B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Georg
Held
,
Federica
Venturini
,
David C.
Grinter
,
Pilar
Ferrer
,
Rosa
Arrigo
,
Liam
Deacon
,
Wilson
Quevedo Garzon
,
Kanak
Roy
,
Alex
Large
,
Christopher
Stephens
,
Andrew
Watts
,
Paul
Larkin
,
Matthew
Hand
,
Hongchang
Wang
,
Linda
Pratt
,
James J.
Mudd
,
Thomas
Richardson
,
Suren
Patel
,
Michael
Hillman
,
Stewart
Scott
Open Access
Abstract: The ambient-pressure endstation and branchline of the Versatile Soft X-ray (VerSoX) beamline B07 at Diamond Light Source serves a very diverse user community studying heterogeneous catalysts, pharmaceuticals and biomaterials under realistic conditions, liquids and ices, and novel electronic, photonic and battery materials. The instrument facilitates studies of the near-surface chemical composition, electronic and geometric structure of a variety of samples using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy in the photon energy range from 170 eV to 2800 eV. The beamline provides a resolving power hν/Δ(hν) > 5000 at a photon flux > 1010 photons s−1 over most of its energy range. By operating the optical elements in a low-pressure oxygen atmosphere, carbon contamination can be almost completely eliminated, which makes the beamline particularly suitable for carbon K-edge NEXAFS. The endstation can be operated at pressures up to 100 mbar, whereby XPS can be routinely performed up to 30 mbar. A selection of typical data demonstrates the capability of the instrument to analyse details of the surface composition of solid samples under ambient-pressure conditions using XPS and NEXAFS. In addition, it offers a convenient way of analysing the gas phase through X-ray absorption spectroscopy. Short XPS spectra can be measured at a time scale of tens of seconds. The shortest data acquisition times for NEXAFS are around 0.5 s per data point.
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Sep 2020
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I09-Surface and Interface Structural Analysis
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Daniel W.
Davies
,
Aron
Walsh
,
James J.
Mudd
,
Chris F.
Mcconville
,
Anna
Regoutz
,
J. Matthias
Kahk
,
David J.
Payne
,
Vin R.
Dhanak
,
David
Hesp
,
Katariina
Pussi
,
Tien-Lin
Lee
,
Russell G.
Egdell
,
Kelvin H. L.
Zhang
Diamond Proposal Number(s):
[8441]
Abstract: Indium oxide is widely used as transparent electrode in optoelectronic devices and as a photocatalyst with activity for reduction of CO2. However, very little is known about the structural and electronic properties of its surfaces, particularly those prepared under reducing conditions. In this report, directional ‘lone-pair’ surface states associated with filled 5s2 orbitals have been identified on vacuum-annealed In2O3(111) through a combination of hard and soft X-ray photoemission spectroscopy and density functional theory calculations. The lone pairs reside on indium ad-atoms in a formal +1 oxidation state, each of which traps two electrons into a localised hybrid orbital protruding away from the surface and lying just above the valence band maximum in photoemission spectra. The third electron associated with the ad-atoms is delocalised into the conduction band, thus producing the surface electron accumulation layer identified previously on vacuum-annealed In2O3(111) (1×1) surfaces. The surface structure is further supported by low energy electron diffraction, but there is no chemical shift in indium core level x-ray photoelectron spectra between surface In(I) ad-atoms and bulk In(III). The 5s2 lone pairs confer Lewis basicity on the surface In sites and may have a pronounced impact on the catalytic or photo-catalytic activity of reduced In2O3.
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Dec 2018
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B18-Core EXAFS
I18-Microfocus Spectroscopy
I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
Controls
Detectors
Optics
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Sofia
Diaz-Moreno
,
Monica
Amboage
,
Mark
Basham
,
Roberto
Boada
,
Nicholas E.
Bricknell
,
Giannantonio
Cibin
,
Thomas
Cobb
,
Jacob
Filik
,
Adam
Freeman
,
Kalotina
Geraki
,
Diego
Gianolio
,
Shusaku
Hayama
,
Konstantin
Ignatyev
,
Luke
Keenan
,
Iuliia
Mikulska
,
J. Frederick W.
Mosselmans
,
James J.
Mudd
,
Stephen A.
Parry
Open Access
Abstract: This manuscript presents the current status and technical details of the Spectroscopy Village at Diamond Light Source. The Village is formed of four beamlines: I18, B18, I20-Scanning and I20-EDE. The village provides the UK community with local access to a hard X-ray microprobe, a quick-scanning multi-purpose XAS beamline, a high-intensity beamline for X-ray absorption spectroscopy of dilute samples and X-ray emission spectroscopy, and an energy-dispersive extended X-ray absorption fine-structure beamline. The optics of B18, I20-scanning and I20-EDE are detailed; moreover, recent developments on the four beamlines, including new detector hardware and changes in acquisition software, are described.
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Jul 2018
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I05-ARPES
Detectors
Metrology
Optics
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M.
Hoesch
,
T. K.
Kim
,
P.
Dudin
,
H.
Wang
,
S.
Scott
,
P.
Harris
,
S.
Patel
,
M.
Matthews
,
D.
Hawkins
,
S. G.
Alcock
,
T.
Richter
,
J. J.
Mudd
,
M.
Basham
,
L.
Pratt
,
P.
Leicester
,
E. C.
Longhi
,
A.
Tamai
,
F.
Baumberger
Abstract: A synchrotron radiation beamline in the photon energy range of 18-240 eV and an electron spectroscopy end station have been constructed at the 3 GeV Diamond Light Source storage ring. The instrument features a variable polarisation undulator, a high resolution monochromator, a re-focussing system to form a beam spot of 50 × 50 μm2, and an end station for angle-resolved photoelectron spectroscopy (ARPES) including a 6-degrees-of-freedom cryogenic sample manipulator. The beamline design and its performance allow for a highly productive and precise use of the ARPES technique at an energy resolution of 10-15 meV for fast k-space mapping studies with a photon flux up to 2 ⋅ 1013 ph/s and well below 3 meV for high resolution spectra.
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Jan 2017
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Data acquisition
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Rob
Walton
,
Alun
Ashton
,
Mark
Basham
,
Peter
Chang
,
Tom
Cobb
,
S
Da Graca
,
Andrew
Dent
,
Jacob
Filik
,
Matt
Gerring
,
Charles
Mita
,
James
Mudd
,
C M
Palmer
,
U
Pederson
,
Paul
Quinn
,
Nick
Rees
Open Access
Abstract: Many synchrotron beamlines offer some form of
continuous scanning for either energy scanning or sample
mapping. However, this is normally done on an ad-hoc
beamline by beamline basis. Diamond has recently
embarked on an ambitious project to define how to
implement continuous scanning as the standard way of
doing virtually all mapping tasks on beamlines. The
project is split into four main areas: 1) User interfaces to
describe the mapping process in a scientifically relevant
way, generating a scan description that can be used later;
2) The physical process of scanning and coordinating
hardware motion and detector data capture across the
beamline; 3) Capture of the detector data and all the
associated meta-data to disk, deciding and describing the
layout of the file (or files) for the main use cases; 4)
Display and analysis of live data and display of processed
data. In order to achieve this common approach across
beamlines, the standard software used throughout the
facility (Delta Tau motor controllers, EPICS, GDA and
DAWN), has been built on.
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Oct 2015
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Rob
Walton
,
Alun
Ashton
,
Mark
Basham
,
Peter
Chang
,
Tom
Cobb
,
S
Da Graca
,
Andrew
Dent
,
Jacob
Filik
,
Matt
Gerring
,
Charles
Mita
,
James
Mudd
,
C M
Palmer
,
Ulrik
Pedersen
,
Paul
Quinn
,
Nick
Rees
Open Access
Abstract: Many synchrotron beamlines offer some form of
continuous scanning for either energy scanning or sample
mapping. However, this is normally done on an ad-hoc
beamline by beamline basis. Diamond has recently
embarked on an ambitious project to define how to
implement continuous scanning as the standard way of
doing virtually all mapping tasks on beamlines. The
project is split into four main areas: 1) User interfaces to
describe the mapping process in a scientifically relevant
way, generating a scan description that can be used later;
2) The physical process of scanning and coordinating
hardware motion and detector data capture across the
beamline; 3) Capture of the detector data and all the
associated meta-data to disk, deciding and describing the
layout of the file (or files) for the main use cases; 4)
Display and analysis of live data and display of processed
data. In order to achieve this common approach across
beamlines, the standard software used throughout the
facility (Delta Tau motor controllers, EPICS, GDA and
DAWN), has been built on.
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Oct 2015
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I09-Surface and Interface Structural Analysis
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Abstract: In this thesis a variety of photoelectron spectroscopy techniques have been applied to study CdO, in order to gain a more detailed knowledge of both the bulk and surface electronic properties of this material. Hard x-ray photoelectron spectroscopy (HAXPES) has been used, relaxing the surface preparation requirements of conventional photoemission techniques. This allows CdO to be measured in an as-grown condition with the associated higher carrier concentrations. The effects of conduction band filling and final state screening have been observed, and a discussion of the bulk-like sensitivity of HAXPES is given. The use of synchrotron radiation allows variation of the photon energy used to excite photoelectrons, and this is combined with the associated changes in photoionisation cross-sections to study the orbital character of the CdO valence band (VB). These measurements have been compared to density functional theory (DFT) calculations, using three functionals. It was found that using LDA+U and employing a theoretically calculated value of U = 2.34 eV can adequately reproduce the experimentally measured Cd 4d shallow core level position. The photon energy dependence of the shape of the VB, however, was not reproduced by the DFT calculations, indicating that additional Cd 5p character may be present within the VB, and that the O 2p photoionisation cross-sections may by underestimated at higher photon energies. The electron accumulation layer known to exist at the CdO surface has been tuned by the addition of Rb, which allowed the 2D electron density to be almost doubled. The effects of the increased 2D electron density on the surface band gap narrowing have been investigated by simulating the subband dispersion using the Poisson-Schrödinger model. The effective mass of the subband states has been extracted, and was found to be significantly lower than the reported bulk mass, which is discussed in the context of other recent results.
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Jun 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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Open Access
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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