B21-High Throughput SAXS
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Diamond Proposal Number(s):
[16235]
Open Access
Abstract: Viscoelastic fluids whose rheological properties are tunable with light have the potential to deliver significant impact in fields relying on a change in flow behavior, such as in-use tuning of combined efficient heat-transfer and drag-reduction agents, microfluidic flow and controlled encapsulation and release. However, simple, single-component systems must be developed to allow integration with these applications. Here, we report a single-component viscoelastic fluid, capable of a dramatic light-sensitive rheological response, from a neutral azobenzene photosurfactant, 4-hexyl-4′butyloxymonotetraethylene glycol (C6AzoOC4E4) in water. From cryo-transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and rheology measurements, we observe that the photosurfactant forms an entangled network of wormlike micelles in water, with a high viscosity (28 Pa s) and viscoelastic behaviour. UV irradiation of the surfactant solution creates a less dense micellar network, with some vesicle formation. As a result, the solution viscosity is reduced by four orders of magnitude (to 1.2 × 10−3 Pa s). This process is reversible and the high and low viscosity states can be cycled several times, through alternating UV and blue light irradiation.
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Mar 2020
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Zdenek
Jakub
,
Jan
Hulva
,
Paul T. P.
Ryan
,
David A.
Duncan
,
David J.
Payne
,
Roland
Bliem
,
Manuel
Ulreich
,
Patrick
Hofegger
,
Florian
Kraushofer
,
Matthias
Meier
,
Michael
Schmid
,
Ulrike
Diebold
,
Gareth S.
Parkinson
Open Access
Abstract: The structure of a catalyst often changes in reactive environments, and following the structural evolution is crucial for the identification of the catalyst's active phase and reaction mechanism. Here we present an atomic-scale study of CO oxidation on a model Rh/Fe3O4(001) “single-atom” catalyst, which has a very different evolution depending on which of the two reactants, O2 or CO, is adsorbed first. Using temperature-programmed desorption (TPD) combined with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we show that O2 destabilizes Rh atoms, leading to the formation of RhxOy clusters; these catalyze CO oxidation via a Langmuir–Hinshelwood mechanism at temperatures as low as 200 K. If CO adsorbs first, the system is poisoned for direct interaction with O2, and CO oxidation is dominated by a Mars-van-Krevelen pathway at 480 K.
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Feb 2020
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I06-Nanoscience
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Massimo
Ghidini
,
Rhodri
Mansell
,
Raffaele
Pellicelli
,
David
Pesquera
,
Bhaskaran
Nair
,
Xavier
Moya
,
Saeedeh
Farokhipoor
,
Francesco
Maccherozzi
,
Crispin
Barnes
,
Russell
Cowburn
,
Sarnjeet
Dhesi
,
Neil
Mathur
Diamond Proposal Number(s):
[11843]
Abstract: Using photoemission electron microscopy (PEEM) to image ferromagnetism in polycrystalline Ni disks, and ferroelectricity in their single-crystal BaTiO3 substrates, we find that voltage-driven 90 ferroelectric domain switching serves to reversibly annihilate each magnetic vortex via uniaxial compressive strain, and that the orientation of the resulting bi domain reveals the chirality of the annihilated vortex. (Micromagnetic simulations reveal that only 60% of this strain was required for annihilation.) Voltage control of magnetic vortices is novel, and should be energetically favourable with respect to the use of a magnetic field or an electrical current. In future, stray field from bi domains could be exploited to read vortex chirality. Given that core polarity can already be read via stray field, our work represents a step towards four-state low power memory applications.
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Feb 2020
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I04-1-Macromolecular Crystallography (fixed wavelength)
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Diamond Proposal Number(s):
[16258, 16258]
Open Access
Abstract: The charge distributions of solvent exposed surfaces of complex biomolecules such has proteins are unique fingerprints. The chirality of these charge distributions result in stereo-specific electrostatic interactions which help define how proteins interact with each other, contributing to specificity in protein–protein interactions. Thus it is a key concept in understanding chemical processes in biology. There is currently no known spectroscopic phenomenon that allows rapid characterisation of chiral surface charge distributions. We show that this essential property that is currently “invisible” to optical spectroscopy, can be detected by monitoring asymmetries in the chiroptical response of protein–plasmonic nanostructure complexes. The unique capabilities of the phenomenon are utilised to discriminate between a structurally homologous series of proteins, type II dehydroquinase (DHQase) derived from different organisms. The proteins are indistinguishable with conventional structurally sensitive spectroscopy (i.e. circular dichroism). We show that discrimination between proteins can be achieved by detecting differences in chiral surface charge distributions. The phenomenon is explained with a simple model whereby the chiroptical properties of the plasmonic structures are perturbed by the induction of an enantiomeric mirror image charge distribution of the protein in the metal. This new phenomenon has broad impact, it is a powerful tool for discriminating between structurally homologous biomaterials, but will also provide information relevant to macromolecular interactions.
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Oct 2019
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I15-1-X-ray Pair Distribution Function (XPDF)
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Lei
Tan
,
Alston J.
Misquitta
,
Andrei
Sapelkin
,
Le
Fang
,
Rory M.
Wilson
,
Dean S.
Keeble
,
Baowei
Zhang
,
Tingting
Zhu
,
Frank S.
Riehle
,
Shuo
Han
,
Kui
Yu
,
Martin T.
Dove
Diamond Proposal Number(s):
[22866, 23168]
Abstract: Four types of magic-size CdS clusters and three different CdS quantum dots have been studied using the technique of X-ray total scattering and pair distribution function analysis. We found that the CdS quantum dots could be modelled as a mixed phase of atomic structures based on the two bulk crystalline phases, which is interpreted as representing the effects of random stacking of layers. However, the results for the magic-size clusters are significantly different. On one hand, the short-range features in the pair distribution function reflect the bulk, indicating that these structures are based on the same tetrahedral coordination found in the bulk phases (and therefore excluding new types of structures such as cage-like arrangements of atoms). But on the other hand, the longer-range atomic structure clearly does not reflect the layer structures found in the bulk and the quantum dots. We compare the effect of two ligands, phenylacetic acid and oleic acid, showing that in one case the ligand has little effect on the atomic structure of the magic-size nanocluster, and in another it has a significant effect.
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Oct 2019
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B18-Core EXAFS
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Diamond Proposal Number(s):
[15151]
Abstract: Porous Organic Cages (POCs) are an emerging class of self-assembling, porous materials with novel properties. They offer a key advantage over other porous materials in permitting facile solution processing and re-assembly. The combination of POCs with metal nanoparticles (NPs) unlocks applications in the area of catalysis. In this context, POCs can function as both the template of ultra-small NPs and a porous, but reprocessable, heterogeneous catalyst support. Here, we demonstrate the synthesis of ultra-small Pd NPs with an imine linked POC known as ‘CC3’, and show that hydrogen gas can be used to form metallic NPs at ∼200 °C without the reduction of the organic cage (and the accompanying, unwanted loss of crystallinity). The resulting materials are characterized using a range of techniques (including powder diffraction, scanning transmission electron microscopy and synchrotron X-ray absorption spectroscopy) and shown to be recrystallizable following dissolution in organic solvent. Their catalytic efficacy is demonstrated using the widely studied carbon monoxide oxidation reaction. This demonstration paves the way for using ultra-small NPs synthesized with POCs as solution-processable, self-assembling porous catalytic materials.
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Aug 2019
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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George F.
Tierney
,
Donato
Decarolis
,
Norli
Abdullah
,
Scott M.
Rogers
,
Shusaku
Hayama
,
Martha
Briceno De Gutierrez
,
Alberto
Villa
,
C. Richard A.
Catlow
,
Paul
Collier
,
Nikolaos
Dimitratos
,
Peter
Wells
Diamond Proposal Number(s):
[17283]
Open Access
Abstract: Sol-immobilization is increasingly used to achieve supported metal nanoparticles (NPs) with controllable size and shape; it affords a high degree of control of the metal particle size and yields a narrow particle size distribution. Using state-of-the-art beamlines, we demonstrate how X-ray absorption fine structure (XAFS) techniques are now able to provide accurate structural information on nano-sized colloidal Au solutions at μM concentrations. This study demonstrates: (i) the size of Au colloids can be accurately tuned by adjusting the temperature of reduction, (ii) Au concentration, from 50 μM to 1000 μM, has little influence on the average size of colloidal Au NPs in solution and (iii) the immobilization step is responsible for significant growth in Au particle size, which is further exacerbated at increased Au concentrations. The work presented demonstrates that an increased understanding of the primary steps in sol-immobilization allows improved optimization of materials for catalytic applications.
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May 2019
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[16854]
Abstract: We examine the atomic structure of chemical vapour deposition grown multilayer WS2 pyramids using aberration corrected annular dark field scanning transmission electron microscopy coupled with an in situ heating holder. The stacking orders and specific types of defects after partial degradation by S and W atomic loss at high temperature are resolved layer-by-layer. Our study of an individual WS2 pyramid with at least six layers, reveals a mixed 2H and 3R polytype stacking. Etching occurred both top and bottom of the WS2 pyramid, which aids in determining the exact vertical layer stacking configurations in the thicker regions. We provide an extensive catalogue of the contrast profiles associated with defects in WS2 as a function of layer number and stacking type, as imaged using ADF-STEM. These results provide extensive details about the identification of a wide range of defects in S2 layers, and the unique ADF-STEM contrast patterns that arise from complex multilayer stacking.
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May 2019
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[16256]
Open Access
Abstract: Mesoporous phosphates are a group of nanostructured materials with promising applications, particularly in biomedicine and catalysis. However, their controlled synthesis via conventional template-based routes presents a number of challenges and limitations. Here, we show how to synthesize a mesoporous magnesium phosphate with a high surface area and a well-defined pore structure through thermal decomposition of a crystalline struvite (MgNH4PO4·6H2O) precursor. In a first step, struvite crystals with various morphologies and sizes, ranging from a few micrometers to several millimeters, had been synthesized from supersaturated aqueous solutions (saturation index (SI) between 0.5 and 4) at ambient pressure and temperature conditions. Afterwards, the crystals were thermally treated at 70–250 °C leading to the release of structurally bound water (H2O) and ammonia (NH3). By combining thermogravimetric analyses (TGA), scanning and transmission electron microscopy (SEM, TEM), N2 sorption analyses and small- and wide-angle X-ray scattering (SAXS/WAXS) we show that this decomposition process results in a pseudomorphic transformation of the original struvite into an amorphous Mg-phosphate. Of particular importance is the fact that the final material is characterized by a very uniform mesoporous structure with 2–5 nm wide pore channels, a large specific surface area of up to 300 m2 g−1 and a total pore volume of up to 0.28 cm3 g−1. Our struvite decomposition method is well controllable and reproducible and can be easily extended to the synthesis of other mesoporous phosphates. In addition, the so produced mesoporous material is a prime candidate for use in biomedical applications considering that magnesium phosphate is a widely used, non-toxic substance that has already shown excellent biocompatibility and biodegradability.
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Apr 2019
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[13837]
Abstract: The success of future organic electronic devices distinctively depends on the electronic and geometric properties of thin organic films. Although obviously these properties are strongly influenced by the growth mechanisms, real time growth studies are relatively rare since not many experimental techniques exist that allow in situ studies in ultra high vacuum. In this context, we investigated the prototypical system 1,4,5,8-naphtalene-tetracarboxylic-dianhydride (NTCDA) on Cu(001). We used low-energy electron microscopy (LEEM) for the real-time growth study, and a variety of other techniques for investigating the geometric and electronic structure. While for similar model systems well known and well characterized growth modi occur (e.g., compact, well ordered islands or disordered, gas-like layers), for NTCDA/Cu(001) we observe the growth of dendrite-like, fractal structures. The dendritic structures arise from a strongly preferred one-dimensional growth mode forming a long-range ordered network of thin molecular chains spanning over the entire surface already at small coverages. Later in the growth process, the voids in the network structure are incrementally filled. These results are very unexpected for such a simple adsorbate system consisting of well investigated components, the properties of which were believed to be already well understood. We explain this unexpected behavior by a dendritic growth model that is supported by energetic arguments based on pair-potential calculations. These calculations give reason for the experimentally observed growth of one-dimensional structures, and therefore represent the key to a semi-quantitative understanding of this dendritic growth mode.
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Jan 2019
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