Publications
116 results found
Fernando NK, Cairns AB, Murray CA, et al., 2021, Structural and electronic effects of X-ray irradiation on prototypical [M(COD)Cl](2) catalysts, The Journal of Physical Chemistry A: Isolated Molecules, Clusters, Radicals, and Ions; Environmental Chemistry, Geochemistry, and Astrochemistry; Theory, Vol: 125, Pages: 7473-7488, ISSN: 1089-5639
X-ray characterization techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray-induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever-increasing brilliance are developed. In this paper, systematic studies of X-ray–matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to radiation in X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. From these complementary techniques, changes to structure, chemical environments, and electronic structure are observed as a function of X-ray exposure, allowing comparisons of stability to be made between the two catalysts. Radiation dose is estimated using recent developments to the RADDOSE-3D software for small molecules and applied to powder XRD and XPS experiments. Further insights into the electronic structure of the catalysts and changes occurring as a result of the irradiation are drawn from density functional theory (DFT). The techniques combined here offer much needed insight into the X-ray-induced effects in transition-metal catalysts and, consequently, their intrinsic stabilities. There is enormous potential to extend the application of these methods to other small molecular systems of scientific or industrial relevance.
Buschges MI, Hoffmann RC, Regoutz A, et al., 2021, Atomic Layer Deposition of Ternary Indium/Tin/Aluminum Oxide Thin Films, Their Characterization and Transistor Performance under Illumination., CHEMISTRY-A EUROPEAN JOURNAL, Vol: 27, Pages: 9791-9800, ISSN: 0947-6539
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- Citations: 2
Fernando N, Cairns AB, Murray CA, et al., 2021, Structural and Electronic Effects of X-ray Irradiation on Prototypical [M(COD)Cl]2 Catalysts
<jats:p>X-ray characterisation techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever increasing brilliance are developed. In this paper, systematic studies of X-ray-matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to radiation in X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. From these complimentary techniques, changes to structure, chemical environments, and electronic structure are observed as a function of X-ray exposure, allowing comparisons of stability to be made between the two catalysts. Radiation dose is estimated using recent developments to the RADDOSE-3D software for small molecules and applied to powder XRD and XPS experiments. Further insights into the electronic structure of the catalysts and changes occurring as a result of the irradiation are drawn from density functional theory (DFT). The techniques combined here offer much needed insight into the X-ray induced effects in transition metal catalysts and consequently, their intrinsic stabilities. There is enormous potential to extend the application of these methods to other small molecular systems of scientific or industrial relevance.</jats:p>
Fernando N, Cairns AB, Murray CA, et al., 2021, Structural and Electronic Effects of X-ray Irradiation on Prototypical [M(COD)Cl]2 Catalysts
<jats:p>X-ray characterisation techniques are invaluable for probing material characteristics and properties, and have been instrumental in discoveries across materials research. However, there is a current lack of understanding of how X-ray induced effects manifest in small molecular crystals. This is of particular concern as new X-ray sources with ever increasing brilliance are developed. In this paper, systematic studies of X-ray-matter interactions are reported on two industrially important catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to radiation in X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiments. From these complimentary techniques, changes to structure, chemical environments, and electronic structure are observed as a function of X-ray exposure, allowing comparisons of stability to be made between the two catalysts. Radiation dose is estimated using recent developments to the RADDOSE-3D software for small molecules and applied to powder XRD and XPS experiments. Further insights into the electronic structure of the catalysts and changes occurring as a result of the irradiation are drawn from density functional theory (DFT). The techniques combined here offer much needed insight into the X-ray induced effects in transition metal catalysts and consequently, their intrinsic stabilities. There is enormous potential to extend the application of these methods to other small molecular systems of scientific or industrial relevance.</jats:p>
Kalha C, Fernando NK, Bhatt P, et al., 2021, Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 2020, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 33, ISSN: 0953-8984
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- Citations: 47
Kalha C, Bichelmaier S, Fernando NK, et al., 2021, Thermal and oxidation stability of TixW1−x diffusion barriers investigated by soft and hard x-ray photoelectron spectroscopy, Journal of Applied Physics, Vol: 129, Pages: 1-15, ISSN: 0021-8979
The binary alloy of titanium-tungsten (TiW) is an established diffusion barrier in high-power semiconductor devices, owing to its ability to suppress the diffusion of copper from the metallization scheme into the surrounding silicon substructure. However, little is known about the response of TiW to high-temperature events or its behavior when exposed to air. Here, a combined soft and hard x-ray photoelectron spectroscopy (XPS) characterization approach is used to study the influence of post-deposition annealing and titanium concentration on the oxidation behavior of a 300 nm-thick TiW film. The combination of both XPS techniques allows for the assessment of the chemical state and elemental composition across the surface and bulk of the TiW layer. The findings show that in response to high-temperature annealing, titanium segregates out of the mixed metal system and upwardly migrates, accumulating at the TiW/air interface. Titanium shows remarkably rapid diffusion under relatively short annealing timescales, and the extent of titanium surface enrichment is increased through longer annealing periods or by increasing the bulk titanium concentration. Surface titanium enrichment enhances the extent of oxidation both at the surface and in the bulk of the alloy due to the strong gettering ability of titanium. Quantification of the soft x-ray photoelectron spectra highlights the formation of three tungsten oxidation environments, attributed to WO
Moss B, Wang Q, Butler K, et al., 2021, Linking in situ charge accumulation to electronic structure in doped SrTiO3 reveals design principles for hydrogen-evolving photocatalysts, Nature Materials, Vol: 20, Pages: 511-517, ISSN: 1476-1122
Recently, high solar-to-hydrogen efficiencies were demonstrated using La and Rh co-doped SrTiO3 (La,Rh:SrTiO3) incorporated into a low-cost and scalable Z-scheme device, known as a photocatalyst sheet. However, the unique properties that enable La,Rh:SrTiO3 to support this impressive performance are not fully understood. Combining in situ spectroelectrochemical measurements with density functional theory and photoelectron spectroscopy produces a depletion model of Rh:SrTiO3 and La,Rh:SrTiO3 photocatalyst sheets. This reveals remarkable properties, such as deep flatband potentials (+2 V versus the reversible hydrogen electrode) and a Rh oxidation state dependent reorganization of the electronic structure, involving the loss of a vacant Rh 4d mid-gap state. This reorganization enables Rh:SrTiO3 to be reduced by co-doping without compromising the p-type character. In situ time-resolved spectroscopies show that the electronic structure reorganization induced by Rh reduction controls the electron lifetime in photocatalyst sheets. In Rh:SrTiO3, enhanced lifetimes can only be obtained at negative applied potentials, where the complete Z-scheme operates inefficiently. La co-doping fixes Rh in the 3+ state, which results in long-lived photogenerated electrons even at very positive potentials (+1 V versus the reversible hydrogen electrode), in which both components of the complete device operate effectively. This understanding of the role of co-dopants provides a new insight into the design principles for water-splitting devices based on bandgap-engineered metal oxides.
Hartley P, Egdell RG, Zhang KHL, et al., 2021, Experimental and Theoretical Study of the Electronic Structures of Lanthanide Indium Perovskites LnInO<sub>3</sub>, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 125, Pages: 6387-6400, ISSN: 1932-7447
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- Citations: 10
Regoutz A, Wolinska MS, Fernando NK, et al., 2021, A combined density functional theory and x-ray photoelectron spectroscopy study of the aromatic amino acids, Electronic Structure, Vol: 2, Pages: 1-11, ISSN: 2516-1075
Amino acids are essential to all life. However, our understanding of some aspects of their intrinsic structure, molecular chemistry, and electronic structure is still limited. In particular the nature of amino acids in their crystalline form, often essential to biological and medical processes, faces a lack of knowledge both from experimental and theoretical approaches. An important experimental technique that has provided a multitude of crucial insights into the chemistry and electronic structure of materials is x-ray photoelectron spectroscopy. While the interpretation of spectra of simple bulk inorganic materials is often routine, interpreting core level spectra of complex molecular systems is complicated to impossible without the help of theory. We have previously demonstrated the ability of density functional theory to calculate binding energies of simple amino acids, using ΔSCF implemented in a systematic basis set for both gas phase (multiwavelets) and solid state (plane waves) calculations. In this study, we use the same approach to successfully predict and rationalise the experimental core level spectra of phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), and histidine (His) and gain an in-depth understanding of their chemistry and electronic structure within the broader context of more than 20 related molecular systems. The insights gained from this study provide significant information on the nature of the aromatic amino acids and their conjugated side chains.
Swallow JEN, Palgrave RG, Murgatroyd PAE, et al., 2021, Indium Gallium Oxide Alloys: Electronic Structure, Optical Gap, Surface Space Charge, and Chemical Trends within Common-Cation Semiconductors, ACS APPLIED MATERIALS & INTERFACES, Vol: 13, Pages: 2807-2819, ISSN: 1944-8244
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- Citations: 37
Dutta G, Regoutz A, Moschou D, 2020, Enzyme-assisted glucose quantification for a painless Lab-on-PCB patch implementation, BIOSENSORS & BIOELECTRONICS, Vol: 167, ISSN: 0956-5663
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- Citations: 14
Isakov I, Faber H, Mottram AD, et al., 2020, Quantum Confinement and Thickness-Dependent Electron Transport in Solution-Processed In<sub>2</sub>O<sub>3</sub>Transistors, ADVANCED ELECTRONIC MATERIALS, Vol: 6, ISSN: 2199-160X
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- Citations: 12
Mielewczyk-Gryn A, Wachowski S, Witkowska A, et al., 2020, Antimony substituted lanthanum orthoniobate proton conductor - Structure and electronic properties, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Vol: 103, Pages: 6575-6585, ISSN: 0002-7820
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- Citations: 4
Papamatthaiou S, Zupancic U, Kalha C, et al., 2020, Ultra stable, inkjet-printed pseudo reference electrodes for lab-on-chip integrated electrochemical biosensors, SCIENTIFIC REPORTS, Vol: 10, ISSN: 2045-2322
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- Citations: 8
Swallow JEN, Vorwerk C, Mazzolini P, et al., 2020, Influence of Polymorphism on the Electronic Structure of Ga<sub>2</sub>O<sub>3</sub>, CHEMISTRY OF MATERIALS, Vol: 32, Pages: 8460-8470, ISSN: 0897-4756
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- Citations: 30
Minh HT, Malik AM, Duerrschnabel M, et al., 2020, Experimental and theoretical investigation of the chemical exfoliation of Cr-based MAX phase particles, DALTON TRANSACTIONS, Vol: 49, Pages: 12215-12221, ISSN: 1477-9226
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- Citations: 9
Berens J, Bichelmaier S, Fernando NK, et al., 2020, Effects of nitridation on SiC/SiO(2)structures studied by hard X-ray photoelectron spectroscopy, The Journal of High Energy Physics, Vol: 2, Pages: 1-11, ISSN: 1029-8479
SiC is set to enable a new era in power electronics impacting a wide range of energy technologies, from electric vehicles to renewable energy. Its physical characteristics outperform silicon in many aspects, including band gap, breakdown field, and thermal conductivity. The main challenge for further development of SiC-based power semiconductor devices is the quality of the interface between SiC and its native dielectric SiO2. High temperature nitridation processes can improve the interface quality and ultimately the device performance immensely, but the underlying chemical processes are still poorly understood. Here, we present an energy-dependent hard x-ray photoelectron spectroscopy (HAXPES) study probing non-destructively SiC and SiO2 and their interface in device stacks treated in varying atmospheres. We successfully combine laboratory- and synchrotron-based HAXPES to provide unique insights into the chemistry of interface defects and their passivation through nitridation processes.
Leung AHM, García-Trenco A, Phanopoulos A, et al., 2020, Cu/M:ZnO (M = Mg, Al, Cu) colloidal nanocatalysts for the solution hydrogenation of carbon dioxide to methanol, Journal of Materials Chemistry A, Vol: 8, Pages: 11282-11291, ISSN: 2050-7488
Doped-ZnO nanoparticles, capped with dioctylphosphinate ligands, are synthesised by the controlled hydrolysis of a mixture of organometallic precursors. Substitutional doping of the wurtzite ZnO nanoparticles with 5 mol% Mg(II), Al(III) and Cu(I) is achieved by the addition of sub-stoichiometric amounts of the appropriate dopant [(n-butyl)(sec-butyl)magnesium, triethylaluminium or mesitylcopper] to diethylzinc in the precursor mixture. After hydrolysis, the resulting colloidal nanoparticles (sizes of 2–3 nm) are characterised by powder X-ray crystallography, transmission electron microscopy, inductively-coupled plasma optical emission spectrometry and X-ray photoelectron spectroscopy. A solution of the doped-ZnO nanoparticles and colloidal Cu(0) nanoparticles [M:ZnO : Cu = 1 : 1] are applied as catalysts for the hydrogenation of CO2 to methanol in a liquid-phase continuous flow stirred tank reactor [210 °C, 50 bar, CO2 : H2 = 1 : 3, 150 mL min−1, mesitylene, 20 h]. All the catalyst systems display higher rates of methanol production and better stability than a benchmark heterogeneous catalyst, Cu–ZnO–Al2O3 [480 μmol mmolmetal−1 h−1], with approximately twice the activity for the Al(III)-doped nanocatalyst. Despite outperforming the benchmark catalyst, Mg(II) doping is detrimental towards methanol production in comparison to undoped ZnO. X-Ray photoelectron spectroscopy and transmission electron microscopy analysis of the most active post-catalysis samples implicate the migration of Al(III) to the catalyst surface, and this surface enrichment is proposed to facilitate stabilisation of the catalytic ZnO/Cu interfaces.
Doiron B, Gusken NA, Lauri A, et al., 2020, Hot Carrier Optoelectronics with Titanium Nitride, Lasers and Electro-Optics Society Annual Meeting-LEOS, ISSN: 1092-8081
© 2020 OSA. Titanium oxynitride enables a range of plasmonic and optoelectronic functionality using long-lived photo-generated hot carriers. We explore the time scale of hot carriers in TiN and their use in photochemical reduction and Schottky detectors.
Deacy AC, Kilpatrick AFR, Regoutz A, et al., 2020, Understanding metal synergy in heterodinuclear catalysts for the copolymerization of CO<sub>2</sub> and epoxides, NATURE CHEMISTRY, Vol: 12, Pages: 372-+, ISSN: 1755-4330
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- Citations: 163
Williamson BAD, Featherstone TJ, Sathasivam SS, et al., 2020, Resonant Ta Doping for Enhanced Mobility in Transparent Conducting SnO<sub>2</sub>, CHEMISTRY OF MATERIALS, Vol: 32, Pages: 1964-1973, ISSN: 0897-4756
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- Citations: 35
Pi JM, Stella M, Fernando NK, et al., 2020, Predicting core level photoelectron spectra of amino acids using density functional theory., Journal of Physical Chemistry Letters, Vol: 11, Pages: 2256-2262, ISSN: 1948-7185
Core level photoelectron spectroscopy is a widely used technique to study amino acids. Interpretation of the individual contributions from functional groups and their local chemical environments to overall spectra requires both high-resolution reference spectra and theoretical insights, for example, from density functional theory calculations. This is a particular challenge for crystalline amino acids due to the lack of experimental data and the limitation of previous calculations to gas phase molecules. Here, a state of the art multiresolution approach is used for high-precision gas phase calculations and to validate core hole pseudopotentials for plane-wave calculations. This powerful combination of complementary numerical techniques provides a framework for accurate ΔSCF calculations for molecules and solids in systematic basis sets. It is used to successfully predict C and O 1s core level spectra of glycine, alanine, and serine and identify chemical state contributions to experimental spectra of crystalline amino acids.
Bigi C, Tang Z, Pierantozzi GM, et al., 2020, Distinct behavior of localized and delocalized carriers in anatase TiO<sub>2</sub> (001) during reaction with O<sub>2</sub>, PHYSICAL REVIEW MATERIALS, Vol: 4, ISSN: 2475-9953
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- Citations: 22
Swallow JEN, Williamson BAD, Sathasivam S, et al., 2020, Resonant doping for high mobility transparent conductors: the case of Mo-doped In<sub>2</sub>O<sub>3</sub>, MATERIALS HORIZONS, Vol: 7, Pages: 236-243, ISSN: 2051-6347
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- Citations: 50
Gusken NA, Lauri A, Li Y, et al., 2020, IR hot carrier based photodetection in titanium nitride oxide thin film-Si junctions, MRS Advances, Vol: 5, Pages: 1843-1850, ISSN: 2059-8521
Hot carrier based methods constitute a valuable approach for efficient and silicon compatible sub-bandgap photodetection. Although, hot electron excitation and transfer have been studied extensively on traditional materials such as Au and Ti, reports on alternative materials such as titanium nitride (TiN) are rare. Here, we perform hot hole photodetection measurements on a p-Si/metal thin film junction using Ti, Au and TiN. This material is of interest as it constitutes a refractory alternative to Au which is an important property for plasmonic applications where high field intensities can occur. In contrast to Au, a TiN/Si junction does not suffer from metal diffusion into the Si, which eases the integration with current Si-fabrication techniques. This work shows that a backside illuminated p-Si/TiN system can be used for efficient hot hole extraction in the IR, allowing for a responsivity of 1 mA/W at an excitation wavelength of 1250 nm and at zero bias. Via a comparison between TiN and other commonly used materials such as Au, the origin of this comparably high photoresponse can be traced back to be directly linked to a thin TiO2-x interfacial layer allowing for a distinct hot-hole transfer mechanism. Moreover, the fabrication of TiN nanodisk arrays is demonstrated which bears great promise to further boost the device efficiency.
Hankin A, Bedoya-Lora FE, Alexander JC, et al., 2019, Flat band potential determination: avoiding the pitfalls, Journal of Materials Chemistry A, Vol: 7, Pages: 26162-26176, ISSN: 2050-7488
The flat band potential is one of the key characteristics of photoelectrode performance. However, its determination on nanostructured materials is associated with considerable uncertainty. The complexity, applicability and pitfalls associated with the four most common experimental techniques used for evaluating flat band potentials, are illustrated using nanostructured synthetic hematite (α-Fe2O3) in strongly alkaline solutions as a case study. The motivation for this study was the large variance in flat band potential values reported for synthetic hematite electrodes that could not be justified by differences in experimental conditions, or by differences in their charge carrier densities. We demonstrate through theory and experiments that different flat band potential determination methods can yield widely different results, so could mislead the analysis of the photoelectrode performance. We have examined: (a) application of the Mott–Schottky (MS) equation to the interfacial capacitance, determined by electrochemical impedance spectroscopy as a function of electrode potential and potential perturbation frequency; (b) Gärtner–Butler (GB) analysis of the square of the photocurrent as a function of electrode potential; (c) determination of the potential of transition between cathodic and anodic photocurrents during slow potentiodynamic scans under chopped illumination (CI); (d) open circuit electrode potential (OCP) under high irradiance. Methods GB, CI and OCP were explored in absence and presence of H2O2 as hole scavenger. The CI method was found to give reproducible and the most accurate results on hematite but our overall conclusion and recommendation is that multiple methods should be employed for verifying a reported flat band potential.
Shankar R, Sachs M, Francas L, et al., 2019, Porous boron nitride for combined CO2 capture and photoreduction, Journal of Materials Chemistry A, Vol: 7, Pages: 23931-23940, ISSN: 2050-7488
Porous and amorphous materials are typically not employed for photocatalytic purposes, like CO2 photoreduction, as their high number of defects can lead to low charge mobility and favour bulk electron–hole recombination. Yet, with a disordered nature can come porosity, which in turn promotes catalyst/reactant interactions and fast charge transfer to reactants. Here, we demonstrate that moving from h-BN, a well-known crystalline insulator, to amorphous BN, we create a semiconductor, which is able to photoreduce CO2 in the gas/solid phase, under both UV-vis and pure visible light and ambient conditions, without the need for cocatalysts. The material selectively produces CO and maintains its photocatalytic stability over several catalytic cycles. The performance of this un-optimized material is on par with that of TiO2, the benchmark in the field. For the first time, we map out experimentally the band edges of porous BN on the absolute energy scale vs. vacuum to provide fundamental insight into the reaction mechanism. Owing to the chemical and structural tunability of porous BN, these findings highlight the potential of porous BN-based structures for photocatalysis particularly solar fuel production.
Mielewczyk-Gryn A, Wachowski S, Przesniak-Welenc M, et al., 2019, Water uptake analysis of acceptor-doped lanthanum orthoniobates, Journal of Thermal Analysis and Calorimetry: an international forum for thermal studies, Vol: 138, Pages: 225-232, ISSN: 1588-2926
In this work, lanthanum orthoniobates doped with either antimony, calcium, or both have been synthesized and studied. The water uptake of the investigated materials has been analyzed by means of thermogravimetric studies. The results show the difference between the thermodynamics of hydration between the lanthanum orthoniobate system and other proton conducting ceramics. The relation between the water uptake and effective acceptor doping for the investigated system has been found, and the energetics of the water uptake relation are discussed.
Mezzavilla S, Katayama Y, Rao R, et al., 2019, Activity-or Lack Thereof-of RuO2-Based Electrodes in the Electrocatalytic Reduction of CO2, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 123, Pages: 17765-17773, ISSN: 1932-7447
Wahila MJ, Paez G, Singh CN, et al., 2019, Evidence of a second-order Peierls-driven metal-insulator transition in crystalline NbO<sub>2</sub>, PHYSICAL REVIEW MATERIALS, Vol: 3, ISSN: 2475-9953
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- Citations: 18
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