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36 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I09-Surface and Interface Structural Analysis	The structure of 2D charge transfer salts formed by TCNQ/alkali metal coadsorption on Ag(111) P. J. Blowey , L. A. Rochford , D. A. Duncan , P. T. O. Ryan , D. A. Warr , T.-l. Lee , G. Costantini , D. P. Woodruff Surface Science 701 DOI: 10.1016/j.susc.2020.121687 Diamond Proposal Number(s): [15899, 18191] Show Abstract ▼ Abstract: The structure of coadsorption phases formed on Ag(111) by TCNQ (7,7,8,8-tetracyanoquinodimethane) with Cs are compared with previously reported coadsorption phases formed with K, following investigation by scanning tunnelling microscopy (STM), low energy electron diffraction, soft X-ray photoelectrons spectroscopy and normal incidence X-ray standing waves (NIXSW). For each alkali we identify two ordered phases, one with an alkali: TCNQ stoichiometry of 1:1 and the other 2:1. STM images show the molecular organisation is the same for Cs and K, although only the K2TCNQ phase is commensurate with the substrate. A previously-published detailed structure determination of the K2TCNQ phase, complemented by density function theory calculations that identify bonding strengths, showed that the binding within the layer is much stronger than that of the layer to the substrate. Insensitivity to commensuration is thus to be expected. The situation for KTCNQ and CsTCNQ is less clear; these ordered incommensurate overlayers clearly have strong intralayer bonding, but the relative strength of the average overlayer-substrate bonding is unknown. NIXSW data show that the alkalis in these phases occupy adsorption sites far more distant from the substrate than the TCNQ molecules when compared to the near coplanar alkali-TCNQ geometry of K2TCNQ and Cs2TCNQ. Ultraviolet photoelectron spectra show increasing bonding shifts of TCNQ orbital states with alkali coverage.	Nov 2020
	Stabilisation of tri-valent ions with vacant coordination site at a corrole-metal interface Peter S. Deimel , Pablo Casado Aguilar , Mateusz Paszkiewicz , David A. Duncan , Johannes Barth , Florian Klappenberger , Wolfgang Schöfberger , Francesco Allegretti Chemical Communications DOI: 10.1039/D0CC03947K Show Abstract ▼ Abstract: By exploiting an established on-surface metallation strategy, we address the ability of the corrolic macrocycle to stabilise transition metal ions in high-valent (III) oxidation states in metal-supported molecular layers. This approach offers a route to engineer adsorbed metal complexes that cannot be easily fabricated by organic synthesis methods and bear a vacant axial coordination site for catalytic conversions.	Aug 2020
I09-Surface and Interface Structural Analysis	Alkali doping leads to charge-transfer salt formation in a two-dimensional metal–organic framework Phil J. Blowey , Billal Sohail , Luke A. Rochford , Timothy Lafosse , David A. Duncan , Paul Ryan , Daniel Andrew Warr , Tien-lin Lee , Giovanni Costantini , Reinhard J. Maurer , David Phillip Woodruff Acs Nano DOI: 10.1021/acsnano.0c03133 Diamond Proposal Number(s): [15899, 18191] Show Abstract ▼ Abstract: Efficient charge transfer across metal–organic interfaces is a key physical process in modern organic electronics devices, and characterization of the energy level alignment at the interface is crucial to enable a rational device design. We show that the insertion of alkali atoms can significantly change the structure and electronic properties of a metal–organic interface. Coadsorption of tetracyanoquinodimethane (TCNQ) and potassium on a Ag(111) surface leads to the formation of a two-dimensional charge transfer salt, with properties quite different from those of the two-dimensional Ag adatom TCNQ metal–organic framework formed in the absence of K doping. We establish a highly accurate structural model by combination of quantitative X-ray standing wave measurements, scanning tunnelling microscopy, and density-functional theory (DFT) calculations. Full agreement between the experimental data and the computational prediction of the structure is only achieved by inclusion of a charge-transfer-scaled dispersion correction in the DFT, which correctly accounts for the effects of strong charge transfer on the atomic polarizability of potassium. The commensurate surface layer formed by TCNQ and K is dominated by strong charge transfer and ionic bonding and is accompanied by a structural and electronic decoupling from the underlying metal substrate. The consequence is a significant change in energy level alignment and work function compared to TCNQ on Ag(111). Possible implications of charge-transfer salt formation at metal–organic interfaces for organic thin-film devices are discussed.	May 2020
	Re-evaluation of human BDCA-2+ DC during acute sterile skin inflammation Yi-ling Chen , Tomas Gomes , Clare S. Hardman , Felipe A. Vieira Braga , Danuta Gutowska-owsiak , Maryam Salimi , Nicki Gray , David A. Duncan , Gary Reynolds , David Johnson , Mariolina Salio , Vincenzo Cerundolo , Jillian L. Barlow , Andrew N. J. Mckenzie , Sarah A. Teichmann , Muzlifah Haniffa , Graham Ogg The Journal Of Experimental Medicine 217 DOI: 10.1084/jem.20190811 Show Abstract ▼ Abstract: Plasmacytoid dendritic cells (pDCs) produce type I interferon (IFN-I) and are traditionally defined as being BDCA-2+CD123+. pDCs are not readily detectable in healthy human skin, but have been suggested to accumulate in wounds. Here, we describe a CD1a-bearing BDCA-2+CD123int DC subset that rapidly infiltrates human skin wounds and comprises a major DC population. Using single-cell RNA sequencing, we show that these cells are largely activated DCs acquiring features compatible with lymph node homing and antigen presentation, but unexpectedly express both BDCA-2 and CD123, potentially mimicking pDCs. Furthermore, a third BDCA-2–expressing population, Axl+Siglec-6+ DCs (ASDC), was also found to infiltrate human skin during wounding. These data demonstrate early skin infiltration of a previously unrecognized CD123intBDCA-2+CD1a+ DC subset during acute sterile inflammation, and prompt a re-evaluation of previously ascribed pDC involvement in skin disease.	Mar 2020
I09-Surface and Interface Structural Analysis	Validation of the inverted adsorption structure for free-base tetraphenyl porphyrin on Cu(111) P. T. P. Ryan , P. L. Lalaguna , F. Haag , M. M. Braim , P. Ding , D. J. Payne , J. V. Barth , Tien-lin Lee , D. P. Woodruff , F. Allegretti , D. A. Duncan Chemical Communications 70 DOI: 10.1039/C9CC09638H Diamond Proposal Number(s): [24113] Open Access Show Abstract ▼ Abstract: Utilising normal incidence X-ray standing waves we rigourously scrutinise the “inverted model” as the adsorption structure of free-base tetraphenyl porphyrin on Cu(111). We demonstrate that the iminic N atoms are anchored at near-bridge adsorption sites on the surface displaced laterally by 1.1 ± 0.2 Å in excellent agreement with previously published calculations.	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
	Adsorbate-induced structural evolution changes the mechanism of CO oxidation on a Rh/Fe 3 O 4 (001) model catalyst Zdenek Jakub , Jan Hulva , Paul T. P. Ryan , David A. Duncan , David J. Payne , Roland Bliem , Manuel Ulreich , Patrick Hofegger , Florian Kraushofer , Matthias Meier , Michael Schmid , Ulrike Diebold , Gareth S. Parkinson Nanoscale 55 DOI: 10.1039/C9NR10087C Open Access Show Abstract ▼ Abstract: The structure of a catalyst often changes in reactive environments, and following the structural evolution is crucial for the identification of the catalyst's active phase and reaction mechanism. Here we present an atomic-scale study of CO oxidation on a model Rh/Fe3O4(001) “single-atom” catalyst, which has a very different evolution depending on which of the two reactants, O2 or CO, is adsorbed first. Using temperature-programmed desorption (TPD) combined with scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we show that O2 destabilizes Rh atoms, leading to the formation of RhxOy clusters; these catalyze CO oxidation via a Langmuir–Hinshelwood mechanism at temperatures as low as 200 K. If CO adsorbs first, the system is poisoned for direct interaction with O2, and CO oxidation is dominated by a Mars-van-Krevelen pathway at 480 K.	Feb 2020
I09-Surface and Interface Structural Analysis	X-ray standing waves reveal lack of OH termination at hydroxylated ZnO(0001) surfaces Jens Niederhausen , Antoni Franco-cañellas , Simon Erker , Thorsten Schultz , Katharina Broch , Alexander Hinderhofer , Steffen Duhm , Pardeep K. Thakur , David A. Duncan , Alexander Gerlach , Tien-lin Lee , Oliver T. Hofmann , Frank Schreiber , Norbert Koch Physical Review Materials 4 DOI: 10.1103/PhysRevMaterials.4.020602 Diamond Proposal Number(s): [11415, 13740, 19033] Open Access Show Abstract ▼ Abstract: The vertical adsorption distances of the planar conjugated organic molecule 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) on hydroxylated ZnO(0001), determined with the x-ray standing wave technique (XSW), are at variance with adsorption geometries simulated with density functional theory for surface-structure models that consider terminating OH, whereas good agreement is found for PTCDI in direct contact with the topmost Zn layer. The consequential assignment of OH to subsurface sites is supported by additional, independent XSW and energy scanned photoelectron diffraction data and calls for a reconsideration of the prevalent surface models with important implications for the understanding of ZnO(0001) surfaces.	Feb 2020
I09-Surface and Interface Structural Analysis	Corrugated graphene exposes the limits of a widely used ab initio van der Waals DFT functional David A. Duncan , Nicolae Atodiresei , Simone Lisi , Phil J. Blowey , Vasile Caciuc , James Lawrence , Tien-lin Lee , Maria Grazia Betti , Pardeep Kumar Thakur , Ada Della Pia , Stefan Blügel , Giovanni Costantini , D. Phil Woodruff Physical Review Materials 3 DOI: 10.1103/PhysRevMaterials.3.124001 Diamond Proposal Number(s): [13625] Open Access Show Abstract ▼ Abstract: Theoretical formulations capable of modeling chemical interactions over 3–4 orders of magnitude of bond strength, from covalent to van der Waals (vdW) forces, are one of the primary goals in materials physics, and chemistry. Development of vdW corrections for density-functional theory has thus been a major research field for two decades. While many of these corrections are semiempirical, more theoretically rigorous ab initio functionals have been developed. The ab initio functional vdW-DF2, when coupled with the reoptimized B86 exchange function (vdW-DF2-rB86), has typically performed as well, if not better than most semiempirical formulations. Here we present a system, Co intercalation of graphene on Ir(111), for which a semiempirical correction predicts local corrugation maxima in locations at which the vdW-DF2-rB86 functional predicts global minima. Sub-angstrom precision quantitative structural measurements show better agreement with the semiempirical correction. We posit that it is balancing the weak vdW interaction with the stronger, even covalent, interactions that proves a challenge for the vdW-DF2-rB86 functional.	Dec 2019
	Bottom up fabrication of a metal supported oxo-metal porphyrin David A. Duncan , Peter S. Deimel , Alissa Wiengarten , Mateusz Paszkiewicz , Pablo Casado Aguilar , Robert G. Acres , Florian Klappenberger , Willi Auwärter , Ari Paavo Seitsonen , Johannes V. Barth , Francesco Allegretti The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.9b08661 Show Abstract ▼ Abstract: In situ preparation of oxotitanium tetraphenylporphyrin (TiO-TPP) on Ag(111) under ultra-high vacuum conditions was achieved in a multi-step procedure starting from adsorbed free-base tetraphenylporphyrin (2H-TPP). The final product as well as the intermediate titanium tetraphenylporphyrin (Ti-TPP) were characterized by a suite of surface-sensitive spectroscopic tools combined with scanning tunneling microscopy and density functional theory (DFT), and compared against the parent 2H-TPP species. Facile oxidation of Ti-TPP with molecular oxygen was observed at 300 K, with X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) from the Ti 2p core levels supporting a change in the oxidation state from Ti2+ to Ti4+. N K-edge and Ti L-edge NEXAFS suggest that the tetrapyrrole macrocycle conformation is modified upon binding to oxygen, in agreement with DFT calculations that predict a marked change of the local environment of the Ti centers upon oxygen attachment. O K-edge NEXAFS and O 1s energy-scanned photoelectron diffraction from the resulting TiO-TPP monolayer provide strong evidence for the presence of a titanium-oxygen double bond, with the latter technique yielding a bond length of 1.56 ± 0.02 Å. The majority of adsorbed TiO-TPP species have the oxo group pointing away from the surface rather than towards it, and thus the oxygen atom can potentially interact coordinatively with external species. Both the highly reactive, intermediate Ti TPP species and the final product TiO-TPP are of great interest for catalytic applications.	Nov 2019

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