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98 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS	Ammonia oxidation over a Pt25Rh75(001) model catalyst surface: an operando study Andrea Resta , Uta Hejral , Sara Blomberg , Stefano Albertin , Alina Vlad , Yves Garreau , Corentin Chatelier , Federica Venturini , Pilar Ferrer , Georg Held , Dave Grinter , Edvin Lundgren , Alessandro Coati The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c07128 Diamond Proposal Number(s): [21936] Show Abstract ▼ Abstract: The reaction of ammonia oxidation over PtRh binary alloy has been studied with a surface science approach by operando techniques such as Near Ambient Pressure X-Ray Photoemission Spectroscopy (NAP-XPS) and Surface X-Ray Diffraction (SXRD) combined with mass spectrometry. The article will explore the surface evolution across five different oxygen to ammonia ratios in the millibar regime for two different temperatures. The presented data-set allows to link variations in the atomic structures measured by diffraction methods and surface species information from NAP-XPS to reaction products in the gas phase. We will show that NO production coincides with significant changes of the surface structure and the formation of a RhO2 surface oxide. It was also observed that the RhO2 surface oxide only fully forms when the nitrogen signal in the N1s has disappeared.	Sep 2020
I07-Surface & interface diffraction	The calcite (104) surface - electrolyte structure: A 3D comparison of surface x-ray diffraction and simulations Sander J. T. Brugman , Paolo Raiteri , Paolo Accordini , Frank Megens , Julian D Gale , Elias Vlieg The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c04094 Diamond Proposal Number(s): [18591] Show Abstract ▼ Abstract: Adsorption and incorporation of ions is known to influence the morphology and growth of calcite. Using surface X-ray diffraction, the interfacial structure of calcite in contact with CaCO3, MgCl2, CaCl2 and BaCl2 solutions was determined. All of these conditions yield a comparable interfacial structure, meaning that there is no significant ion adsorption on the terraces under the investigated conditions. This allows for the first time a thorough comparison in all three dimensions with state-of-the-art computer simulations, involving molecular dynamics based on both DFT and two different force field models. Additionally, the simulated structures are used to calculate the corresponding structure factors, which in turn are compared to those obtained from experiment, thereby avoiding the need for fitting or subjective interpretation. In general, there is a good agreement between experiment and the simulations, though there are some small discrepancies in the atomic positions, which lead to an inadequate fit of certain features characteristic of the structure of water at the interface. Of the three simulation methods examined, the DFT results were found to agree best with the experimental structure.	Jul 2020
I09-Surface and Interface Structural Analysis	Incorporation of europium in Bi2Te3 topological insulator epitaxial films Celso I. Fornari , Hendrik Bentmann , Sergio L. Morelhao , Thiago R. F. Peixoto , Paulo Rappl , Abdul Tcakaev , Volodymyr Zabolotnyy , Martin Kamp , Tien-lin Lee , Chul-hee Min , Philipp Kagerer , Raphael Vidal , Anna Isaeva , Michael Ruck , Vladimir Hinkov , Friedrich Reinert , Eduardo Abramof The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c05077 Show Abstract ▼ Abstract: In the field of topological materials, the interaction between band topology and magnetism remains a current frontier for the advance of new topological states and spintronic functionalities. Doping with rare-earth elements with large magnetic moment is a current approach to exploit the phenomenology of such interaction. However, dopant solubility into the main matrix plays a major role. In this sense, the present work is focused on elucidating how Eu incorporates into Bi2Te3 lattice as a function of doping. This work reports a systematic investigation of the structural and electronic properties of bismuth telluride epitaxial layers doped with Eu. Bi2Te3 films were grown by molecular beam epitaxy (MBE) on (111) BaF2 substrates with nominal Eu doping ranging from 0 % up to 9 %. X-ray diffraction (XRD) analysis and scanning transmission electron microscopy (TEM) reveal that Eu atoms enter substitutionally on Bi sites up to 4 % of Eu doping. In contrast, the 9 % Eu-doped sample contains epitaxially oriented nanoclusters of EuTe. X ray photoelectron (XPS) and absorption (XAS) spectroscopies show that Eu atoms enter into the Bi2Te3 crystal matrix in the divalent Eu2+ state for all Eu concentrations. Angle resolved photoemission (ARPES) experiments indicate that the topological surface state is preserved in the presence of the local magnetic moments introduced by the Eu impurities.	Jun 2020
I15-1-X-ray Pair Distribution Function (XPDF)	Dye-anchoring modes at the dye...TiO2 interface of n3- and n749-sensitized solar cells revealed by glancing-angle pair distribution function analysis Karim T. Mukaddem , Philip A. Chater , Leon R. Devereux , Othman K. K. Al Bahri , Apoorv Jain , Jacqueline M. Cole The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c02314 Diamond Proposal Number(s): [16036, 19288] Show Abstract ▼ Abstract: The efficient transport of electrons from the sunlight-harvesting dye molecules into the electrical circuit of a dye-sensitized solar cell (DSSC) is imperative to its effective operation. A dye···semiconductor interface comprises the working electrode of a DSSC. Dye molecules adsorb onto the semiconductor surface, whereupon they transfer electronic charge into the conduction band of the semiconductor; this process initiates the electrical circuit. It is therefore important to characterize this interfacial structure in order to understand how efficiently the dye binds, or anchors, onto the semiconductor surface and imparts charge transfer to it. Armed with such knowledge, the performance of DSSCs may then be improved systematically. The structural determination of a thin-film interface is nonetheless a challenging task. We herein report the results of a glancing-angle pair distribution function (gaPDF) experiment that generated synchrotron x-ray diffraction patterns of N3- and N749-sensitized DSSC working electrodes. This gaPDF experimental approach represents the first diffraction-based strategy for the characterization of intact DSSC working electrodes. The gaPDF structural signatures were compared with PDFs simulated from two possible interfacial structures that were computed using density functional theory (DFT); these simulated structures showed the dyes anchoring in two distinct modes: a bridging bidentate and a monodentate ester configuration. The differences between the experimental observation and these simulated structures revealed a preference for each dye, N3 and N749, to adopt a bidentate bridging dye anchoring mode when sensitized onto TiO2. This work not only demonstrates the successful application of a gaPDF method to DSSC research, it also advocates the applicability of gaPDF to many types of thin-film samples.	May 2020
I07-Surface & interface diffraction	In-situ observations of the growth mode of vacuum deposited α-sexithiophene Thomas L. Derrien , Andreas E. Lauritzen , Pascal Kaienburg , Josue F. M. Hardigree , Christopher Nicklin , Moritz K. Riede The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c00447 Diamond Proposal Number(s): [20426, 24871] Open Access Show Abstract ▼ Abstract: The real-time morphological evolution of vacuum deposited α-sexithiophene (α-6T) on a weakly interacting (glass) substrate at ambient temperature is reported. In-situ grazing incidence small angle X-ray scattering (GISAXS) enabled the observation of nanoscale aggregates while in-situ grazing incidence wide angle scattering (GIWAXS) allowed the study of the molecular-scale morphology. The in-situ GISAXS measurements revealed that the α-6T growth proceeds via a Stranski-Krastanov mode, whereby 2-4 complete monolayers are deposited followed by subsequent layers formed via island growth. In-situ GIWAXS also showed the evolution of the polymorph composition during the thin film growth. Initially the disordered β-phase and the low-temperature (LT) phase are deposited in nearly equal proportion until a thickness of 8 nm whereby the LT-phase begins to dominate until a final α-6T thickness of 50 nm where the scattering intensity of the LT-phase is more than double that of the β-phase. The change in polymorph composition coincided with an increase in the LT-phase d-spacing, indicating a lattice strain relief as the thin film moves from surface to bulk mediated growth. The GISAXS findings were confirmed through direct imaging using ex-situ atomic force microscopy (AFM) at various thicknesses revealing the existence of both initial monolayers and intermediate and final island morphologies. The findings reveal the real-time morphological evolution of α-6T across both the molecular scale and the nanoscale and highlight the role of strain in polymorph growth. Due to the importance of thin film microstructure in device performance, it is expected that these results will aid in the development of the structure-property relationships necessary to realise the full potential of organic electronics.	May 2020
I09-Surface and Interface Structural Analysis	Improving capacity retention of Li2VO2F Li-rich cathodes with film-forming additives Ida Kallquist , Jean-frederic Martin , Andrew Naylor , Christian Baur , Maximilian Fichtner , Jean-francois Colin , Daniel Brandell , Kristina Edstrom , Maria Hahlin The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c02840 Diamond Proposal Number(s): [20870] Show Abstract ▼ Abstract: Li-rich disordered rock-salt structures have due to their high theoretical capacity gained large attention as a promising class of cathode materials for battery applications. However, the cycling stability of these materials have so far been less satisfactory. Here, we present three different film forming electrolyte additives; lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), and glycolide, which all improve the cycling performance of the high capacity Li-rich disordered rock-salt material Li2VO2F. The best performing additive, LiODFB, show a 12.5% increase of capacity retention after 20 cycles. The improved cycling performance is explained by the formation of a more robust cathode interphase on the electrode surface. Photoelectron spectroscopy is used to show that the surface layer is created from oxidation of the electrolyte salt and additive co-salts. This passivating layer can mitigate oxidation and following degradation of the active material, and thus a higher degree of redox active vanadium can be maintained after 20 cycles.	May 2020
	Length-dependent electron spin polarization in oligopeptides and DNA Suryakant Mishra , Amit Kumar Mondal , Shubhadeep Pal , Tapan Kumar Das , Eilam Z. B. Smolinsky , Giuliano Siligardi , Ron Naaman The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c02291 Show Abstract ▼ Abstract: The effect of spin polarization in conduction and electric field-induced polarization was measured for double-stranded DNA oligonucleotides and oligopeptides of different lengths. The measurements were conducted using magnetic contact AFM, spin-dependent electrochemistry, spin-dependent polarization, and magnetoresistance studies. It was established that the spin-dependent conduction through chiral molecules depends on the voltage applied with a power of d, when d is larger than unity, and that there is a different voltage threshold for conducting each of the spin polarizations. In addition, there is no spin flipping during the conduction through the chiral system. The spin polarization depends linearly on the length, within the range of lengths studied, and it seems to scale like the optical activity. These results suggest the importance of the electric polarizability in the chiral-induced spin selectivity process.	Apr 2020
I22-Small angle scattering & Diffraction	Nucleation pathway of calcium sulfate hemihydrate (bassanite) from solution: Implications for calcium sulfates on Mars Tomasz M. Stawski , Rogier Besselink , Konstantinos Chatzipanagis , Jorn Hovelmann , Liane G. Benning , Alexander E. S. Van Driessche The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c01041 Diamond Proposal Number(s): [16256] Show Abstract ▼ Abstract: CaSO4 minerals (i.e. gypsum, anhydrite and bassanite) are widespread in natural and industrial environments. During the last several years, a number of studies have revealed that nucleation in the CaSO4-H2O system is non-classical, where the formation of crystalline phases involves several steps. Based on these recent insights we have formulated a tentative general model for calcium sulfate precipitation from solution. This model involves primary species that are formed through the assembly of multiple Ca2+ and SO42- ions into nanoclusters. These nanoclusters assemble into poorly ordered (i.e. amorphous) hydrated aggregates, which in turn undergo ordering into coherent crystalline units. The thermodynamic (meta)stability of any of the three CaSO4 phases is regulated by temperature, pressure and ionic strength with gypsum being the stable form at low temperatures and low to medium ionic strengths, and anhydrite the stable phase at high temperatures and lower temperature at high salinities. Bassanite is metastable across the entire phase diagram but readily forms as the primary phase at high ionic strengths across a wide range of temperatures, and can persist up to several months. Although the physicochemical conditions leading to bassanite formation in aqueous systems are relatively well established, nanoscale insights into the nucleation mechanisms and pathways are still lacking. To fill this gap, and to further improve our general model for calcium sulfate precipitation, we conducted in situ scattering measurements at small- and wide-angles (SAXS/WAXS) and complemented these with in situ Raman spectroscopic characterization. Based on these experiments we show that the process of formation of bassanite from aqueous solutions is very similar to the formation of gypsum: it involves the aggregation of small primary species into larger disordered aggregates, only from which the crystalline phase develops. These data thus confirm our general model of CaSO4 nucleation and provide clues to explain the abundant occurrence of bassanite on the surface of Mars (and not on the surface of Earth).	Mar 2020
	Adsorbate isotherm analysis by reflection anisotropy spectroscopy on copper (110) in hydrochloric acid Saul Vazquez-miranda , Vladyslav Solokha , Raul E. Balderas-navarro , Kurt Hingerl , Christoph Cobet The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.9b11326 Open Access Show Abstract ▼ Abstract: Reflectance anisotropy spectroscopy (RAS) is a powerful optical probe that works on a polarization contrast basis. It can be operated in any environment, ranging from ultrahigh vacuum to vapor phases and liquids. The measured optical anisotropies are caused by several symmetry breaking effects and are exclusively assigned to the surface for otherwise bulk isotropic materials. In this work, we present a systematic study comprising in situ RAS-transient to assess the surface thermodynamics of the chloride adsorption on Cu(110) upon systematic variations of the applied electrode potentials in comparison to cyclic voltammetry (CV). Numerical time-derivatives of the measured RAS-transients are shown to be exclusively associated with electrical currents of those electrochemical reactions, which change the properties of the electrode surface. The recorded transient line-shapes track the Frumkin type isotherm properties related to chloride coverage. Both connections are theoretically discussed. Owing to the surface and interface specificity, RAS is shown to exhibit a high surface sensitivity. In particular, processes taking place in parallel, namely, the hydrogen evolution reaction (HER) as well as the copper dissolution as Cu+ and Cu2+, do not contribute to the RAS response.	Feb 2020
I15-Extreme Conditions	Small ionic radius limits magnesium water interaction in amorphous calcium/magnesium carbonates Anders C. S. Jensen , Silvia Imberti , Wouter J. E. M. Habraken , Luca Bertinetti The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.9b11594 Diamond Proposal Number(s): [15157] Show Abstract ▼ Abstract: The stabilizing effect of magnesium ions on amorphous calcium carbonate has been studied extensively due to its wide spread occurrence in biogenic minerals. It has long been suggested that magnesium binds water more strongly compared to calcium given its relatively high dehydration energy. However, recent work has shown that mobility increases in the presence of magnesium ion relative to the pure calcium phase. Using total scattering and EPSR modelling, we show here that in amorphous magnesium carbonate, because of the small size of the ion, the coordination number of magnesium is smaller and the interaction with water are therefore limited. As a result, ~35% of water molecules are bound exclusively by hydrogen bonds mainly to the anions.	Feb 2020

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