I09-Surface and Interface Structural Analysis
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Celso I.
Fornari
,
Hendrik
Bentmann
,
Sergio L.
Morelhao
,
Thiago R. F.
Peixoto
,
Paulo
Rappl
,
Abdul
Tcakaev
,
Volodymyr
Zabolotnyy
,
Martin
Kamp
,
Tien-lin
Lee
,
Chul-hee
Min
,
Philipp
Kagerer
,
Raphael
Vidal
,
Anna
Isaeva
,
Michael
Ruck
,
Vladimir
Hinkov
,
Friedrich
Reinert
,
Eduardo
Abramof
Abstract: In the field of topological materials, the interaction between band topology and magnetism remains a current frontier for the advance of new topological states and spintronic functionalities. Doping with rare-earth elements with large magnetic moment is a current approach to exploit the phenomenology of such interaction. However, dopant solubility into the main matrix plays a major role. In this sense, the present work is focused on elucidating how Eu incorporates into Bi2Te3 lattice as a function of doping. This work reports a systematic investigation of the structural and electronic properties of bismuth telluride epitaxial layers doped with Eu. Bi2Te3 films were grown by molecular beam epitaxy (MBE) on (111) BaF2 substrates with nominal Eu doping ranging from 0 % up to 9 %. X-ray diffraction (XRD) analysis and scanning transmission electron microscopy (TEM) reveal that Eu atoms enter substitutionally on Bi sites up to 4 % of Eu doping. In contrast, the 9 % Eu-doped sample contains epitaxially oriented nanoclusters of EuTe. X ray photoelectron (XPS) and absorption (XAS) spectroscopies show that Eu atoms enter into the Bi2Te3 crystal matrix in the divalent Eu2+ state for all Eu concentrations. Angle resolved photoemission (ARPES) experiments indicate that the topological surface state is preserved in the presence of the local magnetic moments introduced by the Eu impurities.
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Jun 2020
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I09-Surface and Interface Structural Analysis
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Galo J.
Paez
,
Christopher N.
Singh
,
Matthew J.
Wahila
,
Keith E.
Tirpak
,
Nicholas F.
Quackenbush
,
Shawn
Sallis
,
Hanjong
Paik
,
Yufeng
Liang
,
Darrell G.
Schlom
,
Tien-lin
Lee
,
Christoph
Schlueter
,
Wei-cheng
Lee
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[13812, 25355]
Abstract: Recent reports have identified new metaphases of
VO
2
with strain and/or doping, suggesting the structural phase transition and the metal-to-insulator transition might be decoupled. Using epitaxially strained
VO
2
/
Ti
O
2
(001) thin films, which display a bulklike abrupt metal-to-insulator transition and rutile to monoclinic transition structural phase transition, we employ x-ray standing waves combined with hard x-ray photoelectron spectroscopy to simultaneously measure the structural and electronic transitions. This x-ray standing waves study elegantly demonstrates the structural and electronic transitions occur concurrently within experimental limits (±1K).
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May 2020
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I09-Surface and Interface Structural Analysis
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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
Diamond Proposal Number(s):
[15899, 18191]
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.
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May 2020
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I09-Surface and Interface Structural Analysis
|
Judith Veronika
Berens
,
Sebastian
Bichelmaier
,
Nathalie K.
Fernando
,
Pardeep Kumar
Thakur
,
Tien-lin
Lee
,
Manfred
Mascheck
,
Tomas
Wiell
,
Susanna K.
Eriksson
,
J. Matthias
Kahk
,
Johannes
Lischner
,
Manesh
Mistry
,
Thomas
Aichinger
,
Gregor
Pobegen
,
Anna
Regoutz
Diamond Proposal Number(s):
[19885]
Open Access
Abstract: SiC is set to enable a new era in power electronics impacting a wide range of energy technologies, from electric vehicles to renewable energy. Its physical characteristics outperform silicon in many aspects, including band gap, breakdown field, and thermal conductivity. The main challenge for further development of SiC-based power semiconductor devices is the quality of the interface between SiC and its native dielectric SiO2. High temperature nitridation processes can improve the interface quality and ultimately the device performance immensely, but the underlying chemical processes are still poorly understood. Here, we present an energy-dependent hard X-ray photoelectron spectroscopy (HAXPES) study probing non-destructively SiC and SiO2 and their interface in device stacks treated in varying atmospheres. We successfully combine laboratory- and synchrotron-based HAXPES to provide unique insights into the chemistry of interface defects and their passivation through nitridation processes.
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Apr 2020
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I09-Surface and Interface Structural Analysis
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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
Diamond Proposal Number(s):
[24113]
Open Access
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.
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Mar 2020
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I09-Surface and Interface Structural Analysis
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Theodore D. C.
Hobson
,
Laurie J
Phillips
,
Oliver S
Hutter
,
Huw
Shiel
,
Jack E. N.
Swallow
,
Christopher N.
Savory
,
Pabitra K
Nayak
,
Silvia
Mariotti
,
Bhaskar
Das
,
Leon
Bowen
,
Leanne A. H.
Jones
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Mark A
Farnworth
,
Guillaume
Zoppi
,
Pardeep K.
Thakur
,
Tien-lin
Lee
,
Henry J.
Snaith
,
Chris
Leighton
,
David O.
Scanlon
,
Vinod R.
Dhanak
,
Ken
Durose
,
Tim D.
Veal
,
Jonathan D
Major
Diamond Proposal Number(s):
[21431]
Open Access
Abstract: The carrier type of Sb2Se3 was evaluated for both thin films and bulk crystals via a range of complementary techniques. X-ray photoelectron spectroscopy (XPS), hot-probe, hall effect and surface photo-voltage spectroscopy showed material synthesized from Sb2Se3 granulate mate-rial to be n-type with chlorine identified as an unintentional n-type dopant via secondary ion mass spectrometry analysis. The validity of chlorine as a dopant was con-firmed by synthesis of intrinsic crystals from metallic precursors and subsequent n-type doping by the addition of MgCl2. Chlorine was also shown to be a substitutional n-type shallow dopant by density functional theory calculations. TiO2/Sb2Se3 n-n isotype heterojunction solar cells of 7.3% efficiency based are demonstrated with band alignment analyzed via XPS.
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Mar 2020
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I09-Surface and Interface Structural Analysis
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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
Diamond Proposal Number(s):
[13817]
Open Access
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.
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Feb 2020
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I09-Surface and Interface Structural Analysis
I10-Beamline for Advanced Dichroism
|
Georgios
Araizi-kanoutas
,
Jaap
Geessinck
,
Nicolas
Gauquelin
,
Steef
Smit
,
Xanthe H.
Verbeek
,
Shrawan K.
Mishra
,
Peter
Bencok
,
Christoph
Schlueter
,
Tien-lin
Lee
,
Dileep
Krishnan
,
Jarmo
Fatermans
,
Jo
Verbeeck
,
Guus
Rijnders
,
Gertjan
Koster
,
Mark S.
Golden
Abstract: We report charge transfer up to a single electron per interfacial unit cell across nonpolar heterointerfaces from the Mott insulator
LaTi
O
3
to the charge transfer insulator
LaCo
O
3
. In high-quality bi- and trilayer systems grown using pulsed laser deposition, soft x-ray absorption, dichroism, and scanning transmission electron microscopy-electron energy loss spectroscopy are used to probe the cobalt-
3
d
electron count and provide an element-specific investigation of the magnetic properties. The experiments show the cobalt valence conversion is active within 3 unit cells of the heterointerface, and able to generate full conversion to
3
d
7
divalent Co, which displays a paramagnetic ground state. The number of
LaTi
O
3
/
LaCo
O
3
interfaces, the thickness of an additional, electronically insulating “break” layer between the
LaTi
O
3
and
LaCo
O
3
, and the
LaCo
O
3
film thickness itself in trilayers provide a trio of control knobs for average charge of the cobalt ions in
LaCo
O
3
, illustrating the efficacy of
O
−
2
p
band alignment as a guiding principle for property design in complex oxide heterointerfaces.
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Feb 2020
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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
|
Benjamin A. D.
Williamson
,
Thomas J.
Featherstone
,
Sanjayan S.
Sathasivam
,
Jack E. N.
Swallow
,
Huw
Shiel
,
Leanne A. H.
Jones
,
Matthew J
Smiles
,
Anna
Regoutz
,
Tien-lin
Lee
,
Xueming
Xia
,
Christopher
Blackman
,
Pardeep K.
Thakur
,
Claire J.
Carmalt
,
Ivan P.
Parkin
,
Tim D.
Veal
,
David O.
Scanlon
Diamond Proposal Number(s):
[18195, 21431]
Abstract: Transparent conducting oxides (TCOs) are ubiquitous in modern consumer electronics. SnO2 is an earth abundant, cheaper alternative to In2O3 as a TCO however, its performance in terms of electrical properties lags behind that of In2O3. Based on the recent discovery of mobility and conductivity enhancements in In2O3 from resonant dopants, we use a combination of state-of-the-art hybrid density functional theory calculations, high resolution photoelectron spectroscopy and semiconductor statistics modelling to understand what the optimal dopant is to maximise performance of SnO2-based TCOs. We demonstrate that Ta is the optimal dopant for high performance SnO2, as it is a resonant dopant which is readily incorporated into SnO2 with the Ta 5d states sitting ca. 1.4 eV above the conduction band minimum. Experimentally, the electron effective mass of Ta doped SnO2 was shown to be 0.23m0, compared to 0.29m0 seen with conventional Sb doping, explaining its ability to yield higher mobilities and conductivities.
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Feb 2020
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