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

Instruments / Technical Area	Publication Details	Published
I22-Small angle scattering & Diffraction	"Sounding" out crystal nuclei - A mathematical-physical and experimental investigation Megan J. Povey , Rammile Ettelaie , Ken Lewtas , Andy Price , Xiaojun Lai , Fei Sheng The Journal Of Chemical Physics 158 DOI: 10.1063/5.0139811 Diamond Proposal Number(s): [20481, 27656] Open Access Show Abstract ▼ Abstract: We outline techniques for the control and measurement of the nucleation of crystalline material. SAXS/WAXS XRD measurements are presented that demonstrate the impact of low power, continuous, non-cavitational ultrasound on the nucleation and crystallisation of a wax; n-eicosane dissolved in heptane/toluene solvent. A mathematical-physical approach based on rectification of heat and mass transport by such a low power oscillating pressure field is outlined and it is suggested that this approach be combined with dissipative particle dynamics (DPD) computational modelling to develop a predictive method capable of modelling the impact of low power oscillating pressure fields (acoustics and ultrasonics) on a wide range of nucleating systems. Combining ultrasound pitch and catch speed of sound measurements with low power harmonically oscillating pressure fields to monitor and control nucleation presents the prospect of entirely new industrially significant methods of process control in crystallisation. It also offers new insights into nucleation processes in general. However, for the acoustic control technique to be applied widely, further theoretical and modelling work will be necessary since at present, we are unable to predict the precise effect of low power ultrasound in any given situation.	May 2023
I24-Microfocus Macromolecular Crystallography	Hemoglycin visible fluorescence induced by X-rays Malcolm W. Mcgeoch , Robin Owen , Sofia Jaho , Julie E. M. Mcgeoch The Journal Of Chemical Physics DOI: 10.1063/5.0143945 Diamond Proposal Number(s): [31420] Open Access Show Abstract ▼ Abstract: Hemoglycin, a 1494 Da polymer composed of iron and glycine has been detected in several carbonaceous meteorites. Iron atoms close out the ends of a 5nm anti-parallel glycine beta sheet and contribute visible and near infrared absorptions that are not present with glycine alone. The 483nm absorption of hemoglycin was discovered in theory and then observed on beamline I24 at Diamond Light Source. Light absorption in a molecule involves a coupled lower set of states receiving light energy that causes a transition into an upper set of states. In the reverse process some energy source, such as an X-ray beam, populates the upper set of molecular states, which then radiates light as it returns to the lower "ground" set of states. We report on visible light re-emission during X-ray irradiation of a hemoglycin crystal. The emission is dominated by bands centered at 489nm and 551nm.	Feb 2023
I22-Small angle scattering & Diffraction	Influence of hydrophobic moieties on the crystallization of amphiphilic DNA nanostructures Michal Walczak , Ryan A. Brady , Adrian Leathers , Jurij Kotar , Lorenzo Di Michele The Journal Of Chemical Physics 158 DOI: 10.1063/5.0132484 Diamond Proposal Number(s): [24537, 29072] Open Access Show Abstract ▼ Abstract: Three-dimensional crystalline frameworks with nanoscale periodicity are valuable for many emerging technologies, from nanophotonics to nanomedicine. DNA nanotechnology has emerged as a prime route for constructing these materials, with most approaches taking advantage of the structural rigidity and bond directionality programmable for DNA building blocks. Recently, we have introduced an alternative strategy reliant on flexible, amphiphilic DNA junctions dubbed C-stars, whose ability to crystallize is modulated by design parameters, such as nanostructure topology, conformation, rigidity, and size. While C-stars have been shown to form ordered phases with controllable lattice parameter, response to stimuli, and embedded functionalities, much of their vast design space remains unexplored. Here, we investigate the effect of changing the chemical nature of the hydrophobic modifications and the structure of the DNA motifs in the vicinity of these moieties. While similar design variations should strongly alter key properties of the hydrophobic interactions between C-stars, such as strength and valency, only limited differences in self-assembly behavior are observed. This finding suggests that long-range order in C-star crystals is likely imposed by structural features of the building block itself rather than the specific characteristics of the hydrophobic tags. Nonetheless, we find that altering the hydrophobic regions influences the ability of C-star crystals to uptake hydrophobic molecular cargoes, which we exemplify by studying the encapsulation of antibiotic penicillin V. Besides advancing our understanding of the principles governing the self-assembly of amphiphilic DNA building blocks, our observations thus open up new routes to chemically program the materials without affecting their structure.	Feb 2023
B16-Test Beamline	Single-orientation colloidal crystals from capillary-action-induced shear Nicholas H. P. Orr , Taiki Yanagishima , Igor P. Dolbnya , Andrei V. Petukhov , Roel P. A. Dullens The Journal Of Chemical Physics DOI: 10.1063/5.0112602 Open Access Show Abstract ▼ Abstract: We study the crystallisation of colloidal dispersions under capillary-action-induced shear as the dispersion is drawn into flat walled capillaries. Using confocal microscopy and small angle x-ray scattering, we find that the shear near the capillary walls influences the crystallisation to result in large random hexagonal close-packed (RHCP) crystals with long-range orientational order over tens of thousands of colloidal particles. We investigate the crystallisation mechanism and find partial crystallisation under shear, initiating with hexagonal planes at the capillary walls, where shear is highest, followed by epitaxial crystal growth from these hexagonal layers after the shear is stopped. We then characterise the three dimensional crystal structure finding that the shear-induced crystallisation leads to larger particle separations parallel to the shear and vorticity directions as compared to the equilibrium RHCP structure. Confocal microscopy reveals that competing shear directions, where the capillary walls meet at a corner, create differently oriented hexagonal planes of particles. The single-orientation RHCP colloidal crystals remain stable after formation and are produced without the need of complex shear cell arrangements.	Oct 2022
I15-1-X-ray Pair Distribution Function (XPDF)	Liquid structure and dynamics in the choline acetate:urea 1:2 deep eutectic solvent Alessandro Triolo , Maria Enrica Di Pietro , Andrea Mele , Fabrizio Lo Celso , Martin Brehm , Valerio Di Lisio , Andrea Martinelli , Philip Chater , Olga Russina The Journal Of Chemical Physics 154 DOI: 10.1063/5.0054048 Diamond Proposal Number(s): [27222] Open Access Show Abstract ▼ Abstract: We report on the thermodynamic, structural, and dynamic properties of a recently proposed deep eutectic solvent, formed by choline acetate (ChAc) and urea (U) at the stoichiometric ratio 1:2, hereinafter indicated as ChAc:U. Although the crystalline phase melts at 36–38 °C depending on the heating rate, ChAc:U can be easily supercooled at sub-ambient conditions, thus maintaining at the liquid state, with a glass–liquid transition at about −50 °C. Synchrotron high energy x-ray scattering experiments provide the experimental data for supporting a reverse Monte Carlo analysis to extract structural information at the atomistic level. This exploration of the liquid structure of ChAc:U reveals the major role played by hydrogen bonding in determining interspecies correlations: both acetate and urea are strong hydrogen bond acceptor sites, while both choline hydroxyl and urea act as HB donors. All ChAc:U moieties are involved in mutual interactions, with acetate and urea strongly interacting through hydrogen bonding, while choline being mostly involved in van der Waals mediated interactions. Such a structural situation is mirrored by the dynamic evidences obtained by means of 1H nuclear magnetic resonance techniques, which show how urea and acetate species experience higher translational activation energy than choline, fingerprinting their stronger commitments into the extended hydrogen bonding network established in ChAc:U.	Jun 2021
I09-Surface and Interface Structural Analysis	Probing the dye–semiconductor interface in dye-sensitized NiO solar cells Nathan T. Z. Potts , Tamara Sloboda , Maria Wächtler , Ruri Agung Wahyuono , Valeria D’annibale , Benjamin Dietzek , Ute B. Cappel , Elizabeth A. Gibson The Journal Of Chemical Physics 153 DOI: 10.1063/5.0023000 Diamond Proposal Number(s): [18517, 22807] Show Abstract ▼ Abstract: The development of p-type dye-sensitized solar cells (p-DSSCs) offers an opportunity to assemble tandem photoelectrochemical solar cells with higher efficiencies than TiO2-based photoanodes, pioneered by O’Regan and Grätzel [Nature 353, 737–740 (1991)]. This paper describes an investigation into the behavior at the interfaces in p-DSSCs, using a series of BODIPY dyes, BOD1-3. The three dyes have different structural and electronic properties, which lead to different performances in p-DSSCs. We have applied photoelectron spectroscopy and transient absorption spectroscopy to rationalize these differences. The results show that the electronic orbitals of the dyes are appropriately aligned with the valence band of the NiO semiconductor to promote light-induced charge transfer, but charge-recombination is too fast for efficient dye regeneration by the electrolyte. We attribute this fast recombination, which limits the efficiency of the solar cells, to the electronic structure of the dye and the presence of Ni3+ recombination sites at the NiO surface.	Nov 2020
I07-Surface & interface diffraction	Structure of two-dimensional Fe3O4 Lindsay R. Merte , Pär A. T. Olsson , Mikhail Shipilin , Johan Gustafson , Florian Bertram , Chu Zhang , Henrik Grönbeck , Edvin Lundgren The Journal Of Chemical Physics 152 DOI: 10.1063/1.5142558 Diamond Proposal Number(s): [10342] Show Abstract ▼ Abstract: We have investigated the structure of an ultrathin iron oxide phase grown on Ag(100) using surface x-ray diffraction in combination with Hubbard-corrected density functional theory (DFT+U) calculations. The film exhibits a novel structure composed of one close-packed layer of octahedrally coordinated Fe2+ sandwiched between two close-packed layers of tetrahedrally coordinated Fe3+ and an overall stoichiometry of Fe3O4. As the structure is distinct from bulk iron oxide phases and the coupling with the silver substrate is weak, we propose that the phase should be classified as a metastable two-dimensional oxide. The chemical and physical properties are potentially interesting, thanks to the predicted charge ordering between atomic layers, and analogy with bulk ferrite spinels suggests the possibility of synthesis of a whole class of two-dimensional ternary oxides with varying electronic, optical, and chemical properties.	Mar 2020
I09-Surface and Interface Structural Analysis	Probing structural changes upon carbon monoxide coordination to single metal adatoms P. T. P. Ryan , M. Meier , Z. Jakub , J. Balajka , J. Hulva , D. J. Payne , T.-L. Lee , C. Franchini , F. Allegretti , G. S. Parkinson , D. A. Duncan The Journal Of Chemical Physics 152 DOI: 10.1063/1.5137904 Diamond Proposal Number(s): [13817] Open Access Show Abstract ▼ Abstract: In this work, the adsorption height of Ag adatoms on the Fe3O4(001) surface after exposure to CO was determined using normal incidence x-ray standing waves. The Ag adatoms bound to CO ( Ag CO 1 Ag1CO ) are found to be pulled out of the surface to an adsorption height of 1.15 Å ± 0.08 Å, compared to the previously measured height of 0.96 Å ± 0.03 Å for bare Ag adatoms and clusters. Utilizing DFT+vdW+U calculations with the substrate unit cell dimension fixed to the experimental value, the predicted adsorption height for Ag CO 1 Ag1CO was 1.16 Å, in remarkably good agreement with the experimental results.	Feb 2020
I15-Extreme Conditions	Experimental and simulation study of the high-pressure behavior of squalane and poly-α-olefins Iain J. Prentice , Xiaojiao Liu , Oleg A. Nerushev , Sashi Balakrishnan , Colin Pulham , Philip J. Camp The Journal Of Chemical Physics 152 DOI: 10.1063/1.5139723 Diamond Proposal Number(s): [193351] Show Abstract ▼ Abstract: The equation of state, dynamical properties, and molecular-scale structure of squalane and mixtures of poly-α-olefins at room temperature are studied with a combination of state-of-the-art, high-pressure experiments and molecular-dynamics simulations. Diamond-anvil cell experiments indicate that both materials are non-hydrostatic media at pressures above ∼1 GPa. The equation of state does not exhibit any sign of a first-order phase transition. High-pressure x-ray diffraction experiments on squalane show that there are no Bragg peaks, and hence, the apparent solidification occurs without crystallization. These observations are complemented by a survey of the equation of state and dynamical properties using simulations. The results show that molecular diffusion is essentially arrested above about 1 GPa, which supports the hypothesis that the samples are kinetically trapped in metastable amorphous-solid states. The shear viscosity becomes extremely large at very high pressures, and the coefficient governing its increase from ambient pressure is in good agreement with the available literature data. Finally, simulated radial distribution functions are used to explore the evolution of the molecular-scale structure with increasing pressure. Subtle changes in the short-range real-space correlations are related to a collapse of the molecular conformations with increasing pressure, while the evolution of the static structure factor shows excellent correlation with the available x-ray diffraction data. These results are of indirect relevance to oil-based lubricants, as the pressures involved are comparable to those found in engines, and hence, the ability of lubricating thin films to act as load-bearing media can be linked to the solidification phenomena studied in this work.	Feb 2020
I06-Nanoscience	Photoemission core level binding energies from multiple sized nanoparticles on the same support: TiO 2 (110)/Au Andrew Mellor , Axel Wilson , Chi L. Pang , Chi M. Yim , Francesco Maccherozzi , Sarnjeet S. Dhesi , Christopher A. Muryn , Hicham Idriss , Geoff Thornton The Journal Of Chemical Physics 152 DOI: 10.1063/1.5135760 Diamond Proposal Number(s): [13723] Show Abstract ▼ Abstract: A novel method of measuring the core level binding energies of multiple sized nanoparticles on the same substrate is demonstrated using the early stage of Au nanoparticle growth on reduced r-TiO2(110). This method employed in situ scanning tunneling microscopy (STM) and microfocused X-ray photoemission spectroscopy. An STM tip-shadowing method was used to synthesize patterned areas of Au nanoparticles on the substrate with different coverages and sizes. Patterns were identified and imaged using a UV photoelectron emission microscope. The Au 4f core level binding energies of the nanoparticles were investigated as a function of Au nanoparticle coverage and size. A combination of initial and final state effects modifies the binding energies of the Au 4f core levels as the nanoparticle size changes. When single Au atoms and Au3 clusters are present, the Au 4f7/2 binding energy, 84.42 eV, is similar to that observed at a high coverage (1.8 monolayer equivalent), resulting from a cancellation of initial and final state effects. As the coverage is increased, there is a decrease in binding energy, which then increases at a higher coverage to 84.39 eV. These results are consistent with a Volmer-Weber nucleation-growth model of Au nanoparticles at oxygen vacancies, resulting in electron transfer to the nanoparticles.	Jan 2020

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