Mark Baker

Dr Mark Baker

Reader in Surface Science and Engineering
+44 (0)1483 686294
10 AB 03
9am - 6pm


Areas of specialism

Surface analysis, surface engineering, inorganic thin films and coatings, corrosion, materials characterisation, XPS, AES, SEM, TEM, XRD, AFM

University roles and responsibilities

  • Departmental Senior Tutor for Professional Training
  • Faculty Senior Tutor for Professional Training

    My qualifications

    BSc (Hons) - Chemical Physics
    University of Kent
    PhD - Materials Science
    University of Surrey

    Affiliations and memberships

    Fellow of the Institute of Materials, Minerals and Mining (FIMMM)
    Chartered Scientist (CSci)

    Business, industry and community links

    Thermo Scientific Ltd, Plasma Quest Ltd, Pilkington, Torr Scientific Ltd, Smiths Interconnects, TISICS Ltd, National Physical Laboratory,


    Research interests

    Research projects

    Research collaborations

    Indicators of esteem

      • Chairman of the Technical Programme Committee for a 1 day UK meeting Thin Film and Coating Technologies for Science and Industry at the Vacuum Symposium (2010 - present)
      • Member of the Advisory Panel for a 1 day UK meeting Surface Analysis at the Vacuum Symposium (2017 - present)
      • Editorial Board member for a new MDPI journal Surfaces (2018 - present)
      • Editorial Board member for the Journal of Spectroscopy


      Postgraduate research supervision




      • I have published over 150 journal articles and book chapters
      • Total citation count > 3000 (scopus)
      • h-index 31 (scopus)
      Tim Nunney, Paul Mack, Robin Simpson, Rick Passey, Helen Oppong-Mensah, Mark Baker (2020)Extending XPS Surface Analysis with Correlative Spectroscopy and Microscopy, In: Microscopy and microanalysis26(S2)pp. 1016-1016 Cambridge University Press
      FILIPE MASUCH RIBEIRO RICHHEIMER, David Toth, Bekele Hailegnaw, MARK ALAN BAKER, ROBERT ANDREW DOREY, Ferry Kienberger, Fernando A. Castro, Martin Kaltenbrunner, Markus C. Scharber, Georg Gramse, Sebastian Wood (2022)Ion-driven nanograin formation in early-stage degradation of tri-cation perovskite films, In: Nanoscale Royal Society of Chemistry

      The operational stability of organic–inorganic halide perovskite based solar cells is a challenge for widespread commercial adoption. The mobility of ionic species is a key contributor to perovskite instability since ion migration can lead to unfavourable changes in the crystal lattice and ultimately destabilisation of the perovskite phase. Here we study the nanoscale early-stage degradation of mixed-halide mixed-cation perovskite films under operation-like conditions using electrical scanning probe microscopy to investigate the formation of surface nanograin defects. We identify the nanograins as lead iodide and study their formation in ambient and inert environments with various optical, thermal, and electrical stress conditions in order to elucidate the different underlying degradation mechanisms. We find that the intrinsic instability is related to the polycrystalline morphology, where electrical bias stress leads to the build-up of charge at grain boundaries and lateral space charge gradients that destabilise the local perovskite lattice facilitating escape of the organic cation. This mechanism is accelerated by enhanced ionic mobility under optical excitation. Our findings highlight the importance of inhibiting the formation of local charge imbalance, either through compositions preventing ionic redistribution or local grain boundary passivation, in order to extend operational stability in perovskite photovoltaics.

      K Polychronopoulou, J Neidhardt, C Rebholz, MA Baker, M O'Sullivan, AE Reiter, AE Gunnaes, K Giannakopoulos, C Mitterer (2008)Synthesis and characterization of Cr-B-N coatings deposited by reactive arc evaporation, In: JOURNAL OF MATERIALS RESEARCH23(11)pp. 3048-3055 CAMBRIDGE UNIV PRESS
      D Avisar, I Horovitz, H Mamane, L Lozzi, F Ruggieri, M Baker, M-L Abel (2013)Impact of water quality on removal of carbamazepine in natural waters by N-doped TiO photo-catalytic thin film surfaces, In: Journal of Hazardous Materials244-24pp. 463-471 Elsevier

      Photocatalytic experiments on the pharmaceutical pollutant carbamazepine (CBZ) were conducted using sol-gel nitrogen-doped TiO-coated glass slides under a solar simulator. CBZ was stable to photodegradation under direct solar irradiation. No CBZ sorption to the catalyst surface was observed, as further confirmed by surface characterization using X-ray photoelectron spectroscopic analysis of N-doped TiO surfaces. When exposing the catalyst surface to natural organic matter (NOM), an excess amount of carbon was detected relative to controls, which is consistent with NOM remaining on the catalyst surface. The catalyst surface charge was negative at pH values from 4 to 10 and decreased with increasing pH, correlated with enhanced CBZ removal with increasing medium pH in the range of 5-9. A dissolved organic carbon concentration of 5mg/L resulted in ∼20% reduction in CBZ removal, probably due to competitive inhibition of the photocatalytic degradation of CBZ. At alkalinity values corresponding to CaCO addition at 100mg/L, an over 40% decrease in CBZ removal was observed. A 35% reduction in CBZ occurred in the presence of surface water compared to complete suppression of the photocatalytic process in wastewater effluent. © 2012 Elsevier B.V.

      Hayley L. Brown, Sarah A. Thornley, Steve J. Wakeham, Mike J. Thwaites, Richard J. Curry, Mark A Baker (2015)The Impact of Substrate Bias on a Remote Plasma Sputter Coating Process for Conformal Coverage of Trenches and 3D Structures., In: Journal of Physics D: Applied Physics48(33) IoP

      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.

      Filipe Richheimer, Tom Vincent, Alessandro Catanzaro, Nathaniel J. Huang, Mark A. Baker, Robert A. Dorey, Cristina E. Giusca, Fernando A. Castro, Olga Kazakova, Sebastian Wood (2022)Probing Nanoscale Schottky Barrier Characteristics at WSe2/Graphene Heterostructures via Electrostatic Doping, In: Advanced electronic materials8(9)2200196 Wiley

      The adoption of 2D transition metal dichalcogenide (TMD) based optoelectronic devices is limited by Fermi level pinning effects and consequent large contact resistances upon contacting TMDs with bulk metal electrodes. A potential solution for near-ideal Schottky-Mott behavior and concomitant Schottky barrier height control is proposed by contacting TMDs and (semi-)metals in van der Waals heterostructures. However, measurement approaches to directly assess interface parameters relevant to the Schottky-Mott rule on a local scale are still lacking. In the present work, a heterostructure of monolayer tungsten diselenide (WSe2) with monolayer graphene (1LG) and bilayer graphene (2LG) is investigated on a bottom-gate substrate. Kelvin probe force microscopy and tip-enhanced photoluminescence measurements at different electrostatic doping induced Fermi levels in graphene enable decoupling and quantification of contributions from the interface dipole and electrode work function. These are used to locally probe Schottky barrier characteristics with below 32 nm lateral resolution, demonstrating that the WSe2/1LG junction operates at the Schottky-Mott limit (S approximate to 1). At the WSe2/2LG junction, a reduction of the interface dipole is directly related to changes in excitonic emission properties. These are attributed to charge transfer modulation across the interface, critical for obtaining high-performance transfer characteristics in transistors and related devices.

      Kyriaki Polychronopoulou, Sara AlKhoori, Shaima AlBedwawi, Seba Alareeqi, Aseel G. S. Hussien, Michalis A. Vasiliades, Angelos M. Efstathiou, Klito C. Petallidou, Nirpendra Singh, Dalaver H. Anjum, Lourdes F. Vega, Mark A. Baker (2022)Decoupling the Chemical and Mechanical Strain Effect on Steering the CO2 Activation over CeO2-Based Oxides: An Experimental and DFT Approach, In: ACS applied materials & interfaces14(29)pp. 33094-33119 Amer Chemical Soc

      Doped ceria-based metal oxides are widely used as supports and stand-alone catalysts in reactions where CO2 is involved. Thus, it is important to understand how to tailor their CO(2 )adsorption behavior. In this work, steering the CO2 activation behavior of Ce-La- Cu-O ternary oxide surfaces through the combined effect of chemical and mechanical strain was thoroughly examined using both experimental and ab initio modeling approaches. Doping with aliovalent metal cations (La3+ or La3+/Cu2+) and post-synthetic ball milling were considered as the origin of the chemical and mechanical strain of CeO2, respectively. Experimentally, microwave-assisted reflux-prepared Ce-La-Cu-O ternary oxides were imposed into mechanical forces to tune the structure, redox ability, defects, and CO2 surface adsorption properties; the latter were used as key descriptors. The purpose was to decouple the combined effect of the chemical strain (epsilon C) and mechanical strain (epsilon M) on the modification of the Ce-La-Cu-O surface reactivity toward CO2 activation. During the ab initio calculations, the stability (energy of formation, EOvf) of different configurations of oxygen vacant sites (Ov) was assessed under biaxial tensile strain (epsilon > 0) and compressive strain (epsilon < 0), whereas the CO2-philicity of the surface was assessed at different levels of the imposed mechanical strain. The EOv f values were found to decrease with increasing tensile strain. The Ce-La-Cu-O(111) surface exhibited the lowest EOv f values for the single subsurface sites, implying that Ov may occur spontaneously upon Cu addition. The mobility of the surface and bulk oxygen anions in the lattice contributing to the Ov population was measured using 16O/18O transient isothermal isotopic exchange experiments; the maximum in the dynamic rate of 16O18O formation, Rmax(16O18O), was 13.1 and 8.5 mu mol g-1 s-1 for pristine (chemically strained) and dry ball-milled (chemically and mechanically strained) oxides, respectively. The CO2 activation pathway (redox vs associative) was experimentally probed using in situ diffuse reflectance infrared Fourier transform spectroscopy. It was demonstrated that the mechanical strain increased up to 6 times the CO2 adsorption sites, though reducing their thermal stability. This result supports the mechanical actuation of the "carbonate "-bound species; the latter was in agreement with the density functional theory (DFT)-calculated C-O bond lengths and O-C-O angles. Ab initio studies shed light on the CO2 adsorption energy (Eads), suggesting a covalent bonding which is enhanced in the presence of doping and under tensile strain. Bader charge analysis probed the adsorbate/surface charge distribution and illustrated that CO2 interacts with the dual sites (acidic and basic ones) on the surface, leading to the formation of bidentate carbonate species. Density of states (DOS) studies revealed a significant Eg drop in the presence of double Ov and compressive strain, a finding with design implications in covalent type of interactions. To bridge this study with industrially important catalytic applications, Ni-supported catalysts were prepared using pristine and ball-milled oxides and evaluated for the dry reforming of methane reaction. Ball milling was found to induce modification of the metal-support interface and Ni catalyst reducibility, thus leading to an increase in the CH4 and CO2 conversions. This study opens new possibilities to manipulate the CO2 activation for a portfolio of heterogeneous reactions.

      Gerardo D.J. Guerrero Peña, K. Suresh Kumar Reddy, Anish Mathai Varghese, Azhagapillai Prabhu, Aasif A. Dabbawala, Kyriaki Polychronopoulou, Mark A. Baker, Dalaver Anjum, Gobind Das, Cyril Aubry, Mohamed I. Hassan Ali, Georgios N. Karanikolos, Abhijeet Raj, Mirella Elkadi (2023)Carbon dioxide adsorbents from flame-made diesel soot nanoparticles, In: The Science of the total environment859(Pt 1)160140pp. 160140-160140 Elsevier B.V

      Carbon dioxide (CO2) is the top contributor to global warming. On the other, soot particles formed during fuel combustion and released into the atmosphere are harmful and also contribute to global warming. It would therefore be highly advantageous to capture soot and make use of it as a feedstock to synthesize carbon-based materials for applications such as carbon dioxide adsorption. In this work, flame-made diesel soot nanoparticles were used to produce a variety of activated carbons by combined oxidative treatment with hydrogen peroxide (H2O2) and potassium hydroxide (KOH), and their performance towards CO2 adsorption was evaluated. The effect of the chemical activation of soot with H2O2 for different reaction times and with KOH on the physicochemical properties of the activated carbons was investigated and compared to fresh soot. Interestingly, hollow aggregates of carbonaceous nanoparticles of a high interplanar distance, reduced polycyclic aromatic hydrocarbons (PAH) size, shorter PAH stacks, mesoporous structure, and a high content of oxygen functionalities along with other structural defects in PAHs were obtained in the synthesized activated carbons. Among the various analysis techniques employed, Raman spectroscopy indicated that the ID/IG ratio in soot decreased after simultaneous chemical treatment, though it did not indicate any enhancement in the graphitic character since the carbonyl and carboxylic containing PAHs and monovacancies (which cause defects in PAHs) also contribute to the increase in the intensity of the graphitic band. The activated carbons possessed promising CO2 adsorption capacities, adsorption kinetics and CO2/N2 selectivity. For example, one of the activated carbons, following H2O2 treatment for 9 h and a subsequent KOH activation, exhibited a CO2 adsorption capacity of 1.78 mmol/g at 1 bar and 25 °C, representing an increase of 161 % in capacity as compared to fresh soot. Hollow aggregates of carbonaceous nanoparticles consisting of shorter PAHs with a larger number of defects led to enhanced CO2 adsorption rate and CO2/N2 selectivity on activated carbons. [Display omitted] •Flame soot used to produce activated carbon.•High surface area and large fraction of oxygenated functional groups•CO2 adsorption capacity of 1.73 mmol/g at 25 °C and 1 bar•Activated carbon with defects led to enhanced CO2 adsorption.

      Kyriaki Polychronopoulou, Aasif A. Dabbawala, Muhammad Sajjad, Nirpendra Singh, Dalaver H. Anjum, Mark A. Baker, Nikolaos D. Charisiou, Maria A. Goula (2022)Hydrogen production via steam reforming of glycerol over Ce-La-Cu-O ternary oxide catalyst: An experimental and DFT study, In: Applied surface science586152798 Elsevier B.V

      The cost-efficient Ce-La-Cu-O based catalysts were fabricated under two different microwave conditions for efficient glycerol steam reforming to produce higher yield of hydrogen. [Display omitted] •Ce-La-xCu-O catalysts were fabricated through conventional (MW) and air cooling-assisted (AC) microwave methods.•Synthesis methods (MW & AC) influence the degree of Cu incorporation into catalysts.•Ceria doping tunes the chemisorption of glycerol; strength and distance from surface.•MW catalysts exhibit H2 yield in the range of 3.8–5.0 mol/mole of glycerol.•AC catalyst displayed higher catalytic performance and stability than MW catalyst. In this study, Ce-La-xCu-O catalysts with distinct Cu contents were fabricated through two different microwave methods; conventional microwave (MW) method and enhanced microwave method, where air cooling (AC) during heating was applied and studied for glycerol steam reforming. The characterization of catalysts reveals that the synthesis methods (MW and AC) influence mainly on the degree of Cu incorporation into the Ce-La-O fluorite lattice, thus leading to one or two phases system. In glycerol steam reforming, MW catalysts showed improvement in glycerol conversion (X) and glycerol conversion to gaseous products (Xgas) with an increase of temperature from 400 to 750 °C; a higher tradeoff between total conversion X (93–94%) and Xgas (89–93%) was attained at 750 °C. The H2 yield over MW catalysts was attained in the range of 3.8–5.0 mol/mole of glycerol. Interestingly, Ce-La-10Cu-O (AC) catalyst exhibits higher glycerol conversion, conversion to gaseous products and higher yield of H2 (5.3 mol/mole of glycerol) as compared to MW catalyst. Moreover, the Ce-La-10Cu-O (AC) catalyst exhibited high stability and deactivated at slower rate. The improved performance of AC catalyst can correlate to a more homogeneous Cu incorporation into Ce-La-O mixed oxide thus forming more accessible active sites to reactants which overall impact on the catalytic performance. DFT calculations showed that doping ceria (111) surface greatly facilitates the adsorption of glycerol compared to the undoped ceria surface by tuning the adsorption energy and the surface-glycerol distance, to −1.42 eV and 1.09 Å, respectively, and by shifting the Fermi level into the valence band (p-type doping), enhancing with the latter the glycerol chemisorption.

      Samira M. N. de Assumpcao, Sirlene B. Lima, Jordan G. A. B. Silva, Ronaldo C. Santos, Leila M. A. Campos, Jose M. Ferreira, Gustavo F. Trindade, Mark A. Baker, Luiz A. M. Pontes (2022)5-Hydroxymethylfurfural Oxidation Over Platinum Supported on Acai Seed Coal for Synthesis of 2,5-Furandicarboxylic Acid, In: Biointerface Research in Applied Chemistry12(5)pp. 6632-6650 Biointerface Research Applied Chemistry

      2,5-furandicarboxylic acid (FDCA) is produced from the selective oxidation of 5-hydroxymethylfurfural (HMF) and is an important platform molecule applied in the pharmaceutical andpetrochemical industries. Activated carbons produced from renewable resources are useful materials due to their physicochemical properties, defined mainly by the oxygenated functional groups on their surface. This work studies the oxidation of HMF to FDCA over Pt catalysts supported on acai coal. The catalysts were characterized by N-2 adsorption, XPS, ToF-SIMS, FTIR, XRD, Raman, TEM, SEM, TPR-H-2, and TGA/DTA. The conversion of HMF to FDCA in an alkaline medium occurred via hydroxymethyl-2-furancarboxylic acid (HMFCA), which was oxidized to 5-formylfurancarboxylic acid (FFCA) and FDCA. The catalytic tests showed a high conversion of HMF with a 93.6% yield of FDCA. The excellent results were attributed to the high dispersion of Pt on the support and the presence of oxygenated functional groups on the coal surface. The functional groups increased the interaction between Pt-HMF and Pt-furan intermediates and favored a higher dispersion of platinum (53.3%) due to an anchoring effect.

      J. M. Ferreira, M. Oliveira, G. F. Trindade, L. C. L. Santos, C. R. Tomachuk, M. A. Baker (2020)Development and characterisation of zinc oxalate conversion coatings on zinc (vol 137, pg 13, 2018), In: Corrosion science176108992 Elsevier
      DHILAN DEVADASAN, MARK ALAN BAKER, JOHN FARNHAM WATTS (2022)Quantitative Atomic Force Microscopy: A Statistical Treatment of High-Speed AFM Data for Quality Control Applications, In: Ultramicroscopy239113546 Elsevier

      Prior to the recent developments of high-speed atomic force microscopy (HS-AFM), atomic force microscopy (AFM) was not favoured by industry because of its complexity and slow image acquisition speed which may lead to poor resolution and unreliable quantified results. HS-AFM, however, is capable of imaging several frames per second and thus capable of quick, accurate, and representative measurements – ideal for quality control applications. This study demonstrates HS-AFM as a useful quality control tool by assessing the roughness of silicon carbide (SiC) monofilament fibres as a challenging example of how large HS-AFM datasets in excess of 200 images can be collected and used for reliable quantification. A comparison of two roughness methods utilising either area or line roughness parameters has been conducted, where very little difference was noted apart from the lower statistical significance of line roughness. The roughness of ten SiC fibre samples was measured with Sa (the area equivalent to Ra) roughness results varying from 34 nm to 53 nm. The small measurement uncertainties, as a result of the large number of measurements, meant that the roughness results were distinguishable from one another even though all ten SiC fibres were very similar to each other, having been produced by the same manufacturer and process. The robustness of the methods have been tested by repeating the analysis for each fibre, and in the one instance where the repeated data did not agree, a further dataset proved which one was incorrect, illustrating how industry can use these methods for quality control. A methodology of identifying the minimum number of frames required to account for sample variability, as well as recommendations on how to use HS-AFM for quantitative measurements in quality control, are also included to enable easy reproduction and adaptation of this work for other samples and measurements.

      A Saliba-Silva, RN Faria, MA Baker, I Costa (2004)Improving the corrosion resistance of NdFeB magnets: an electrochemical and surface analytical study, In: SURFACE & COATINGS TECHNOLOGY185(2-3)pp. 321-328 ELSEVIER SCIENCE SA
      C Scheuerlein, M Taborelli, N Hilleret, A Brown, MA Baker (2002)An AES study of the room temperature conditioning of technological metal surfaces by electron irradiation, In: APPLIED SURFACE SCIENCE202(1-2)PII S0169-pp. 57-67 ELSEVIER SCIENCE BV
      Nikolaos D. Charisiou, Georgios I. Siakavelas, Binlin Dou, Victor Sebastian, Steven Hinder, Mark Baker, Kyriaki Polychronopoulou, Maria A. Goula (2019)Nickel Supported on AlCeO3 as a Highly Selective and Stable Catalyst for Hydrogen Production via the Glycerol Steam Reforming Reaction, In: Catalysts9(5)

      In this study, a critical comparison between two low metal (Ni) loading catalysts is presented, namely Ni/Al2O3 and Ni/AlCeO3 for the glycerol steam reforming (GSR) reaction. The surface and bulk properties of the catalysts were evaluated using a plethora of techniques, such as N2 adsorption/desorption, ICP-AES, XRD, XPS, SEM/EDX, TEM, CO2-TPD, NH3-TPD, H2-TPR. Carbon deposited on the catalysts surfaces was probed using TPO, SEM and TEM. It is demonstrated that Ce-modification of Al2O3 induces an increase of the surface basicity and Ni dispersion. These features lead to a higher conversion of glycerol to gaseous products (60% to 80%), particularly H2 and CO2, enhancement of WGS reaction and a higher resistance to coke deposition. Allyl alcohol was found to be the main liquid product for the Ni/AlCeO3 catalyst, the production of which ceases over 700 oC. It is also highly significant that the Ni/AlCeO3 catalyst demonstrated stable values for H2 yield (2.9-2.3) and selectivity (89-81%), in addition to CO2 (75-67%) and CO (23-29%) selectivity during a (20h) long time-on-stream study. Following the reaction, SEM/EDX and TEM analysis showed heavy coke deposition over the Ni/Al2O3 catalyst, whereas for the Ni/AlCeO3 catalyst TPO studies showed the formation of more defective coke, the latter being more easily oxidized

      N.D. Charisiou, G. Siakavelas, L. Tzounis, B. Dou, V. Sebastian, S.J. Hinder, M.A. Baker, K. Polychronopoulou, M.A. Goula (2019)Ni/Y₂O₃–ZrO₂ catalyst for hydrogen production through the glycerol steam reforming reaction, In: International Journal of Hydrogen Energy Elsevier

      In the study presented herein, the catalytic activity and stability of a Ni catalyst supported on Y2O3–ZrO2 was examined for the first time in the glycerol steam reforming reaction and compared with a Ni/ZrO2. The addition of Y2O3 stabilized the ZrO2 tetragonal phase, increased the O2 storage capacity of the support and the medium strength acid sites of the catalyst, and although the Ni/Zr catalyst had a higher concentration of basic sites, the Ni/YZr presented more stable monodentate carbonates. Moreover, the Ni/YZr had substantially higher Ni surface concentration and smaller Ni particles. These properties influence the gaseous products’ distribution by increasing the H2 yield and selectivity and preventing the transformation of CO2 to CO, by inhibiting the reverse water gas shift (RWGS) reaction from taking place. For both catalysts the main liquid products identified were allyl alcohol, acetaldehyde, acetone, acrolein, acetic acid and acetol; these were subsequently quantified. The time-on-stream experiments showed that the Ni/YZr was more stable during reaction and had a higher H2 yield after 20 h (2.17 in comparison to 1.50 mol H2/mol C3H8O3, for the Ni/Zr). Extensive investigation of the carbon deposits showed that although lower amounts of coke were deposited on the Ni/Zr catalyst, these structures were more graphitic in nature and had fewer defects, which means they were harder to oxidize. Moreover, transmission electron microscopy (TEM) analysis showed that sintering of Ni nanoparticles during the reaction was significant for the Ni/Zr catalyst, as the mean particle diameter increased from an initial value of 48.2 to 67.9 nm, while it was almost absent on the Ni/YZr catalyst (the mean particle diameter increased from 42.1 to 47.4 nm).

      SJ Hinder, MA Baker, M Audronis, V Bellido-Gonzalez, P MacK (2012)Surface characterisation of PET modified using a p-DC or HIPIMS reactive sputter pre-treatment, In: Surface and Interface Analysis44(8)pp. 1063-1067

      Surface-sensitive techniques have been employed to characterise a model polymer substrate surface, poly(ethylene terephthalate) (PET), after a reactive sputter pre-treatment using magnetically enhanced Cu or Ti sputter targets in a mixed Ar-O glow discharge plasma. The plasmas are produced using either medium-frequency pulsed direct current (p-DC) or low-frequency high power impulse (HIPIMS) sources. X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and sessile drop water contact angles were employed to investigate changes in PET surface chemistry and properties following surface modification using different p-DC and HIPIMS process parameters. The XPS results indicate that the chemical composition of plasma-treated PET surfaces (p-DC or HIPIMS) depends strongly on the processing parameters employed such as sputter target material, magnetic array type and power supply technology. XPS results demonstrate that the sputter target material employed is of primary importance as it dictates the quantity of metal deposited/implanted into the PET surface. XPS results show that the use of a Cu target resulted in ∼ 31-35 at.% of Cu incorporated into the PET surface (as CuO), while the use of a Ti target resulted in only 1-4 at. % incorporation (as TiO ). The SIMS spectra and XPS depth profiles of Cu-treated PET indicate that the CuO has formed a discrete film at the surface, offering predominant or total coverage of the underlying PET. However, for Ti-treated PET, both PET and Ti SIMS peaks are observed, and the XPS C1s peak shape is characteristic of PET, indicating that Ti has not formed a discrete film, but instead TiO species have been incorporated, probably as an island-like distribution into the surface of the PET. The formation of CuO and TiO on the PET surface leads to a reduction in the contact angle compared to native PET. Hence, both p-DC and HIPIMS reactive plasma pre-treatments result in a more hydrophilic surface, promoting adhesion and offering a flexible means to introduce a wide range of surface chemistries and properties to polymeric surfaces. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd.

      Chunyang Zhang, Sanket Bhoyate, Chen Zhao, Pawan Kahol, Nikolaos Kostoglou, Christian Mitterer, Steven Hinder, Mark Baker, Georgios Constantinides, Kyriaki Polychronopoulou, Claus Rebholz, Ram Gupta (2019)Electrodeposited Nanostructured CoFe2O4 for Overall Water Splitting and Supercapacitor Applications, In: Catalysts9(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.

      M. AlKetbi, K. Polychronopoulou, Abdallah. F. Zedan, V. Sebastián, Mark A. Baker, A. AlKhoori, M.A. Jaoude, O. Alnuaimi, Steve S. Hinder, Anjana Tharalekshmy, Amina S. AlJaber (2018)Tuning the activity of Cu-containing rare earth oxide catalysts for CO oxidation reaction: Cooling while heating paradigm in microwave-assisted synthesis, In: Materials Research Bulletin108pp. 142-150 Elsevier

      (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.

      Robin Simpson, RG White, John Watts, Mark Baker (2017)XPS Investigation of Monatomic and Cluster Argon Ion Sputtering of Tantalum Pentoxide, In: Applied Surface Science405pp. 79-87 Elsevier

      In recent years, gas cluster ion beams (GCIB) have become the cutting edge of ion beam technology to sputter etch organic materials in surface analysis. However, little is currently known on the ability of argon cluster ions (Arn+) to etch metal oxides and other technologically important inorganic compounds and no depth profiles have previously been reported. In this work, XPS depth profiles through a certified (European standard BCR-261T) 30 nm thick Ta2O5 layer grown on Ta foil using monatomic Ar+ and Ar1000+ cluster ions have been performed at different incident energies. The preferential sputtering of oxygen induced using 6 keV Ar1000+ ions is lower relative to 3 keV and 500 eV Ar+ ions. The depth profiling etch rate and depth resolution is substantially better for the monatomic beam compared to the cluster beam. Ar+ ions exhibit a steady state O/Ta ratio through the bulk oxide but Ar1000+ ions show a gradual decrease in the O/Ta ratio as a function of depth. Higher residual O concentrations are observed on the Ta bulk metal for the Ar1000+ profiles compared to the Ar+ profiles.

      Gustavo F. Trindade, Jose M. Ferreira, Marie-Laure Abel, Mark Baker, John Watts (2017)Dicarboxylic acids analyzed by time-of-flight secondary ion mass spectrometry (Introduction to parts 0 to VI), In: Surface Science Spectra24(2) AIP Publishing

      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).

      Chen Zhao, Chunyang Zhang, Sanket Bhoyate, Pawan Kahol, Nikolaos Kostoglou, Christian Mitterer, Steven Hinder, Mark Baker, Georgios Constantinides, Kyriaki Polychronopoulou, Claus Rebholz, Ram Gupta (2019)Nanostructured Fe-Ni Sulfide: A Multifunctional Material for Energy Generation and Storage, In: Catalysts MDPI AG
      R Grilli, D Di Camillo, L Lozzi, I Horovitz, H Mamane, D Avisar, MA Baker (2015)Surface characterisation and photocatalytic performance of N-doped TiO2 thin films deposited onto 200 nm pore size alumina membranes by sol-gel methods, In: Materials Chemistry and Physics159pp. 25-37 Elsevier

      © 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.

      Dan A. Lamb, Craig Underwood, Vincent Barrioz, Russell Gwilliam, James Hall, Mark Baker, Stuart J. C. Irvine (2017)Proton Irradiation of CdTe Thin Film Photovoltaics Deposited on Cerium-Doped Space Glass, In: Progress in Photovoltaics25(12)pp. 1059-1067 Wiley

      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.

      K Polychronopoulou, C Rebholz, Mark Baker, L Theodorou, NG Demas, Steven Hinder, AA Polycarpou, CC Doumanidis, K Boebel (2008)Nanostructure, mechanical and tribological properties of reactive magnetron sputtered TiCx coatings, In: DIAMOND AND RELATED MATERIALS17(12)pp. 2054-2061 ELSEVIER SCIENCE SA
      C Tsotsos, K Kanakis, A Davison, MA Baker, A Matthews, A Leyland (2006)Mechanical and tribological properties of CrTiCu(B,N) glassy-metal coatings deposited by reactive magnetron sputtering, In: SURFACE & COATINGS TECHNOLOGY200(14-15)pp. 4601-4611 ELSEVIER SCIENCE SA
      Ayesha A. AlKhoori, Kyriaki Polychronopoulou, Abderrezak Belabbes, Maguy Abi Jaoude, Lourdes F. Vega, Victor Sebastian, Steven Hinder, Mark A. Baker, Abdallah F. Zedan (2020)Cu, Sm co-doping effect on the CO oxidation activity of CeO2. A combined experimental and density functional study, In: Applied Surface Science521146305 Elsevier

      The co-doping effect of a rare earth (RE) metal and a transition metal (TM) on ceria oxidation catalysis through the evaluation of samarium-copper co-doped catalysts with Ce-Sm-xCu-O (x: 0–20 at.%, Ce/Sm = 1) nominal compositions, is discussed. The CO oxidation reaction was used as a prototype reaction due to its pivotal role in the fuel cell technology. Ce-Sm-20Cu-O catalyst presented a 64% increase in the CO oxidation activity compared to that of pristine ceria. Diffraction and Raman studies proved that the Cu, Sm co-doping induces many defects related to the dopants (Sm, Cu) and the oxygen vacant sites, while the presence of hybrid CuO/Ce-Sm(Cu)-O fluorite/SmO8 (cubic metastable) phases is the most representative scenario of this oxide microstructure. A size polydispersity of CuO phases was achieved by introducing air cooling during the microwave heating. Cu, Sm atoms were uniformly doped in CeO2 structure according to the HAADF-STEM studies. These results are in agreement with EDS analysis, where Cu, Sm and Ce are located in all the analyzed areas without any preferential distribution. The XPS studies demonstrated the co-presence of Cu2+/Cu1+ and Ce4+/Ce3+ redox couples in agreement with the Bader charge analysis from the ab initio calculations, the latter influencing greatly the oxidation activity of the catalysts. Density functional theory (DFT) calculations shed light on the oxide surface and the underlying mechanism governing the oxidation catalysis taking place. In particular, Cu2+ and Sm3+ dopants were found to be located in the nearest neighbor (NN) sites of oxygen vacancies. Different oxygen vacancies configurations were studied (single vs. double, surface vs. subsurface), where the single vacancies are more stable on the surface, whereas the double vacancies configurations are more stable on the subsurface. Regarding the Ce3+ location, in the presence of single and double oxygen vacancy, the Ce3+ ions prefer to be located in the 1st NN/2nd NN and 2nd NN of the first Ce layer, relative to the oxygen vacancy, respectively. The total Density of States (DOS) analysis of the co-doped systems revealed that the dopants induced new surface states inside the ceria band gap, which can accommodate the unpaired electrons of the vacant oxygen sites. These electronic modifications justify the much lower energy of oxygen vacancy formation (Evf) in both cases, the Sm-doped, and Cu, Sm -doped CeO2 (1 1 1) geometries. Specifically, the Evf lowering upon doping was found to be almost two times larger for the Cu adjacent oxygen vacancies (Cu2+-□) compared to the Sm ones (Sm3+-□), consistent with the CO adsorption trend as the Cu-Sm-CeO2 (1 1 1) system is energetically more favorable than the Sm-CeO2 (1 1 1) and pure CeO2 (1 1 1) surfaces.

      David Stupple, V Kemp, Matthew Oldfield, John Watts, Mark Baker (2018)Modeling of Heat Transfer in an Aluminum X-ray Anode Employing a CVD Diamond Heat Spreader, In: Journal of Heat Transfer140(12)124501 American Society of Mechanical Engineers

      X-ray sources are used for both scientific instrumentation and inspection applications. In X-ray photoelectron spectroscopy (XPS), aluminum Kα 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 μm 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.

      I Horovitz, D Avisar, MA Baker, R Grilli, L Lozzi, D Di Camillo, H Mamane (2016)Carbamazepine degradation using a N-doped TiO2 coated photocatalytic membrane reactor: Influence of physical parameters., In: J Hazard Mater310pp. 98-107 Elsevier

      Commercial α-Al2O3 photocatalytic membranes with a pore size of 200 and 800-nm were coated with N-doped TiO2 photocatalytic film using a sol-gel technique for concurrent bottom-up filtration and photocatalytic oxidation. X-ray diffraction confirmed that the deposited N-doped TiO2 films are in the form of anatase with 78-84% coverage of the membrane surface. The concentration of N found by X-ray photoelectron spectroscopy was in the range of 0.3-0.9 atomic percentage. Membrane permeability after coating decreased by 50% and 12% for the 200- and 800-nm membrane substrates, respectively. The impact of operational parameters on the photocatalytic activity (PCA) of the N-doped TiO2-coated membranes was examined in a laboratory flow cell based on degradation of the model micropollutant carbamazepine, using a solar simulator as the light source. The significant gap in degradation rate between flow through the membrane and flow on the surface of the membrane was attributed both to the hydraulic effect and in-pore PCA. N-doped TiO2-coated membranes showed enhanced activity for UV wavelengths, in addition to activity under visible light. Experiments of PCA under varying flow rates concluded that the process is in the mass-transfer control regime. Carbamazepine removal rate increased with temperature, despite the decrease in dissolved oxygen concentration.

      DA Lamb, SJC Irvine, AJ Clayton, G Kartopu, V Barrioz, SD Hodgson, MA Baker, R Grilli, J Hall, CI Underwood, R Kimber (2016)Characterization of MOCVD Thin-Film CdTe Photovoltaics on Space-Qualified Cover Glass, In: IEEE Journal of Photovoltaics6(2)pp. 557-561 IEEE

      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 μm). 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.

      MA Baker, PJ Kench, MC Joseph, C Tsotsos, A Leyland, A Matthews (2003)The nanostructure and mechanical properties of PVD CrCu (N) coatings, In: SURFACE & COATINGS TECHNOLOGY162(2-3)PII S0257-pp. 222-227 ELSEVIER SCIENCE SA
      SJ Bell, MA Baker, DD Duarte, A Schneider, P Seller, PJ Sellin, MC Veale, MD Wilson (2015)Characterization of the metal-semiconductor interface of gold contacts on CdZnTe formed by electroless deposition, In: JOURNAL OF PHYSICS D-APPLIED PHYSICS48(27)ARTN 2 IOP PUBLISHING LTD

      Fully spectroscopic x/γ-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.

      C Tsotsos, K Polychronopoulou, NG Demas, G Constantinides, S Gravani, K Böbel, MA Baker, AA Polycarpou, C Rebholz (2010)Mechanical and high pressure tribological properties of nanocrystalline Ti(N,C) and amorphous C:H nanocomposite coatings, In: Diamond and Related Materials19(7-9)pp. 960-963 Elsevier

      This paper reports on the mechanical and high pressure tribological properties of nanocrystalline (nc-) Ti(N,C)/amorphous (a-) C:H deposited, using low temperature (∼ 200 °C) DC reactive magnetron sputtering. The mechanical properties are affected by the nc-Ti(N,C)/a-C:H phase fraction ratio. For increasing C contents (from 31 to 47 at.%) an increase of the a-C:H phase content and a degradation of the nanocrystalline phase occurs leading to a reduction in nanoindentation hardness (H) values (from 15 to 9 GPa) and reduced modulus (Er) values (from 150 to 80 GPa). A strong correlation between H/E ratio and wear performance was exhibited by the coatings. The synthesized coatings survived up to 100 m sliding distance when tested using pin-on-disc sliding configuration at > 4.5 GPa contact pressures and the measured friction coefficient values were similar for all films (μ ∼ 0.21–0.25).

      K.N Papageridis, N.D Charisiou, S.L Douvartzides, V. Sebastian, S.J Hinder, M.A Baker, S. AlKhoori, K. Polychronopoulou, M.A Goula (2020)Effect of operating parameters on the selective catalytic deoxygenation of palm oil to produce renewable diesel over Ni supported on Al2O3, ZrO2 and SiO2 catalysts, In: Fuel Processing Technology Elsevier

      The present work investigated the production of Green Diesel through the deoxygenation of palm oil over Ni catalysts supported on γ-Αl2O3, ZrO2 and SiO2 for a continuous flow fixed bed reactor. A comprehensive experimental study was carried out in order to examine the effects of temperature, pressure, LHSV and H2/oil feed ratio on catalytic activity during short (6 h) and long (20 h) time-on-stream experiments. The catalysts were prepared through the wet impregnation method (8 wt.% Ni) and were extensively characterized by N2 adsorption/desorption, XRD, NH3-TPD, CO2-TPD, H2-TPD, H2-TPR, XPS, TEM/HR-TEM and Raman. The characterization of the materials prior to reaction revealed that although relatively small Ni nanoparticles were achieved for all catalysts (4.3 ± 1.6 nm, 6.1 ± 1.8 nm and 6.0 ± 1.8 nm for the Ni/Al2O3, Ni/ZrO2 and Ni/SiO2 catalysts, respectively), NiO was better dispersed on the Ni/ZrO2 catalyst, while the opposite was true for the Ni/SiO2 sample. In the case of Ni/Al2O3, part of Ni could not participate in the reaction due to its entrapment in the NiAl2O4 spinel phase. Regarding performance, although an increase in H2 pressure led to increases in paraffin conversion, the increase of temperature was beneficial only up to a critical value which differed for each catalytic system under consideration (375 oC, 300 oC and 350 oC for the Ni/Al2O3, Ni/ZrO2 and Ni/SiO2 catalysts, respectively). All catalysts favored the deCO2 and deCO deoxygenation paths much more extensively than HDO, irrespective of testing conditions. Time-on-stream experiments showed that all catalysts deactivated after about 6 h, which was attributed to the sintering of the Ni particles and/or their covering by a thin graphitic carbon shell.

      C Tsotsos, MA Baker, K Polychronopoulou, PN Gibson, K Giannakopoulos, AA Polycarpou, K Böbel, C Rebholz (2010)Structure and mechanical properties of low temperature magnetron sputtered nanocrystalline (nc-)Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings, In: Thin Solid Films519(1)pp. 24-30 Elsevier

      This paper reports on the structure and mechanical properties of ~ 2 μm thick nanocomposite (nc-) Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings deposited on 100Cr6 steel substrates, using low temperature (~ 200 °C) DC reactive magnetron sputtering. The carbon content was varied with acetylene partial pressure in order to obtain single layer coatings with different a-C:H carbon phase fractions. The nanocrystalline Ti(N,C) phase is approximately stoichiometric for all coatings and the a-C:H phase fraction increases from 31 to 47 at.% as the coatings stoichiometry changed from TiC1.34 N0.51 to TiC2.48 N0.48, respectively. TiC1.34 N0.51 coatings showed the highest nanoindentation hardness (H) of ~ 14 GPa and a modulus (Er) of ~ 144 GPa; H reduced to < 6 GPa and Er to < 70 GPa for TiC2.48 N0.48 coatings. nc-Ti(N,C)/a-C:H coatings are promising candidates for applications where better matching of the modulus between a relatively low modulus substrate, hard loading support layer and low modulus-high H/E ratio top layer is required.

      AJ Clayton, Mark Baker, S Babar, R Grilli, PN Gibson, G Kartopu, DA Lamb, V Barrioz, SJC Irvine (2017)Effects of Cd1-xZnxS alloy composition and post-deposition air anneal on ultra-thin CdTe solar cells produced by MOCVD, In: Materials Chemistry and Physics192pp. 244-252 Elsevier

      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%.

      S Gravani, K Polychronopoulou, V Stolojan, Q Cui, PN Gibson, SJ Hinder, Z Gu, CC Doumanidis, MA Baker, C Rebholz (2010)Growth and characterization of ceria thin films and Ce-doped gamma-Al2O3 nanowires using sol-gel techniques, In: NANOTECHNOLOGY21(46)465606 IOP PUBLISHING LTD

      γ-Al2O3 is a well known catalyst support. The addition of Ce to γ-Al2O3 is known to beneficially retard the phase transformation of γ-Al2O3 to α-Al2O3 and stabilize the γ-pore structure. In this work, Ce-doped γ-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 γ-Al2O3 nanowires. Ce3 + ions within the nanowires were present at a concentration of < 1 at.%. On the template surface, a nanocrystalline CeO2 thin film was deposited with a cubic fluorite structure and a crystallite size of 6–7 nm. Characterization of the nanowires and thin films was performed using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. The nanowire formation mechanism and urea hydrolysis kinetics are discussed in terms of the pH evolution during the reaction. The Ce-doped γ-Al2O3 nanowires are likely to find useful applications in catalysis and this novel method can be exploited further for doping alumina nanowires with other rare earth elements.

      AJ Clayton, MA Baker, S Babar, PN Gibson, SJC Irvine, G Kartopu, DA Lamb, V Barrioz (2015)Influence of CdCl2 activation treatment on ultra-thin Cd1-xZnxS/CdTe solar cells, In: THIN SOLID FILMS590pp. 241-247 ELSEVIER SCIENCE SA
      M Audronis, SJ Hinder, P Mack, V Bellido-Gonzalez, D Bussey, A Matthews, MA Baker (2011)A comparison of reactive plasma pre-treatments on PET substrates by Cu and Ti pulsed-DC and HIPIMS discharges, In: Thin Solid Films520(5)pp. 1564-1570 Elsevier

      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 (< 5 at.%), in the form of TiO2 on the PET treated surface. The TiO2 is probably distributed as an island-like distribution covering the PET surface. Presence of Cu and Ti oxide constituents on the treated PET is beneficial in aiding the adhesion but alone (i.e. without oxygen plasma activation) is not enough to provide very high levels of hydrophilicity as is clear from sessile drop water contact angle measurements on aged samples. Exposure to the plasma treatments leads to a small amount of roughening of the substrate surface, but the average surface roughness in all cases is below 2.5 nm. The PET structure at the interface with a coating is mostly or wholly preserved. The oxygen plasma treatment, metal oxide deposition and surface roughening resulting from the HIPIMS and p-DC treatments will promote adhesion to any subsequent thin film that is deposited immediately following the plasma treatment.

      Kyriaki Polychronopoulou, Nikolaos D Charisiou, Kyriakos N Papageridis, Victor Sebastian, Steven Hinder, Aasif A Dabbawala, Ayesha A. AlKhoori, Mark Baker, Maria A. Goula (2018)The effect of Ni addition onto a Cu-based ternary support on the H₂ production over glycerol steam reforming reaction, In: Nanomaterials8(11)931pp. 1-27 MDPI

      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 temperature-programmed reduction (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 (400–750 °C) range; from ≈84% at 400 °C to ≈94% at 750 °C. Ni/Ce-Sm-10Cu catalyst showed the lowest XC3H8O3-gas implying the Cu content has a detrimental effect on performance, especially between 450–650 °C. 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 ˂ Ni/Ce-Sm-7Cu ˂ Ni/Ce-Sm-10Cu (52, 65 and 79 wt.%, respectively) based on the thermogravimetric analysis (TGA) studies. Raman studies showed that the incorporation of Cu in the support matrix controls the extent of carbon graphitization deposited during the reaction at hand.

      R Grilli, R Simpson, CF Mallinson, MA Baker (2014)Comparison of Ar+ monoatomic and cluster ion sputtering of Ta2O5 at different ion energies, by XPS: Part 2 - Cluster ions, In: Surface Science Spectra21(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.

      ME Özsan, PJ Sellin, P Veeramani, SJ Hinder, MLT Monnier, G Prekas, A Lohstroh, MA Baker (2010)Chemical etching and surface oxidation studies of cadmium zinc telluride radiation detectors, In: Surface and Interface Analysis42(6-7)pp. 795-798 Wiley-Blackwell
      MA Baker, MA Monclus, C Rebholz, PN Gibson, A Leyland, A Matthews (2010)A study of the nanostructure and hardness of electron beam evaporated TiAlBN Coatings, In: THIN SOLID FILMS518(15)pp. 4273-4280 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.

      R Grilli, R Simpson, CF Mallinson, MA Baker (2014)Comparison of Ar+ monoatomic and cluster ion sputtering of Ta2O5 at different ion energies, by XPS: Part 1 - Monoatomic ions, In: Surface Science Spectra21(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.

      W Smith, H Fakhouri, J Pulpytel, S Mori, R Grilli, MA Baker, F Arefi-Khonsari (2012)Visible Light Water Splitting via Oxidized TiN Thin Films, In: JOURNAL OF PHYSICAL CHEMISTRY C116(30)pp. 15855-15866 AMER CHEMICAL SOC
      Nikolaos Kostoglou, Chi-Wei Liao, Cheng-Yu Wang, Junko N. Kondo, Christos Tampaxis, Theodore Steriotis, Konstantinos Giannakopoulos, Athanassios G. Kontos, Steven Hinder, Mark Baker, Etienne Bousser, Allan Matthews, Claus Rebholz, Christian Mitterer (2021)Effect of Pt nanoparticle decoration on the H2 storage performance of plasma-derived nanoporous graphene, In: CARBON171pp. 294-305 PERGAMON-ELSEVIER SCIENCE LTD

      A nanoporous and large surface area (∼800 m2/g) graphene-based material was produced by plasma treatment of natural flake graphite and was subsequently surface decorated with platinum (Pt) nano-sized particles via thermal reduction of a Pt precursor (chloroplatinic acid). The carbon-metal nanocomposite showed a ∼2 wt% loading of well-dispersed Pt nanoparticles (

      J Ferreira, GF Trindade, Rene Tshulu, John Watts, Mark Baker (2017)Dicarboxylic acids analysed by x-ray photoelectron spectrscopy, Part III - pentanedioic acid anhydrous, In: Surface Science Spectra24(1)011103 AIP Publishing for American Vacuum Society

      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.

      DP Graham, A Rezai, MA Baker, PA Smith, JF Watts (2014)The development and scalability of a high strength, damage tolerant, hybrid joining scheme for Composite–metal structures, In: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING64pp. 11-24 ELSEVIER SCI LTD

      Advanced hybrid joints, which incorporate a specially designed array of macro-scale pins that provide mechanical interlocking reinforcement, have been developed in order to address the challenges associated with joining fibre reinforced composites to metals. In the present work, important joint characteristics including strength, mechanical fatigue, damage tolerance and durability have been studied and discussed. The results indicate that with advanced hybrid joints it is possible to achieve the benefits of the respective bonded and bolted systems but with virtually zero net weight gain, or conceivably a weight reduction as the increased performance of the hybrid scheme could facilitate smaller joints. The authors also present initial results from a comprehensive manufacturing and scalability trial, and demonstrate that low-cost, large-scale manufacture of hybrid joints is now feasible.

      SJ Hinder, R Grilli, M Rustame, WIA Santos, MA Baker, I Costa (2014)A surface analytical investigation of cerium-based conversion coatings deposited onto an AA2024-T3 aluminium alloy cladding layer, In: Surface and Interface Analysis46(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.

      AD Yeadon, SJ Wakeham, HL Brown, MJ Thwaites, MJ Whiting, MA Baker (2011)Remote plasma sputtering of indium tin oxide thin films for large area flexible electronics, In: Thin Solid Films520(4)pp. 1207-1211 Elsevier

      Indium tin oxide (ITO) thin films with a specific resistivity of 3.5 × 10− 4 Ω cm and average visible light transmission (VLT) of 90% have been reactively sputtered onto A4 Polyethylene terephthalate (PET), glass and silicon substrates using a remote plasma sputtering system. This system offers independent control of the plasma density and the target power enabling the effect of the plasma on ITO properties to be studied. Characterization of ITO on glass and silicon has shown that increasing the plasma density gives rise to a decrease in the specific resistivity and an increase in the optical band gap of the ITO films. Samples deposited at plasma powers of 1.5 kW, 2.0 kW and 2.5 kW and optimized oxygen flow rates exhibited specific resistivity values of 3.8 × 10− 4 Ω cm, 3.7 × 10− 4 Ω cm and 3.5 × 10− 4 Ω cm and optical gaps of 3.48 eV, 3.51 eV and 3.78 eV respectively. The increase in plasma density also influenced the crystalline texture and the VLT increased from 70 to 95%, indicating that more oxygen is being incorporated into the growing film. It has been shown that the remote plasma sputter technique can be used in an in-line process to produce uniform ITO coatings on PET with specific resistivities of between 3.5 × 10− 4 and 4.5 × 10− 4 Ω cm and optical transmission of greater than 85% over substrate widths of up to 30 cm.

      Damaso De Bono, T London, Mark Baker, Mark Whiting (2017)A robust inverse analysis method to estimate the local tensile properties of heterogeneous materials from nano-indentation data, In: International Journal of Mechanical Sciences123pp. 162-176 Elsevier

      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.

      Mehmet O. Tas, Mark A. Baker, Mateus G. Masteghin, Jedidiah Bentz, Keir Boxshall, Vlad Stolojan (2019)Highly Stretchable, Directionally Oriented Carbon Nanotube/PDMS Conductive Films with Enhanced Sensitivity as Wearable Strain Sensors, In: ACS Applied Materials & Interfaces American Chemical Society

      Recent interest in the fields of human motion monitoring, electronic skin, and human–machine interface technology demands strain sensors with high stretchability/compressibility (ε > 50%), high sensitivity (or gauge factor (GF > 100)), and long-lasting electromechanical compliance. However, current metal- and semiconductor-based strain sensors have very low (ε < 5%) stretchability or low sensitivity (GF < 2), typically sacrificing the stretchability for high sensitivity. Composite elastomer sensors are a solution where the challenge is to improve the sensitivity to GF > 100. We propose a simple, low-cost fabrication of mechanically compliant, physically robust metallic carbon nanotube (CNT)-polydimethylsiloxane (PDMS) strain sensors. The process allows the alignment of CNTs within the PDMS elastomer, permitting directional sensing. Aligning CNTs horizontally (HA-CNTs) on the substrate before embedding in the PDMS reduces the number of CNT junctions and introduces scale-like features on the CNT film perpendicular to the tensile strain direction, resulting in improved sensitivity compared to vertically-aligned CNT-(VA-CNT)-PDMS strain sensors under tension. The CNT alignment and the scale-like features modulate the electron conduction pathway, affecting the electrical sensitivity. Resulting GF values are 594 at 15% and 65 at 50% strains for HA-CNT-PDMS and 326 at 25% and 52 at 50% strains for VA-CNT-PDMS sensors. Under compression, VA-CNT-PDMS sensors show more sensitivity to small-scale deformation than HA-CNT-PDMS sensors due to the CNT orientation and the continuous morphology of the film, demonstrating that the sensing ability can be improved by aligning the CNTs in certain directions. Furthermore, mechanical robustness and electromechanical durability are tested for over 6000 cycles up to 50% tensile and compressive strains, with good frequency responses with negligible hysteresis. Finally, both types of sensors are shown to detect small-scale human motions, successfully distinguishing various human motions with reaction and recovery times of as low as 130 ms and 0.5 s, respectively.

      R Gilmore, MA Baker, PN Gibson, W Gissler (1998)Preparation and characterisation of low-friction TiB2-based coatings by incorporation of C or MoS2, In: SURFACE & COATINGS TECHNOLOGY105(1-2)pp. 45-50 ELSEVIER SCIENCE SA
      TP Mollart, PN Gibson, MA Baker (1997)An EXAFS and XRD study of the structure of nanocrystalline Ti-B-N thin films, In: JOURNAL OF PHYSICS D-APPLIED PHYSICS30(13)pp. 1827-1832 IOP PUBLISHING LTD
      S Richards, MA Baker, MD Wilson, A Lohstroh, P Seller (2016)"Femtosecond laser ablation of cadmium tungstate for scintillator arrays ", In: Optics and Lasers in Engineering83pp. 116-125 Elsevier

      Ultrafast pulsed laser ablation has been investigated as a technique to machine CdWO4 single crystal scintillator and segment it into small blocks with the aim of fabricating a 2D high energy X-ray imaging array. Cadmium tungstate (CdWO4) is a brittle transparent scintillator used for the detection of high energy X-rays and γ-rays. A 6 W Yb:KGW Pharos-SP pulsed laser of wavelength 1028 nm was used with a tuneable pulse duration of 10 ps to 190 fs, repetition rate of up to 600 kHz and pulse energies of up to 1 mJ was employed. The effect of varying the pulse duration, pulse energy, pulse overlap and scan pattern on the laser induced damage to the crystals was investigated. A pulse duration of ≥500 fs was found to induce substantial cracking in the material. The laser induced damage was minimised using the following operating parameters: a pulse duration of 190 fs, fluence of 15.3 J cm−2 and employing a serpentine scan pattern with a normalised pulse overlap of 0.8. The surface of the ablated surfaces was studied using scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy. Ablation products were found to contain cadmium tungstate together with different cadmium and tungsten oxides. These laser ablation products could be removed using an ammonium hydroxide treatment.

      R Grilli, MA Baker, B Dunn, JF Watts (2008)Failure characteristics of adhesively bonded aluminium for spacecraft applications, In: SURFACE AND INTERFACE ANALYSIS40(3-4)pp. 132-136 JOHN WILEY & SONS LTD
      MC Joseph, C Tsotsos, MA Baker, PJ Kench, C Rebholz, A Matthews, A Leyland (2005)Characterisation and tribological evaluation of nitrogen-containing molybdenum-copper PVD metallic nanocomposite films, In: SURFACE & COATINGS TECHNOLOGY190(2-3)pp. 345-356 ELSEVIER SCIENCE SA
      Mehmet O. Tas, Mark A. Baker, Vishal Musaramthota, Hasan Uppal, Mateus G. Masteghin, Jedidiah Bentz, Keir Boxshall, Vlad Stolojan (2019)Carbon nanotube micro-contactors on ohmic substrates for on-chip microelectromechanical probing applications at wafer level, In: Carbon150pp. 117-127 Elsevier

      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-μm-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 μm of compliance, with contact resistance as low as 460 mΩ (3.6 kΩ/μm) and network resistivity of 1.8 × 10−5 Ω cm, after 2500 touchdowns, with 50 μm 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.

      J Ferreira, GF Trindade, Rene Tshulu, John Watts, Mark Baker (2017)Dicarboxylic acids analysed by x-ray photoelectron spectroscopy, Part I - propanedioic acid anhydrous, In: Surface Science Spectra24(1)011101 AIP Publishing for American Vacuum Society

      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.

      N.D. Charisiou, G. Siakavelas, L. Tzounis, V. Sebastian, A. Monzon, M.A. Baker, S.J. Hinder, K. Polychronopoulou, I.V. Yentekakis, M.A. Goula (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, In: International Journal of Hydrogen Energy43(41)pp. 18955-18976 Elsevier

      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.

      DA Lamb, SJC Irvine, AJ Clayton, V Barrioz, G Kartopu, MA Baker, CI Underwood, R Grilli, R Kimber, J Hall (2015)Lightweight and low-cost thin film photovoltaics for large area extra-terrestrial applications, In: IET Renewable Power Generation9(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 Ω·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.

      J Ferreira, GF Trindade, Rene Tshulu, John Watts, Mark Baker (2017)Dicarboxylic acids analysed by x-ray photoelectron spectroscopy, Part II - butanedioic acid anhydrous, In: Surface Science Spectra24(1)011102 AIP Publishing for American Vacuum Society

      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.

      C Massaro, MA Baker, F Cosentino, PA Ramires, S Klose, E Milella (2001)Surface and biological evaluation of hydroxyapatite-based coatings on titanium deposited by different techniques, In: JOURNAL OF BIOMEDICAL MATERIALS RESEARCH58(6)pp. 651-657 JOHN WILEY & SONS INC
      R Grilli, ML Abel, MA Baker, B Dunn, JF Watts (2011)The adsorption of an epoxy acrylate resin on aluminium alloy conversion coatings, In: International Journal of Adhesion and Adhesives31(7)pp. 687-694 Elsevier

      A thermodynamic study of the adsorption of an epoxy acrylate resin used for UV-cured coatings on two different anticorrosion pretreatments on aluminium alloys relevant to aerospace industry has been undertaken. Aluminium alloy Al2219 specimens, treated with an inorganic chromate based conversion coating (Alodine 1200S) and an organic titanium based conversion coating (Nabutan STI/310), were immersed in solutions of different concentrations of the resin and adsorption isotherms were determined by assessing the uptake of the adsorbate, as a function of solution concentration, by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results show different behaviour for the two substrates, which can be attributed to the organic component of the titanium based coating. In the case of the inorganic conversion coating a clear plateau is achieved at relatively low concentrations and at a lower level of adsorption than for the hybrid coating. The data for both the coatings conform well to the Langmuir model, the organic coating, as well as showing a higher level of adsorption of the resin, also presents oscillatory behaviour at low concentration, which is shown to be complementary to the behaviour of the reactive diluent included with the epoxy acrylate to aid processing. A discussion of this competitive adsorption of the epoxy resin and the diluent on the different substrates is presented, based on considerations of the chemistry of the systems under investigation.

      MA Baker, H Fakhouri, R Grilli, J Pulpytel, W Smith, F Arefi-Khonsari (2014)Effect of total gas pressure and O2/N2 flow rate on the nanostructure of N-doped TiO2 thin films deposited by reactive sputtering, In: Thin Solid Films552pp. 10-17 Elsevier

      N-doped TiO2 thin films have been deposited by reactive RF magnetron sputtering at different total gas pressures and varying O 2/N2 gas flow rates at 300 C. The thin film nanostructure has been studied by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Increasing the deposition pressure leads to reduced crystallinity of the thin films and a higher N2 flow rate was required to incorporate N into the growing film. This is attributed to the lower energy ion bombardment of the surface and N adatom chemical reactivity being reduced at higher total gas pressures. Ar+ ion sputtering of the deposited N-doped TiO2 thin films has enabled a detailed XPS investigation of the surface and bulk N species to be performed. Adsorbed N species have been identified on all the deposited thin film surfaces, with the most prevalent adsorbed N species occurring at a binding energy of approximately 400 eV, shown to originate from atmospheric contamination, most probably N containing organic species. The bulk N content varies between 0.6 and 6.0 at.% and N is located predominantly at substitutional sites in the TiO2. The presence of interstitial N, in the form of NO species, has been identified by XPS in some thin films deposited at higher deposition pressures. Hence, varying the total gas pressure may provide a route for tailoring the location of N in the bulk structure. At higher N contents (> 3 at.%), TiN is found as a secondary phase within the bulk structure and the presence of TiN leads to a sharp reduction in the band gap. Post-deposition annealing of low N containing films results in an N-doped TiO2 single phase anatase structure. © 2013 Elsevier B.V.

      MA Baker, PJ Kench, C Tsotsos, PN Gibson, A Leyland, A Matthews (2005)Investigation of the nanostructure and wear properties of physical vapor deposited CrCuN nanocomposite coatings, In: JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A23(3)pp. 423-433 A V S AMER INST PHYSICS
      PN Gibson, MA Baker, ME Ozsan (2002)Investigation of sulphur diffusion at the CdS/CdTe interface of thin-film solar cells, In: SURFACE AND INTERFACE ANALYSIS33(10-11)pp. 825-829 JOHN WILEY & SONS LTD
      R Grilli, MA Baker, JE Castle, B Dunn, JF Watts (2011)Corrosion behaviour of a 2219 aluminium alloy treated with a chromate conversion coating exposed to a 3.5% NaCl solution, In: Corrosion Science53(4)pp. 1214-1223 Elsevier

      This study investigates the formation of a chromate conversion coating at Al–Cu–Fe–Mn intermetallic sites of an Al2219 alloy and the corrosion initiation at these sites in a 3.5% NaCl solution, using SEM, AES and EDX. Changes in the surface chemistry were monitored after progressive exposures to the solution up to 42 h. The coating was found to be thinner and more defective on the intermetallic. Initially, Al is dissolved and Al(OH)3 deposited on and around the intermetallic. After 42 h of exposure, Al(OH)3, Fe and Mn oxides and small particles of elemental Cu are deposited as corrosion products.

      N.D. Charisiou, K.N. Papageridis, G. Siakavelas, V. Sebastian, S.J. Hinder, M.A. Baker, K. Polychronopoulou, M.A. Goula (2018)The influence of SiO2 doping on the Ni/ZrO2 supported catalyst for hydrogen production through the glycerol steam reforming reaction, In: Catalysis Today319pp. 206-219 Elsevier

      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.

      The performance of single crystal CdZnTe radiation detectors is dependent on both the bulk and the surface properties of the material. After single crystal fabrication and mechanical polishing, modification of the surface to remove damage and reduce the surface leakage current is generally achieved through chemical etching followed by a passivation treatment. In this work, CdZnTe single crystals have been chemically etched using a bromine in methanol (BM) treatment. The BM concentrations employed were 0.2 and 2.0 (v/v) % and exposure times varied between 5 and 120 s. Angle resolved XPS and sputter depth profiling has been employed to characterize the surfaces for the different exposure conditions. A Te rich surface layer was formed for all exposures and the layer thickness was found to be independent of exposure time. The enriched Te layer thickness was accurately determined by calibrating the sputter rate against a CdTe layer of known thickness. For BM concentrations of 0.2 (v/v) % and 2 (v/v) %, the Te layer thickness was determined to be 1.3 ± 0.2 and 1.8 ± 0.2 nm, respectively. The BM etched surfaces have subsequently been passivated in a 30 wt.% HO solution employing exposure time of 15 s. The oxide layer thickness has been calculated using two standard XPS methodologies, based on the Beer-Lambert expression. The TeO thickness calculated from ARXPS data are slightly higher than the thickness obtained by the simplified Beer-Lambert expression. For BM exposures of 30-120 s followed by a passivation treatment of 30 wt. % HO solution employing an exposure time 15 s, the ARXPS method gave an average TeO thickness value of 1.20 nm and the simplified Beer-Lambert expression gave an average thickness value of 0.99 nm. © 2012 Elsevier B.V. All rights reserved.

      DD Duarte, SJ Bell, J Lipp, A Schneider, P Seller, MC Veale, MD Wilson, MA Baker, PJ Sellin, V Kachkanov, KJS Sawhney (2013)Edge effects in a small pixel CdTe for X-ray imaging, In: JOURNAL OF INSTRUMENTATION8ARTN Ppp. ?-? IOP PUBLISHING LTD

      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

      Michael Rix, Mark Baker, Mark Whiting, Ray P Durman, Robert A Shatwell (2017)An Improved Silicon Carbide Monofilament for the Reinforcement of Metal Matrix Composites, In: M Meyers, HAC Benavides, SP Brühl, HA Colorado, E Dalgaard, CN Elias, RB Figueiredo, O Garcia-Rincon, M Kawasaki, TG Langdon, RV Mangalaraja, MCG Marroquin, A da Cunha Rocha, JM Schoenung, A Costa e Silva, M Wells, W Yang (eds.), Proceedings of the 3rd Pan American Materials Congresspp. 317-324 Springer

      As part of ongoing research in the UK, TISICS have developed an improved 140 µm carbon coated silicon carbide monofilament for the reinforcement of metal matrix composites. The monofilament is fabricated in a single reactor using a high speed chemical vapor deposition process at a rate of 8 m/min (26 ft/min). Statistical analysis of monofilament properties over two years of production has demonstrated excellent reproducibility of the process. The monofilaments have an average tensile strength of 4.0 ± 0.2 GPa with a Weibull modulus of 50 ± 10. Composites incorporating the monofilaments show similar low variability in yield and tensile strength with the latter exhibiting a mean value above 90% of the maximum theoretical strength predicted by the rule of mixtures. By varying the volume fraction and orientation of the monofilament reinforcement, composite properties can be tailored to fit design requirements. Examples are given of demonstrator components made for the European aerospace sector.

      R Grilli, JF Watts, MA Baker, B Dunn (2010)Localised corrosion on 2219 aluminium alloy coated with a titanium based conversion coating, In: Surface and Interface Analysis42(6-7)pp. 610-615 Wiley
      SJ Bell, Mark Baker, DD Duarte, A Schneider, P Seller, Paul Sellin, MC Veale, MD Wilson (2017)Comparison of the surfaces and interfaces formed for sputter and electroless deposited gold contacts on CdZnTe, In: Applied Surface Science427(A)pp. 1257-1270 Elsevier

      Cadmium zinc telluride (CdZnTe) is a leading sensor material for spectroscopic X/-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.

      SJ Bell, A Schneider, P Seller, MC Veale, MD Wilson, MA Baker, V Perumal, PJ Sellin, H Chen, P Marthandam (2013)A multi-technique characterization of electroless gold contacts on single crystal CdZnTe radiation detectors, In: Journal of Physics D: Applied Physics46(45)

      Cadmium zinc telluride (CdZnTe) is now established as a popular choice of sensor for the detection of γ-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.

      Camila Zequine, Sanket Bhoyate, Khamis Siam, Pawan K. Kahol, Nikolaos Kostoglou, Christian Mitterer, Steven Hinder, Mark Baker, Georgios Constantinides, Claus Rebholz, Gautam Gupta, Xianglin Li, Ram K. Gupta (2018)Needle grass array of nanostructured nickel cobalt sulfide electrode for clean energy generation, In: Surface and Coatings Technology354pp. 306-312 Elsevier

      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.

      DD Duarte, JD Lipp, A Schneider, P Seller, MC Veale, MD Wilson, MA Baker, PJ Sellin (2016)Simulation of active-edge pixelated CdTe radiation detectors, In: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT806pp. 139-145 ELSEVIER SCIENCE BV

      The edge surfaces of single crystal CdTe play an important role in the electronic properties and performance of this material as an X-ray and γ-ray radiation detector. Edge effects have previously been reported to reduce the spectroscopic performance of the edge pixels in pixelated CdTe radiation detectors without guard bands. A novel Technology Computer Aided Design (TCAD) model based on experimental data has been developed to investigate these effects. The results presented in this paper show how localized low resistivity surfaces modify the internal electric field of CdTe creating potential wells. These result in a reduction of charge collection efficiency of the edge pixels, which compares well with experimental data.

      E Luster, D Avisar, I Horovitz, L Lozzi, Mark Baker, R Grilli, H Mamane (2017)N-Doped TiO2-Coated Ceramic Membrane for Carbamazepine Degradation in Different Water Qualities, In: Nanomaterials7(8) MDPI

      The photocatalytic degradation of the model pollutant carbamazepine (CBZ) was investigated under simulated solar irradiation with an N-doped TiO2-coated Al2O3 photocatalytic membrane, using different water types. The photocatalytic membrane combines photocatalysis and membrane filtration in a single step. The impact of each individual constituent such as acidity, alkalinity, dissolved organic matter (DOM), divalent cations (Mg2+ and Ca2+), and Cl

      ND Charisiou, KN Papageridis, G Siakavelas, L Tzounis, K Kousi, Mark Baker, Steven Hinder, VS Cabeza, K Polychronopoulou, MA Goula (2017)Glycerol Steam Reforming for Hydrogen Production over Nickel Supported on Alumina, Zirconia and Silica Catalysts, In: Topics in Catalysis60(15-16)pp. 1226-1250 Springer Verlag

      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

      K Polychronopoulou, AF Zedan, MS Katsiotis, Mark Baker, AA AlKhoori, SY AlQaradawi, Steven Hinder, S AlHassan (2017)Rapid Microwave Assisted Sol-Gel Synthesis of CeO2 and CexSm1-xO2 Nanoparticle Catalysts for CO Oxidation, In: Journal of Molecular Catalysis A: Chemical428pp. 41-55 Elsevier

      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.

      MA Baker, R Gilmore, C Lenardi, W Gissler (1999)XPS investigation of preferential sputtering of S from MoS2 and determination of MoSx stoichiometry from Mo and S peak positions, In: APPLIED SURFACE SCIENCE150(1-4)pp. 255-262 ELSEVIER SCIENCE BV
      Christopher Mallinson, PM Yates, Mark Baker, James Castle, A Harvey, John Watts (2017)The Localised Corrosion Associated with Individual Second Phase Particles in AA7075-T6: A Study by SEM, EDX, AES, SKPFM and FIB-SEM, In: Materials and Corrosion68(7)pp. 748-763 Wiley-VCH

      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.

      JE Castle, MA Baker (1999)The feasibility of an XPS expert system demonstrated by a rule set for carbon contamination, In: JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA105(2-3)pp. 245-256 ELSEVIER SCIENCE BV
      K Polychronopoulou, MA Baker, C Rebholz, J Neidhardt, M O'Sullivan, AE Reiter, K Kanakis, A Leyland, A Matthews, C Mitterer (2009)The nanostructure, wear and corrosion performance of arc-evaporated CrBxNy nanocomposite coatings, In: SURFACE & COATINGS TECHNOLOGY204(3)pp. 246-255 ELSEVIER SCIENCE SA
      R Grilli, MA Baker, JE Castle, B Dunn, JF Watts (2010)Localized corrosion of a 2219 aluminium alloy exposed to a 3.5% NaCl solution, In: Corrosion Science52(9)pp. 2855-2866
      S Bell, Mark Baker, D Duarte, A Schneider, P Seller, Paul Sellin, M Veale, M Wilson (2017)Performance comparison of small-pixel CdZnTe radiation detectors with gold contacts formed by sputter and electroless deposition, In: Journal of Instrumentation12P06015 IOP Publishing

      Recent improvements in the growth of wide-bandgap semiconductors, such as cadmium zinc telluride (CdZnTe or CZT), has enabled spectroscopic X/γ-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 μm pixels on a 250 μm pitch and bump-bonded to the HEXITEC ASIC. The X/γ-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.

      N.D. Charisiou, K.N. Papageridis, L. Tzounis, V. Sebastian, S.J. Hinder, M.A. Baker, M. AlKetbi, K. Polychronopoulou, M.A. Goula (2018)Ni supported on CaO-MgO-Al 2 O 3 as a highly selective and stable catalyst for H 2 production via the glycerol steam reforming reaction, In: International Journal of Hydrogen Energy Elsevier

      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.

      DA Lamb, Craig Underwood, V Barrioz, Russell Gwilliam, James Hall, Mark Baker, SJC Irvine (2017)Proton irradiation of CdTe thin film photovoltaics deposited on cerium‐doped space glass, In: Progress in Photovoltaics25(12)pp. 1059-1067 Wiley

      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.

      O Jimenez, M Audronis, MA Baker, A Matthews, A Leyland (2008)Structure and mechanical properties of nitrogen-containing Zr-Cu based thin films deposited by pulsed magnetron sputtering, In: JOURNAL OF PHYSICS D-APPLIED PHYSICS41(15)ARTN 15530 IOP PUBLISHING LTD
      N.D. Charisiou, L. Tzounis, V. Sebastian, S.J. Hinder, M.A. Baker, K. Polychronopoulou, M.A. Goula (2018)Investigating the correlation between deactivation and the carbon deposited on the surface of Ni/Al2O3 and Ni/La2O3-Al2O3 catalysts during the biogas reforming reaction, In: Applied Surface Science Elsevier

      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.

      M Abi Jaoude, K Polychronopolou, SJ Hinder, MS Katsiotis, MA Baker, YE Greish, SM Alhassan (2016)Synthesis and properties of 1D Sm-doped CeO2 composite nanofibers fabricated using a coupled electrospinning and sol-gel methodology, In: Ceramics International42(9)pp. 10734-10744 Elsevier

      Ce1-xSmxO2(x=0, 0.2, 0.5 and 0.8) nanofibers (NFs) were synthesized by coupling sol-gel with electrospinning and using poly-vinyl pyrrolidone (PVP) as the polymer medium, in an ethanol/water mixture. Control over the fabrication conditions was achieved through analysis of the most key synthetic factors, which include: (i) the applied field strength; (ii) the solution feed rate and (iii) the PVP content in the electrospinning solution. The optimum microstructural fiber morphology (high quality beeds-free fibers) was achieved using the following electrospinning parameters: an applied voltage of 18.5 kV, a 7 ml/hr of solution feed rate and a 12% (w/w) of PVP composition. Morphological features of the resulting fibers were examined by scanning electron microscopy (SEM). The average fiber diameter was typically found to be in the range of 200-1100 nm and 50-300 nm, before and after calcination at 500 oC, respectively. X-ray diffraction (XRD) results showed that the fluorite cubic structure was preserved for the entire Ce1-xSmxO2 compositional range studied, while elemental analysis using EELS and X-ray photoelectron spectroscopy (XPS) confirmed the purity of the bulk and surface composition of the fibers. Selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) proved that the NFs are highly crystalline. The thermal stability of the composite (polymer/inorganic nitrate salts) NFs was further investigated in an inert atmosphere (N2) using thermogravimetric analysis (TGA), which allowed the transformation process of the NFs from composite to oxide to be monitored. The reducibility of the metal oxide NFs (mobility of oxygen species in the fluorite cubic lattice) as well as their thermal stability in successive oxidation-reduction cycles was evaluated using temperature-programmed reduction in a H2 atmosphere (H2-TPR). Acidic-basic features of the NFs and powder surfaces were studied through temperature programmed desorption (TPD) using NH3 and CO2 as probe molecules, where weak, medium and strong acid sites were successfully traced with profound differences depending on the morphology. The NFs’ potential performance towards NH3 oxidation was also evaluated. Two types of basic sites, hydroxyl groups and surface lattice oxygen are present on the NFs, as probed by CO2 adsorption. Pyridine adsorption followed by infrared spectroscopy (Py-FT-IR) studies unveiled the more profound Lewis acid presence in Ce0.5Sm0.5O2 NFs compared to bulk powder Ce0.5Sm0.5O2.

      P Hammer, MA Baker, C Lenardi, W Gissler (1997)Synthesis of carbon nitride films at low temperature, In: JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS15(1)pp. 107-112 AMER INST PHYSICS
      M. Abi Jaoude, Emad Alhseinat, K. Polychronopoulou, G. Bharath, Ismail Farouq Fahmi Darawsheh, Shoaib Anwer, Mark A. Baker, Steven J. Hinder, Fawzi Banat (2020)Morphology-dependent electrochemical performance of MnO₂ nanostructures on graphene towards efficient capacitive deionization, In: Electrochimica Acta330135202 Elsevier

      Capacitive deionization (CDI) is an emerging desalination technology that still needs further development to enhance its performance for practical implementation. Herein, we present a hybrid CDI approach, which integrates the electrical double-layer (EDL) with the sodium-ion battery concept to improve the separation of sodium and chloride ions from saline water. The hybrid CDI cell is achieved by using hydrothermally-grown and uniformly dispersed prawn-like α-MnO₂/graphene (α-MnO₂/G) nanocomposite as anode material, and graphene at the cathode. In this paper, the effect of MnO₂ morphology on the electrode electrochemical performance and its effect on capacitive deionization performance have been fully investigated. In this configuration, the Na⁺ ions are inserted by the electrochemical reaction at the α-MnO₂/G electrode, whereas Cl⁻ ions are captured by the graphene-based electrode. The morphological dependent electrochemical properties of the obtained nanocomposites were studied deeply through CV and EIS analysis. The established hybrid CID cell provides an electrical capacitance as high as 375 F g⁻¹ at 10 mV s⁻¹, cation-selectivity, good electrical stability and low internal resistance. The hybrid CDI device also shows a stable and reversible salt insertion/de-insertion capacity up to 29.5 mg g⁻¹ at 1.2 V. These results demonstrate the suitability of prawn-like α-MnO₂/G nanocomposite to produce high-performance hybrid CDI cells.

      Maitha Al Ketbi, Kyriaki Polychronopoulou, Maguy Abi Jaoude, Michalis A Vasiliades, Victor Sebastian, Steven J Hinder, Mark A Baker, Abdallah F Zedan, Angelos M Efstathiou (2019)Cu-Ce-La-Ox as efficient CO oxidation catalysts: effect of Cu content, In: Applied Surface Science Elsevier

      Nanograins of Ce-La-xCu-O oxides, of 16 nm2 area size, are tested as materials towards the CO oxidation . Preservation of the cubic lattice structure following La3+ and Cu2+ metal cations doping is confirmed based on the powder X-ray diffraction and Raman studies. From XPS, the presence of mixed Ce3+/Ce4+ and Cu2+/Cu1+ oxidation states was confirmed, which was more profound in the low Cu-content Ce-La-xCu-O catalysts. Cu increases the concentration of oxygen vacant sites in the doped-CeO2 according to the Raman intensity ratio IOv/IF2g of 1.58 and 1.78 with the increase in copper content from 7 to 20 at.% as compared to the lower value of 0.44 for the Ce-La. The mobility of the surface and bulk lattice oxygen is further investigated using 16O/18O isotopic exchange (TIIE), and is found to be Cu at.% dependent. For the case of Ce-La-20Cu, the participation of the lattice oxygen (OL) in the reaction mechanism has been demonstrated using transient experiments. Accordingly, the specific rate (μmol CO m-2s-1) of the CO oxidation reaction is found to be higher for the Ce-La-20Cu and Ce-La-7Cu catalysts, corroborating thus the presence of more mobile/labile oxygen species in those ternary catalysts as opposed to the other lower copper compositions.

      MA Baker, TP Mollart, PN Gibson, W Gissler (1997)Combined x-ray photoelectron Auger electron spectroscopy glancing angle x-ray diffraction extended x-ray absorption fine structure investigation of TiBxNy coatings, In: JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS15(2)pp. 284-291 AMER INST PHYSICS
      J M Ferreira, M Oliveira, G F Trindade, LCL Santos, C R Tomachuk, M A Baker (2018)Development and characterisation of zinc oxalate conversion coatings on zinc, In: Corrosion science137pp. 13-32 Elsevier BV

      The interactions between oxalic acid and zinc substrates have been studied through the deposition of zinc oxalate coating by immersion. The corrosion behaviour of zinc was investigated by surface observation and electrochemical impedance spectroscopy (EIS). Better protective properties were observed for samples treated with 10−1 M oxalic acid compared to other concentrations and the enrichment of corrosion product by Na was observed. The electrochemical results reveal that the oxalate coating increases corrosion protection in corrosive medium. It is proposed that the zinc oxalate coating formed act as a basis for anchoring zinc corrosion products forming simonkolleite improving corrosion resistance.

      J. M. Ferreira, V. Rajendran, G. Simonelli, A. C. M. Silva, L. C. L. Santos, S. Mattedi, L. A. M. Pontes, I. Costa, J. L. Rossi, M. A. Baker (2020)Deposition and characterization of a sol-gel Mg-substituted fluorapatite coating with new stoichiometries, In: Applied surface science505 Elsevier

      The calcium substitution for magnesium on fluorapatite is attractive because this element is a natural substitute in biological apatites. There are several published stoichiometries for calcium substituted by magnesium fluorapatites and most works point out that the formation and fixation of biomimetic Ca-P coatings in Ringer's solution were strongly related to Mg2+ content and furthermore the Mg replacement improves the bioactivity of apatite. In the present study, fluorapatite (FA) and fluorapatite substituted with 6% and 7% of magnesium were obtained by deposition via sol-gel coating on substrates of AISI 316L stainless steel to investigate the effect of magnesium substitution on fluorapatite with not yet investigated stoichiometry. Characterization of coating thickness, chemical composition and crystalline structure was performed using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The coating adhesion was evaluated using the pull-out test and the corrosion resistance was undertaken using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The electrochemical results showed improvement in the corrosion resistance of magnesium-fluorapatite compared to fluorapatite coated on AISI 316L stainless steel substrates. The improvement corrosion protection and adhesion performance indicate that such magnesium fluorapatites coatings are very interesting candidates as bioactive coatings for implants.

      Andrius Subacius, Bill Baloukas, Etienne Bousser, Steve J. Hinder, Mark A. Baker, Claus Rebholz, Allan Matthews (2020)Nanostructural Characterisation and Optical Properties of Sputter-Deposited Thick Indium Tin Oxide (ITO) Coatings, In: Coatings (Basel)10(11)pp. 1-7 Mdpi

      Indium tin oxide (ITO) thin films, used in many optoelectronic applications, are typically grown to a thickness of a maximum of a few hundred nanometres. In this work, the composition, microstructure and optical/electrical properties of thick ITO coatings deposited by radio frequency magnetron sputtering from a ceramic ITO target in an Ar/O-2 gas mixture (total O-2 flow of 1%) on unheated glass substrates are reported for the first time. In contrast to the commonly observed (200) or (400) preferential orientations in ITO thin films, the approximately 3.3 mu m thick coatings display a (622) preferential orientation. The ITO coatings exhibit a purely nanocrystalline structure and show good electrical and optical properties, such as an electrical resistivity of 1.3 x 10(-1) Omega center dot cm, optical transmittance at 550 nm of similar to 60% and optical band gap of 2.9 eV. The initial results presented here are expected to provide useful information for future studies on the synthesis of high-quality thick ITO coatings.

      Anastasios I. Tsiotsias, Nikolaos D. Charisiou, Ayesha AlKhoori, Safa Gaber, Victor Sebastian, Steven J. Hinder, Mark A. Baker, Kyriaki Polychronopoulou, Maria A. Goula (2022)Towards maximizing conversion of ethane and carbon dioxide into synthesis gas using highly stable Ni-perovskite catalysts, In: Journal of CO2 utilization61 Elsevier Ltd

      Dry ethane reforming (DER) aims to utilize captured CO2 and ethane, which is found in large quantities in shale gas, towards the production of high-value synthesis gas. During the dry reforming of hydrocarbons, the interaction between the active metal and the underlying support, along with the choice of the operating temperature, are considered to be the main factors influencing a catalyst’s stability and coking resistance. In this work, the DER catalytic performance and stability of Ni-doped perovskite systems is compared with that of a typical impregnated Ni/Al2O3 catalyst. The calcined, reduced and spent catalysts are assessed using the ICP, XRD, N2 physisorption, H2-TPR, CO2-TPD, TEM, HAADF-STEM, EDS Mapping, XPS and TPO techniques. Ni-CaZrO3 (CZNO) consisting of partly exsolved Ni nanoparticles with a strong metal-support interaction is shown to be particularly stable and accumulate only a fraction of the coke that is deposited on the impregnated Ni/Al2O3 catalyst, which suffers from severe and rapid degradation under the reactant stream. By increasing the operating temperature to 750 °C, Ni-CaZrO3 can achieve almost total conversion of ethane and around 90% conversion of carbon dioxide towards synthesis gas, with no apparent loss of catalytic activity. [Display omitted] •Ni-CaZrO3 and Ni-SrZrO3 catalysts were tested for the dry reforming of ethane.•Ni-perovskite catalysts exhibit superior stability compared to impregnated Ni/Al2O3.•Ni/Al2O3 accumulates the most carbon on its surface.•Coke deposition is the best descriptor of catalytic activity loss at 600 °C.•Increasing the reaction temperature promotes catalytic activity and stability.

      B.C. Bussell, PN Gibson, JOSEPH DANIEL LAWTON, PIERRE COUTURE, M.K. Sharpe, J. England, STEVEN JOHN HINDER, VLAD STOLOJAN, S.A. Thornley, MARK ALAN BAKER (2022)The effect of RF plasma power on remote plasma sputtered AZO thin films, In: Surface and Coatings Technology Elsevier

      Aluminium-doped ZnO (AZO) thin films were deposited by remote plasma sputtering of a ZnO:Al2O3 98:2 wt.% ceramic target in a pulsed DC configuration. The target power was kept constant at 445 W and the RF plasma power was varied between 0.5 and 2.5 kW. The as-deposited AZO thin films exhibited an optimum resistivity of 6.35 x 10-4 .cm and optical transmittance of 92 % at a RF plasma power 1.5 kW. The thin film microstructure, chemical composition, and residual stress were investigated using SEM, RBS, XPS and XRD. Accurate determination of the chemical composition and correct interpretation of GIXRD data for AZO thin films are a particular focus of this work. The AZO layer thickness was 500 - 700 nm and Al content in the range of 2.3 - 3.0 at.%, determined by RBS. The AZO thin films exhibited a strong (002) preferential orientation and grain sizes between 70 and 110 nm. The (103) peak intensity enhancement in GIXRD is proven to be a result of the strong (002) preferential orientation and GIXRD geometrical configuration rather than a change in the crystallite orientation at the surface. XPS depth profiles show preferential sputtering of O and Al using a 500 eV Ar+ beam, which can be reduced, but not eradicated using an 8 keV Ar150+ beam. The preferential sputtering can be successfully modelled using the simulation software TRIDYN. A plasma power of 1.5 kW corresponds to a highly ionised plasma and various microstructural and compositional factors have all contributed to the optimum low resistivity occurring at this plasma power. The grain size exhibits a maximum in the 1.25 - 1.5 kW range and there is improved (002) orientation, minimising grain boundary scattering. The highest carrier concentration and mobility was observed at the plasma power of 1.5 kW which may be associated with the maximum in the aluminium doping concentration (3.0 at.%). The lowest residual stress is also observed at 1.5 kW.

      MARK ALAN BAKER, Xinnan Lu, Dalaver H. Anjum, Georgia Basina, STEVEN JOHN HINDER, Wassilios Papawassiliou, Andrew J. Pell, Marina Karagianni, Georgios Papavassiliou, Dinesh Shetty, Dina Abdullah Ali Gaber, Safa Abdullah Ali Gaber, Yasser Al Wahedi, Kyriaki Polychronopoulou (2021)Ni2P Nanoparticles Embedded in Mesoporous SiO2 for Catalytic Hydrogenation of SO2 to Elemental S, In: ACS Applied Nano Material American Chemical Society

      Highly active nickel phosphide nano clusters (Ni2P) confined in mesoporous SiO2 catalyst were synthesized by a two-step process targeting tight control over the Ni2P size and phase. The Ni precursor was incorporated into the MCM-41 matrix by one-pot synthesis, followed by the phosphorization step which was accomplished in oleylamine with trioctylphosphine at 300 oC so to achieve the phase transformation from Ni to Ni2P. For benchmarking, Ni confined by the mesoporous SiO2 (absence of phosphorization) and 11 nm Ni2P nanoparticles (absence of SiO2), were also prepared. From the microstructural analysis, it was found that the growth of Ni2P nano clusters was restricted by the mesoporous channels, thus forming ultrafine and highly dispersed Ni2P nano clusters (< 2 nm). The above approach led to promising catalytic performance following the order: u-Ni2P@m-SiO2 > n-Ni2P > u-Ni@m-SiO2 > c-Ni2P in the selective hydrogenation of SO2 to S. In particular, u-Ni2P@m-SiO2 exhibited an SO2 conversion of 94 % at 220 oC and ~99 % at 240 oC, which is higher than the 11 nm stand-alone Ni2P particles (43 % at 220 oC and 94 % at 320 oC), highlighting the importance of the role played by SiO2 in stabilizing ultrafine nanoparticles of Ni2P. The reaction activation energy Ea over u-Ni2P@m-SiO2 is ~33 kJ/mol, which is lower than over n-Ni2P (~36 kJ/mol) and c-Ni2P (~66 kJ/mol), suggesting that the reaction becomes energetically favored over the ultrafine Ni2P nano clusters.

      Xinnan Lu, MARK ALAN BAKER, Dalaver H. Anjum, Wassilios Papawassiliou, Andrew J. Pell, Michael Fardis, Georgios Papavassiliou, STEVEN JOHN HINDER, Safa Abdullah Ali Gaber, Dina Abdullah Ali Gaber, Yasser Al Wahedi, Kyriaki Polychronopoulou (2021)Nickel Phosphide Nanoparticles for Selective Hydrogenation of SO2 to H2S, In: ACS Applied Nano Material American Chemical Society

      Highly mesoporous SiO2 encapsulated NixPy crystals, where (x, y) = (5, 4), (2, 1), and (12, 5) were successfully synthesized by adopting thermolytic method using oleylamine (OAm), trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO). The Ni5P4@SiO2 system shows the highest reported activity for the selective hydrogenation of SO2 towards H2S at 320 oC (96 % conversion of SO2 and 99 % selectivity to H2S) which was superior to the activity of the commercial CoMoS@Al2O3 catalyst (64 % conversion of SO2 and 71 % selectivity to H2S at 320 oC). The morphology of the Ni5P4 crystal was finely tuned via adjustment of the synthesis parameters receiving a wide spectrum of morphologies (hollowed, macroporous-network and SiO2 confined ultra-fine clusters). Intrinsic characteristics of the materials were studied using XRD, HRTEM/STEM-HAADF, EDX, BET, H2-TPR, XPS, and experimental and calculated 31P MAS ssNMR towards establishing the structure-performance correlation for the reaction of interest. Characterization of the catalysts after the SO2 hydrogenation reaction proved the preservation of the morphology, crystallinity and Ni/P ratio for all the catalysts.

      J. C. Lourenço, L. P. Souza, M. I. S. T. Faria, C. A. Nunes, C. R. Tomachuk, M. A. Baker (2021)Influence of the iron content on the microstructure and electrochemical behavior of as-cast modified Inconel 625, In: Corrosion Science Elsevier

      Inconel 625 based alloys with different iron contents were prepared by arc-melting. Alloys with up to 5 wt.% iron are composed of the γ matrix, metal monocarbides (MC) and Laves precipitates. Alloys with 10-15 wt.% iron comprise the γ matrix and γ/Laves eutectic-like constituent. MC precipitates are cathodic and the Laves phase anodic with respect to the matrix. In 3.5 wt.% NaCl, alloys with 10-15 wt.%, iron showed improved corrosion behaviour compared to 5 wt.% iron due to absence of MC phase formation. The results are important as they potentially allow faster and more economical welding processes to be employed.

      M. A. Baker, G. I. Siakavelas, N.D. Charisiou, A. AlKhoori, S. AlKhoori, V. Sebastian, S. J. Hinder, I.V. Yentekakis, K. Polychronopoulou, M.A. Goula (2021)Highly selective and stable Ni/La-M (M=Sm, Pr, and Mg)-CeO2 catalysts for CO2 methanation, In: Journal of CO₂ Utilization51101618 Elsevier

      In the study presented herein, nickel catalysts supported on CeO2 and, for the first time in the literature, on La2O3-Sm2O3-CeO2, La2O3-Pr2O3-CeO2 and La2O3-MgO-CeO2 were prepared and evaluated for the reaction of CO2 methanation. The carriers were prepared through a sol-gel microwave assisted method and the catalysts were obtained following wet impregnation. The physicochemical properties of the catalysts prior to reaction were determined through H2-TPR, H2-TPD, Raman spectroscopy, XRD, CO2-TPD, N2 physisorption-desorption, XPS and TEM. The spent catalysts, after the time-on-stream experiments were further characterised using TEM and TGA. It was shown that the simultaneous incorporation of La3+, Pr3+ and La3+, Sm3+ into the crystal structure of cerium oxide created higher population of oxygen vacant sites. Moreover, the co-presence of La3+, Mg2+ and La3+, Pr3+ into the CeO2 increased the plethos of moderate basic sites. These physicochemical properties increased the rate of CO2 methanation reaction at relatively low temperatures. Furthermore, it is argued that the addition of La3+ stabilized the Ni active sites via the probable formation of a new compound (La-O-Ni) on the catalyst surface or synergetic catalytic centers at the interfacial area improving the catalytic properties (activity and stability). Finally, the catalytic performance tests revealed that the addition of La3+ mainly improved the conversion of CO2 and yield of CH4 for the Ni/La-Mg-Ce and Ni/La-Sm-Ce samples. The rCO2 and XCO2 values at 300oC followed the order Ni/La-Sm-Ce >> Ni/La-Mg-Ce > Ni/La-Pr-Ce > Ni/Ce.

      Kyriaki Polychronopoulou, Ayesha A AlKhoori, Angelos M Efstathiou, Maguy Abi Jaoude, C. M Damaskinos, Mark A Baker, Alia Almutawa, Dalaver H Anjum, Michalis A Vasiliades, Abderrezak Belabbes, Lourdes F Vega, Abdallah Fathy Zedan, Steven J Hinder (2021)Design Aspects of Doped CeO2 for Low-Temperature Catalytic CO Oxidation: Transient Kinetics and DFT Approach, In: ACS applied materials & interfaces13(19)pp. 22391-22415 American Chemical Society

      CO elimination through oxidation over highly active and cost-effective catalysts is a way forward for many processes of industrial and environmental importance. In this study, doped CeO2 with transition metals (TM = Cu, Co, Mn, Fe, Ni, Zr, and Zn) at a level of 20 at. % was tested for CO oxidation. The oxides were prepared using microwave-assisted sol–gel synthesis to improve catalyst’s performance for the reaction of interest. The effect of heteroatoms on the physicochemical properties (structure, morphology, porosity, and reducibility) of the binary oxides M–Ce–O was meticulously investigated and correlated to their CO oxidation activity. It was found that the catalytic activity (per gram basis or TOF, s–1) follows the order Cu–Ce–O > Ce–Co–O > Ni–Ce–O > Mn–Ce–O > Fe–Ce–O > Ce–Zn–O > CeO2. Participation of mobile lattice oxygen species in the CO/O2 reaction does occur, the extent of which is heteroatom-dependent. For that, state-of-the-art transient isotopic 18O-labeled experiments involving 16O/18O exchange followed by step-gas CO/Ar or CO/O2/Ar switches were used to quantify the contribution of lattice oxygen to the reaction. SSITKA-DRIFTS studies probed the formation of carbonates while validating the Mars–van Krevelen (MvK) mechanism. Scanning transmission electron microscopy-high-angle annular dark field imaging coupled with energy-dispersive spectroscopy proved that the elemental composition of dopants in the individual nanoparticle of ceria is less than their composition at a larger scale, allowing the assessment of the doping efficacy. Despite the similar structural features of the catalysts, a clear difference in the Olattice mobility was also found as well as its participation (as expressed with the α descriptor) in the reaction, following the order αCu > αCo> αMn > αZn. Kinetic studies showed that it is rather the pre-exponential (entropic) factor and not the lowering of activation energy that justifies the order of activity of the solids. DFT calculations showed that the adsorption of CO on the Cu-doped CeO2 surface is more favorable (−16.63 eV), followed by Co, Mn, Zn (−14.46, −4.90, and −4.24 eV, respectively), and pure CeO2 (−0.63 eV). Also, copper compensates almost three times more charge (0.37e −) compared to Co and Mn, ca. 0.13e − and 0.10e −, respectively, corroborating for its tendency to be reduced. Surface analysis (X-ray photoelectron spectroscopy), apart from the oxidation state of the elements, revealed a heteroatom–ceria surface interaction (Oa species) of different extents and of different populations of Oa species.

      Kyriakos N Papageridis, Nikolaos D Charisiou, Savvas Douvartzides, Victor Sebastian, Steven J Hinder, Mark A Baker, Ayesha A AlKhoori, Sara I AlKhoori, Kyriaki Polychronopoulou, Maria A Goula (2021)Continuous selective deoxygenation of palm oil for renewable diesel production over Ni catalysts supported on Al2O3 and La2O3–Al2O3, In: RSC advances11(15)pp. 8569-8584 Royal Society of Chemistry

      The present study provides, for the first time in the literature, a comparative assessment of the catalytic performance of Ni catalysts supported on γ-Al2O3 and γ-Al2O3 modified with La2O3, in a continuous flow trickle bed reactor, for the selective deoxygenation of palm oil. The catalysts were prepared via the wet impregnation method and were characterized, after calcination and/or reduction, by N2 adsorption/desorption, XRD, NH3-TPD, CO2-TPD, H2-TPR, H2-TPD, XPS and TEM, and after the time-on-stream tests, by TGA, TPO, Raman and TEM. Catalytic experiments were performed between 300–400 °C, at a constant pressure (30 bar) and different LHSV (1.2–3.6 h−1). The results show that the incorporation of La2O3 in the Al2O3 support increased the Ni surface atomic concentration (XPS), affected the nature and abundance of surface basicity (CO2-TPD), and despite leading to a drop in surface acidity (NH3-TPD), the Ni/LaAl catalyst presented a larger population of medium-strength acid sites. These characteristics helped promote the SDO process and prevented extended cracking and the formation of coke. Thus, higher triglyceride conversions and n-C15 to n-C18 hydrocarbon yields were achieved with the Ni/LaAl at lower reaction temperatures. Moreover, the Ni/LaAl catalyst was considerably more stable during 20 h of time-on-stream. Examination of the spent catalysts revealed that both carbon deposition and degree of graphitization of the surface coke, as well as, the extent of sintering were lower on the Ni/LaAl catalyst, explaining its excellent performance during time-on-stream.

      G.I Siakavelas, N.D Charisiou, S AlKhoori, A.A AlKhoori, V Sebastian, S.J Hinder, M.A Baker, I.V Yentekakis, K Polychronopoulou, M.A Goula (2021)Highly selective and stable nickel catalysts supported on ceria promoted with Sm2O3, Pr2O3 and MgO for the CO2 methanation reaction, In: Applied Catalysis. B, Environmental282 Elsevier B.V

      [Display omitted] •Microwave assisted sol gel method produces selective CO2 methanation Ni catalysts.•The incorporation of Sm3+ and Pr3+ into the CeO2 lattice generates basic positions.•Sm3+ and Pr3+ oxygen vacancies suppress the agglomeration of Ni sites.•Presence of Mg2+ increases basicity and prevents Ni sintering during reaction.•Ni on Pr-Ce highly active, selective and stable for CO2 methanation reaction. The present work reports on the investigation of the catalytic performance for the methanation of CO2 over Ni catalysts based on CeO2, and for the first time, of Ni catalysts supported on binary CeO2-based oxides, namely, Sm2O3-CeO2, Pr2O3-CeO2 and MgO-CeO2. The supports were obtained using the microwave assisted sol-gel method under reflux, while the catalysts were prepared by the wet impregnation method. For the investigation of the morphological, textural, structural and other intrinsic properties of the catalytic materials a variety of characterization techniques were used, i.e., Raman spectroscopy, XRD, N2 physisorption-desorption, CO2-TPD, H2-TPR, H2-TPD, XPS and TEM. Carbon deposition and sintering were investigated using TEM. It was shown that the addition of Sm3+ or Pr3+, incorporated into the lattice of CeO2, generated oxygen vacancies, but the Ni/Pr-Ce catalyst was found to possess more surface oxygen vacancies (e.g. Ce4+-Ov-Pr3+ entities). Moreover, modification of CeO2 using Sm3+ or Pr3+ restricted the agglomeration of nickel active sites and led to the genesis of Lewis basic positions. These characteristics improved the hydrogenation reaction at lower temperature. On the other hand, the addition of Mg2+ resulted at strong metal support interactions reinforcing the resistance of the Ni/Mg-Ce catalyst against sintering. Furthermore, the addition of Sm3+, Pr3+ and Mg2+ cations increased the overall basicity and the moderate adsorption sites and led to the formation of smaller Ni nano particles; these physico-chemical properties enhanced the CO2 methanation reaction. Finally, the activity experiments (WGHSV = 25,000 mL g−1 h−1, H2/CO2 = 4:1, T =350 °C) showed that at lower reaction temperature the Ni/Pr-Ce had the highest catalytic performance in terms of CO2 conversion (54.5%) and CH4 yield (54.5%) and selectivity (100%). The TOF values were found to follow the order Ni/Pr-Ce >> Ni/Mg-Ce > Ni/Sm-Ce > Ni/Ce.

      N.J Sutemire, M.V Rix, R.P Durman, M.A Baker, M.J Whiting (2021)Growth Anomalies in CVD Silicon Carbide Monofilaments for Metal Matrix Composites, In: Materialia101087 Elsevier B.V

      The industrial scale production of silicon carbide monofilaments by chemical vapour deposition (CVD) can be disrupted by growth anomalies that initiate filament fracture during its manufacture. The anomalies take the form of growth warts on the surface of the silicon carbide fibre. Complementary 3D imaging techniques, micro X-ray computed topography (XCT) and plasma focused ion beam scanning electron microscopy (PFIB-SEM), in combination with other materials characterisation techniques (Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analysis) have been used to investigate the nature and cause of the anomalies. Metallic tungsten particulates with an unusual dendritic morphology attached to the tungsten core were found to be the origin of the anomalies. Further investigation of the CVD system led to the observation of process-induced W oxide particulate agglomerates accumulating at the cleaning stage inlet to the reactor. These particulates became attached to tungsten wire in the cleaning stage of the CVD reactor and were rapidly reduced to elemental tungsten prior to entering the silicon carbide deposition chamber. Silicon carbide growth on the tungsten particulates results in the development of a wart-like morphology on the fibre surface. An understanding of this mechanism enabled minor modifications to reactor conditions, which prevented W oxide particulate formation and greatly reduced the occurrence of such growth anomalies. [Display omitted]

      Daniel Lamb, Stuart Irvine, CRAIG IAN UNDERWOOD, MARK ALAN BAKER, Simran Mardhani (2021)Thin Film Cadmium Telluride Solar cells on ultra-thin glass in Low Earth Orbit – 3 years of performance data on the AlSat-1N CubeSat Mission, In: Progress in Photovoltaics Wiley

      This paper details 3-years of cadmium telluride (CdTe) photovoltaic performance onboard the AlSat- 1N CubeSat in low earth orbit. These are the first CdTe solar cells to yield I-V measurements from space and help to strengthen the argument for further development of this technology for space application. The data has been collected over some 17,000 orbits by the CubeSat with the cells showing no signs of delamination, no deterioration in short circuit current or series resistance. The latter indicating that the aluminium-doped zinc oxide transparent front electrode performance remained stable over the duration. Effects of temperature on open circuit voltage (Voc) were observed with a calculated temperature coefficient for Voc of -0.19 %/⁰C. Light soaking effects were also observed to increase the Voc. The fill factor decreased over the duration of the mission with a major contribution being a decrease in shunt resistance of all 4 of the cells. The decrease in shunt resistance is speculated to result from gold diffusion from the rear contacts into the absorber and through to the front interface. This has likely resulted in the formation of a deep trap state within the CdTe and micro-shunts formed between the rear and front contact. Further development of this technology should therefore utilise more stable back contacting methodologies more commonly employed for terrestrial CdTe modules.

      A. T. Fry, M. Patel, D. Gorman, A. Farooqui, J. Wu, L Wright, MARK ALAN BAKER, J. F. Watts (2021)The Effect of Cracking of Thermally Grown Oxide Layers in Thermal Barrier Coatings Examined Using FIB Tomography and Inverse Modelling, In: Oxidation of metals96pp. 157-168

      As a thermal barrier coating (TBC) is exposed to elevated temperatures, oxidation proceeds at the interface between the top coat of the TBC and the bond coat/substrate. This aluminium-rich layer, in the case of the TBC studied in this work, produces an alumina thermally grown oxide (TGO) at the interface. This layer continues to grow as the exposure time increases and is prone to cracking. Failure of the TGO creates a debond which will affect the heat transfer through the system and lead to localised overheating. Samples of an IN6203DS substrate with a CoNiCrAlY bond coat and YSZ top coat have been thermally aged and a selection of these used to determine the morphology of cracking within the TGO. This quantitative information has subsequently been used to determine the effect on the heat transfer performance of the TBC system using a process of inverse modelling.

      G.I. Siakavelas, N.D. Charisiou, AA AlKhoori, V. Sebastian, S.J. Hinder, MARK ALAN BAKER, I.V. Yentekakis, K. Polychronopoulou, M.A. Goula (2022)Cerium oxide catalysts for oxidative coupling of methane reaction: Effect of lithium, samarium and lanthanum dopants, In: Journal of Environmental Chemical Engineering10(2)107259 Elsevier

      The work presented herein reports on the oxidative coupling of methane (OCM) performance of a series of Li-free and Li-doped CeO2 and CeO2 modified with Sm3+ and La3+ catalysts. The supporting materials (Ce, Sm-Ce and La-Sm-Ce metal oxides) were synthesized using the microwave assisted sol-gel method in order to achieve nanophase complex materials with increased particle surface energy and reactivity. Lithium ions were added, using the wet impregnation technique, in order to further improve the physicochemical characteristics and reinforce the activity and selectivity, in terms of C2H6 and C2H4 production. All materials were characterized using N2 adsorption-desorption, XRD, Raman spectroscopy, CO2-TPD, H2-TPR, SEM and XPS. We showed that the addition of lithium species changed the reaction pathway and drastically enhanced the production of ethylene and ethane, mainly for the promoted catalysts (Li/Sm-Ce and Li/La-Sm-Ce). In particular, the presence and the synergy between the electrophilic oxygen species (peroxide and superoxide), population of oxygen vacancy sites and the surface moderate basic sites determined the reaction pathway and the desirable product distribution.

      JM Ferreira, JL Rossi, MA Baker, SJ Hinder, I Costa (2014)Deposition and Characterization of a New Mixed Organic/Inorganic Cerium Containing Coating for the Corrosion Protection of Eletrogalvanized Steel, In: INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE9(4)pp. 1827-1839 ESG

      Protective coatings have been deposited on electrogalvanized steel by immersion in solutions containing 2-Butyne-1.4-diol propoxylate (CHO), 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 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 CeO and CeO which improved the corrosion resistance of the substrate and showed a superior corrosion resistance to that provided by a chromate conversion coating.

      D Barber, S Jenkins, M Whiting, M Baker (2004)Interfacial studies of double carbonate thermionic oxide cathodes over accelerated operational life, In: IVESC2004: THE 5TH INTERNATIONAL VACUUM ELECTRON SOURCES CONFERENCE PROCEEDINGSpp. 108-109
      K Boxshall, MH Wu, Z Cui, ZF Cui, JF Watts, MA Baker (2006)Simple surface treatments to modify protein adsorption and cell attachment properties within a poly(dimethylsiloxane) micro-bioreactor, In: SURFACE AND INTERFACE ANALYSIS38(4)pp. 198-201
      AM Saliba-Silva, MA Baker, HG De Melo, I Costa (2001)Corrosion protection of sintered NdFeB magnets by phosphating, In: Computational and Experimental Methods6pp. 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 (Φ) 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.

      DK Barber, SN Jenkins, MJ Whiting, MA Baker (2004)Investigation of the nickel/emissive oxide interface in thermionic emitters, In: SURFACE AND INTERFACE ANALYSIS36(8)pp. 1190-1194
      MA Baker, W Gissler, S Klose, M Trampert, F Weber (2000)Morphologies and corrosion properties of PVD Zn-Al coatings, In: SURFACE & COATINGS TECHNOLOGY125(1-3)pp. 207-211
      MF Stroosnijder, JD Sunderkotter, MJ Cristobal, H Jenett, K Isenbugel, MA Baker (1996)The influence of yttrium ion implantation on the oxidation behaviour of powder metallurgically produced chromium, In: SURFACE & COATINGS TECHNOLOGY83(1-3)pp. 205-211
      R Gilmore, MA Baker, PN Gibson, W Gissler (1999)Comparative investigation of multilayer TiB2/C and co-sputtered TiB2-C coatings for low-friction applications, In: SURFACE & COATINGS TECHNOLOGY116pp. 1127-1132
      MA Monclus, MA Baker, C Rebhoz, V Stolojan, PN Gibson, A Leyland, A Matthews (2006)Nanostructural studies of PVD TiAlB coatings, In: SURFACE AND INTERFACE ANALYSIS38(4)pp. 731-735
      PN Gibson, MA Baker, ED Dunlop, ME Ozsan, D Lincot, M Froment, G Agostinelli (2001)Correlation of chemical and structural parameters with non-uniform cell performance in CdS/CdTe solar cells, In: THIN SOLID FILMS387(1-2)pp. 92-96
      C Lenardi, MA Baker, V Briois, L Nobili, P Piseri, W Gissler (1999)Properties of amorphous a-CH(: N) films synthesized by direct ion beam deposition and plasma-assisted chemical vapour deposition, In: DIAMOND AND RELATED MATERIALS8(2-5)pp. 595-600
      MA Baker, R Gilmore, PN Gibson, W Gissler (1997)The microstructure and properties of Ti-B-C coatings for tribological applications, In: I Olefjord, L Nyborg, D Briggs (eds.), ECASIA 97: 7TH EUROPEAN CONFERENCE ON APPLICATIONS OF SURFACE AND INTERFACE ANALYSISpp. 1127-1130
      DK Barber, SN Jenkins, MJ Whiting, MA Baker (2005)Analytical interfacial studies of double carbonate thermionic oxide cathodes over accelerated operational life, In: APPLIED SURFACE SCIENCE251(1-4)pp. 42-49
      R Goller, P Torri, MA Baker, R Gilmore, W Gissler (1999)The deposition of low-friction TiN-MoSx hard coatings by a combined are evaporation and magnetron sputter process, In: SURFACE & COATINGS TECHNOLOGY120pp. 453-457
      C Lenardi, MA Baker, V Briois, GC Lecis, P Piseri, W Gissler (2000)Near-edge X-ray absorption fine structure study of carbon nitride films, In: SURFACE & COATINGS TECHNOLOGY125(1-3)pp. 317-321
      C Rebholz, MA Monclus, MA Baker, PH Mayrhofer, PN Gibson, A Leyland, A Matthews (2007)Hard and superhard TiAlBN coatings deposited by twin electron-beam evaporation, In: SURFACE & COATINGS TECHNOLOGY201(13)pp. 6078-6083
      MA Monclus, MA Baker, C Tsotsos, A Davison, A Leyland, A Matthews (2005)Investigation of the nanostructure and post-coat thermal treatment of wear-resistant PVD CrTiCuBN coatings, In: SURFACE & COATINGS TECHNOLOGY200(1-4)pp. 310-314
      J Li, Z Cui, MA Baker (2004)A study of the surface chemistry, morphology and wear of silicon based MEMS, In: SURFACE AND INTERFACE ANALYSIS36(8)pp. 1254-1258
      MA Baker (2007)Advanced characterisation of nanocomposite coatings, In: SURFACE & COATINGS TECHNOLOGY201(13)pp. 6105-6111
      MA Baker (1995)Encyclopedia of Analytical Science: Sam-Sur, In: A Townshend (eds.), Encyclopedia of Analytical Science: Sam-Sur
      MA Baker, S Klose, C Rebholz, A Leyland, A Matthews (2002)Evaluating the microstructure and performance of nanocomposite PVD TiAlBN coatings, In: SURFACE & COATINGS TECHNOLOGY151pp. 338-343
      P Colpo, G Ceccone, P Sauvageot, M Baker, F Rossi (2000)Characterization of zirconia coatings deposited by inductively coupled plasma assisted chemical vapor deposition, In: JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS18(4)pp. 1096-1101
      W Gissler, MA Baker, J Haupt, PN Gibson, R Gilmore, TP Mollart (1997)Phase composition and tribological behavior of titanium boron nitride coatings, In: DIAMOND FILMS AND TECHNOLOGY7(3)pp. 165-180 MYU K K
      MA Baker (1994)Materials Science and Technology, Characterization of Materials, In: E Lifshin, RW Cahn, P Haasen, EJ Kramer (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.

      AM Saliba-Silva, HG de Melo, MA Baker, AM Brown, I Costa (2003)Characterization of sintered NdFeB magnets after phosphating in alkaline and acidic environments, In: L Salgado, FA Filho (eds.), ADVANCED POWDER TECHNOLOGY III416-4pp. 54-59
      Nikolaos Charisiou, Georgios Siakavelas, Victor Sebastian , STEVEN JOHN HINDER, MARK ALAN BAKER, Vagelis Papadakis, Wen Wang , Kyriaki Polychronopoulou, Maria Goula (2020)Structural Investigation of the Carbon Deposits on Ni/Al2O3 Catalyst Modified by CaO-MgO for the Biogas Dry Reforming Reaction

      Ni/Al2O3 and Ni/CaO-MgO-Al2O3 catalysts were investigated for the biogas dry reforming reaction using CH4/CO2 mixtures with minimal dilution. Stability tests were conducted between 600 and 800 oC 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/Al2O3 sample (650–750°C). Stability tests confirmed that the Ni/CaO-MgO-Al2O3 catalyst deactivates at a more gradual rate and is more active and selective in comparison to the Ni/Al2O3 for all temperatures. The Ni/CaO-MgO-Al2O3 exhibits good durability in terms of conversion and selectivity, whereas the Ni/Al2O3 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 CaO-MgO enhances catalytic performance 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.

      MA Baker, P Tsakiropoulos, AF Norman (1997)Porosity and oxide distribution in spray-formed Al-5Cr-1.5Zr alloy, In: JOURNAL OF MATERIALS SYNTHESIS AND PROCESSING5(1)pp. 105-110
      J Li, Z Cui, MA Baker (2004)Surface characterisation of silicon based MEMS, In: CHEMICAL RESEARCH IN CHINESE UNIVERSITIES20(4)pp. 407-410
      B Bozzini, MA Baker, PL Cavallotti, E Cerri, C Lenardi (2000)Electrodeposition of ZnTe for photovoltaic cells, In: THIN SOLID FILMS361pp. 388-395
      MA Baker, P Hammer (1997)A study of the chemical bonding and microstructure of ion beam-deposited CNx films including an XPS C 1s peak simulation, In: SURFACE AND INTERFACE ANALYSIS25(9)pp. 629-642 WILEY-BLACKWELL
      MA Baker, P Hammer, C Lenardi, J Haupt, W Gissler (1997)Low-temperature sputter deposition and characterisation of carbon nitride films, In: SURFACE & COATINGS TECHNOLOGY97(1-3)pp. 544-551
      MA Baker, C Rebholz, A Leyland, A Matthews (2002)Electron spectroscopic studies of nanocomposite PVD TiAlBN coatings, In: VACUUM67(3-4)pp. 471-476
      R Gilmore, MA Baker, PN Gibson, W Gissler, M Stoiber, P Losbichler, C Mitterer (1998)Low-friction TiN-MoS2 coatings produced by dc magnetron co-deposition, In: SURFACE & COATINGS TECHNOLOGY108(1-3)pp. 345-351