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153 items found (0 items not approved), displaying 11 to 20.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
	Photoelectron Emission Excited by a Hard X-ray Standing Wave Joseph C. Woicik , Jorg Zegenhagen , Tien-lin Lee , Sebastian Thiess DOI: 10.1007/978-3-319-24043-5_12 Show Abstract ▼ Abstract: The following chapter describes the basics and some applications for the case that photoelectrons are emitted from a hard X-ray interference field instead of by a travelling wave. The dipole approximation holds astonishingly well even for hard X-rays as far as the magnitude of the transition matrix element is concerned. However, the forward-backward asymmetry caused by higher order multipole terms needs to be considered when the photoelectron is emitted by the coherent action of two X-ray waves travelling in different directions. This has implications on the chosen experimental set-up which will be briefly discussed together with other experimental aspects. Finally, some examples of X-ray standing wave analysis using hard X-ray photoelectron spectroscopy will be presented yielding the geometric and electronic structure of (crystalline) materials with pm resolution.	Dec 2015
	Site specific XPS: structural and electronic properties investigated by X-ray standing waves S. Thiess , W. Drube , T. Lee , F. Bottin , A. Gloskovskii , J. Zegenhagen Synchrotron Radiation In Natural Science 9 (1-2), 54-55	Jun 2010
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
B16-Test Beamline Optics	Design, Build & Test of a Double Crystal Monochromator for Beamlines I09 & I23 at the Diamond Light Source Jon Kelly , Tien-lin Lee , Simon Alcock , Hiten Patel Journal of Physics: Conference Series 425 11th InternationalConferenceonSynchrotronRadiationInstrumentation(SRI2012) DOI: 10.1088/1742-6596/425/5/052009 Show Abstract ▼ Abstract: A high stability Double Crystal Monochromator has been developed at The Diamond Light Source for beamlines I09 and I23. The design specification was a cryogenic, fixed exit, energy scanning monochromator, operating over an energy range of 2.1 – 25 keV using a Si(111) crystal set. The novel design concepts are the direct drive, air bearing Bragg axis, low strain crystal mounts and the cooling scheme. The instrument exhibited superb stability and repeatability on the B16 Test Beamline. A 20 keV Si(555), 1.4 ?rad rocking curve was demonstrated. The DCM showed good stability without any evidence of vibration or Bragg angle nonlinearity.	Mar 2013
I05-ARPES I09-Surface and Interface Structural Analysis	Electronic structure of the candidate 2D Dirac semimetal SrMnSb2: a combined experimental and theoretical study Shyama V. Ramankutty , Jans Henke , Adriaan Schiphorst , Rajah Nutakki , Stephan Bron , Georgios Araizi-Kanoutas , Shrawan K. Mishra , Lei Li , Yingkai Huang , Timur Kim , Moritz Hoesch , Christoph Schlueter , Tien-Lin Lee , Anne De Visser , Zhicheng Zhong , Jasper Van Wezel , Erik Van Heumen , Mark Golden Scipost Physics 4 DOI: 10.21468/SciPostPhys.4.2.010 Diamond Proposal Number(s): [15189, 16433, 18410] Open Access Show Abstract ▼ Abstract: SrMnSb2 is suggested to be a magnetic topological semimetal. It contains square, 2D Sb planes with non-symmorphic crystal symmetries that could protect band crossings, offering the possibility of a quasi-2D, robust Dirac semi-metal in the form of a stable, bulk (3D) crystal. Here, we report a combined and comprehensive experimental and theoretical investigation of the electronic structure of SrMnSb2, including the first ARPES data on this compound. SrMnSb2 possesses a small Fermi surface originating from highly 2D, sharp and linearly dispersing bands (the Y-states) around the (0,π/a)-point in k-space. The ARPES Fermi surface agrees perfectly with that from bulk-sensitive Shubnikov de Haas data from the same crystals, proving the Y−states to be responsible for electrical conductivity in SrMnSb2. DFT and tight binding (TB) methods are used to model the electronic states, and both show good agreement with the ARPES data. Despite the great promise of the latter, both theory approaches show the Y-states to be gapped above EF, suggesting trivial topology. Subsequent analysis within both theory approaches shows the Berry phase to be zero, indicating the non-topological character of the transport in SrMnSb2, a conclusion backed up by the analysis of the quantum oscillation data from our crystals.	Feb 2018
I05-ARPES I09-Surface and Interface Structural Analysis	Probing spin correlations using angle-resolved photoemission in a coupled metallic/Mott insulator system Veronika Sunko , F. Mazzola , S. Kitamura , S. Khim , P. Kushwaha , O. J. Clark , M. D. Watson , I. Markovic , D. Biswas , L. Pourovskii , T. K. Kim , T.-L. Lee , P. K. Thakur , H. Rosner , A. Georges , R. Moessner , T. Oka , A. P. Mackenzie , P. D. C. King Science Advances 6 DOI: 10.1126/sciadv.aaz0611 Diamond Proposal Number(s): [19479, 17699] Open Access Show Abstract ▼ Abstract: A nearly free electron metal and a Mott insulating state can be thought of as opposite ends of the spectrum of possibilities for the motion of electrons in a solid. Understanding their interaction lies at the heart of the correlated electron problem. In the magnetic oxide metal PdCrO2, nearly free and Mott-localized electrons exist in alternating layers, forming natural heterostructures. Using angle-resolved photoemission spectroscopy, quantitatively supported by a strong coupling analysis, we show that the coupling between these layers leads to an “intertwined” excitation that is a convolution of the charge spectrum of the metallic layer and the spin susceptibility of the Mott layer. Our findings establish PdCrO2 as a model system in which to probe Kondo lattice physics and also open new routes to use the a priori nonmagnetic probe of photoemission to gain insights into the spin susceptibility of correlated electron materials.	Feb 2020
I06-Nanoscience	Manipulating the metal-to-insulator transition and magnetic properties in manganite thin films via epitaxial strain Dong Li , Bonan Zhu , Dirk Backes , Larissa S. I. Veiga , Tien-Lin Lee , Hongguang Wang , Qian He , Pinku Roy , Jiaye Zhang , Jueli Shi , Aiping Chen , Peter A. Van Aken , Quanxi Jia , Sarnjeet S. Dhesi , David O. Scanlon , Kelvin H. L. Zhang , Weiwei Li Physical Review B 105 DOI: 10.1103/PhysRevB.105.165426 Diamond Proposal Number(s): [25425, 26901, 29616] Show Abstract ▼ Abstract: Strain engineering of epitaxial transition metal oxide heterostructures offers an intriguing opportunity to control electronic structures by modifying the interplay between spin, charge, orbital, and lattice degrees of freedom. Here, we demonstrate that the electronic structure, magnetic and transport properties of La 0.9 Ba 0.1 MnO 3 thin films can be effectively controlled by epitaxial strain. Spectroscopic studies and first-principles calculations reveal that the orbital occupancy in Mn e g orbitals can be switched from the d 3 z 2 − r 2 orbital to the d x 2 − y 2 orbital by varying the strain from compressive to tensile. The change of orbital occupancy associated with Mn 3 d -O 2 p hybridization leads to dramatic modulation of the magnetic and electronic properties of strained La 0.9 Ba 0.1 MnO 3 thin films. Under moderate tensile strain, an emergent ferromagnetic insulating state with an enhanced ferromagnetic Curie temperature of 215 K is achieved. These findings not only deepen our understanding of electronic structures, magnetic and transport properties in the La 0.9 Ba 0.1 MnO 3 system, but also demonstrate the use of epitaxial strain as an effective knob to tune the electronic structures and related physical properties for potential spintronic device applications.	Apr 2022
I07-Surface & interface diffraction I09-Surface and Interface Structural Analysis	Direct experimental evidence for substrate adatom incorporation into a molecular overlayer Philip J. Mousley , Luke A. Rochford , Paul T. P. Ryan , Philip Blowey , James Lawrence , David A. Duncan , Hadeel Hussain , Billal Sohail , Tien-Lin Lee , Gavin R. Bell , Giovanni Costantini , Reinhard J. Maurer , Christopher Nicklin , D. Phil Woodruff The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.2c01432 Diamond Proposal Number(s): [14884, 4884] Open Access Show Abstract ▼ Abstract: While the phenomenon of metal substrate adatom incorporation into molecular overlayers is generally believed to occur in several systems, the experimental evidence for this relies on the interpretation of scanning tunneling microscopy (STM) images, which can be ambiguous and provides no quantitative structural information. We show that surface X-ray diffraction (SXRD) uniquely provides unambiguous identification of these metal adatoms. We present the results of a detailed structural study of the Au(111)-F4TCNQ system, combining surface characterization by STM, low-energy electron diffraction, and soft X-ray photoelectron spectroscopy with quantitative experimental structural information from normal incidence X-ray standing wave (NIXSW) and SXRD, together with dispersion-corrected density functional theory (DFT) calculations. Excellent agreement is found between the NIXSW data and the DFT calculations regarding the height and conformation of the adsorbed molecule, which has a twisted geometry rather than the previously supposed inverted bowl shape. SXRD measurements provide unequivocal evidence for the presence and location of Au adatoms, while the DFT calculations show this reconstruction to be strongly energetically favored.	Apr 2022
I09-Surface and Interface Structural Analysis	Hard x-ray photoelectron spectroscopy as a probe of the intrinsic electronic properties of CdO J. J. Mudd , T.-l. Lee , V. Muñoz-sanjosé , J. Zúñiga-pérez , D. Hesp , J. M. Kahk , D. J. Payne , R. G. Egdell , C. F. Mcconville Physical Review B 89 (3), 954 DOI: 10.1103/PhysRevB.89.035203 Show Abstract ▼ Abstract: Hard x-ray photoelectron spectroscopy (HAXPES) is used to investigate the intrinsic electronic properties of single crystal epitaxial CdO(100) thin films grown by metal organic vapor phase epitaxy (MOVPE). The reduced surface sensitivity of the HAXPES technique relaxes stringent surface preparation requirements, thereby allowing the measurement of as-grown samples with intrinsically higher carrier concentration (n = 2.4 × 1020 cm−3). High-resolution HAXPES spectra of the valence band and core levels measured at photon energy of 6054 eV are presented. The effects of conduction band filling and band gap renormalization are discussed to explain the observed binding energy shifts. The measured bandwidth of the partially occupied conduction band feature indicates that a plasmon contribution may be present at higher carrier concentrations. The Cd 3d5/2 andO 1s core-level line shapes are found to exhibit an increased asymmetry with increased carrier concentration, interpreted as evidence for final state screening ef ects from the carriers in the conduction band. Alternatively the core-level line shape is interpreted as arising from strong conduction electron plasmon satellites. The natureof these two competing models to describe core-level line shapes in metallic oxides is explored.	Jan 2014
I09-Surface and Interface Structural Analysis	Valence-band orbital character of CdO: A synchrotron-radiation photoelectron spectroscopy and density functional theory study J. J. Mudd , T.-l. Lee , V. Muñoz-sanjosé , J. Zúñiga-pérez , D. J. Payne , R. G. Egdell , C. F. Mcconville Physical Review B 89 (16) DOI: 10.1103/PhysRevB.89.165305 Diamond Proposal Number(s): [8441] Open Access Show Abstract ▼ Abstract: N-type CdO is a transparent conducting oxide (TCO) which has promise in a number of areas including solar cell applications. In order to realize this potential a detailed knowledge of the electronic structure of the material is essential. In particular, standard density functional theory (DFT) methods struggle to accurately predict fundamental material properties such as the band gap. This is largely due to the underestimation of the Cd 4d binding energy, which results in a strong hybridization with the valence-band (VB) states. In order to test theoretical approaches, comparisons to experiment need to be made. Here, synchrotron-radiation photoelectron spectroscopy (SR-PES) measurements are presented, and comparison with three theoretical approaches are made. In particular the position of the Cd 4d state is measured with hard x-ray PES, and the orbital character of the VB is probed by photon energy dependent measurements. It is found that LDA + U using a theoretical U value of 2.34 eV is very successful in predicting the position of the Cd 4d state. The VB photon energy dependence reveals the O 2p photoionization cross section is underestimated at higher photon energies, and that an orbital contribution from Cd 5p is underestimated by all the DFT approaches.	Apr 2014

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