I07-Surface & interface diffraction
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Diamond Proposal Number(s):
[21922]
Open Access
Abstract: A high-throughput method for the fabrication of ordered arrays of Au nanoparticles is presented. It is based on pulsed electrodeposition into porous anodic alumina templates. In contrast to many synthesis routes, it is cyanide-free, prior separation of the alumina template from the aluminium substrate is not required, and the use of contaminating surfactants/capping agents often found in colloidal synthesis is avoided. The aspect ratio of the nanoparticles can also be tuned by selecting an appropriate electrodeposition time. We show how to fabricate arrays of nanoparticles, both with branched bases and with hemispherical bases. Furthermore, we compare the different morphologies produced with electron microscopies and grazing-incidence synchrotron X-ray diffraction. We find the nanoparticles are polycrystalline in nature and are compressively strained perpendicular to the direction of growth, and expansively strained along the direction of growth. We discuss how this can produce dislocations and twinning defects that could be beneficial for catalysis.
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May 2022
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B18-Core EXAFS
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Diamond Proposal Number(s):
[20060]
Abstract: Various electrode materials are considered for sodium-ion batteries (SIBs) and one important prerequisite for developments of SIBs is a detailed understanding about charge storage mechanisms. Herein, we present a rigorous study about Na storage properties of ultra-small Fe3S4 nanoparticles, synthesized applying a solvothermal route, which exhibit a very good electrochemical performance as anode material for SIBs. A closer look into electrochemical reaction pathways on the nanoscale, utilizing synchrotron-based X-ray diffraction and X-ray absorption techniques, reveals a complicated conversion mechanism. Initially, separation of Fe3S4 into nanocrystalline intermediates occurs accompanied by reduction of Fe3+ to Fe2+ cations. Discharge to 0.1 V leads to formation of strongly disordered Fe0 finely dispersed in a nanosized Na2S matrix. The resulting volume expansion leads to a worse long-term stability in the voltage range 3.0–0.1 V. Adjusting the lower cut-off potential to 0.5 V, crystallization of Na2S is prevented and a completely amorphous intermediate stage is formed. Thus, the smaller voltage window is favorable for long-term stability, yielding highly reversible capacity retention, e.g., 486 mAh g−1 after 300 cycles applying 0.5 A g−1 and superior coulombic efficiencies >99.9%. During charge to 3.0 V, Fe3S4 with smaller domains are reversibly generated in the 1st cycle, but further cycling results in loss of structural long-range order, whereas the local environment resembles that of Fe3S4 in subsequent charged states. Electrokinetic analyses reveal high capacitive contributions to the charge storage, indicating shortened diffusion lengths and thus, redox reactions occur predominantly at surfaces of nanosized conversion products.
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Jan 2022
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I24-Microfocus Macromolecular Crystallography
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Helen M. E.
Duyvesteyn
,
Isaac
Santos-Perez
,
Francesca
Peccati
,
Ane
Martinez-Castillo
,
Thomas S.
Walter
,
David
Reguera
,
Felix M.
Goñi
,
Gonzalo
Jiménez-Osés
,
Hanna M.
Oksanen
,
David I.
Stuart
,
Nicola G. A.
Abrescia
Diamond Proposal Number(s):
[14744]
Open Access
Abstract: Viruses are very attractive biomaterials owing to their capability as nanocarriers of genetic material. Efforts have been made to functionalize self-assembling viral protein capsids on their exterior or interior to selectively take up different payloads. PRD1 is a double-stranded DNA bacteriophage comprising an icosahedral protein outer capsid and an inner lipidic vesicle. Here, we report the three-dimensional structure of PRD1 in complex with the antipsychotic drug chlorpromazine (CPZ) by cryo-electron microscopy. We show that the jellyrolls of the viral major capsid protein P3, protruding outwards from the capsid shell, serve as scaffolds for loading heterocyclic CPZ molecules. Additional X-ray studies and molecular dynamics simulations show the binding modes and organization of CPZ molecules when complexed with P3 only and onto the virion surface. Collectively, we provide a proof of concept for the possible use of the lattice-like organisation and the quasi-symmetric morphology of virus capsomers for loading heterocyclic drugs with defined properties.
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Dec 2021
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[15729]
Abstract: Structural characterization in on-surface synthesis is primarily carried out by Scanning Probe Microscopy (SPM) which provides high lateral resolution. Yet, important fresh perspectives on surface interactions and molecular conformations are gained from adsorption heights that remain largely inaccessible to SPM, but can be precisely measured with both elemental and chemical sensitivity by Normal-Incidence X-ray Standing Wave (NIXSW) analysis. Here, we study the evolution of adsorption heights in the on-surface synthesis and post-synthetic decoupling of porous covalent triazine–phenylene networks obtained from 2,4,6-tris(4-bromophenyl)-1,3,5-triazine (TBPT) precursors on Ag(111). Room temperature deposition of TBPT and mild annealing to ∼150 °C result in full debromination and formation of organometallic intermediates, where the monomers are linked into reticulated networks by C–Ag–C bonds. Topologically identical covalent networks comprised of triazine vertices that are interconnected by biphenyl units are obtained by a thermally activated chemical transformation of the organometallic intermediates. Exposure to iodine vapor facilitates decoupling by intercalation of an iodine monolayer between the covalent networks and the Ag(111) surface. Accordingly, Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS) and NIXSW experiments are carried out for three successive sample stages: organometallic intermediates, covalent networks directly on Ag(111) and after decoupling. NIXSW analysis facilitates the determination of adsorption heights of chemically distinct carbon species, i.e. in the phenyl and triazine rings, and also for the organometallic carbon atoms. Thereby, molecular conformations are assessed for each sample stage. The interpretation of experimental results is informed by Density Functional Theory (DFT) calculations, providing a consistent picture of adsorption heights and molecular deformations in the networks that result from the interplay between steric hindrance and surface interactions. Quantitative adsorption heights, i.e. vertical distances between adsorbates and surface, provide detailed insight into surface interactions, but are underexplored in on-surface synthesis. In particular, the direct comparison with an in situ prepared decoupled state unveils the surface influence on the network structure, and shows that iodine intercalation is a powerful decoupling strategy.
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Dec 2021
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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E.
Arias-Egido
,
M. A.
Laguna-Marco
,
C.
Piquer
,
P.
Jimenez-Cavero
,
I.
Lucas
,
L.
Morellon
,
F.
Gallego
,
A.
Rivera-Calzada
,
M.
Cabero
,
J.
Santamaría
,
G.
Fabbris
,
D.
Haskel
,
R.
Boada
,
S.
Diaz-Moreno
Diamond Proposal Number(s):
[17266]
Open Access
Abstract: A metal–insulator transition is observed in spin–orbit-coupled IrO2 thin films upon reduction of the film thickness. In the epitaxially grown samples, the critical thickness (t ∼ 1.5–2.2 nm) is found to depend on growth orientation (001), (100) or (110). Interestingly from the applied point of view, the insulating behavior is found even in polycrystalline ultrathin films. By analyzing the experimental electrical response with various theoretical models, we find good fits to the Efros–Shklovskii-VRH and the Arrhenius-type behaviors, which suggests an important role of electron correlations in determining the electrical properties of IrO2. Our magnetic measurements also point to a significant role of magnetic order. Altogether, our results would point to a mixed Slater- and Mott-type of insulator.
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Oct 2021
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I09-Surface and Interface Structural Analysis
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Qi
Wang
,
Jiacheng
Yang
,
Antoni
Franco-Canellas
,
Christoph
Buerker
,
Jens
Niederhausen
,
Pierre
Dombrowski
,
Felix
Widdascheck
,
Tobias
Breuer
,
Gregor
Witte
,
Alexander
Gerlach
,
Steffen
Duhm
,
Frank
Schreiber
Diamond Proposal Number(s):
[18860]
Open Access
Abstract: As crucial element in organic opto-electronic devices, heterostructures are of pivotal importance. In this context, a comprehensive study of the properties on a simplified model system of a donor–acceptor (D–A) bilayer structure is presented, using ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED) and normal-incidence X-ray standing wave (NIXSW) measurements. Pentacene (PEN) as donor and perfluoropentacene (PFP) as acceptor material are chosen to produce bilayer structures on Au(111) and Cu(111) by sequential monolayer deposition of the two materials. By comparing the adsorption behavior of PEN/PFP bilayers on such weakly and strongly interacting substrates, it is found that: (i) the adsorption distance of the first layer (PEN or PFP) indicates physisorption on Au(111), (ii) the characteristics of the bilayer structure on Au(111) are (almost) independent of the deposition sequence, and hence, (iii) in both cases a mixed bilayer is formed on the Au substrate. This is in striking contrast to PFP/PEN bilayers on Cu(111), where strong chemisorption pins PEN molecules to the metal surface and no intermixing is induced by subsequent PFP deposition. The results illustrate the strong tendency of PEN and PFP molecules to mix, which has important implications for the fabrication of PEN/PFP heterojunctions.
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Mar 2021
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I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[17574]
Open Access
Abstract: Deep eutectic solvents (DES) and their hydrated mixtures are used for solvothermal routes towards greener functional nanomaterials. Here we present the first static structural and in situ studies of the formation of iron oxide (hematite) nanoparticles in a DES of choline chloride[thin space (1/6-em)]:[thin space (1/6-em)]urea where xurea = 0.67 (aka. reline) as an exemplar solvothermal reaction, and observe the effects of water on the reaction. The initial speciation of Fe3+ in DES solutions was measured using extended X-ray absorption fine structure (EXAFS), while the atomistic structure of the mixture was resolved from neutron and X-ray diffraction and empirical potential structure refinement (EPSR) modelling. The reaction was monitored using in situ small-angle neutron scattering (SANS), to determine mesoscale changes, and EXAFS, to determine local rearrangements of order around iron ions. It is shown that iron salts form an octahedral [Fe(L)3(Cl)3] complex where (L) represents various O-containing ligands. Solubilised Fe3+ induced subtle structural rearrangements in the DES due to abstraction of chloride into complexes and distortion of H-bonding around complexes. EXAFS suggests the complex forms [–O–Fe–O–] oligomers by reaction with the products of thermal hydrolysis of urea, and is thus pseudo-zero-order in iron. In the hydrated DES, the reaction, nucleation and growth proceeds rapidly, whereas in the pure DES, the reaction initially proceeds quickly, but suddenly slows after 5000 s. In situ SANS and static small-angle X-ray scattering (SAXS) experiments reveal that nanoparticles spontaneously nucleate after 5000 s of reaction time in the pure DES before slow growth. Contrast effects observed in SANS measurements suggest that hydrated DES preferentially form 1D particle morphologies because of choline selectively capping surface crystal facets to direct growth along certain axes, whereas capping is restricted by the solvent structure in the pure DES.
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Jan 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[16372]
Open Access
Abstract: The exact formation mechanism of tantalum oxides (and in general, metal/mixed metal oxides) from alkoxide precursors is still not fully understood, particularly when forming cluster-like or amorphous materials. The structural evolution of Ta-based oxides was studied in detail using X-ray total scattering experiments along with subsequent pair distribution function (PDF) analyses. Starting from a tantalum alkoxide precursor (Ta2(OEt)10), the formation of hydrolysed TaxOyHz clusters in highly diluted aqueous solution was analysed. From the PDF data, the connectivity and arrangement of TaxOy octahedra in the cluster could be deduced as well as the approximate size of the clusters (<1 nm). Construction of cluster models allowed for identification of common structural motifs in the TaxOyHz clusters, ruling out the formation of chain- or ring-like clusters. More likely, bulky clusters with a high number of corner-sharing octahedra are formed. After separation of the amorphous solid from the liquid, temperature-induced crystallisation processes were monitored via in situ total scattering experiments. Between room temperature and 600 °C, only small rearrangements of the amorphous structure are observed. At about 610 °C, amorphous TaxOyHz transforms directly into crystalline orthorhombic L-Ta2O5 without formation of any crystalline intermediate structures.
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Nov 2020
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Ye
Fan
,
Kenichi
Nakanishi
,
Vlad P.
Veigang-Radulescu
,
Ryo
Mizuta
,
J. Callum
Stewart
,
Jack E. N.
Swallow
,
Alice E.
Dearle
,
Oliver J.
Burton
,
Jack A.
Alexander-Webber
,
Pilar
Ferrer
,
Georg
Held
,
Barry
Brennan
,
Andrew J.
Pollard
,
Robert S
Weatherup
,
Stephan
Hofmann
Diamond Proposal Number(s):
[22123]
Open Access
Abstract: We find that the use of Au substrate allows fast, self-limited WS2 monolayer growth using a simple sequential exposure pattern of low cost, low toxicity precursors, namely tungsten hexacarbonyl and dimethylsulfide (DMS). We use this model reaction system to fingerprint the technologically important metal organic chemical vapour deposition process by operando X-ray photoelectron spectroscopy (XPS) to address the current lack of understanding of the underlying fundamental growth mechanisms for WS2 and related transition metal dichalcogenides. Au effectively promotes the sulfidation of W with simple organosulfides, enabling WS2 growth with low DMS pressure (<1 mbar) and a suppression of carbon contamination of as-grown WS2, which to date has been a major challenge with this precursor chemistry. Full WS2 coverage can be achieved by one exposure cycle of 10 minutes at 700 °C. We discuss our findings in the wider context of previous literature on heterogeneous catalysis, 2D crystal growth, and overlapping process technologies such as atomic layer deposition (ALD) and direct metal conversion, linking to future integrated manufacturing processes for transition metal dichalcogenide layers.
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Oct 2020
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I11-High Resolution Powder Diffraction
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Qi
Xue
,
Yi
Xie
,
Simson
Wu
,
Tai-Sing
Wu
,
Yun-Liang
Soo
,
Sarah
Day
,
Chiu C.
Tang
,
Ho W.
Man
,
Sha T.
Yuen
,
Kwok-Yin
Wong
,
Yin
Wang
,
Benedict T. W.
Lo
,
Shik C. E.
Tsang
Diamond Proposal Number(s):
[23230]
Abstract: We investigate the geometric and electronic properties of single-atom catalysts (SACs) within metal–organic frameworks (MOFs) with respect to electrocatalytic CO2 reduction as a model reaction. A series of mid-to-late 3d transition metals have been immobilised within the microporous cavity of UiO-66-NH2. By employing Rietveld refinement of new-generation synchrotron diffraction, we not only identified the crystallographic and atomic parameters of the SACs that are stabilised with a robust M⋯N(MOF) bonding of ca. 2.0 Å, but also elucidated the end-on coordination geometry with CO2. A volcano trend in the FEs of CO has been observed. In particular, the confinement effect within the rigid MOF can greatly facilitate redox hopping between the Cu SACs, rendering high FEs of CH4 and C2H4 at a current density of −100 mA cm−2. Although only demonstrated in selected SACs within UiO-66-NH2, this study sheds light on the rational engineering of molecular interactions(s) with SACs for the sustainable provision of fine chemicals.
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Oct 2020
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