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119 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
I18-Microfocus Spectroscopy	Intermediates during the nucleation of platinum nanoparticles by a reaction with ethylene glycol: operando X-ray absorption spectroscopy studies with a microfluidic cell Sylvia Britto , Christopher M. A. Parlett , Stuart Bartlett , Joshua D. Elliott , Konstantin Ignatyev , Sven L. M. Schroeder The Journal Of Physical Chemistry C 38 DOI: 10.1021/acs.jpcc.2c08749 Diamond Proposal Number(s): [21484] Open Access Show Abstract ▼ Abstract: Using operando X-ray absorption spectroscopy in a continuous-flow microfluidic cell, we have investigated the nucleation of platinum nanoparticles from aqueous hexachloroplatinate solution in the presence of the reducing agent ethylene glycol. By adjusting flow rates in the microfluidic channel, we resolved the temporal evolution of the reaction system in the first few seconds, generating the time profiles for speciation, ligand exchange, and reduction of Pt. Detailed analysis of the X-ray absorption near-edge structure and extended X-ray absorption fine structure spectra with multivariate data analysis shows that at least two reaction intermediates are involved in the transformation of the precursor H2PtCl6 to metallic platinum nanoparticles, including the formation of clusters with Pt–Pt bonding before complete reduction to Pt nanoparticles.	May 2023
I09-Surface and Interface Structural Analysis	Zinc-porphine on coinage metal surfaces: adsorption configuration and ligand-induced central atom displacement Aleksandr Baklanov , Johannes T. Kuchle , David A. Duncan , Reinhard J. Maurer , Martin Schwarz , Eduardo Corral Rascon , Ignacio Piquero-Zulaica , Huynh Thien Ngo , Alexander Riss , Francesco Allegretti , Willi Auwärter , Paul T. P. Ryan The Journal Of Physical Chemistry C 35 DOI: 10.1021/acs.jpcc.3c00232 Diamond Proposal Number(s): [18874, 24276] Show Abstract ▼ Abstract: We present a comprehensive, quantitative multimethod characterization of the geometric and electronic interfacial structure of zinc-porphine (Zn-P) on coinage metal supports, namely, Ag(111) and Cu(111). Complementary techniques including X-ray standing waves, X-ray photoelectron spectroscopy, scanning tunneling microscopy, bond-resolved atomic force microscopy, and density functional theory calculations reveal the molecular conformations, signal a temperature-dependence of element-specific adsorption heights, rule out a decisive role of the d10 nature of the Zn center for the adsorption configuration, and uncover a considerably increased Zn-P adsorption height on Ag(111) compared to Cu(111). Furthermore, a pronounced out-of-plane displacement of the Zn center upon water ligation is demonstrated, a manifestation of the surface trans-effect. This study thus sheds light on effects of temperature, chemical nature of the metal center, its ligation, and the coinage metal support on interfacial structure and molecular deformation of an archetypical surface-anchored metal-tetrapyrrole.	Apr 2023
I07-Surface & interface diffraction	Direct experimental determination of Ag adatom locations in TCNQ-Ag 2D metal–organic framework on Ag(111) Philip J. Mousley , Luke A. Rochford , Hadeel Hussain , Stefania Moro , Pengcheng Ding , Gavin R. Bell , Giovanni Costantini , Christopher Nicklin , D. Phil Woodruff The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.2c07683 Diamond Proposal Number(s): [24284] Open Access Show Abstract ▼ Abstract: A previous investigation of the structure of TCNQ adsorbed on Ag(111) using normal-incidence X-ray standing waves (NIXSW) and density functional theory (DFT) provided indirect evidence that Ag adatoms must be incorporated into the molecular overlayer. New surface X-ray diffraction (SXRD) results, presented here, provide direct evidence for the presence and location of these Ag adatoms and clearly distinguishes between two alternative models of the adatom registry favored by two different DFT studies.	Feb 2023
I11-High Resolution Powder Diffraction I15-1-X-ray Pair Distribution Function (XPDF)	On the local structure in ordered and disordered closo-hydroborate solid electrolytes Paul Till , Ryo Asakura , Arndt Remhof , Wolfgang G. Zeier The Journal Of Physical Chemistry C 1413 DOI: 10.1021/acs.jpcc.2c07835 Diamond Proposal Number(s): [26379] Show Abstract ▼ Abstract: Na+closo-hydroborates are a heavily researched solid electrolyte class for applications in all-solid-state Na batteries. The structural characterization of these materials is notoriously challenging due to the elements involved and the fast rotational motion of hydroborate cages. The average structures obtained by Bragg diffraction have numerous atomic positions with low occupancies, complicating the determination of actual atom–atom distances. Total average scattering and derived pair distribution functions display atom–atom distances in real space, providing additional structure information to the average crystal structure. In this work, we present the pair distribution functions of the five different Na+closo-hydroborates: Na2B10H10, Na2B12H12, NaCB11H12, and the mixtures of 1:1 Na2B12H12/Na2B10H10 and 2:1 NaCB11H12/Na2B12H12. All pair distribution functions show a fast decay of peak height with increasing atom–atom distance on the local scale, suggesting a low correlation of atom motions between hydroborate cages, as observed in various other molecular crystals. The combination of Bragg diffraction, showing the average ordering of closo-hydroborate cages, and pair distribution function analysis, providing local atom–atom distances, is a useful tool to develop a deeper understanding of the closo-hydroborates and also of other plastic crystals.	Jan 2023
I11-High Resolution Powder Diffraction	Donor–acceptor co-adsorption ratio controls the structure and electronic properties of two-dimensional alkali–organic networks on Ag(100) B. Sohail , P. J. Blowey , L. A. Rochford , P. T. P. Ryan , D. A. Duncan , T.-L. Lee , P. Starrs , G. Costantini , D. Phil Woodruff , R. J. Maurer The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.2c08688 Diamond Proposal Number(s): [17261, 20785] Open Access Show Abstract ▼ Abstract: The results are presented of a detailed combined experimental and theoretical investigation of the influence of coadsorbed electron-donating alkali atoms and the prototypical electron acceptor molecule 7,7,8,8-tetracyanoquinodimethane (TCNQ) on the Ag(100) surface. Several coadsorption phases were characterized by scanning tunneling microscopy, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy. Quantitative structural data were obtained using normal-incidence X-ray standing wave (NIXSW) measurements and compared with the results of density functional theory (DFT) calculations using several different methods of dispersion correction. Generally, good agreement between theory and experiment was achieved for the quantitative structures, albeit with the prediction of the alkali atom heights being challenging for some methods. The adsorption structures depend sensitively on the interplay of molecule–metal charge transfer and long-range dispersion forces, which are controlled by the composition ratio between alkali atoms and TCNQ. The large difference in atomic size between K and Cs has negligible effects on stability, whereas increasing the ratio of K/TCNQ from 1:4 to 1:1 leads to a weakening of molecule–metal interaction strength in favor of stronger ionic bonds within the two-dimensional alkali–organic network. A strong dependence of the work function on the alkali donor–TCNQ acceptor coadsorption ratio is predicted.	Jan 2023
	Characterizing molecule–metal surface chemistry with ab initio simulation of X-ray absorption and photoemission spectra Samuel J. Hall , Benedikt P. Klein , Reinhard J. Maurer The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.2c06996 Open Access Show Abstract ▼ Abstract: X-ray photoemission and X-ray absorption spectroscopy are important techniques to characterize chemical bonding at surfaces and are often used to identify the strength and nature of adsorbate–substrate interactions. In this study, we judge the ability of X-ray spectroscopic techniques to identify different regimes of chemical bonding at metal–organic interfaces. To achieve this, we sample different interaction strength regimes in a comprehensive and systematic way by comparing two topological isomers, azulene and naphthalene, adsorbed on three metal substrates with varying reactivity, namely the (111) facets of Ag, Cu, and Pt. Using density functional theory, we simulate core-level binding energies and X-ray absorption spectra of the molecular carbon species. The simulated spectra reveal three distinct characteristics based on the molecule-specific spectral features which we attribute to types of surface chemical bonding with varying strength. We find that weak physisorption only leads to minor changes compared to the gas-phase spectra, weak chemisorption leads to charge transfer and significant spectral changes, and strong chemisorption leads to a loss of the molecule-specific features in the spectra. The classification we provide is aimed at assisting interpretation of experimental X-ray spectra for complex metal–organic interfaces.	Jan 2023
I09-Surface and Interface Structural Analysis	Band alignments, electronic structure, and core-level spectra of bulk molybdenum dichalcogenides (MoS2, MoSe2, and MoTe2) Leanne A. H. Jones , Zongda Xing , Jack E. N. Swallow , Huw Shiel , Thomas J. Featherstone , Matthew J. Smiles , Nicole Fleck , Pardeep K. Thakur , Tien-Lin Lee , Laurence J. Hardwick , David O. Scanlon , Anna Regoutz , Tim D. Veal , Vinod R. Dhanak The Journal Of Physical Chemistry C 44 DOI: 10.1021/acs.jpcc.2c05100 Diamond Proposal Number(s): [25980] Open Access Show Abstract ▼ Abstract: A comprehensive study of bulk molybdenum dichalcogenides is presented with the use of soft and hard X-ray photoelectron (SXPS and HAXPES) spectroscopy combined with hybrid density functional theory (DFT). The main core levels of MoS2, MoSe2, and MoTe2 are explored. Laboratory-based X-ray photoelectron spectroscopy (XPS) is used to determine the ionization potential (IP) values of the MoX2 series as 5.86, 5.40, and 5.00 eV for MoSe2, MoSe2, and MoTe2, respectively, enabling the band alignment of the series to be established. Finally, the valence band measurements are compared with the calculated density of states which shows the role of p-d hybridization in these materials. Down the group, an increase in the p-d hybridization from the sulfide to the telluride is observed, explained by the configuration energy of the chalcogen p orbitals becoming closer to that of the valence Mo 4d orbitals. This pushes the valence band maximum closer to the vacuum level, explaining the decreasing IP down the series. High-resolution SXPS and HAXPES core-level spectra address the shortcomings of the XPS analysis in the literature. Furthermore, the experimentally determined band alignment can be used to inform future device work.	Dec 2022
I09-Surface and Interface Structural Analysis	Indium epitaxy on SiC(0001): a roadmap to large scale growth of the quantum spin hall insulator indenene Jonas Erhardt , Maximilian Bauernfeind , Philipp Eck , Martin Kamp , Judith Gabel , Tien-Lin Lee , Giorgio Sangiovanni , Simon Moser , Ralph Claessen The Journal Of Physical Chemistry C 260 DOI: 10.1021/acs.jpcc.2c05809 Diamond Proposal Number(s): [25151] Show Abstract ▼ Abstract: Indenene─the triangular single layer phase of indium─is a novel large gap (∼120 meV) quantum spin Hall (QSH) insulator that stabilizes on SiC(0001) substrates. Thanks to excellent lattice matching, indenene nucleates in monodomains that are promising for devices if synthesized in the micrometer range. Here, we establish a simple, but robust and scalable indenene fabrication protocol based on an initial Stranski–Krastanov growth stage followed by a short anneal whose temperature selects between a three, two, or one monolayer In coverage. Their specific structural and electronic properties produce distinct fingerprints in experimental surface characterization by electron microscopy, diffraction, and spectroscopy, thus providing an efficient metric for the synthesis of large scale high-quality indenene on SiC.	Sep 2022
I07-Surface & interface diffraction	Ordered and disordered carboxylic acid monolayers on calcite (104) and muscovite (001) surfaces Sander J. T. Brugman , Paolo Accordini , Frank Megens , Jan-Joris Devogelaer , Elias Vlieg The Journal Of Physical Chemistry C 2 DOI: 10.1021/acs.jpcc.2c01157 Diamond Proposal Number(s): [18591] Open Access Show Abstract ▼ Abstract: The adsorption of carboxylic acid molecules at the calcite (104) and the muscovite (001) surface was investigated using surface X-ray diffraction. All four investigated carboxylic acid molecules, hexanoic acid, octanoic acid, lauric acid, and stearic acid, were found to adsorb at the calcite surface. Whereas the shortest two carboxylic acid molecules, hexanoic acid and octanoic acid, showed limited ordering and a flexible, disordered chain, the two longest carboxylic acid molecules form fully ordered monolayers, i.e., these form highly structured self-assembled monolayers. The latter molecules are oriented almost fully upright, with a tilt of up to 10°. The oxygen atoms of the organic molecules are found at similar positions to those of water molecules at the calcite–water interface. This suggests that in both cases, the oxygen atoms compensate for the broken bonds at the calcite surface. Under the same experimental conditions, stearic acid does not adsorb to K+ and Ca2+-functionalized muscovite mica because the neutral molecules do not engage in the ionic bonds typical for the mica interface. These differences in adsorption behavior are characteristic for the differences of the oil–solid interactions in carbonate and sandstone reservoirs.	May 2022
E01-JEM ARM 200CF	Atomic structure and valence state of cobalt nanocrystals on carbon under syngas versus hydrogen reduction Ofentse A. Makgae , Tumelo N. Phaahlamohlaka , Benzhen Yao , Manfred E. Schuster , Thomas J. A. Slater , Peter P. Edwards , Neil J. Coville , Emanuela Liberti , Angus I. Kirkland The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.2c00482 Diamond Proposal Number(s): [20403] Open Access Show Abstract ▼ Abstract: The composition of the reducing gas in the activation of Co Fischer-Tropsch synthesis catalysts determines the nature of the catalytically active Co species. This study reports on the effect of H2 versus syngas (H2/CO = 2) on the reducibility of Co3O4 nanoparticles supported on hollow carbon spheres, using ex situ and in situ high-resolution aberration-corrected analytical electron microscopy. High-resolution images revealed twinned fcc Co particles encapsulated in carbon from syngas treatment while H2-treated particles were mostly CoO. Moreover, the electron energy loss of the Co-L3,2 and O-K edge fine structures show improved reducibility in syngas than in H2 at 350 °C. The effect of high temperature on the reducibility of the Co3O4 nanoparticles is also explored. Carbon fiber encapsulation of twinned fcc Co particles observed during the syngas treatment provides sinter resistance at high temperatures. Both ex situ and in situ results indicate that syngas activation is efficient for obtaining highly reduced Co nanoparticles at lower temperatures.	Apr 2022

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