B16-Test Beamline
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Diamond Proposal Number(s):
[6092]
Abstract: The shape and strain field of a needle domain in a barium titanate single crystal are modelled using a distribution of dislocations and line charges. The arrangement of these dislocations and charges is a result of the balance of modified Peach-Koehler forces acting among the dislocations and a lattice friction assumed to act at each dislocation site. Based on measurements of needle shape by synchrotron X-ray diffraction, dislocation pile-up theory is used to compute the distribution of discrete dislocations along the needle and hence estimate the lattice friction. It is found that the lattice friction in this model is proportional to the opening angle of a wedge-shape needle domain and consistent with the observed magnitude of stress required to mobilize needle domains. The microstrain distribution around an a-a needle domain tip, obtained from X-ray diffraction measurement, is further used to test the dislocation model, with a similar pattern and magnitude of strains identified in the model and the experiment.
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May 2023
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I22-Small angle scattering & Diffraction
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Abstract: In this thesis, we report the ability to fabricate hydrogels using low molecular weight gelators (LMWGs) and the subsequent characterisation of their mechanical properties over a variety of different length scales. These materials have been investigated due to their potential use in a wide range of biomedical applications including drug delivery, tissue engineering, cell culture and wound healing.
We describe the localised gelation of LMWGs on electrode surfaces via electrochemically generated pH gradients. The electrofabrication of hydrogels on electrode surfaces has shown great potential in the field of biomedicine, with applications ranging from antimicrobial wound dressings, tissue engineering scaffolds and biomimetic materials.
First, we describe the largest reported di- and tri-peptide-based hydrogels on electrode surfaces via the electrochemical oxidation of hydroquinone. Expanding upon previous work which focuses on the fabrication of hydrogels on the nanometre to millimetre scale, we deposit hydrogels around 3 cm3 in size. Furthermore, we demonstrate that there is an upper limit to how large the hydrogels can grow which is determined by the size of the pH gradient from the electrode surface. To grow hydrogels of this size, much longer deposition times of two to five hours are required than in previous reports. When the gelator/hydroquinone solution is left exposed to the open atmosphere for this amount of time, the hydroquinone in solution oxidises to benzoquinone/quinhydrone before it can be consumed electrochemically. This inhibits the electrochemical reaction and reduces gelation efficiency. To prevent this, we build a system that can perform the fabrication process under an inert nitrogen atmosphere. Using this system, we show how the choice of gelator affects the mechanical properties of the hydrogel and the resulting material phenomena that cause these changes. As well as this, we show how this approach can be used to grow multi-layered hydrogels, with each layer presenting different chemical and mechanical properties.
Secondly, we report the first known example of electrodeposition for a LMWG molecule using an electrochemically generated basic pH gradient at electrode surfaces. This approach has previously been used to fabricate hydrogels of the biopolymer chitosan using the galvanostatic reduction of hydrogen peroxide. During the electrochemical reduction of hydrogen peroxide, hydroxide ions are produced. As a result, a basic pH zone is generated at the electrode, triggering solutions of chitosan to form immobilised hydrogels on the electrode surface. Using this approach, we show how electrodeposition at high pH can be applied to our LMWG system.
We then show that we can electrochemically form hydrogels at high pH, with the gel properties being greatly improved by the addition and increased concentration of hydrogen peroxide. Following from this, we then show the simultaneous formation of two low molecular weight hydrogels at acidic and basic pH extremes. To achieve this, we couple the electrochemical reduction of hydrogen peroxide and the electrochemical oxidation of hydroquinone described in the previous chapter.
Finally, we report the electrodeposition of five carbazole-protected amino acid hydrogels on electrode surfaces via the electrochemical oxidation of hydroquinone. As well as this, we report the full to partial electropolymerisation of the pre-assembled hydrogels in perchloric acid. For the less bulky carbazole-protected amino acids, the full collapse of the hydrogel to form electrochromic polymers on the electrode surface is achieved. However, for the bulkier gelators, little to no evidence of polymerisation occurs. We believe this is due to the bulky side chain on the gelator backbone preventing the molecular reorganization required for polymerization to occur.
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May 2023
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Open Access
Abstract: A photon carrying one unit of angular momentum can change the spin angular momentum of a magnetic system with one unit (ΔMs = ±1) at most. This implies that a two-photon scattering process can manipulate the spin angular momentum of the magnetic system with a maximum of two units. Herein we describe a triple-magnon excitation in α-Fe2O3, which contradicts this conventional wisdom that only 1- and 2-magnon excitations are possible in a resonant inelastic X-ray scattering experiment. We observe an excitation at exactly three times the magnon energy, along with additional excitations at four and five times the magnon energy, suggesting quadruple and quintuple-magnons as well. Guided by theoretical calculations, we reveal how a two-photon scattering process can create exotic higher-rank magnons and the relevance of these quasiparticles for magnon-based applications.
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May 2023
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Danny
Broberg
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Kyle
Bystrom
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Shivani
Srivastava
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Diana
Dahliah
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Benjamin A. D.
Williamson
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Leigh
Weston
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David O.
Scanlon
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Gian-Marco
Rignanese
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Shyam
Dwaraknath
,
Joel
Varley
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Kristin A.
Persson
,
Mark
Asta
,
Geoffroy
Hautier
Open Access
Abstract: Calculations of point defect energetics with Density Functional Theory (DFT) can provide valuable insight into several optoelectronic, thermodynamic, and kinetic properties. These calculations commonly use methods ranging from semi-local functionals with a-posteriori corrections to more computationally intensive hybrid functional approaches. For applications of DFT-based high-throughput computation for data-driven materials discovery, point defect properties are of interest, yet are currently excluded from available materials databases. This work presents a benchmark analysis of automated, semi-local point defect calculations with a-posteriori corrections, compared to 245 “gold standard” hybrid calculations previously published. We consider three different a-posteriori correction sets implemented in an automated workflow, and evaluate the qualitative and quantitative differences among four different categories of defect information: thermodynamic transition levels, formation energies, Fermi levels, and dopability limits. We highlight qualitative information that can be extracted from high-throughput calculations based on semi-local DFT methods, while also demonstrating the limits of quantitative accuracy.
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May 2023
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Abstract: A method for synthesizing microspheres of the zeolite gmelinite (GME) with mean diameter 8 µm, and narrow dispersion, has been developed and establishes the key role of aging the gel prior to heating to produce a narrow size distribution. Fluoride adsorption from acidic media has been evaluated for GME microspheres following post-synthetic modifications by calcium ion exchange, iron(III) surface modification, and dealumination. In each instance, the post-synthetic modification leads to appreciable equilibrium fluoride loadings, with the highest loadings observed for dealuminated GME microspheres, capable of 97.4% fluoride removal from acidified 22 ppm fluoride solutions at equilibrium. Accordingly, dealuminated GME microspheres show promise as a potential adsorbent for reducing the aqueous fluoride content in dangerously high natural sources (up to 30 ppm) to safe drinking levels (≤1.5 ppm) in one treatment.
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May 2023
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Krios II-Titan Krios II at Diamond
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Diamond Proposal Number(s):
[25452]
Open Access
Abstract: Phages are viruses that infect bacteria and dominate every ecosystem on our planet. As well as impacting microbial ecology, physiology and evolution, phages are exploited as tools in molecular biology and biotechnology. This is particularly true for the Ff (f1, fd or M13) phages, which represent a widely distributed group of filamentous viruses. Over nearly five decades, Ffs have seen an extraordinary range of applications, yet the complete structure of the phage capsid and consequently the mechanisms of infection and assembly remain largely mysterious. In this work, we use cryo-electron microscopy and a highly efficient system for production of short Ff-derived nanorods to determine a structure of a filamentous virus including the tips. We show that structure combined with mutagenesis can identify phage domains that are important in bacterial attack and for release of new progeny, allowing new models to be proposed for the phage lifecycle.
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May 2023
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Yue
Pang
,
Nils
Nöthling
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Markus
Leutzsch
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Liqun
Kang
,
Eckhard
Bill
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Maurice
Van Gastel
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Edward
Reijerse
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Richard
Goddard
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Lucas
Wagner
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Daniel
Santalucia
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Serena
Debeer
,
Frank
Neese
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Josep
Cornella
Diamond Proposal Number(s):
[30449]
Abstract: Large Spin-Orbit Coupling (SOC) is an intrinsic property of the heavy-elements that directly affects the electronic structures of the compounds. Herein we report the synthesis and characterization of a mono-coordinate bismuthinidene featuring a rigid and bulky ligand. All magnetic measurements (SQUID, NMR) point to a diamagnetic compound. However, multiconfigurational quantum chemical calculations predict the ground state of the compound to be dominated (76%) by a spin-triplet. The apparent diamagnetism is explained by an extremely large SOC induced positive zero-field-splitting of more than 4500 cm−1 that leaves the MS = 0 magnetic sublevel thermally isolated in the electronic ground state.
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May 2023
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E02-JEM ARM 300CF
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Xudong
Pei
,
Liqi
Zhou
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Chen
Huang
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Mark
Boyce
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Judy S.
Kim
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Emanuela
Liberti
,
Yiming
Hu
,
Takeo
Sasaki
,
Peter D.
Nellist
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Peijun
Zhang
,
David I.
Stuart
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Angus I.
Kirkland
,
Peng
Wang
Diamond Proposal Number(s):
[17918]
Open Access
Abstract: Advances in cryogenic transmission electron microscopy have revolutionised the determination of many macromolecular structures at atomic or near-atomic resolution. This method is based on conventional defocused phase contrast imaging. However, it has limitations of weaker contrast for small biological molecules embedded in vitreous ice, in comparison with cryo-ptychography, which shows increased contrast. Here we report a single-particle analysis based on the use of ptychographic reconstruction data, demonstrating that three dimensional reconstructions with a wide information transfer bandwidth can be recovered by Fourier domain synthesis. Our work suggests future applications in otherwise challenging single particle analyses, including small macromolecules and heterogeneous or flexible particles. In addition structure determination in situ within cells without the requirement for protein purification and expression may be possible.
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May 2023
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B18-Core EXAFS
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Open Access
Abstract: Co-precipitation was used to prepare a copper, zinc, and aluminium hydrotalcite-like precursor to make a methanol synthesis catalyst. Treatment of the wet precursor with an aqueous miscible organic solvent led to the delamination of the sheet-like structure of the precursor phase, dramatically increasing the surface area to 340 m2 g−1 in comparison to 22 m2 g−1 for the untreated material. We show that the copper is initially sequestered within the hydrotalcite phase, and during calcination a CuO phase evolves out from the lamellar structures. Reduction proceeds to Cu0, and neither the calcination nor reduction of the material cause the loss of the lamellar morphology. This leads to high Cu0 surface areas in the final catalyst (66 m2 g−1) and high activity in the methanol synthesis reaction.
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May 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Open Access
Abstract: Membranes with ultrahigh permeance and practical selectivity could greatly decrease the cost of difficult industrial gas separations, such as CH4/N2 separation. Advanced membranes made from porous materials, such as metal–organic frameworks, can achieve a good gas separation performance, although they are typically formed on support layers or mixed with polymeric matrices, placing limitations on gas permeance. Here an amorphous glass foam, agfZIF-62, wherein a, g and f denote amorphous, glass and foam, respectively, was synthesized by a polymer-thermal-decomposition-assisted melting strategy, starting from a crystalline zeolitic imidazolate framework, ZIF-62. The thermal decomposition of incorporated low-molecular-weight polyethyleneimine evolves CO2, NH3 and H2O gases, creating a large number and variety of pores. This greatly increases pore interconnectivity but maintains the crystalline ZIF-62 ultramicropores, allowing ultrahigh gas permeance and good selectivity. A self-supported circular agfZIF-62 with a thickness of 200–330 µm and area of 8.55 cm2 was used for membrane separation. The membranes perform well, showing a CH4 permeance of 30,000–50,000 gas permeance units, approximately two orders of magnitude higher than that of other reported membranes, with good CH4/N2 selectivity (4–6).
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May 2023
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