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37 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I07-Surface & interface diffraction	In-situ investigation of crystallization and structural evolution of a metallic glass in three dimensions at nano-scale Bo Chen , Jiecheng Diao , Qiang Luo , Jonathan Rawle , Xianping Liu , Chris Nicklin , Jun Shen , Ian Robinson Materials & Design DOI: 10.1016/j.matdes.2020.108551 Diamond Proposal Number(s): [17445, 14918] Open Access Show Abstract ▼ Abstract: The crystallization behaviour of metallic glasses (MGs) has been investigated since the discovery of these important functional materials in order to optimize their synthesis procedures and improve their performances. Methods including powder X-ray diffraction and transmission electron microscopy are usually combined to characterize the crystalline structure in these “amorphous” materials. Until now, these methods, however, have failed to show the crystallization of individual crystals in three dimensions. In this work, in-situ Bragg coherent X-ray diffraction imaging (BCDI) reveals the growth and the strain variation of individual crystals in the Fe-based MGs during annealing. There is preferential growth along the surface of the MG sample particles during the crystal formation and fractal structure formation around the developing crystal surfaces; there is also strain relaxation happening from the inner parts to the surfaces of the developing crystals while cooling. The work leads to propose that during the crystallization of Fe-based MGs, the growth of the individual crystals follows a two-step procedure; and at higher temperature after the first crystallization period of the Fe-based MGs, the crystallization of α-Fe could be a competitive process between the growth of α-Fe crystals and the erosion from other elements.	Feb 2020
I07-Surface & interface diffraction	Dye nanoaggregate structures in MK-2, N3, and N749 dye…TiO2 interfaces that represent dye-sensitized solar cell working electrodes Ke Deng , Jacqueline M. Cole , Jonathan L. Rawle , Christopher Nicklin , Hao Chen , Angel Yanguas-gil , Jeffrey W. Elam , Gavin B. G. Stenning Acs Applied Energy Materials DOI: 10.1021/acsaem.9b02002 Diamond Proposal Number(s): [15487] Show Abstract ▼ Abstract: The working electrode of a dye-sensitized solar cell (DSSC) consists of dye molecules adsorbed onto nanoparticles of a semiconductor such as TiO2. A reliable prediction of the DSSC photovoltaic performance of a given dye requires in-depth knowledge about the precise structure of the dye···TiO2 interface. X-ray reflectometry (XRR) and grazing-incidence small angle X-ray scattering (GISAXS) are herein employed to determine the dye···TiO2 interfacial structure and associated dye aggregation behavior of three high-performance DSSC dyes: an organic metal-free dye, MK-2, and the two archetypal ruthenium-based organometallic dyes, N3, and N749 (Black Dye). Results show that all three dyes form nanoaggregates in dye···TiO2 interfaces. We determine the dye nanoaggregate separations, sizes, distribution densities and the extent of short-range order within each dye self-assembly in the longitudinal and lateral directions. Dye···TiO2 composites fabricated using dye solutions of varying concentrations are analyzed. We find that nanoaggregates of the three dyes are separated by several hundred nanometers (158-203 nm) in dye···TiO2 interfaces that have been fabricated using concentrated dye solutions (0.5 mM or 1.0 mM). MK-2 and N749 dyes also display smaller inter-particle separations. Dye nanoparticle diameters are of the order of 156-198 nm, sizes that are comparable to the largest inter-particle separations. Thus, no extraneous dye particles can be fitted into gaps between particles, so the dye self-assembly is saturated. Self-assemblies of all three dyes exhibit both lateral and longitudinal short-range order; N3 displays a particularly short coherence length along the TiO2 surface, with extensive structured disorder along the longitudinal direction. The operation of DSSC working electrodes would therefore seem to be dependent on a dye self-assembly that may exhibit several levels of structural granularity and dye aggregation effects.	Dec 2019
I07-Surface & interface diffraction	Water-induced reversal of the TiO2 (011)-(2x1) surface reconstruction: observed with in situ surface X-ray diffraction Hadeel Hussain , Mahmoud H. M. Ahmed , Xavier Torrelles , David Grinter , Gregory Cabailh , Oier Bikondoa , Christopher Nicklin , Ulrich Aschauer , Robert Lindsay , Geoff Thornton The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.9b04383 Diamond Proposal Number(s): [8952] Show Abstract ▼ Abstract: The (011) termination of rutile TiO2 is reported to be particularly effective for photocatalysis. Here the structure of the interface formed between this substrate and water is revealed using surface X-ray diffraction. While the TiO2(011) surface exhibits a (2x1) reconstruction in ultra-high vacuum, this is lifted in the presence of a multilayer of water at room temperature. This change is driven by the formation of Ti-OH at the interface, which has a bond distance of 1.93 ± 0.02 Å. The experimental solution is in good agreement with density functional theory and first principles molecular dynamics calculations. These results point to the important differences that can arise between the structure of oxide surfaces in ultra-high vacuum and technical environments and will ultimately lead to an atomistic understanding of the photocatalytic process of water splitting on TiO2 surfaces.	May 2019
I07-Surface & interface diffraction	Structure of a superhydrophilic surface: wet chemically prepared rutile-TiO2 (110)(1×1) Jon P. W. Treacy , Hadeel Hussain , Xavier Torrelles , Gregory Cabailh , Oier Bikondoa , Christopher Nicklin , Geoff Thornton , Robert Lindsay The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.9b00245 Show Abstract ▼ Abstract: Surface X-ray diffraction (SXRD) has been employed to quantitatively determine the geometric structure of an X-ray-induced superhydrophilic rutile-TiO2(110)(1×1) surface. A scatterer, assumed to be oxygen, is found at a distance of 1.90 ± 0.02 Å above the fivefold co-ordinated surface Ti atom, indicating surface hydroxylation. Two more oxygen atoms, situated further from the substrate, are also included to achieve the optimal agreement between experimental and simulated diffraction data. It is concluded that these latter scatterers are from water molecules, surface localised through hydrogen bonding. Comparing this interfacial structure with previous studies suggests that the superhydophilicity of titania is most likely to be a result of the depletion of surface carbon contamination, coupled with extensive surface hydroxylation.	Feb 2019
I07-Surface & interface diffraction	Microscopy and spectroscopy study of nanostructural phase transformation from β-moo3 to mo under uhv – mbe conditions Paramita Maiti , Puspendu Guha , Hadeel Hussain , Ranveer Singh , Chris Nicklin , Parlapalli V. Satyam Surface Science DOI: 10.1016/j.susc.2018.12.008 Show Abstract ▼ Abstract: We report a simple reduction of molybdenum oxide (β-MoO3) grown on reconstructed Si(100) by thermal annealing in ultra-high vacuum (UHV) using molecular beam epitaxy (MBE). By increasing the substrate temperature during deposition or the annealing temperature after growth, the morphologies of as-deposited structures were found to vary from nanoribbons (NRs) of β-MoO3 to nanoparticles (NPs) of Mo. The change in morphologies have been associated with a structural transition from β-MoO3 to MoO2 at 400°C and MoO2 to Mo at 750°C. The in-situ X-ray photoelectron spectroscopy (XPS) measurements revealed a shift of the Mo 3d peaks towards lower binding energies, representing the reduction in Mo oxidation states until a pure Mo 3d peak at 750°C was observed. The ex-situ KPFM measurements showed a decrease in the local work function (Φ) (from ≈ 5.27 ± 0.05 eV to ≈ 4.83 ± 0.05 eV) with increasing substrate temperature. A gradual reduction of the band gap from ≈ 3.32 eV for β-MoO3 NRs to zero band gap for Mo NPs is also observed during the annealing up to 750°C.	Jan 2019
I07-Surface & interface diffraction	Atomistics of pre-nucleation layering of liquid metals at the interface with poor nucleants Sida Ma , Adam J. Brown , Rui Yan , Ruslan L. Davidchack , Paul B. Howes , Chris Nicklin , Qijie Zhai , Tao Jing , Hongbiao Dong Communications Chemistry 2 DOI: 10.1038/s42004-018-0104-1 Diamond Proposal Number(s): [12083, 6663] Open Access Show Abstract ▼ Abstract: Liquid layering at heterogeneous solid/liquid interfaces is a general phenomenon, which provides structural templates for nucleation of crystalline phases on potent nucleants. However, its efficacy near poor nucleants is incompletely understood. Here we use a combination of X-ray crystal truncation rod analysis and ab initio molecular dynamics to probe the pre-nucleation liquid layering at the sapphire–aluminium solid/liquid interface. At the sapphire side, a ~1.6 aluminium-terminated structure develops, and at the liquid side, two pre-nucleation layers emerge at 950 K. No more pre-nucleation layer forms with decreasing temperature indicating that nucleation of crystalline aluminium through layer-by-layer atomic adsorption of liquid atoms is not favoured. Instead, the appearance of stochastically-formed nuclei near the substrate is supported by our experiments. Nucleation on poor nucleants is dominated by the stochastic nucleation events which are substantially influenced by the pre-nucleation layers that determine the surface structure in contact with the nuclei.	Jan 2019
I07-Surface & interface diffraction	Bragg coherent diffraction imaging of iron diffusion into gold nanocrystals Ana Katrina Estandarte , Christopher Lynch , Marianne Monteforte , Jonathan Rawle , Chris Nicklin , Ian K. Robinson New Journal Of Physics DOI: 10.1088/1367-2630/aaebc1 Open Access Show Abstract ▼ Abstract: Understanding how diffusion takes place within nanocrystals is of great importance for their stability and for controlling their synthesis. In this study, we used the strain sensitivity of Bragg coherent diffraction imaging (BCDI) to study the diffusion of iron into individual gold nanocrystals in situ at elevated temperatures. The BCDI experiments were performed at the I-07 beamline at Diamond Light Source, UK. The diffraction pattern of individual gold nanocrystals was measured around the (11-1) Bragg peak of gold before and after iron deposition as a function of temperature and time. Phase retrieval algorithms were used to obtain real space reconstructions of the nanocrystals from their measured diffraction patterns. Alloying of iron with gold at sample temperatures of 300°C-500°C and dealloying of iron from gold at 600°C were observed. The volume of the alloyed region in the nanocrystals was found to increase with the dose of iron. However, no significant time dependence was observed for the structure following each iron deposition, suggesting that the samples reached equilibrium relatively quickly. The resulting phase distribution within the gold nanocrystals after the iron depositions suggests a contraction due to diffusion of iron. Our results show that BCDI is a useful technique for studying diffusion in three dimensions (3D) and alloying behaviour in individual crystalline grains.	Oct 2018
I07-Surface & interface diffraction	Molecular structure of the substrate-induced thin-film phase of tetracene Linus Pithan , Dmitrii Nabok , Caterina Cocchi , Paul Beyer , Giuliano Duva , Joseph Simbrunner , Jonathan Rawle , Chris Nicklin , Peter Schäfer , Claudia Draxl , Frank Schreiber , Stefan Kowarik The Journal Of Chemical Physics 149 DOI: 10.1063/1.5043379 Diamond Proposal Number(s): [12895] Show Abstract ▼ Abstract: We present a combined experimental and theoretical study to solve the unit-cell and molecular arrangement of the tetracene thin film (TF) phase. TF phases, also known as substrate induced phases (SIPs), are polymorphs that exist at interfaces and decisively impact the functionality of organic thin films, e.g., in a transistor channel, but also change the optical spectra due to the different molecular packing. As SIPs only exist in textured ultrathin films, their structure determination remains challenging compared to bulk materials. Here, we use grazing incidence X-ray diffraction and atomistic simulations to extract the TF unit-cell parameters of tetracene together with the atomic positions within the unit-cell.	Oct 2018
I07-Surface & interface diffraction	The role of crystal orientation in the dissolution of uo2 thin films S. Rennie , E. Lawrence Bright , J. E. Sutcliffe , J. E. Darnbrough , R. Burrows , J. Rawle , C. Nicklin , G. H. Lander , R. Springell Corrosion Science DOI: 10.1016/j.corsci.2018.09.012 Diamond Proposal Number(s): [13089] Show Abstract ▼ Abstract: Single crystal [0 0 1], [1 1 0], and [1 1 1]-oriented UO2 thin films were utilised to investigate the orientational dependence of radiolytic dissolution. The films were exposed to water in the presence of a synchrotron x-ray source to induce dissolution, with X-ray Reflectivity (XRR) used to observe changes in morphology as a function of exposure time. The [0 0 1] and [1 1 0]-oriented films were found to corrode at comparable rates, however, the [1 1 1] film was significantly more corrosion resistant, passivating after the initial 90 s dissolution period. This result shows the orientational dependence of UO2 dissolution, which may have important consequences for theoretical dissolution models.	Sep 2018
I07-Surface & interface diffraction	Water dissociates at the aqueous interface with reduced anatase TiO 2 (101) Immad M. Nadeem , Jon P. W. Treacy , Sencer Selcuk , Xavier Torrelles , Hadeel Hussain , Axel Wilson , David C. Grinter , Gregory Cabailh , Oier Bikondoa , Chris Nicklin , Annabella Selloni , Jorg Zegenhagen , Robert Lindsay , Geoff Thornton The Journal Of Physical Chemistry Letters DOI: 10.1021/acs.jpclett.8b01182 Diamond Proposal Number(s): [8634, 11345] Show Abstract ▼ Abstract: Elucidating the structure of the interface between natural (reduced) anatase TiO2 (101) and water is an essential step towards understanding the associated photo-assisted water splitting mechanism. Here we present surface X-ray diffraction results for the room temperature interface with ultra-thin and bulk water, which we explain by reference to density functional theory calculations. We find that both interfaces contain a 25:75 mixture of molecular H2O and terminal OH bound to titanium atoms along with bridging OH species in the contact layer. This is in complete contrast to the inert character of room temperature anatase TiO2 (101) in ultra-high vacuum. A key difference between the ultra-thin and bulk water interfaces is that in the latter, water in the second layer is also ordered. These molecules are hydrogen bonded to the contact layer, modifying the bond angles.	May 2018

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