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Open Access
Abstract: Diamond Light Source's Surface and Interface Structural Analysis beamline (I09) is the first in the world designed to deliver both hard and soft X-rays with optimized, independent sources and optics. With the extended energy range, we offer a wide variety of X-ray techniques that are based primarily on X-ray photoelectron and absorption spectroscopies, which can be combined to maximize the information one can extract from a visit to the beamline. For photoelectron spectroscopy, this energy range corresponds to an information depth from 0.5 to more than 20 nm, providing the bulk as well as surface sensitivity for depth-profiling of heterostructures and buried interfaces.
This unique combination has allowed I09 to develop, since becoming operational in 2013, a user community that is interested in two interconnected research areas. One concentrates on surface chemistry and structures, in particular adsorption of organic molecules on solid surfaces and epitaxial growth of two-dimensional materials. The other area of research deals with the electronic structures of oxide heterointerfaces, electron correlations and metal-insulator transitions, energy research, functionalized materials, and material design. The vast majority of these studies, particularly those on surface structures and lithium ion batteries, have benefited from the use of both soft and hard X-rays at I09. In the following sections, we outline the design, science cases, and future plans of the beamline.
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Jul 2018
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Arian
Arab
,
Xiaoran
Liu
,
Okan
Koksal
,
Weibing
Yang
,
Ravini U.
Chandrasena
,
Srimanta
Middey
,
Mikhail
Kareev
,
Siddharth
Kumar
,
Marius-adrian
Husanu
,
Zhenzhong
Yang
,
Lin
Gu
,
Vladimir N.
Strocov
,
Tien-lin
Lee
,
Jan
Minar
,
Rossitza
Pentcheva
,
Jak
Chakhalian
,
Alexander X.
Gray
Abstract: Artificial complex-oxide heterostructures containing ultrathin buried layers grown along the pseudocubic [111] direction have been predicted to host a plethora of exotic quantum states arising from the graphene-like lattice geometry and the interplay between strong electronic correlations and band topology. To date, however, electronic-structural investigations of such atomic layers remain an immense challenge due to the shortcomings of conventional surface-sensitive probes, with typical information depths of a few Ångstroms. Here, we use a combination of bulk-sensitive soft x-ray angle-resolved photoelectron spectroscopy (SX-ARPES), hard x-ray photoelectron spectroscopy (HAXPES) and state-of-the-art first-principles calculations to demonstrate a direct and robust method for extracting momentum-resolved and angle-integrated valence-band electronic structure of an ultrathin buckled graphene-like layer of NdNiO3 confined between two 4-unit cell-thick layers of insulating LaAlO3. The momentum-resolved dispersion of the buried Ni d states near the Fermi level obtained via SX-ARPES is in excellent agreement with the first-principles calculations and establishes the realization of an antiferro-orbital order in this artificial lattice. The HAXPES measurements reveal the presence of a valence-band (VB) bandgap of 265 meV. Our findings open a promising avenue for designing and investigating quantum states of matter with exotic order and topology in a few buried layers.
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Oct 2019
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B16-Test Beamline
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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.
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Jul 2009
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B16-Test Beamline
Optics
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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.
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Mar 2013
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I05-ARPES
I09-Surface and Interface Structural Analysis
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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
Diamond Proposal Number(s):
[15189, 16433, 18410]
Open Access
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.
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Feb 2018
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I05-ARPES
I09-Surface and Interface Structural Analysis
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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
Diamond Proposal Number(s):
[19479, 17699]
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.
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Feb 2020
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I09-Surface and Interface Structural Analysis
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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.
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Jan 2014
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I09-Surface and Interface Structural Analysis
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Benjamin
Stadtmuller
,
Sonja
Schroder
,
Francois
Bocquet
,
Caroline
Henneke
,
Christoph
Kleimann
,
Serguei
Soubatch
,
Martin
Willenbockel
,
Blanka
Detlefs
,
Jorg
Zegenhagen
,
Tien-lin
Lee
,
Stefan
Tautz
,
Christian
Kumpf
Diamond Proposal Number(s):
[8449, 9231]
Abstract: The formation of metalorganic hybrid interfaces is determined by the fine balance between molecule-substrate and molecule-molecule interactions at the interface. Here, we report on a systematic investigation of interfaces between a metal surface and organic monolayer films that consist of two different molecular species, one donor and one acceptor of electronic charge. Our x-ray standing wave data show that in heteromolecular structures, the molecules tend to align themselves to an adsorption height between those observed in the respective homomolecular structures. We attribute this alignment effect to a substrate-mediated charge transfer between the molecules, which causes a mutual enhancement of their respective donor and acceptor characters. We argue that this effect is of general validity for π-conjugated molecules adsorbing on noble metal surfaces.
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Apr 2014
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[8441]
Open Access
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.
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Apr 2014
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[8450]
Abstract: We present a systematic X-ray standing wave (XSW) study of the π-conjugated organic compound 2H-tetraphenylporphyrin (2HTPP) and copper(II)-tetraphenylporphyrin (CuTPP) on Cu(111) at room and low temperatures. We exploit the feature of thermally activated self-metalation of 2HTPP to CuTPP to study the influence of the central metal atom on the bonding distance of the molecule to the substrate surface. Comparison between the average adsorption distances of the carbon and nitrogen atoms of 2HTPP reveals a distorted molecule with the nitrogen atoms being closer to the surface than the carbon ones on average. Additionally, the measured positions of the two chemically inequivalent types of nitrogen atoms (iminic and aminic) of 2HTPP indicate a distorted porphyrin ring. After the chemical reaction from 2HTPP to CuTPP at 500 K, no change of the adsorption distance of the carbon skeleton is seen, but the entire molecule becomes flattened. Despite the changes upon metalation, adsorption distances for both molecules show a strong interaction with the substrate in comparison to similar π-conjugated molecules.
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May 2014
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