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132 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
I09-Surface and Interface Structural Analysis	Structure of monolayer 2H − TaS2 on Au(111) Caio C. Silva , Daniela Dombrowski , Abdus Samad , Jiaqi Cai , Wouter Jolie , Joshua Hall , Paul Ryan , Pardeep K. Thakur , David A. Duncan , Tien-Lin Lee , Udo Schwingenschlögl , Carsten Busse Physical Review B 104 DOI: 10.1103/PhysRevB.104.205414 Diamond Proposal Number(s): [14799, 16710, 19801] Show Abstract ▼ Abstract: We determined the structure of epitaxial 2H-TaS2 on Au(111) using the method of x-ray standing waves (XSW), supported by density functional theory (DFT) calculations and scanning tunneling microscopy (STM). The lattice mismatch between substrate and overlayer gives rise to a moiré superstructure, which modulates the structural and electronic properties. For a specific registry (S atoms directly above Au substrate atoms), local covalentlike bonds form, whereas globally weak van der Waals bonding prevails. Still, the TaS2 layer remains rather flat. Significant charge transfer from Au(111) into the conduction band of the two-dimensional material is found.	Nov 2021
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS	Identification of adsorbed species and surface chemical state on Ag(111) in the presence of ethylene and oxygen studied with infrared and X-ray spectroscopies Adva Ben Yaacov , Roey Ben David , David C. Grinter , Georg Held , Baran Eren Physchem 1, 259 - 271 DOI: 10.3390/physchem1030020 Diamond Proposal Number(s): [25970] Open Access Show Abstract ▼ Abstract: Using a combination of two surface-sensitive spectroscopy techniques, the chemical state of the Ag(111) surface and the nature of the adsorbed species in the presence of ethylene and oxygen gases are identified. In the 10 mbar pressure range and 25–200 °C studied here, Ag(111) remains largely metallic even in O2-rich conditions. The only adsorbed molecular species with a low but discernible coverage is surface carbonate, which forms due to further oxidation of produced CO2, in a similar manner to its formation in ambient air on Ag surfaces. Its formation is also pressure-dependent, for instance, it is not observed when the total pressure is in the 1 mbar pressure range. Production of carbonate, along with carbon dioxide and water vapor as the main gas-phase products, suggests that an unpromoted Ag(111) surface catalyzes mainly the undesired full oxidation reaction.	Nov 2021
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS	Near-ambient pressure XPS and NEXAFS study of a superbasic ionic liquid with CO2 Jordan Cole , Zoe Henderson , Andrew G. Thomas , Claudia L. Compeán-González , Adam Greer , Christopher Hardacre , Federica Venturini , Wilson Quevedo Garzon , Pilar Ferrer , David C. Grinter , Georg Held , Karen L. Syres The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.1c05738 Diamond Proposal Number(s): [20532] Show Abstract ▼ Abstract: In situ photoemission and near-edge X-ray absorption fine structure (NEXAFS) techniques have been used to study the interaction of CO2 with an ionic liquid thin film. A thin film of the superbasic ionic liquid (SBIL) trihexyltetradecylphosphonium benzimidazolide ([P66614][benzim]) was prepared on a rutile TiO2 (110) surface and exposed to CO2 at near-ambient pressures. NEXAFS measurements combined with density functional theory calculations indicate a realignment of [benzim]− anions from 27° from the surface normal to 54° upon exposure to CO2. Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) shows evidence of irreversible CO2 absorption in thin films of [P66614][benzim] and a greater concentration of CO2-reacted anions in the deeper layers. These results give a new perspective on CO2 uptake in ionic liquids and fundamental interactions at the liquid–gas interface. Understanding this interfacial behavior is important for developing ILs for gas capture applications and may influence the performance of other IL-based technologies.	Oct 2021
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS I11-High Resolution Powder Diffraction	Importance of hydrogen migration in catalytic ammonia synthesis over yttrium-doped barium zirconate-supported ruthenium nanoparticles: Visualization of proton trap sites Christopher Foo , Joshua Fellowes , Huihuang Fang , Alexander Large , Simson Wu , Georg Held , Elizabeth Raine , Ping-Luen Ho , Chiu Tang , Shik Chi Edman Tsang The Journal Of Physical Chemistry C 2 DOI: 10.1021/acs.jpcc.1c04002 Show Abstract ▼ Abstract: Barium zirconate perovskites have been systematically investigated as protonic supports for ruthenium nanoparticles in the Haber–Bosch ammonia synthesis reaction. A series of supports based on barium zirconate were synthesized, for which the B-site of the ABO3 perovskite was doped with different aliovalent acceptor cations and in varying ratios, resulting in varying proton conductivities and trapping behaviors. Crucially, we provide direct evidence of the importance of a hydrogen-migration mechanism for ammonia synthesis over these proton-conducting materials from the studies of reaction kinetics, in situ X-ray photoelectron spectroscopy, and neutron powder diffraction (NPD), which requires the proper balance of oxygen vacancy concentration (B-site doping), trapping-site concentration, and proton-hopping activation energy. We report evidence of a large dynamic coverage of OH groups on the support and the first visualization of both weak and strong proton trap sites within the perovskite lattice through the use of NPD.	Oct 2021
I09-Surface and Interface Structural Analysis	Tuning band alignment at a semiconductor-crystalline oxide heterojunction via electrostatic modulation of the interfacial dipole M. Chrysler , J. Gabel , T.-L. Lee , A. N. Penn , B. E. Matthews , D. M. Kepaptsoglou , Q. M. Ramasse , J. R. Paudel , R. K. Sah , J. D. Grassi , Z. Zhu , A. X. Gray , J. M. Lebeau , S. R. Spurgeon , S. A. Chambers , P. V. Sushko , J. H. Ngai Physical Review Materials 5 DOI: 10.1103/PhysRevMaterials.5.104603 Diamond Proposal Number(s): [25582, 26487] Show Abstract ▼ Abstract: We demonstrate that the interfacial dipole associated with bonding across the SrTi O 3 / Si heterojunction can be tuned through space charge, thereby enabling the band alignment to be altered via doping. Oxygen impurities in Si act as donors that create space charge by transferring electrons across the interface into SrTi O 3 . The space charge induces an electric field that modifies the interfacial dipole, thereby tuning the band alignment from type II to III. The transferred charge, accompanying built-in electric fields, and change in band alignment are manifested in electrical transport and hard x-ray photoelectron spectroscopy measurements. Ab initio models reveal the interplay between polarization and band offsets. We find that band offsets can be tuned by modulating the density of space charge across the interface. Modulating the interface dipole to enable electrostatic altering of band alignment opens additional pathways to realize functional behavior in semiconducting hybrid heterojunctions.	Oct 2021
I09-Surface and Interface Structural Analysis	Identification of hidden orbital contributions in the La0.65Sr0.35MnO3 valence band F. Offi , K. Yamauchi , S. Picozzi , V. Lollobrigida , A. Verna , C. Schlueter , T.-L. Lee , A. Regoutz , D. J. Payne , A. Petrov , G. Vinai , G. M. Pierantozzi , T. Pincelli , G. Panaccione , F. Borgatti Physical Review Materials 5 DOI: 10.1103/PhysRevMaterials.5.104403 Diamond Proposal Number(s): [11322] Show Abstract ▼ Abstract: Hybridization of electronic states and orbital symmetry in transition metal oxides are generally considered key ingredients in the description of both their electronic and magnetic properties. In the prototypical case of La 0.65 Sr 0.35 MnO 3 (LSMO), a landmark system for spintronics applications, a description based solely on Mn 3 d and O 2 p electronic states is reductive. We thus analyzed elemental and orbital distributions in the LSMO valence band through a comparison between density functional theory calculations and experimental photoelectron spectra in a photon energy range from soft to hard x rays. We reveal a number of hidden contributions, arising specifically from La 5 p , Mn 4 s , and O 2 s orbitals, considered negligible in previous analyses; our results demonstrate that all these contributions are significant for a correct description of the valence band of LSMO and of transition metal oxides in general.	Oct 2021
I09-Surface and Interface Structural Analysis	Atomic-scale structure of chemically distinct surface oxygens in redox reactions Anusheela Das , Haesun Park , Yanna Chen , Devika Choudhury , Tien-Lin Lee , Jeffrey W. Elam , Peter Zapol , Michael J. Bedzyk Journal Of The American Chemical Society DOI: 10.1021/jacs.1c07926 Diamond Proposal Number(s): [15748] Show Abstract ▼ Abstract: During redox reactions, oxide-supported catalytic systems undergo structural and chemical changes. Improving subsequent catalytic properties requires an understanding of the atomic-scale structure with chemical state specificity under reaction conditions. For the case of 1/2 monolayer vanadia on α-TiO2(110), we use X-ray standing wave (XSW) excited X-ray photoelectron spectroscopy to follow the redox induced atomic positional and chemical state changes of this interface. While the resulting XSW 3D composite atomic maps include the Ti and O substrate atoms and V surface atoms, our focus in this report is on the previously unseen surface oxygen species with comparison to density functional theory predictions.	Oct 2021
I09-Surface and Interface Structural Analysis	A halogen-free and flame-retardant sodium electrolyte compatible with hard carbon anodes Lars Olow Simon Colbin , Ronnie Mogensen , Alexander Buckel , Yong‐lei Wang , Andrew J. Naylor , Jolla Kullgren , Reza Younesi Advanced Materials Interfaces DOI: 10.1002/admi.202101135 Diamond Proposal Number(s): [26551] Open Access Show Abstract ▼ Abstract: For sodium-ion batteries, two pressing issues concerning electrolytes are flammability and compatibility with hard carbon anode materials. Non-flammable electrolytes that are sufficiently stable against hard carbon have—to the authors’ knowledge—previously only been obtained by either the use of high salt concentrations or additives. Herein, the authors present a simple, fluorine-free, and flame-retardant electrolyte which is compatible with hard carbon: 0.38 m sodium bis(oxalato)borate (NaBOB) in triethyl phosphate (TEP). A variety of techniques are employed to characterize the physical properties of the electrolyte, and to evaluate the electrochemical performance in full-cell sodium-ion batteries. The results reveal that the conductivity is sufficient for battery operation, no significant self-discharge occurs, and a satisfactory passivation is enabled by the electrolyte. In fact, a mean discharge capacity of 107 ± 4 mAh g−1 is achieved at the 1005th cycle, using Prussian white cathodes and hard carbon anodes. Hence, the studied electrolyte is a promising candidate for use in sodium-ion batteries.	Oct 2021
I09-Surface and Interface Structural Analysis	Ge 4s2 lone pairs and band alignments in GeS and GeSe for photovoltaics Matthew J. Smiles , Jonathan M. Skelton , Huw Shiel , Leanne A. H. Jones , Jack E. N. Swallow , Holly J. Edwards , Thomas Featherstone , Philip A. E. Murgatroyd , Pardeep K. Thakur , Tien-Lin Lee , Vinod R. Dhanak , Tim D. Veal Journal Of Materials Chemistry A DOI: 10.1039/D1TA05955F Diamond Proposal Number(s): [21431, 23160] Open Access Show Abstract ▼ Abstract: Germanium sulfide and germanium selenide bulk crystals were prepared using a melt growth technique. X-ray photoemission spectroscopy (XPS) was used to determine ionisation potentials of 5.74 and 5.48 eV for GeS and GeSe respectively. These values were used with the previously-measured band gaps to establish the natural band alignments with potential window layers for solar cells and to identify CdS and TiO2 as sensible choices. The ionisation potential of GeS is found to be smaller than in comparable materials. Using XPS and hard x-ray photoemission (HAXPES) measurements in conjunction with density-functional theory calculations, we demonstrate that stereochemically active Ge 4s lone pairs are present at the valence-band maxima. Our work thus provides direct evidence for active lone pairs in GeS and GeSe, with important implications for the applications of these and related materials, such as Ge-based perovskites.	Sep 2021
I09-Surface and Interface Structural Analysis	Chemical shielding of H2O and HF encapsulated inside a C60 cage Samuel P. Jarvis , Hongqian Sang , Filipe Junqueira , Oliver Gordon , Joe E. A. Hodgkinson , Alex Saywell , Philipp Rahe , Salvatore Mamone , Simon Taylor , Adam Sweetman , Jeremy Leaf , David A. Duncan , Tien-Lin Lee , Pardeep K. Thakur , Gabriella Hoffman , Richard J. Whitby , Malcolm H. Levitt , Georg Held , Lev Kantorovich , Philip Moriarty , Robert G. Jones Communications Chemistry 4 DOI: 10.1038/s42004-021-00569-0 Diamond Proposal Number(s): [12979, 15022] Open Access Show Abstract ▼ Abstract: Molecular surgery provides the opportunity to study relatively large molecules encapsulated within a fullerene cage. Here we determine the location of an H2O molecule isolated within an adsorbed buckminsterfullerene cage, and compare this to the intrafullerene position of HF. Using normal incidence X-ray standing wave (NIXSW) analysis, coupled with density functional theory and molecular dynamics simulations, we show that both H2O and HF are located at an off-centre position within the fullerene cage, caused by substantial intra-cage electrostatic ﬁelds generated by surface adsorption of the fullerene. The atomistic and electronic structure simulations also reveal signiﬁcant internal rotational motion consistent with the NIXSW data. Despite this substantial intra-cage interaction, we ﬁnd that neither HF or H2O contribute to the endofullerene frontier orbitals, conﬁrming the chemical isolation of the encapsulated molecules. We also show that our experimental NIXSW measurements and theoretical data are best described by a mixed adsorption site model.	Sep 2021

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