to the surface, similar to that observed in UO2 samples. H2 and H2O have been shown to dissociatively adsorb onto a uranium metal surface, with the latter causing partial surface oxidation. O2 exposure caused irreversible surface oxidation of uranium metal, which could be described by a precursor state model whereby adsorption directly onto the surface is more probable than adsorption mediated by a physisorbed second layer. A high purity UO2 surface was formed by heating the uranium metal in an O2 atmosphere. The interaction of D2O with UO2 at sub-ambient temperatures exhibited the formation of transient ice multilayers. The dynamics of D2 on the oxide surface suggested the occurrence of trap-desorption, rather than rotationally inelastic scattering.
Gas cluster ion beam instruments represent the cutting edge in polymer depth profiling
technology. This is because they can be used to analyse polymer samples while preserving
the delicate chemical structure often lost when more conventional ion beams are used. In this
thesis thorough investigations are conducted into the various advantages and disadvantages
of using both Ar+ and Ar+n
ions to analyse organic, inorganic and multi-layer samples by
XPS and ToF-SIMS depth profiling. Analytical techniques including XPS, ToF-SIMS, AFM
and laser interferometry were utilised to measure chemical and physical changes induced in
samples by the two Ar ion species both during depth profiling and following crater formation.
Significant observations were made in Ar+n
depth profiling of inorganic metal oxide samples
of effects not previously reported in the literature as well as the detection of the damage
layer induced in polymer samples by cluster ions. This includes a reduction in levels of
preferential sputtering in Ar+n
compared to Ar+ depth profiles. Ar+n
depth profiles of Ta2O5
on Ta and SiO2 on PET are also shown to lack the so-called ?steady-state? region observed in
Ar+ depth profiles. Evidence of O diffusion from the Ta2O5 layer to the underlying Ta metal
is also reported in depth profiles acquired using Ar+n
ions but not Ar+ ions. A method for
the measurement of the rapid ejection of organic material at an inorganic/organic multi-layer
interface is demonstrated showing a clear variation between the material ejection between
Ar+ and Ar+n
ion exposure. The observations discussed have serious implications for the
current understanding of Ar+n
bombardment of inorganic sample materials some of which
have been published in the literature.
Recent improvements in the growth of wide-bandgap semiconductors, such as cadmium zinc telluride (CdZnTe or CZT), has enabled spectroscopic X/³-ray imaging detectors to be developed. These detectors have applications covering homeland security, industrial analysis, space science and medical imaging. At the Rutherford Appleton Laboratory (RAL) a promising range of spectroscopic, position sensitive, small-pixel Cd(Zn)Te detectors have been developed. The challenge now is to improve the quality of metal contacts on CdZnTe in order to meet the demanding energy and spatial resolution requirements of these applications. The choice of metal deposition method and fabrication process are of fundamental importance. Presented is a comparison of two CdZnTe detectors with contacts formed by sputter and electroless deposition. The detectors were fabricated with a 74 × 74 array of 200 ¼m pixels on a 250 ¼m pitch and bump-bonded to the HEXITEC ASIC. The X/³-ray emissions from an 241Am source were measured to form energy spectra for comparison. It was found that the detector with contacts formed by electroless deposition produced the best uniformity and energy resolution; the best pixel produced a FWHM of 560 eV at 59.54 keV and 50% of pixels produced a FWHM better than 1.7 keV . This compared with a FWHM of 1.5 keV for the best pixel and 50% of pixels better than 4.4 keV for the detector with sputtered contacts.
A comparative study of the GSR performance for Ni/CaO-MgO-Al2O3 and Ni/Al2O3 catalysts is reported. Catalysts were synthesized applying the wet impregnation method at a constant metal loading (8 wt %). Synthesized samples were characterized by N2 adsorption/desorption, ICP, BET, XRD, NH3-TPD, CO2-TPD, H2-TPR, XPS, TEM, STEM-HAADF and EDS. The carbon deposited on their surface under reaction conditions was characterized by TPO, Raman and TEM. It was proven that the use of CaO-MgO as alumina modifiers leads to smaller nickel species crystallite size, increased basicity and surface amount of Ni0 phase. Thus, it increases the conversion to gaseous products favoring H2 and CO2 production to the detriment of CO formation, by enhancing the water gas-shift (WGS) reaction. No liquid products were produced by the Ni/modAl catalyst over 550 °C, whereas time on stream results confirmed that deactivation can be prevented, as apart from decreasing the amount of coke deposition the nature of carbon was altered towards less graphitic and more defective structures.
The glycerol steam reforming (GSR) reaction for H2 production was studied comparing the performance of Ni supported on ZrO2 and SiO2-ZrO2 catalysts. The surface and bulk properties were determined by ICP, BET, XRD, TPD, TPR, TPO, XPS, SEM and STEM-HAADF. It was suggested that the addition of SiO2 stabilizes the ZrO2 monoclinic structure, restricts the sintering of nickel particles and strengthens the interaction between Ni2+ species and support. It also removes the weak acidic sites and increases the amount of the strong acidic sites, whereas it decreases the amount of the basic sites. Furthermore, it influences the gaseous products? distribution by increasing H2 yield and not favouring the transformation of CO2 in CO. Thus, a high H2/CO ratio can be achieved accompanying by negligible value for CO/CO2. From the liquid products quantitative analysis, it was suggested that acetone and acetaldehyde were the main products for the Ni/Zr catalyst, for 750oC, whereas for the Ni/SiZr catalyst allyl alcohol was the only liquid product for the same temperature. It was also concluded that the Ni/SiZr sample seems to be more resistant to deactivation however, for both catalysts a substantial amount of carbon exists on the catalytic surface in the shape of carbon nanotubes and amorphous carbon.
Secondary ion mass spectrometry (SIMS) is a technique that has evolved to be one of the most powerful techniques for the analysis of organic samples. Modern instruments are capable of obtaining three-dimensional information with high spatial resolution of a material with information as rich as a full mass spectrum at every voxel of the 3D structure, thus generating very large and complex datasets. Multivariate analysis (MVA) methods are used within the SIMS community, however, the absence of MVA in the software packages of instrument manufacturers together with constant increase in data and data analysis complexity demands practical data analysis solutions that are accessible to scientists of diverse backgrounds. This thesis aims to expand the applicability of three major MVA methods to complex SIMS datasets: Principal component analysis (PCA), non-negative matrix factorisation (NMF) and k-means clustering. This is achieved by establishing and validating existing and novel methodologies for the processing of large and complex datasets. Furthermore, it presents the development of a software that encompasses these methodologies and provide accessible and flexible analysis and data visualisation tools. Finally, it presents the application of the software to a series of experiments carried out at The Surface Analysis Laboratory of the University of Surrey in which data processing enabled deeper interpretation of the results and helped to achieve insights towards scientific and industrial problem solving.
X-ray sources are used for both scientific instrumentation and inspection applications. In X-ray photoelectron spectroscopy (XPS), aluminum K± X-rays are generated through electron beam irradiation of a copper-based X-ray anode incorporating a thin surface layer of aluminum. The maximum power operation of the X-ray anode is limited by the relatively low melting point of the aluminum. Hence, optimization of the materials and design of the X-ray anode to transfer heat away from the aluminum thin film is key to maximizing performance. Finite element analysis has been employed to model the heat transfer of a water-cooled copper-based X-ray anode with and without the use of a CVD (chemical vapour deposited) diamond heat spreader. The modeling approach was to construct a representative baseline model, and then to vary different parameters systematically, solving for a steady state thermal condition, and observing the effect of on the maximum temperature attained. The model indicates that a CVD diamond heat spreader (with isotropic thermal properties) brazed into the copper body reduces the maximum temperature in the 4 ¼m aluminum layer from 613 °C to 301 °C. Introducing realistic anisotropy in the TC (thermal conductivity) of the CVD diamond has no significant effect on heat transfer if the aluminum film is on the CVD diamond growth face (with the highest TC). However, if the aluminum layer is on the CVD diamond nucleation face (with the lowest TC), the maximum temperature is 575 °C. Implications for anode design are discussed.
Ni/Al2O3 and Ni/La2O-Al2O3 catalysts were investigated for the biogas reforming reaction using CH4/CO2 mixtures with minimal dilution. Stability tests at various reaction temperatures were conducted and TGA/DTG, Raman, STEM-HAADF, HR-TEM, XPS techniques were used to characterize the spent samples. Graphitized carbon allotrope structures, carbon nanotubes (CNTs) and amorphous carbon were formed on all samples. Metallic Ni0 was recorded for all (XPS), whereas a strong peak corresponding to Ni2O3/NiAl2O4, was observed for the Ni/Al sample (650?750°C). Stability tests confirm that the Ni/LaAl catalyst deactivates at a more gradual rate and is more active and selective in comparison to the Ni/Al for all temperatures. The Ni/LaAl exhibits good durability in terms of conversion and selectivity, whereas the Ni/Al gradually loses its activity in CH4 and CO2 conversion, with a concomitant decrease of the H2 and CO yield. It can be concluded that doping Al2O3 with La2O3 stabilizes the catalyst by (a) maintaining the Ni0 phase during the reaction, due to higher dispersion and stronger active phase-support interactions, (b) leading to a less graphitic and more defective type of deposited carbon and (c) facilitating the deposited carbon gasification due to the enhanced CO2 adsorption on its increased surface basic sites.
AlKetbi M., Polychronopoulou K., Zedan Abdallah. F., Sebastián V., Baker Mark A., AlKhoori A., Jaoude M.A., Alnuaimi O., Hinder Steve S., Tharalekshmy Anjana, AlJaber Amina S. (2018) Tuning the activity of Cu-containing rare earth oxide catalysts for CO oxidation reaction: Cooling while heating paradigm in microwave-assisted synthesis, Materials Research Bulletin 108 pp. 142-150
(Ce-La-xCu)O2 catalysts with low (3 at.%) and high (10 at.%) Cu content were prepared by conventional microwave (MW) and enhanced microwave methods where air cooling (AC), while heating, was applied. The catalysts were tested for the CO oxidation reaction in the 25?500 °C range using 4%CO/20%O2/He feed gas. Varying spectroscopic, microscopic and catalytic studies were used to probe the effect of synthesis on the nanostructure and the CO oxidation performance. It was found that the synthesis method adopted impacts on the extent of the Cu doping into the (Ce-La)O2 fluorite lattice, hence leading to one and two phases system in the case of catalyst prepared through enhanced (AC) and conventional (MW) microwave methods, respectively. Furthermore, only Ce4+ species were found on the surface of the (Ce-La-10Cu)O2 catalysts synthesized using MW and AC (XPS studies), whereas oxygen vacant sites which are associated with Ce3+ ions were indicated in the sub-surface/bulk (Raman studies). Ultimately, the catalysts with the low and high Cu loading, prepared under the AC-promoted microwave method, presented a superior performance against CO oxidation, exhibiting an overall improvement of the catalytic activity by 16% and 32%, respectively.
Zequine Camila, Bhoyate Sanket, Siam Khamis, Kahol Pawan K., Kostoglou Nikolaos, Mitterer Christian, Hinder Steven, Baker Mark, Constantinides Georgios, Rebholz Claus, Gupta Gautam, Li Xianglin, Gupta Ram K. (2018) Needle grass array of nanostructured nickel cobalt sulfide electrode for clean energy generation, Surface and Coatings Technology 354 pp. 306-312
Significant efforts have been focused on the search of earth-abundant elements to solve growing energy issues and to provide bifunctional behavior for both hydrogen and oxygen evolution reaction. Mixed transition metals could provide promising synergistic electrochemical properties and serve as bi-catalyst for overall water splitting process. In this study, a needle grass array of nanostructured nickel cobalt sulfide (NiCo2S4) was synthesized using a hydrothermal process. The synthesized NiCo2S4 electrodes showed promising electrocatalytic activity with a low overpotential of 148/mV and 293/mV for hydrogen and oxygen evolution reactions, respectively. The electrolyzer cell consisting of two NiCo2S4 electrodes displayed excellent performance with high electrochemical stability and low overall cell potential of 1.61/V to achieve a current density of 10/mA/cm2. Our study suggests that mixed transition metal chalcogenides such as NiCo2S4 could be used as efficient and stable electrocatalyst for overall water splitting process.
Charisiou N.D., Siakavelas G., Tzounis L., Sebastian V., Monzon A., Baker M.A., Hinder S.J., Polychronopoulou K., Yentekakis I.V., Goula M.A. (2018) An in depth investigation of deactivation through carbon formation during the biogas dry reforming reaction for Ni supported on modified with CeO2 and La2O3 zirconia catalysts, International Journal of Hydrogen Energy 43 (41) pp. 18955-18976
The dry reforming of biogas on a Ni catalyst supported on three commercially available materials (ZrO2, La2O3-ZrO2 and CeO2-ZrO2), has been investigated, paying particular attention to carbon deposition. The DRM efficiency of the catalysts was studied in the temperature range of 500-800oC at three distinct space velocities, and their time-on-stream stability at four temperatures (550, 650, 750 and 800oC) was determined for 10 or 50 h operation. The morphological, textural and other physicochemical characteristics of fresh and spent catalysts together with the amount and type of carbon deposited were examined by a number of techniques including BET-BJH method, CO2 and NH3-TPD, XPS, SEM, TEM, STEM-HAADF, Raman spectroscopy, and TGA/DTG. The impact of the La2O3 and CeO2 modifiers on the DRM performance and time-on-stream stability of the Ni/ZrO2 catalyst was found to be very beneficial: up to 20 and 30% enhancement in CH4 and CO2 conversions respectively, accompanied with a CO-enriched syngas product, while the 50 h time-on-stream catalytic performance deterioration of ~30-35% on Ni/ZrO2 was limited to less than ~15-20% on the La2O3 and CeO2 modified samples. Their influence on the amount and type of carbon formed was substantial: it was revealed that faster oxidation of the deposited carbon at elevated temperatures occurs on the modified catalysts. Correlations between the La2O3 and CeO2-induced modifications on the surface characteristics and physicochemical properties of the catalyst with their concomitant support-mediated effects on the overall DRM performance and carbon deposition were revealed.
In the present study Ni/Ce-Sm-xCu (x=5, 7, 10 at.%) catalysts were prepared using microwave radiation coupled with sol-gel and followed by wetness impregnation method for the Ni incorporation. Highly dispersed nanocrystallites of CuO and NiO on the Ce-Sm-Cu support were found. Increase of Cu content seems to facilitate the reducibility of the catalyst according to the H2-TPR. All the catalysts had a variety of weak, medium and strong acid/basic sites that regulate the reaction products. All the catalysts had very high XC3H8O3 for the entire temperature (400-750oC) range; from H84% at 400oC to H94% at 750oC. Ni/Ce-Sm-10Cu catalyst showed the lowest XC3H8O3-gas implying the Cu content detrimental effect to performance, especially between 450-650oC. In terms of H2 selectivity (SH2) and H2 yield (YH2) both appeared to vary in the following order: Ni/Ce-Sm-10Cu > Ni/Ce-Sm-7Cu > Ni/Ce-Sm-5Cu, demonstrating the high impact of Cu content. Following stability tests, all the catalysts accumulated high amounts of carbon, following the order Ni/Ce-Sm-5Cu
In the search for improvements in the environmental credentials of the organic coatings industry, several different aspects are currently being addressed, including the reduction of volatile organic compounds, development of UV curable coatings and the reduction of potentially hazardous components in the coatings formulations. The aim of this work was to develop the water based primers for coil coating applications as a substitution for chromate conversion coatings.
The performance and durability of three novel water based systems applied on alkali cleaned HDGS has been investigated; XPS and ToF-SIMS have been employed to analyse the failure interfaces generated by various test methods designed to assess the performance and durability of each of the systems.
In depth analysis has been carried out using ULAM for sample preparation, and XPS and ToF-SIMS were employed to analyse the buried metal/ primer interface, in order to investigate the interface chemistry. A method of post processing data, obtained by surface analysis techniques, was invented to gain a clear understanding of the possible chemical interactions occurred at the metal/primer interface.
Adsorption studies were also carried out to encode the interfacial chemistry. The method was used to understand the role of adhesion promoter in the primer formulation, particularly the manner in which it interacts with the substrate and the topcoat and the way it improves the performance and durability; also to determine the role of anti-corrosive additives, especially the manner in which it prevents the corrosion and therefore its contribution toward the performance and durability. The distribution of these components across the primer layer was also investigated considering the possible opportunities of such components enhancing the primer interaction at either interfaces. The finding has been used for re-adjustment of some of process parameters in coil coating systems and specifically water based primers.
Spectroscopic X-ray imaging is an emerging technology with applications in the fields of medical imaging, security, science and industrial analysis. The wide bandgap semiconductor cadmium zinc telluride (CdZnTe) is the leading sensor material for this technology. Refinements in the growth process have delivered consistent improvements in both yield and quality of single crystal CdZnTe. The fabrication of metal contacts required for electronic readout is now considered to be the limiting factor for small pixel CdZnTe detector performance. This includes preparation of the CdZnTe surface, deposition of the metal contacts and pixellation. The current work is concerned with understanding and improving the detector fabrication process. A range of complementary characterisation techniques have been used to analyse the metal-semiconductor interface formed by electroless and sputter deposition of gold contacts onto CdZnTe. The characterisation included focused ion beam (FIB) cross section imaging, chemical analysis with X-ray photoelectron spectroscopy (XPS) and electronic analysis with current-voltage (IV) measurements. The electroless deposition was found to produce a complicated interface consisting of a surface gold layer on top of a mixed interface of gold, tellurium oxide and cadmium chloride. The effective barrier height of this contact was measured to be 0.78 ± 0.04 eV under positive bias and 0.83 ± 0.02 eV under negative bias. The interface of sputter deposited gold contacts was simple in comparison, with a sharp interface between the gold and CdZnTe and a barrier height of 0.64 ± 0.02 eV under positive bias and 0.78 ± 0.02 eV under negative bias. An optimised detector fabrication process has been developed. This process involves forming gold contacts on mechanically polished-only CdZnTe by electroless deposition. Pixellation is achieved with a positive photoresist prior to gold deposition. A small pixel (250 ¼m pitch) CdZnTe detector fabricated in this manner and bonded to the HEXITEC ASIC has produced a single pixel FWHM energy resolution at 59.54 keV of 560 eV, with a modal FWHM resolution of 1.5 keV across the full 74 × 74 pixel array.
Zhang Chunyang, Bhoyate Sanket, Zhao Chen, Kahol Pawan, Kostoglou Nikolaos, Mitterer Christian, Hinder Steven, Baker Mark, Constantinides Georgios, Polychronopoulou Kyriaki, Rebholz Claus, Gupta Ram (2019) Electrodeposited Nanostructured CoFe2O4 for Overall Water Splitting and Supercapacitor Applications, Catalysts 9 (2)
To contribute to solving global energy problems, a multifunctional CoFe2O4 spinel was synthesized and used as a catalyst for overall water splitting and as an electrode material for supercapacitors. The ultra-fast one-step electrodeposition of CoFe2O4 over conducting substrates provides an economic pathway to high-performance energy devices. Electrodeposited CoFe2O4 on Ni-foam showed a low overpotential of 270 mV and a Tafel slope of 31 mV/dec. The results indicated a higher conductivity for electrodeposited compared with dip-coated CoFe2O4 with enhanced device performance. Moreover, bending and chronoamperometry studies suggest excellent durability of the catalytic electrode for long-term use. The energy storage behavior of CoFe2O4 showed high specific capacitance of 768 F/g at a current density of 0.5 A/g and maintained about 80% retention after 10,000 cycles. These results demonstrate the competitiveness and multifunctional applicability of the CoFe2O4 spinel to be used for energy generation and storage devices.
CNTs can have the ability to act as compliant small-scale springs or as shock resistance micro-contactors. This work investigates the performance of vertically-aligned CNTs (VA-CNTs) as micro-contactors in electromechanical testing applications for testing at wafer-level chip-scale-packaging (WLCSP) and wafer-level-packaging (WLP). Fabricated on ohmic substrates, 500-¼m-tall CNT-metal composite contact structures are electromechanically characterized. The probe design and architecture are scalable, allowing for the assembly of thousands of probes in short manufacturing times, with easy pitch control. We discuss the effects of the metallization morphology and thickness on the compliance and electromechanical response of the metal-CNT composite contacts. Pd-metallized CNT contactors show up to 25/¼m of compliance, with contact resistance as low as 460/m© (3.6/k©/¼m) and network resistivity of 1.8/×/10?5/©/cm, after 2500 touchdowns, with 50/¼m of over-travel; they form reproducible and repeatable contacts, with less than 5% contact resistance degradation. Failure mechanisms are studied in-situ and after cyclic testing and show that, for top-cap-and-side metallized contacts, the CNT-metal shell provides stiffness to the probe structure in the elastic region, whilst reducing the contact resistance. The stable low resistance achieved, the high repeatability and endurance of the manufactured probes make CNT micro-contacts a viable candidate for WLP and WLCSP testing.