E02-JEM ARM 300CF
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Yi-Chao
Zou
,
Lucas
Mogg
,
Nick
Clark
,
Cihan
Bacaksiz
,
Slavisa
Milanovic
,
Vishnu
Sreepal
,
Guang-Ping
Hao
,
Yi-Chi
Wang
,
David G.
Hopkinson
,
Roman
Gorbachev
,
Samuel
Shaw
,
Kostya S.
Novoselov
,
Rahul
Raveendran-Nair
,
Francois M.
Peeters
,
Marcelo
Lozada-Hidalgo
,
Sarah
Haigh
Diamond Proposal Number(s):
[21981, 21597]
Abstract: The physical properties of clays and micas can be controlled by exchanging ions in the crystal lattice. Atomically thin materials can have superior properties in a range of membrane applications, yet the ion-exchange process itself remains largely unexplored in few-layer crystals. Here we use atomic-resolution scanning transmission electron microscopy to study the dynamics of ion exchange and reveal individual ion binding sites in atomically thin and artificially restacked clays and micas. We find that the ion diffusion coefficient for the interlayer space of atomically thin samples is up to 104 times larger than in bulk crystals and approaches its value in free water. Samples where no bulk exchange is expected display fast exchange at restacked interfaces, where the exchanged ions arrange in islands with dimensions controlled by the moiré superlattice dimensions. We attribute the fast ion diffusion to enhanced interlayer expandability resulting from weaker interlayer binding forces in both atomically thin and restacked materials. This work provides atomic scale insights into ion diffusion in highly confined spaces and suggests strategies to design exfoliated clay membranes with enhanced performance.
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Aug 2021
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I19-Small Molecule Single Crystal Diffraction
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David P.
August
,
Robert A. W.
Dryfe
,
Sarah J.
Haigh
,
Paige R. C.
Kent
,
David A.
Leigh
,
Jean-Francois
Lemonnier
,
Zheling
Li
,
Christopher A.
Muryn
,
Leoni I.
Palmer
,
Yiwei
Song
,
George F. S.
Whitehead
,
Robert J.
Young
Diamond Proposal Number(s):
[17379]
Abstract: Fabrics—materials consisting of layers of woven fibres—are some of the most important materials in everyday life. Previous nanoscale weaves include isotropic crystalline covalent organic frameworks that feature rigid helical strands interlaced in all three dimensions, rather than the two-dimensional layers of flexible woven strands that give conventional textiles their characteristic flexibility, thinness, anisotropic strength and porosity. A supramolecular two-dimensional kagome weave and a single-layer, surface-supported, interwoven two-dimensional polymer have also been reported. The direct, bottom-up assembly of molecular building blocks into linear organic polymer chains woven in two dimensions has been proposed on a number of occasions, but has not previously been achieved. Here we demonstrate that by using an anion and metal ion template, woven molecular ‘tiles’ can be tessellated into a material consisting of alternating aliphatic and aromatic segmented polymer strands, interwoven within discrete layers. Connections between slowly precipitating pre-woven grids, followed by the removal of the ion template, result in a wholly organic molecular material that forms as stacks and clusters of thin sheets—each sheet up to hundreds of micrometres long and wide but only about four nanometres thick—in which warp and weft single-chain polymer strands remain associated through periodic mechanical entanglements within each sheet. Atomic force microscopy and scanning electron microscopy show clusters and, occasionally, isolated individual sheets that, following demetallation, have slid apart from others with which they were stacked during the tessellation and polymerization process. The layered two-dimensional molecularly woven material has long-range order, is birefringent, is twice as stiff as the constituent linear polymer, and delaminates and tears along well-defined lines in the manner of a macroscopic textile. When incorporated into a polymer-supported membrane, it acts as a net, slowing the passage of large ions while letting smaller ions through.
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Dec 2020
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I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[23490]
Open Access
Abstract: The transient nature of the internal pore structure of particulate wall flow filters, caused by the continuous deposition of particulate matter, makes studying their flow and filtration characteristics challenging. In this article we present a new methodology and first experimental demonstration of time resolved in-situ synchrotron micro X-ray computed tomography (micro-CT) to study aerosol filtration. We directly imaged in 4D (3D plus time) pore scale deposits of TiO2
nanoparticles (nominal mean primary diameter of 25 nm) with a pixel resolution of 1.6 μ
m. We obtained 3D tomograms at a rate of ∼1 per minute. The combined spatial and temporal resolution allows us to observe pore blocking and filling phenomena as they occur in the filter’s pore space. We quantified the reduction in filter porosity over time, from an initial porosity of 0.60 to a final porosity of 0.56 after 20 min. Furthermore, the penetration depth of particulate deposits and filtration rate was quantified. This novel image-based method offers valuable and statistically relevant insights into how the pore structure and function evolves during particulate filtration. Our data set will allow validation of simulations of automotive wall flow filters. Evolutions of this experimental design have potential for the study of a wide range of dry aerosol filters and could be directly applied to catalysed automotive wall flow filters.
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Dec 2020
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[26559]
Open Access
Abstract: Single-particle reconstruction can be used to perform three-dimensional (3D) imaging of homogeneous populations of nano-sized objects, in particular viruses and proteins. Here, it is demonstrated that it can also be used to obtain 3D reconstructions of heterogeneous populations of inorganic nanoparticles. An automated acquisition scheme in a scanning transmission electron microscope is used to collect images of thousands of nanoparticles. Particle images are subsequently semi-automatically clustered in terms of their properties and separate 3D reconstructions are performed from selected particle image clusters. The result is a 3D dataset that is representative of the full population. The study demonstrates a methodology that allows 3D imaging and analysis of inorganic nanoparticles in a fully automated manner that is truly representative of large particle populations.
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Nov 2020
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[19315, 21597]
Abstract: Suspended specimens of 2D crystals and their heterostructures are required for a range of studies including transmission electron microscopy (TEM), optical transmission experiments and nanomechanical testing. However, investigating the properties of laterally small 2D crystal specimens, including twisted bilayers and air sensitive materials, has been held back by the difficulty of fabricating the necessary clean suspended samples. Here we present a scalable solution which allows clean free-standing specimens to be realized with 100% yield by dry-stamping atomically thin 2D stacks onto a specially developed adhesion-enhanced support grid. Using this new capability, we demonstrate atomic resolution imaging of defect structures in atomically thin CrBr3, a novel magnetic material which degrades in ambient conditions.
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Aug 2020
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Isabel C.
De Freitas
,
Luanna S.
Parreira
,
Eduardo C. M.
Barbosa
,
Barbara A.
Novaes
,
Tong
Mou
,
Tiago. V.
Alves
,
Jhon
Quiroz
,
Yi-Chi
Wang
,
Thomas J.
Slater
,
Andrew
Thomas
,
Bin
Wang
,
Sarah J.
Haigh
,
Pedro H. C.
Camargo
Open Access
Abstract: We develop herein plasmonic–catalytic Au–IrO2 nanostructures with a morphology optimized for efficient light harvesting and catalytic surface area; the nanoparticles have a nanoflower morphology, with closely spaced Au branches all partially covered by an ultrathin (1 nm) IrO2 shell. This nanoparticle architecture optimizes optical features due to the interactions of closely spaced plasmonic branches forming electromagnetic hot spots, and the ultra-thin IrO2 layer maximizes efficient use of this expensive catalyst. This concept was evaluated towards the enhancement of the electrocatalytic performances towards the oxygen evolution reaction (OER) as a model transformation. The OER can play a central role in meeting future energy demands but the performance of conventional electrocatalysts in this reaction is limited by the sluggish OER kinetics. We demonstrate an improvement of the OER performance for one of the most active OER catalysts, IrO2, by harvesting plasmonic effects from visible light illumination in multimetallic nanoparticles. We find that the OER activity for the Au–IrO2 nanoflowers can be improved under LSPR excitation, matching best properties reported in the literature. Our simulations and electrocatalytic data demonstrate that the enhancement in OER activities can be attributed to an electronic interaction between Au and IrO2 and to the activation of Ir–O bonds by LSPR excited hot holes, leading to a change in the reaction mechanism (rate-determinant step) under visible light illumination.
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Apr 2020
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E02-JEM ARM 300CF
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Jonas
Bekaert
,
Ekaterina
Khestanova
,
David G.
Hopkinson
,
John
Birkbeck
,
Nick
Clark
,
Mengjian
Zhu
,
Denis
Bandurin
,
Roman
Gorbachev
,
Simon
Fairclough
,
Yichao
Zou
,
Matthew
Hamer
,
Daniel J.
Terry
,
Jonathan J. P.
Peters
,
Ana M.
Sanchez
,
Bart
Partoens
,
Sarah
Haigh
,
Milorad
Milosevic
,
Irina V.
Grigorieva
Diamond Proposal Number(s):
[19315, 21597]
Abstract: When approaching the atomically thin limit, defects and disorder play an increasingly important role in the properties of two-dimensional materials. While defects are generally thought to negatively affect superconductivity in 2D materials, here we demonstrate the contrary in the case of oxygenation of ultrathin tantalum disulfide (TaS2). Our first-principles calculations show that incorporation of oxygen into the TaS2 crystal lattice is energetically favourable and effectively heals sulfur vacancies typically present in these crystals, thus restoring the electronic band structure and the carrier density to the intrinsic characteristics of TaS2. Strikingly, this leads to a strong enhancement of the electron-phonon coupling, by up to 80% in the highly-oxygenated limit. Using transport measurements on fresh and aged (oxygenated) few-layer TaS2, we found a marked increase of the superconducting critical temperature (Tc) upon aging, in agreement with our theory, while concurrent electron microscopy and electron-energy loss spectroscopy confirmed the presence of sulfur vacancies in freshly prepared TaS2 and incorporation of oxygen into the crystal lattice with time. Our work thus reveals the mechanism by which certain atomic-scale defects can be beneficial to superconductivity and opens a new route to engineer Tc in ultrathin materials.
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Apr 2020
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B18-Core EXAFS
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Diamond Proposal Number(s):
[15151]
Abstract: Bimetallic catalysts consisting of Pd and Pt on TiO2-zeolite (mordenite, beta, ZSM-5) supports were prepared and tested for the combustion of methane. The activity of the catalysts was found to be dependent on the zeolite topology and SiO2 : Al2O3 ratio and was linearly dependent on the proportion of Pd and Pt present in a bimetallic phase observed in XRD diffractograms of the catalysts. This linear dependence was valid for a range of zeolites used. STEM-EDS and electron tomography showed the Pd and Pt to be largely co-located and XAS and XPS indicated that the metals are mostly present in the form of oxide nanoparticles with a minor contribution from the metals at high SiO2 : Al2O3 ratios. Catalyst characterization showed there to be little difference overall in the metal loading and physical characteristics of the samples and NH3-TPD suggested that the activation of methane over acid sites is not important. Adding water to the feed, slightly reduced the conversion but did not affect the deactivation profile of the catalysts tested.
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Jan 2020
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E02-JEM ARM 300CF
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David G.
Hopkinson
,
Viktor
Zólyomi
,
Aidan P.
Rooney
,
Nick
Clark
,
Daniel J.
Terry
,
Matthew
Hamer
,
David J.
Lewis
,
Christopher S.
Allen
,
Angus I.
Kirkland
,
Yury
Andreev
,
Zakhar
Kudrynskyi
,
Zakhar
Kovalyuk
,
Amalia
Patanè
,
Vladimir I.
Fal'Ko
,
Roman
Gorbachev
,
Sarah
Haigh
Diamond Proposal Number(s):
[16892, 17837]
Abstract: GaSe and InSe are important members of a class of 2D materials, the III-VI metal monochalcogenides, which are attracting considerable attention due to their promising electronic and optoelectronic properties. Here an investigation of point and extended atomic defects formed in mono-, bi-, and few-layer GaSe and InSe crystals is presented. Using state-of-the-art scanning transmission electron microscopy (STEM), it is observed that these materials can form both metal and selenium vacancies under the action of the electron beam. Selenium vacancies are observed to be healable; recovering the perfect lattice structure in the presence of selenium or enabling incorporation of dopant atoms in the presence of impurities. Under prolonged imaging, multiple point defects are observed to coalesce to form extended defect structures, with GaSe generally developing trigonal defects and InSe primarily forming line defects. These insights into atomic behavior could be harnessed to synthesize and tune the properties of 2D post transition metal monochalcogenide materials for optoelectronic applications.
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Apr 2019
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Xinyuan
Li
,
Muhammad Ahsan
Iqbal
,
Meng
Xu
,
Yi-Chi
Wang
,
Hongzhi
Wang
,
Muwei
Ji
,
Xiaodong
Wan
,
Thomas J. A.
Slater
,
Jia
Liu
,
Jiajia
Liu
,
Hongpan
Rong
,
Wenxing
Chen
,
Stephen V.
Kershaw
,
Sarah J.
Haigh
,
Andrey L.
Rogach
,
Liming
Xie
,
Jiatao
Zhang
Abstract: We have explored the synthesis of Au@HgxCd1-xTe core@shell nanorods by sequential aqueous cation exchange (ACE) for near-infrared photodetector application. A number of related Au@telluride core/shell nanorod structures were put forwarded, taking advantage of multi-step transformations through a binary and then a ternary phase for the telluride shells. The latter have a high degree of crystallinity thanks to the step-wise ACE method. The use of only trace amounts of Cd2+ coordinated with tri-n-butylphosphine, assisted the phase transformation from an amorphous Ag2Te shell to a highly crystalline Ag3AuTe2 shell in the first stage; this was followed by a further cation exchange (CE) step with far higher Cd2+ levels to fabricate a highly crystalline CdTe shell, and with an additional CE with Hg2+ to convert it to a HgxCd1-xTe shell. The composition of the shell components and the well-controlled thickness of the shells enabled tunable surface plasmon resonance properties of the Au@telluride nanorods in the NIR region. Utilizing the enhanced NIR absorption, a hybrid photodetector structure of Au@HgxCd1-xTe nanorods on graphene was fabricated, showing visible to NIR (vis-NIR) broadband detection with high photoresponsivity (~106 A/W).
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Dec 2018
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