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119 items found (0 items not approved), displaying 71 to 80.[First/Prev] 4, 5, 6, 7, 8, 9, 10, 11 [Next/Last]

Instruments / Technical Area	Publication Details	Published
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
B16-Test Beamline	Probing the average size of self-assembled metal nanoparticles using x-ray standing waves M. K. Tiwari , K. J. S. Sawhney , T.-l. Lee , S. G. Alcock , G. S. Lodha Physical Review B 80 (3), 035434 DOI: 10.1103/PhysRevB.80.035434 Show Abstract ▼ Abstract: We report application of x-ray standing-wave field for characterization of average vertical size of metal nanoparticles dispersed on a substrate surface with accuracies better than 1 nm. This method is applied to analyze the distribution of Fe, Co, and Au nanoparticles on Si substrate and W/C multilayer substrates. Results demonstrate that the method is a valuable tool to evaluate the surface morphology of nanoparticles over a large surface area. Unlike conventional probes such as atomic force microscopy or microinterferometry, the present method provides element-specific analysis. It also has the advantage of being able to examine nanoparticles in a liquid medium, or buried inside a coating layer. We anticipate that the proposed method has great potential to infer the internal structure of nanoparticles.	Jul 2009
I09-Surface and Interface Structural Analysis	Probing the geometry of copper and silver adatoms on magnetite: quantitative experiment versus theory Matthias Meier , Zdeněk Jakub , Jan Balajka , Jan Hulva , Roland Bliem , Pardeep K. Thakur , Tien-lin Lee , Cesare Franchini , Michael Schmid , Ulrike Diebold , Francesco Allegretti , David Duncan , Gareth S. Parkinson Nanoscale 328 DOI: 10.1039/C7NR07319D Diamond Proposal Number(s): [13817] Open Access Show Abstract ▼ Abstract: Accurately modelling the structure of a catalyst is a fundamental prerequisite for correctly predicting reaction pathways, but a lack of clear experimental benchmarks makes it difficult to determine the optimal theoretical approach. Here, we utilize the normal incidence X-ray standing wave (NIXSW) technique to precisely determine the three dimensional geometry of Ag1 and Cu1 adatoms on Fe3O4(001). Both adatoms occupy bulk-continuation cation sites, but with a markedly different height above the surface (0.43 ± 0.03 Å (Cu1) and 0.96 ± 0.03 Å (Ag1)). HSE-based calculations accurately predict the experimental geometry, but the more common PBE + U and PBEsol + U approaches perform poorly.	Jan 2018
I09-Surface and Interface Structural Analysis	Probing the interplay between geometric and electronic structure in a two-dimensional K-TCNQ charge transfer network P. J. Blowey , Luke A. Rochford , David Duncan , Daniel Warr , T.-l. Lee , D. P. Woodruff , Giovanni Costantini Faraday Discuss. DOI: 10.1039/C7FD00093F Show Abstract ▼ Abstract: Scanning tunnelling microscopy (STM), low energy electron diffraction (LEED), ultraviolet and soft X-ray photoelectron spectroscopy (UPS and SXPS) have been used to characterise the formation of a coadsorption phase of TCNQ and K on Ag(111), while the normal incident X-ray standing waves (NIXSW) technique has been used to obtain quantitative structural information. STM and LEED show an ordered incommensurate phase is formed in which the K atoms are surrounded by four TCNQ molecules in a ‘windmill’ motif, characteristic of other metal/TCNQ phases, in which the nominal TCNQ:K stoichiometry is 1:1. UPS and SXPS data indicate the TCNQ is in a negatively-charged state. NIXSW results show that the carbon core of the TCNQ is essentially planar at a height above the Ag(111) surface closely similar to that found without coadsorbed K. In the presence of TCNQ the height of the K ions above the surface is significantly larger than on clean Ag(111), and the ions occupy sites above ‘holes’ in the TCNQ network. NIXSW data also show that the N atoms in the molecules must occupy sites with at least two different heights above the surface, which can be reconciled by a tilt or twist of the TCNQ molecules, broadly similar to the geometry that occurs in bulk TCNQ/K crystals.	Mar 2017
I09-Surface and Interface Structural Analysis	Proximity-induced ferromagnetism and chemical reactivity in few-layer VSe 2 heterostructures G. Vinai , C. Bigi , A. Rajan , M. D. Watson , T.-l. Lee , F. Mazzola , S. Modesti , S. Barua , M. Ciomaga Hatnean , G. Balakrishnan , P. D. C. King , P. Torelli , G. Rossi , G. Panaccione Physical Review B 101 DOI: 10.1103/PhysRevB.101.035404 Diamond Proposal Number(s): [21429] Show Abstract ▼ Abstract: Among transition-metal dichalcogenides, mono and few-layers thick VSe 2 has gained much recent attention following claims of intrinsic room-temperature ferromagnetism in this system, which have nonetheless proved controversial. Here, we address the magnetic and chemical properties of Fe / VSe 2 heterostructure by combining element sensitive x-ray absorption spectroscopy and photoemission spectroscopy. Our x-ray magnetic circular dichroism results confirm recent findings that both native mono/few-layer and bulk VSe 2 do not show intrinsic ferromagnetic ordering. Nonetheless, we find that ferromagnetism can be induced, even at room temperature, after coupling with a Fe thin film layer, with antiparallel alignment of the moment on the V with respect to Fe. We further consider the chemical reactivity at the Fe / VSe 2 interface and its relation with interfacial magnetic coupling.	Jan 2020
I09-Surface and Interface Structural Analysis	Quantifying the critical thickness of electron hybridization in spintronics materials T. Pincelli , V. Lollobrigida , F. Borgatti , A. Regoutz , B. Gobaut , C. Schlueter , T.-l. Lee , D. J. Payne , M. Oura , K. Tamasaku , A. Y. Petrov , P. Graziosi , F. Miletto Granozio , M. Cavallini , G. Vinai , R. Ciprian , C. Back , G. Rossi , M. Taguchi , H. Daimon , G. Van Der Laan , G. Panaccione Nature Communications 8 DOI: 10.1038/ncomms16051 Diamond Proposal Number(s): [11322] Show Abstract ▼ Abstract: In the rapidly growing ﬁeld of spintronics, simultaneous control of electronic and magneticproperties is essential, and the perspective of building novel phases is directly linked to the control of tuning parameters, for example, thickness and doping. Looking at the relevanteffects in interface-driven spintronics, the reduced symmetry at a surface and interface corresponds to a severe modiﬁcation of the overlap of electron orbitals, that is, to a change of electron hybridization. Here we report a chemically and magnetically sensitive depth-dependent analysis of two paradigmatic systems, namely La1xSrxMnO3 and (Ga,Mn)As. Supported by cluster calculations, we ﬁnd a crossover between surface and bulk in the electron hybridization/correlation and we identify a spectroscopic ﬁngerprint of bulk metallic character and ferromagnetism versus depth. The critical thickness and the gradient of hybridization are measured, setting an intrinsic limit of 3 and 10 unit cells from the surface,respectively, for (Ga,Mn)As and La1xSrxMnO3, for fully restoring bulk properties.	Jul 2017
I09-Surface and Interface Structural Analysis	Quantitative determination of a model organic/insulator/metal interface structure Martin Schwarz , David A. Duncan , Manuela Garnica , Jacob Ducke , Peter S. Deimel , Pardeep K. Thakur , Tien-lin Lee , Francesco Allegretti , Willi Auwärter Nanoscale 28 DOI: 10.1039/C8NR06387G Diamond Proposal Number(s): [14624] Open Access Show Abstract ▼ Abstract: By combining X-ray photoelectron spectroscopy, X-ray standing waves and scanning tunneling microscopy, we investigate the geometric and electronic structure of a prototypical organic/insulator/metal interface, namely cobalt porphine on monolayer hexagonal boron nitride (h-BN) on Cu(111). Specifically, we determine the adsorption height of the organic molecule and show that the original planar molecular conformation is preserved in contrast to the adsorption on Cu(111). In addition, we highlight the electronic decoupling provided by the h-BN spacer layer and find that the h-BN–metal separation is not significantly modified by the molecular adsorption. Finally, we find indication of a temperature dependence of the adsorption height, which might be a signature of strongly-anisotropic thermal vibrations of the weakly bonded molecules.	Nov 2018
I09-Surface and Interface Structural Analysis	Re-evaluating how charge transfer modifies the conformation of adsorbed molecules P. J. Blowey , S. Velari , L. A. Rochford , Da. A. Duncan , D. A. Warr , T.-l. Lee , A. De Vita , G. Costantini , D. P. Woodruff Nanoscale 4 DOI: 10.1039/C8NR02237B Diamond Proposal Number(s): [8436] Open Access Show Abstract ▼ Abstract: The archetypal electron acceptor molecule, TCNQ, is generally believed to become bent into an inverted bowl shape upon adsorption on the coinage metal surfaces on which it becomes negatively charged. New quantitative experimental structural measurements show that this is not the case for TCNQ on Ag(111). DFT calculations show that the inclusion of dispersion force corrections reduces not only the molecule-substrate layer spacing but also the degree of predicted molecular bonding. However, complete agreement between experimentally-determined and theoretically-predicted structural parameters is only achieved with the inclusion of Ag adatoms into the molecular layer, which is also the energetically favoured configuration. The results highlight the need for both experimental and theoretical quantitative structural methods to reliably understand similar metal–organic interfaces and highlight the need to re-evaluate some previously-investigated systems.	Jul 2018
NONE-No attached Diamond beamline	Relative electron inelastic mean free paths for diamond and graphite at 8 keV and intrinsic contributions to the energy-loss C. Kunz , B. C. C. Cowie , W. Drube , T.-l. Lee , S. Thiess , C. Wild , J. Zegenhagen Journal Of Electron Spectroscopy And Related Phenomena 173 (1), 29-39 DOI: 10.1016/j.elspec.2009.03.022 Show Abstract ▼ Abstract: We used hard X-ray photoelectron spectroscopy (HAXPES) with 8 keV X-rays to investigate the Is emission of carbon. We recorded spectra extending from the peak of the C 1s electrons ("elastic" line) to electrons with Lip to 110 eV energy-loss. Using two samples side by side, we Could compare the inelastic mean free paths (IMFPs) of the electrons of almost 8 keV in diamond and graphite and find them to be practically identical despite about 50% difference in densities. Published extrapolations of their IMFP calculations at lower energies are in good agreement with this result. We show that information from the almost structureless region of overlapping multiple extrinsic energy-losses can be used to quantify the fraction of photoelectrons experiencing intrinsic energy-losses (those due to the sudden creation of the hole). We find that this fraction is 58% of the primary excited C 1s electrons for diamond and is practically the same for graphite. This is at first sight an unexpected result since hole-screening should differ in a semimetal from that in an insulator The observation can be accounted for by dynamic screening in contrast to static screening. (C) 2009 Elsevier B.V. All rights reserved.	Jan 2009
	Resolving CuO chain and CuO 2 plane contributions to the YBa 2 Cu 3 O 7−δ valence band by standing-wave excited hard x-ray photoelectron spectroscopy S. Thiess , Tien-lin Lee , Carmela Aruta , C. T. Lin , F Venturini , N. B. Brookes , B. C. C. Cowie , J. Zegenhagen Physical Review B 92 DOI: 10.1103/PhysRevB.92.075117 Show Abstract ▼ Abstract: We analyzed the valence band (VB) of the 90 K high-temperature superconductor YBa2Cu3O7−δ by photoelectron spectroscopy under standing-wave excitation employing hard x rays. Precisely positioning the standing-wave intensity in the unit cell allows selectively probing the VB yield from the CuO chains and CuO2 planes, respectively. Both contribute strongly over the whole VB but the spectral weight of the planes is significantly higher than the chains within about 2 eV from the Fermi level. In the x-ray regime, the major contribution to the VB emission is coming from Cu 3d.	Aug 2015

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