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.
|
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.
|
Jul 2022
|
|
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.
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Oct 2021
|
|
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
|
|
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
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[9012, 12558]
Abstract: We study the effect of alkali metal intercalation (Cs and Li) on the geometry of graphene on Ir(111) using the x-ray standing waves technique. For both alkali metals, the increase in the mean height of the carbon layer does not depend on the lateral structure or the density of the intercalated layer. For Li, full delamination of graphene from the metal substrate is found already for a small amount of intercalant. Even though Lithium lifts graphene to a smaller height, it is much more efficient in ironing out the corrugation of pristine graphene on Ir(111).
|
May 2019
|
|
I09-Surface and Interface Structural Analysis
|
Anna
Regoutz
,
Alex M.
Ganose
,
Lars
Blumenthal
,
Christoph
Schlueter
,
Tien-Lin
Lee
,
Gregor
Kieslich
,
Anthony K.
Cheetham
,
Gwilherm
Kerherve
,
Ying-Sheng
Huang
,
Ruei-San
Chen
,
Giovanni
Vinai
,
Tommaso
Pincelli
,
Giancarlo
Panaccione
,
Kelvin H. L.
Zhang
,
Russell G.
Egdell
,
Johannes
Lischner
,
David O.
Scanlon
,
David J.
Payne
Diamond Proposal Number(s):
[12673]
Abstract: Theory and experiment are combined to gain an understanding of the electronic properties of OsO2, a poorly studied metallic oxide that crystallizes in the rutile structure. Hard and soft valence-band x-ray photoemission spectra of OsO2 single crystals are in broad agreement with the results of density-functional-theory calculations, aside from a feature shifted to high binding energy of the conduction band. The energy shift corresponds to the conduction electron plasmon energy measured by reflection electron energy loss spectroscopy. The plasmon satellite is reproduced by many-body perturbation theory.
|
Feb 2019
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[12558]
Abstract: Epitaxial hexagonal boron nitride on Ir(111) is significantly modified by adsorption and intercalation of alkali-metal atoms. Regarding geometry, intercalation lifts the two-dimensional layer from its substrate and reduces the characteristic corrugation imprinted by direct contact with the metal substrate. Moreover, the presence of charged species in close proximity to the hexagonal boron nitride (hBN) layer strongly shifts the electronic structure (valence bands and core levels). We used scanning tunneling microscopy, low-energy electron diffraction, x-ray photoelectron spectroscopy (XPS), and the x-ray standing wave technique to study changes in the atomic structure induced by Cs adsorption and intercalation. Depending on the preparation, the alkali-metal atoms can be found on top and underneath the hexagonal boron nitride in ordered and disordered arrangements. Adsorbed Cs does not change the morphology of hBN/Ir(111) significantly, whereas an intercalated layer of Cs decouples the two-dimensional sheet and irons out its corrugation. XPS and angle-resolved photoelectron spectroscopy reveal a shift of the electronic states to higher binding energies, which increases with increasing density of the adsorbed and intercalated Cs. In the densest phase, Cs both intercalates and adsorbs on hBN and shifts the electronic states of hexagonal boron nitride by 3.56 eV. As this shift is not sufficient to move the conduction band below the Fermi energy, the electronic band gap must be larger than 5.85 eV.
|
Nov 2018
|
|
I09-Surface and Interface Structural Analysis
|
Slavomir
Nemsak
,
Mathias
Gehlmann
,
Cheng-Tai
Kuo
,
Shih-Chieh
Lin
,
Christoph
Schlueter
,
Ewa
Mlynczak
,
Tien-Lin
Lee
,
Lukasz
Plucinski
,
Hubert
Ebert
,
Igor
Di Marco
,
Ján
Minár
,
Claus M.
Schneider
,
Charles S.
Fadley
Diamond Proposal Number(s):
[11516, 12032]
Open Access
Abstract: The dilute magnetic semiconductors have promise in spin-based electronics applications due to their potential for ferromagnetic order at room temperature, and various unique switching and spin-dependent conductivity properties. However, the precise mechanism by which the transition-metal doping produces ferromagnetism has been controversial. Here we have studied a dilute magnetic semiconductor (5% manganese-doped gallium arsenide) with Bragg-reflection standing-wave hard X-ray angle-resolved photoemission spectroscopy, and resolved its electronic structure into element- and momentum- resolved components. The measured valence band intensities have been projected into element-resolved components using analogous energy scans of Ga 3d, Mn 2p, and As 3d core levels, with results in excellent agreement with element-projected Bloch spectral functions and clarification of the electronic structure of this prototypical material. This technique should be broadly applicable to other multi-element materials.
|
Aug 2018
|
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