I09-Surface and Interface Structural Analysis
|
O.
Tkach
,
S.
Fragkos
,
Deepnarayan
Biswas
,
J.
Liu
,
O.
Fedchenko
,
Y.
Lytvynenko
,
S.
Babenkov
,
D.
Zimmer
,
Q. L.
Nguyen
,
S.
Chernov
,
D.
Kutnyakhov
,
M.
Scholz
,
N.
Wind
,
A.
Gloskovskii
,
F.
Pressacco
,
J.
Dilling
,
L.
Bruckmeier
,
M.
Heber
,
L.
Wenthaus
,
G.
Brenner
,
D.
Puntel
,
P. E.
Majchrzak
,
D.
Liu
,
F.
Scholz
,
J. A.
Sobota
,
J. D.
Koralek
,
G.
Dakovski
,
A.
Mehta
,
N.
Sirica
,
M.
Hoesch
,
C.
Schlueter
,
L. V.
Odnodvorets
,
Y.
Mairesse
,
T.-L.
Lee
,
A.
Kunin
,
K.
Rossnagel
,
Z. X.
Shen
,
H. J.
Elmers
,
S.
Beaulieu
,
G.
Schönhense
Abstract: A new type of objective lens has recently been proposed for use in x-ray photoemission electron microscopes (XPEEMs) and momentum microscopes. Adding a ring electrode concentric with the extractor allows the field in the gap between the sample and the extractor to be shaped. Forming a lens field in this gap reduces the field strength at the sample by up to an order of magnitude. This mitigates the risk of field emission, particularly for cleaved samples with sharp edges. A retarding field can redirect all slow electrons, thus eliminating the primary contribution to the space-charge interaction. Here, we present the first experimental investigation of the new lens, examining its performance at photon energies ranging from the extreme ultraviolet (XUV) produced by a high-harmonic generation-based source to soft and hard x rays at two synchrotron facilities. The gap lens in a region without electrodes enables large working distances up to 23 mm. Reduced aberrations allow for larger fields of view in both k-space and real-space imaging, with resolutions comparable to those of conventional cathode lenses. However, field strengths are an order of magnitude smaller. The zero-field mode enables the study of 3D structured objects and is, therefore, beneficial for small cleaved samples as well as for operando devices involving top electrodes. The repeller mode reduces space-charge effects but results in a smaller k-field diameter. This reduction ranges from 10% at hard x-ray energies to 50% in the XUV range. The usable energy interval is also reduced by a factor of two. In time-of-flight XPEEM mode, the raw data show a resolution of 250 nm, which can be improved to better than 100 nm through data processing.
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Mar 2026
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I09-Surface and Interface Structural Analysis
|
Isabel
Huck
,
Niels
Kubitza
,
Tom
Keil
,
Marius
Schlapp
,
Robert
Winkler
,
Prajna
Bhatt
,
Christoph
Schlueter
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Paweł P.
Michałowski
,
Leopoldo
Molina-Luna
,
Anna
Regoutz
,
Christina S.
Birkel
Diamond Proposal Number(s):
[36180]
Abstract: MAX phases are an extremely versatile family of layered compounds that usually consist of an early to-mid transition metal (M-element), a main group element (mainly groups 13–15) or late transition metal (A-element) and carbon and/or nitrogen (X-element). It is therefore not too surprising that in addition to the roughly 70 compounds with 211 stoichiometry, there exist many solid solutions with mixed elements on the M- and A-site, respectively. Much less common are solid solution phases with mixed elements on both M- and A-site simultaneously (double-site solid solutions), as well as solid solutions on the X-site (carbonitride MAX phases). Challenging these restrictions in the chemical composition space, we present here for the first time (V0.2Cr0.8)2(Ga0.5Ge0.5)(C0.6N0.4) as a new carbonitride member of the MAX phase family, containing solid solutions on all three lattice sites simultaneously. This triple-site solid solution MAX phase is synthesized by high-temperature solid-state methods, and we demonstrate that it is possible to use two different nitrogen-containing precursors (VN and Cr2N), respectively. Structure, morphology and chemical composition are characterized by X-ray powder diffraction (XRD), electron microscopy (SEM/TEM), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (HAXPES).
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Feb 2026
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I09-Surface and Interface Structural Analysis
|
C.-H.
Min
,
M.
Scholz
,
T.-L.
Lee
,
C.
Schlueter
,
A.
Gloskovskii
,
E. D. L.
Rienks
,
V.
Hinkov
,
H.
Bentmann
,
Y. S.
Kwon
,
F.
Reinert
,
H.-D.
Kim
,
K.
Rossnagel
,
S.
Müller
,
W. J.
Choi
,
V.
Zabolotnyy
,
M.
Heber
,
J. D.
Denlinger
,
C.-J.
Kang
,
M.
Kalläne
,
N.
Wind
,
L.
Dudy
Diamond Proposal Number(s):
[22630]
Abstract: Exotic quasiparticle states have been proposed in mixed-valent compounds exhibiting valence transitions. However, clear spectroscopic evidence identifying these states has remained elusive. Using synchrotron-based hard x-ray and extreme ultraviolet photoemission spectroscopy, we have probed the Tm 3𝑑 and 4𝑓 emissions in TmSe1−𝑥Te𝑥, where a Te concentration-dependent semimetal–insulator transition occurs alongside the valence transition. Our photoemission results, which are characteristic of the bulk, track this combined transition across the critical concentration (𝑥𝑐 =0.29). Notably, our results reveal a noninteger valence for the insulating phase and a novel quasiparticle excitation in the semimetallic phase: a Holstein polaron that extends beyond the standard periodic Anderson model.
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Oct 2025
|
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I09-Surface and Interface Structural Analysis
|
H. J.
Elmers
,
O.
Tkach
,
Y.
Lytvynenko
,
P.
Yogi
,
M.
Schmitt
,
D.
Biswas
,
J.
Liu
,
S. V.
Chernov
,
Quynh
Nguyen
,
M.
Hoesch
,
D.
Kutnyakhov
,
N.
Wind
,
L.
Wenthaus
,
M.
Scholz
,
K.
Rossnagel
,
A.
Gloskovskii
,
C.
Schlueter
,
A.
Winkelmann
,
A. A.
Haghighirad
,
T.-L.
Lee
,
M.
Sing
,
R.
Claessen
,
M.
Le Tacon
,
J.
Demsar
,
G.
Schönhense
,
O.
Fedchenko
Diamond Proposal Number(s):
[33765]
Abstract: Using x-ray photoelectron diffraction (XPD) and angle-resolved photoemission spectroscopy, we study photoemission intensity changes related to changes in the geometric and electronic structure in the kagome metal CsV3Sb5 upon transition to an unconventional charge density wave (CDW) state. The XPD patterns reveal the presence of a chiral atomic structure in the CDW phase. Furthermore, using circularly polarized x-rays, we have found a pronounced nontrivial circular dichroism in the angular distribution of the valence band photoemission in the CDW phase, indicating a chirality of the electronic structure. This observation is consistent with the proposed orbital loop current order. In view of a negligible spontaneous Kerr signal in recent magneto-optical studies, the results suggest an antiferromagnetic coupling of the orbital magnetic moments along the 𝑐 axis. While the inherent structural chirality may also induce circular dichroism, the observed asymmetry values seem to be too large in the case of the weak structural distortions caused by the CDW.
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Mar 2025
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I09-Surface and Interface Structural Analysis
|
Curran
Kalha
,
Laura E.
Ratcliff
,
Giorgio
Colombi
,
Christoph
Schlueter
,
Bernard
Dam
,
Andrei
Gloskovskii
,
Tien-Lin
Lee
,
Pardeep K.
Thakur
,
Prajna
Bhatt
,
Yujiang
Zhu
,
Jürg
Osterwalder
,
Francesco
Offi
,
Giancarlo
Panaccione
,
Anna
Regoutz
Diamond Proposal Number(s):
[29451]
Open Access
Abstract: Metal hydrides are potential candidates for applications in hydrogen-related technologies, such as energy storage, hydrogen compression, and hydrogen sensing, to name just a few. However, understanding the electronic structure and chemical environment of hydrogen within them remains a key challenge. This work presents a new analytical pathway to explore these aspects in technologically relevant systems using hard x-ray photoelectron spectroscopy (HAXPES) on thin films of two prototypical metal dihydrides:
YH
2
−
δ
and
Ti
H
2
−
δ
. By taking advantage of the tunability of synchrotron radiation, a nondestructive depth profile of the chemical states is obtained using core-level spectra. Combining experimental valence-band (VB) spectra collected at varying photon energies with theoretical insights from density functional theory (DFT) calculations, a description of the bonding nature and the role of
d
versus
s
p
contributions to states near the Fermi energy are provided. Moreover, a reliable determination of the enthalpy of formation is proposed by using experimental values of the energy position of metal
s
-band features close to the Fermi energy in the HAXPES VB spectra.
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Nov 2023
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I09-Surface and Interface Structural Analysis
|
Laura E.
Ratcliff
,
Takayoshi
Oshima
,
Felix
Nippert
,
Benjamin M.
Janzen
,
Elias
Kluth
,
Rüdiger
Goldhahn
,
Martin
Feneberg
,
Piero
Mazzolini
,
Oliver
Bierwagen
,
Charlotte
Wouters
,
Musbah
Nofal
,
Martin
Albrecht
,
Jack E. N.
Swallow
,
Leanne A. H.
Jones
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Curran
Kalha
,
Christoph
Schlueter
,
Tim D.
Veal
,
Joel B.
Varley
,
Markus R.
Wagner
,
Anna
Regoutz
Diamond Proposal Number(s):
[21430, 24670]
Open Access
Abstract: Ga2O3 and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga2O3 offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ-Ga2O3 presents a particular challenge across synthesis, characterisation, and theory due to its inherent disorder and resulting complex structure – electronic structure relationship. Here, density functional theory is used in combination with a machine learning approach to screen nearly one million potential structures, thereby developing a robust atomistic model of the γ-phase. Theoretical results are compared with surface and bulk sensitive soft and hard X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, spectroscopic ellipsometry, and photoluminescence excitation spectroscopy experiments representative of the occupied and unoccupied states of γ-Ga2O3. The first onset of strong absorption at room temperature is found at 5.1 eV from spectroscopic ellipsometry, which agrees well with the excitation maximum at 5.17 eV obtained by PLE spectroscopy, where the latter shifts to 5.33 eV at 5 K. This work presents a leap forward in the treatment of complex, disordered oxides and is a crucial step towards exploring how their electronic structure can be understood in terms of local coordination and overall structure.
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Jul 2022
|
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I09-Surface and Interface Structural Analysis
|
F.
Offi
,
K.
Yamauchi
,
S.
Picozzi
,
V.
Lollobrigida
,
A.
Verna
,
C.
Schlueter
,
T.-L.
Lee
,
A.
Regoutz
,
D. J.
Payne
,
A.
Petrov
,
G.
Vinai
,
G. M.
Pierantozzi
,
T.
Pincelli
,
G.
Panaccione
,
F.
Borgatti
Diamond Proposal Number(s):
[11322]
Abstract: Hybridization of electronic states and orbital symmetry in transition metal oxides are generally considered key ingredients in the description of both their electronic and magnetic properties. In the prototypical case of
La
0.65
Sr
0.35
MnO
3
(LSMO), a landmark system for spintronics applications, a description based solely on Mn
3
d
and O
2
p
electronic states is reductive. We thus analyzed elemental and orbital distributions in the LSMO valence band through a comparison between density functional theory calculations and experimental photoelectron spectra in a photon energy range from soft to hard x rays. We reveal a number of hidden contributions, arising specifically from La
5
p
, Mn
4
s
, and O
2
s
orbitals, considered negligible in previous analyses; our results demonstrate that all these contributions are significant for a correct description of the valence band of LSMO and of transition metal oxides in general.
|
Oct 2021
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I09-Surface and Interface Structural Analysis
|
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
I10-Beamline for Advanced Dichroism - scattering
|
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.
|
Feb 2020
|
|
I09-Surface and Interface Structural Analysis
|
Abstract: The electronic properties of
CaCuO
2
/
La
0.7
Sr
0.3
MnO
3
(LSMO) superlattices are determined by the electronic structure of the structural units and in particular their interfaces. The electronic structure of LSMO is governed by a metal-insulator transition, which is controlled by the thickness of the units and the sample temperature, resulting in a systematic downward band shift for metallic samples (i.e., thick LSMO units, low temperature). We present a systematic study of the changes in the valence-band structure and screening features in Mn
2
p
and Cu
2
p
core-level spectra. The results show that hybridization of Cu
3
d
orbitals with out-of-plane O
2
p
orbitals can be systematically tuned by controlling the band alignment at the interface via the metal-to-insulator transition of the LSMO units. This opens a new route to rational design of functional interfaces and control of orbital reconstructions.
|
Sep 2019
|
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