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103 items found (0 items not approved), displaying 51 to 60.[First/Prev] 2, 3, 4, 5, 6, 7, 8, 9 [Next/Last]

Instruments / Technical Area	Publication Details	Published
	Computational and Experimental Study of Ta 2 O 5 Thin Films Sanjayan Sathasivam , Benjamin A. D. Williamson , Andreas Kafizas , Shaeel A. Althabaiti , Abdullah Y. Obaid , Sulaiman N. Basahel , David O. Scanlon , Claire J. Carmalt , Ivan P. Parkin The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.6b11073 Show Abstract ▼ Abstract: This paper reports the novel synthesis of amorphous Ta2O5 and the subsequent isolation of the orthorhombic (β) crystallographic phase, using aerosol-assisted chemical vapor deposition. Hybrid density functional theory was used to obtain the calculated optical band gap (3.83 eV) for the first time, which closely matches our experimental findings (3.85 eV). The films were highly transparent in the visible and near-IR region of the electromagnetic spectrum. The refractive indexes, calculated using the Swanepoel method, showed good agreement with literature findings. The photocatalytic properties of the films, determined through the photominerilization of stearic acid under 254 nm radiation showed the amorphous sample to be an order of magnitude superior over crystalline β-Ta2O5.	Jan 2017
	Adsorption of Methyl Acetoacetate at Ni{111}: Experiment and Theory Jorge Ontaneda , Richard E. J. Nicklin , Alix Cornish , Alberto Roldan , Ricardo Grau-crespo , Georg Held The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.6b10023 Show Abstract ▼ Abstract: The hydrogenation of methyl acetoacetate (MAA) over modified Ni catalysts is one of the most important and best studied reactions in heterogeneous enantioselective catalysis. Yet, very little molecular-level information is available on the adsorption complex of the reactant. Here, we report on a combined experimental and theoretical study of MAA adsorption on Ni{111}. XPS shows that the chemisorbed layer is stable up to 250 K; above 250 K, decomposition sets in. In ultra-high-vacuum conditions, multilayers grow below 150 K. DFT modeling predicts a deprotonated enol species with bidentate coordination on the flat Ni{111} surface. The presence of adatoms on the surface leads to stronger MAA adsorption in comparison with the flat surface, whereby the stabilization energy is high enough for MAA to drive the formation of adatom defects at Ni{111}, assuming the adatoms come from steps. Comparison of experimental XPS and NEXAFS data with theoretical modeling, however, identifies the bidentate deprotonated enol on the flat Ni{111} surface as the dominant species at 250 K, indicating that the formation of adatom adsorption complexes is kinetically hindered at low temperatures.	Nov 2016
I11-High Resolution Powder Diffraction	The Mixing Behavior of Alkanes Adsorbed on Hexagonal Boron Nitride Matt Forster , Julia E. Parker , Akira Inaba , Claire A. Murray , Nicholas A. Strange , John Z. Larese , Thomas Arnold The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.6b07701 Diamond Proposal Number(s): [8994] Open Access Show Abstract ▼ Abstract: In this work we report the mixing behavior of a series of normal-alkanes adsorbed on the surface of hexagonal boron nitride (h-BN) using X-ray powder diffraction. We have investigated a range of simple binary mixtures which are indicative of a rich phase behavior with examples of complete mixing, partial mixing and phase separation. On graphite surfaces, the mixing behavior is strongly influenced by the structure of the pure components; the odd-even effect seen in the pure structures, which favors either a “herringbone” or “parallel” structure, influences the miscibility of alkanes within the monolayer. On h-BN a more complex phase behavior is observed with partial mixing or phase separation depending upon the exact composition of the monolayer. In particular, we see improved miscibility for certain mixtures containing n-decane which we associate with the fact that pure n-decane has been observed with both herringbone and parallel structures on h-BN. This difference between these two very similar substrates is a sensitive indicator of the subtle interplay between surface-molecule and molecule-molecule interactions that govern the phase behavior of these systems.	Oct 2016
I11-High Resolution Powder Diffraction	Cation Control of Molecular Sieving by Flexible Li-Containing Zeolite Rho Magdalena M. Lozinska , Enzo Mangano , Alex G. Greenaway , Robin Fletcher , Stephen P. Thompson , Claire A. Murray , Stefano Brandani , Paul A. Wright The Journal Of Physical Chemistry C 120, 19652 - 19662 DOI: 10.1021/acs.jpcc.6b04837 Diamond Proposal Number(s): [9027, 11830] Show Abstract ▼ Abstract: The adsorption of CO2 on zeolite Li-Rho (unit cell composition Li9.8Al9.8Si38.2O96) has been investigated by the measurement of adsorption isotherms (273–300 K), breakthrough curves with a CO2/CH4/He mixture (308 K), and in situ synchrotron X-ray powder diffraction in CO2 (298 K). The Rho framework distorts when in the Li-form to give a shape selective adsorbent for CO2 over CH4, although breakthrough curves reveal diffusional limitations. In situ synchrotron powder XRD follows the expansion of the Li-Rho unit cell upon adsorption, which remains single phase to a CO2 pressure of ca. 0.6 bar. Partial cation exchange of Li-Rho by Na+ or Cs+ gives two series of M,Li-Rho zeolites (M = Na, Cs). Where the occupancy of window sites (8R, D8R) between lta cages is less than 50%, hysteresis is not observed in CO2 isotherms at 298 K. For Cs1.8Li8-Rho, which has a larger unit cell and a wider window than zeolite Li-Rho due to the presence of large Cs+ cations in double 8-ring sites, breakthrough curves indicate faster CO2 diffusion without significant loss of selectivity. We propose this control of adsorption kinetics of the flexible zeolite Rho via modification of cation content as a mechanism for cation controlled molecular sieving.	Sep 2016
I22-Small angle scattering & Diffraction	Tuning the Interaction of Nanoparticles from Repulsive to Attractive by Pressure Martin Alfred Schroer , Florian Schulz , Felix Lehmkühler , Johannes Möller , Andrew J. Smith , Holger Lange , Tobias Vossmeyer , Gerhard Grübel The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.6b06847 Diamond Proposal Number(s): [11192] Show Abstract ▼ Abstract: We report a high pressure small-angle X-ray scattering (SAXS) study on concentrated aqueous suspensions of gold nanoparticles coated with a poly(ethylene glycol) (PEG)-based ligand shell. Analyzing the experimental SAXS data with a liquid-state theory approach, we find a pressure-induced transition of the interparticle interactions from repulsive to attractive in the pressure range from 1 to 4000 bar that also depends on the particle concentration. This transition is related to structural changes of the ligand shell which is compressed with increasing pressure. Our study highlights the important, yet unexplored role of pressure for the interaction of nanoparticle systems.	Aug 2016
I11-High Resolution Powder Diffraction	In situ Electron Paramagnetic Resonance and X-Ray Diffraction Monitoring of Temperature-Induced Breathing and Related Structural Transformations in Activated V-doped MIL-53(Al) Irena Nevjestic , Hannes Depauw , Karen Leus , Geert Rampelberg , Claire Murray , Christophe Detavernier , Pascal Van Der Voort , Freddy Callens , Henk Vrielinck The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.6b04402 Diamond Proposal Number(s): [12401] Show Abstract ▼ Abstract: The Metal-Organic Framework MIL-53(Al) is characterized by a distinct reversible structural transition between a narrow pore (NP) and a large pore (LP) state, resulting in expansion or contraction of this three-dimensional porous framework also called breathing. This transition is studied for vanadium-doped MIL-53(Al), induced by temperature (T) using in situ Electron Paramagnetic Resonance (EPR) and X-ray Diffraction (XRD) in air and in vacuum. The EPR active VIV=O molecular ions are used as local probes to detect the NP to LP transitions. The EPR spectra of VIV=O embedded in the NP and LP MIL-53(Al) states are clearly distinguishable. The temperature dependent EPR and XRD data can consistently be interpreted in terms of T-ranges in the experiments where one of the states is predominantly present and a narrow T-range in which the two states coexist. In addition the XRD data indicate that the NP state undergoes a transition to a metastable state characterized by different lattice parameters than the NP state at room temperature, before the transition to the LP state occurs. The EPR spectra, on the other hand show that only in the LP state the VIV=O ions can exhibit an interaction with paramagnetic O2 molecules from air.	Jul 2016
I07-Surface & interface diffraction	Structure and Stability of Underpotentially Deposited Ag on Au(111) in Alkaline Electrolyte Naomi Sisson , Yvonne Grunder , Christopher Lucas The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.5b12773 Show Abstract ▼ Abstract: A combination of in situ surface X-ray scattering (SXS) and cyclic voltammetry (CV) measurements have been performed to understand the structure and behavior of underpotentially deposited (UPD) Ag layers on Au(111) following transfer of the electrode to alkaline electrolyte (0.1 M KOH). UPD of Ag from 0.05 M H2SO4 + 1 mM Ag2SO4 electrolyte was used to form a monolayer and bilayer film of Ag on Au(111) before immersion into 0.1 M KOH electrolyte. Analysis of the SXS data shows that, while the bilayer Ag film is stable upon transfer to the alkaline electrolyte, the Ag monolayer film reorders to a partial bilayer structure upon or during the transfer process. The Ag-modified Au(111) electrode shows a potential response for OH– adsorption that is similar to that of Ag single crystal electrode surfaces.	Apr 2016
I09-Surface and Interface Structural Analysis	A-site Cation Substitutions in Strained Y-doped BaZrO3 Multilayer Films Leading to Fast Proton Transport Pathways Carmela Aruta , Chu Han , Si Zhou , Claudia Cantoni , Nan Yang , Antonello Tebano , Tien-lin Lee , Christoph Schlueter , Angelo Bongiorno The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.6b01963 Show Abstract ▼ Abstract: Proton-conducting perovskite oxides form a class of solid electrolytes for novel electrochemical devices operating at moderate temperatures. Here, we use hard X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and density functional theory calculations to investigate the structure and elucidate the origin of the fast proton transport properties of strained ultrathin films of Y-doped BaZrO3 grown by pulsed lased deposition on NdGaO3. Our study shows that our BaZr0.8Y0.2O3 films incorporate a significant amount of Y dopants, and to a lesser extent also Zr ions, substituting for Ba2+, and that these substitutional defects agglomerate forming columnar regions crossing vertically from the surface to the interface the entire film. Our calculations also show that, in regions rich in Y substitutions for both Zr and Ba, the proton transfer process involves nearly zero-energy barriers, indicating that A-site cation substitutions by Y lead to fast transport pathways and hence are responsible for the previously observed enhanced values of the proton conductivity of these perovskite oxide films.	Mar 2016
I07-Surface & interface diffraction	Film and Interface Atomic Structures of Electrodeposited Co/Au(111) Layers: An In–situ X–ray Scattering Study as a Function of the Surface Chemistry and the Electrochemical Potential Christopher Lucas , Fouad Maroun , Naomi Sisson , Paul Thompson , Yvonne Gruender , Robert Cortès , Phillipe Allongue The Journal Of Physical Chemistry C 120 (6) DOI: 10.1021/acs.jpcc.5b11107 Diamond Proposal Number(s): [7260] Show Abstract ▼ Abstract: The growth and atomic structure of thin Co films electrodeposited onto Au(111) have been studied using in situ surface X-ray diffraction (SXRD) and scanning tunneling microscopy (STM). SXRD is used to monitor the growth in real-time and, following Co deposition, the strain of the Co film is characterized as a function of the Co thickness. In-plane SXRD measurements show that Co deposition leads to the formation of a reconstructed Au layer at the Au-Co interface which is composed of an unfaulted, single Au monolayer uniformly compressed with respect to the underlying bulk Au lattice. The surface normal structure of the Au-Co interface and Co films are examined by measurement of the extended X-ray reflectivity (or specular crystal truncation rod (CTR)) for a nominally two monolayer thick (2 ML) Co deposit. In situ STM has also been used to obtain the morphology of the Co films and the Au(111) reconstruction pattern both before and after Co dissolution. The STM data give complementary information to the SXRD results. The influence on the Co structure of the adsorption of carbon monoxide is also investigated in detail for a 2-3 ML thick Co film. It is shown that CO adsorption induces small vertical relaxations in the Co layers. In contrast, varying the electrochemical potential has negligible influence on the Co structure and affects only the electrolyte layering in the electrochemical double layer. The results are discussed in relation to the magnetic properties, in particular the change in the spin reorientation transition caused by CO adsorption.	Jan 2016
	Surface Chemistry of Alanine on Ni{111} Richard E. J. Nicklin , Alix Cornish , Andrey Shavorskiy , Silvia Baldanza , Karina Schulte , Zhi Liu , Roger A. Bennett , Georg Held The Journal Of Physical Chemistry C 119 (47), 26566 - 26574 DOI: 10.1021/acs.jpcc.5b08814 Show Abstract ▼ Abstract: The adsorption of l-alanine on Ni{111} has been studied as a model of enantioselective heterogeneous catalysts. Synchrotron-based X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to determine the chemical state, bond coordination, and out-of-plane orientation of the molecule on the surface. Alanine adsorbs in anionic and zwitterionic forms between 250 and ≈320 K. NEXAFS spectra exhibit a strong angular dependence of the π* resonance associated with the carboxylate group, which is compatible with two distinct orientations with respect to the surface corresponding to the bidentate and tridentate binding modes. Desorption and decomposition begin together at ≈300 K, with decomposition occurring in a multistep process up to ≈450 K. Comparison with previous studies of amino acid adsorption on metal surfaces shows that this is among the lowest decomposition temperatures found so far and lower than typical temperatures used for hydrogenation reactions where modified Ni catalysts are used.	Nov 2015

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