I09-Surface and Interface Structural Analysis
|
Anders L.
Jørgensen
,
David A.
Duncan
,
Claus F. P.
Kastorp
,
Line
Kyhl
,
Zeyuan
Tang
,
Albert
Bruix
,
Mie
Andersen
,
Bjork
Hammer
,
Tien-Lin
Lee
,
Liv
Hornekaer
,
Richard
Balog
Diamond Proposal Number(s):
[16243]
Abstract: Functionalization of graphene on Ir(111) is a promising route to modify graphene by chemical means in a controlled fashion at the nanoscale. Yet, the nature of such functionalized sp3 nanodots remains unknown. Density functional theory (DFT) calculations alone cannot differentiate between two plausible structures, namely true graphane and substrate stabilized graphane-like nanodots. These two structures, however, interact dramatically differently with the underlying substrate. Discriminating which type of nanodots forms on the surface is thus of paramount importance for the applications of such prepared nanostructures. By comparing X-ray standing wave measurements against theoretical model structures obtained by DFT calculations we are able to exclude the formation of true graphane nanodots and clearly show the formation graphane-like nanodots.
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Jun 2019
|
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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.
|
Feb 2020
|
|
I09-Surface and Interface Structural Analysis
|
Peter
Knecht
,
Joachim
Reichert
,
Peter S.
Deimel
,
Peter
Feulner
,
Felix
Haag
,
Francesco
Allegretti
,
Manuela
Garnica
,
Martin
Schwarz
,
Willi
Auwärter
,
Paul T. P.
Ryan
,
Tien-Lin
Lee
,
David A.
Duncan
,
Ari Paavo
Seitsonen
,
Johannes V.
Barth
,
Anthoula Chrysa
Papageorgiou
Diamond Proposal Number(s):
[24320]
Open Access
Abstract: We assess the crucial role of tetrapyrrole flexibility in the CO ligation to distinct Ru‐porphyrins supported on an atomistically well‐defined Ag(111) substrate. Our systematic real space visualisation and manipulation experiments with scanning tunnelling microscopy directly probe the ligation, while bond‐resolving atomic force microscopy and X‐ray standing waves measurements characterise the geometry, X‐ray and ultraviolet photoelectron spectroscopy the electronic structure, and temperature programmed desorption the binding strength. Density functional theory calculations provide additional insight into the functional interface. We unambiguously demonstrate that the substituents regulate the interfacial conformational adaptability, either promoting or obstructing the uptake of axial CO adducts.
|
May 2021
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[15856]
Abstract: Depositing disordered Al on top of
Sr
Ti
O
3
is a cheap and easy way to create a two-dimensional electron system in the
Sr
Ti
O
3
surface layers. To facilitate future device applications, we passivate the heterostructure by a disordered
La
Al
O
3
capping layer to study the electronic properties by complementary x-ray photoemission spectroscopy and transport measurements on the very same samples. We also tune the electronic interface properties by adjusting the oxygen pressure during film growth.
|
Jun 2021
|
|
I09-Surface and Interface Structural Analysis
|
Wei-Cheng
Lee
,
Matthew
Wahila
,
Shantanu
Mukherjee
,
Christopher N.
Singh
,
Tyler
Eustance
,
Anna
Regoutz
,
Hanjong
Paik
,
Jos E.
Boschker
,
Fanny
Rodolakis
,
Tien-Lin
Lee
,
Darrell G.
Schlom
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[20647, 21430]
Abstract: We investigate the electronic structure of epitaxial VO
2
2
films in the rutile phase using density functional theory combined with the slave-spin method (DFT + SS). In DFT + SS, multi-orbital Hubbard interactions are added to a DFT-fit tight-binding model, and slave spins are used to treat electron correlations. We find that while stretching the system along the rutile
c
c
-axis results in a band structure favoring anisotropic orbital fillings, electron correlations favor equal filling of the
t
2g
t2g
orbitals. These two distinct effects cooperatively induce an orbital-dependent redistribution of the electron occupations and spectral weights, driving strained VO
2
2
toward an orbital selective Mott transition (OSMT). The simulated single-particle spectral functions are directly compared to V L-edge resonant X-ray photoemission spectroscopy of epitaxial 10 nm VO
2
2
/TiO
2
2
(001) and (100) strain orientations. Excellent agreement is observed between the simulations and experimental data regarding the strain-induced evolution of the lower Hubbard band. Simulations of rutile NbO
2
2
under similar strain conditions are performed, and we predict that an OSMT will not occur in rutile NbO
2
2
. Our prediction is supported by the high-temperature hard x-ray photoelectron spectroscopy measurement on relaxed NbO
2
2
(110) thin films with no trace of the lower Hubbard band. Our results indicate that electron correlations in VO
2
2
are important and can be modulated even in the rutile phase before the Peierls instability sets in.
|
Feb 2019
|
|
I09-Surface and Interface Structural Analysis
|
David A.
Duncan
,
Nicolae
Atodiresei
,
Simone
Lisi
,
Phil J.
Blowey
,
Vasile
Caciuc
,
James
Lawrence
,
Tien-Lin
Lee
,
Maria Grazia
Betti
,
Pardeep Kumar
Thakur
,
Ada
Della Pia
,
Stefan
Blügel
,
Giovanni
Costantini
,
D. Phil
Woodruff
Diamond Proposal Number(s):
[13625]
Open Access
Abstract: Theoretical formulations capable of modeling chemical interactions over 3–4 orders of magnitude of bond strength, from covalent to van der Waals (vdW) forces, are one of the primary goals in materials physics, and chemistry. Development of vdW corrections for density-functional theory has thus been a major research field for two decades. While many of these corrections are semiempirical, more theoretically rigorous ab initio functionals have been developed. The ab initio functional vdW-DF2, when coupled with the reoptimized B86 exchange function (vdW-DF2-rB86), has typically performed as well, if not better than most semiempirical formulations. Here we present a system, Co intercalation of graphene on Ir(111), for which a semiempirical correction predicts local corrugation maxima in locations at which the vdW-DF2-rB86 functional predicts global minima. Sub-angstrom precision quantitative structural measurements show better agreement with the semiempirical correction. We posit that it is balancing the weak vdW interaction with the stronger, even covalent, interactions that proves a challenge for the vdW-DF2-rB86 functional.
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Dec 2019
|
|
I09-Surface and Interface Structural Analysis
|
Martin
Schwarz
,
Alexander
Riss
,
Manuela
Garnica
,
Jacob
Ducke
,
Peter S.
Deimel
,
David A.
Duncan
,
Pardeep
Kumar Thakur
,
Tien-Lin
Lee
,
Ari Paavo
Seitsonen
,
Johannes V.
Barth
,
Francesco
Allegretti
,
Willi
Auwärter
Diamond Proposal Number(s):
[14624]
Abstract: Atomically thin hexagonal boron nitride (h-BN) layers on metallic supports represent a promising platform for the selective adsorption of atoms, clusters, and molecular nanostructures. Specifically, scanning tunneling microscopy (STM) studies revealed an electronic corrugation of h-BN/Cu(111), guiding the self-assembly of molecules and their energy level alignment. A detailed characterization of the h-BN/Cu(111) interface including the spacing between the h-BN sheet and its support—elusive to STM measurements—is crucial to rationalize the interfacial interactions within these systems. To this end, we employ complementary techniques including high-resolution noncontact atomic force microscopy, STM, low-energy electron diffraction, X-ray photoelectron spectroscopy, the X-ray standing wave method, and density functional theory. Our multimethod study yields a comprehensive, quantitative structure determination including the adsorption height and the corrugation of the sp2 bonded h-BN layer on Cu(111). Based on the atomic contrast in atomic force microscopy measurements, we derive a measurable–hitherto unrecognized–geometric corrugation of the h-BN monolayer. This experimental approach allows us to spatially resolve minute height variations in low-dimensional nanostructures, thus providing a benchmark for theoretical modeling. Regarding potential applications, e.g., as a template or catalytically active support, the recognition of h-BN on Cu(111) as a weakly bonded and moderately corrugated overlayer is highly relevant.
|
Sep 2017
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[21995, 26285]
Abstract: Ni-rich lithium nickel manganese cobalt (NMC) oxide cathode materials promise Li-ion batteries with increased energy density and lower cost. However, higher Ni content is accompanied by accelerated degradation and thus poor cycle lifetime, with the underlying mechanisms and their relative contributions still poorly understood. Here, we combine electrochemical analysis with surface-sensitive X-ray photoelectron and absorption spectroscopies to observe the interfacial degradation occurring in LiNi0.8Mn0.1Co0.1O2–graphite full cells over hundreds of cycles between fixed cell voltages (2.5–4.2 V). Capacity losses during the first ∼200 cycles are primarily attributable to a loss of active lithium through electrolyte reduction on the graphite anode, seen as thickening of the solid-electrolyte interphase (SEI). As a result, the cathode reaches ever-higher potentials at the end of charge, and with further cycling, a regime is entered where losses in accessible NMC capacity begin to limit cycle life. This is accompanied by accelerated transition-metal reduction at the NMC surface, thickening of the cathode electrolyte interphase, decomposition of residual lithium carbonate, and increased cell impedance. Transition-metal dissolution is also detected through increased incorporation into and thickening of the SEI, with Mn found to be initially most prevalent, while the proportion of Ni increases with cycling. The observed evolution of anode and cathode surface layers improves our understanding of the interconnected nature of the degradation occurring at each electrode and the impact on capacity retention, informing efforts to achieve a longer cycle lifetime in Ni-rich NMCs.
|
Feb 2022
|
|
I09-Surface and Interface Structural Analysis
|
Jiaye
Zhang
,
Joe
Willis
,
Zhenni
Yang
,
Xu
Lian
,
Wei
Chen
,
Lai-Sen
Wang
,
Xiangyu
Xu
,
Tien-Lin
Lee
,
Lang
Chen
,
David O.
Scanlon
,
Kelvin H. I.
Zhang
Diamond Proposal Number(s):
[24219]
Open Access
Abstract: Deep UV transparent thin films have recently attracted considerable attention owing to their potential in UV and organic-based optoelectronics. Here, we report the achievement of a deep UV transparent and highly conductive thin film based on Si-doped Ga2O3 (SGO) with high conductivity of 2500 S/cm. The SGO thin films exhibit high transparency over a wide spectrum ranging from visible light to deep UV wavelength and, meanwhile, have a very low work-function of approximately 3.2 eV. A combination of photoemission spectroscopy and theoretical studies reveals that the delocalized conduction band derived from Ga 4s orbitals is responsible for the Ga2O3 films’ high conductivity. Furthermore, Si is shown to act as an efficient shallow donor, yielding high mobility up to approximately 60 cm2/Vs. The superior optoelectronic properties of SGO films make it a promising material for use as electrodes in high-power electronics and deep UV and organic-based optoelectronic devices.
|
Mar 2022
|
|
I09-Surface and Interface Structural Analysis
|
Maximilian
Bauernfeind
,
Jonas
Erhardt
,
Philipp
Eck
,
Pardeep K.
Thakur
,
Judith
Gabel
,
Tien-Lin
Lee
,
Jörg
Schäfer
,
Simon
Moser
,
Domenico
Di Sante
,
Ralph
Claessen
,
Giorgio
Sangiovanni
Diamond Proposal Number(s):
[26419, 25151]
Open Access
Abstract: Large-gap quantum spin Hall insulators are promising materials for room-temperature applications based on Dirac fermions. Key to engineer the topologically non-trivial band ordering and sizable band gaps is strong spin-orbit interaction. Following Kane and Mele’s original suggestion, one approach is to synthesize monolayers of heavy atoms with honeycomb coordination accommodated on templates with hexagonal symmetry. Yet, in the majority of cases, this recipe leads to triangular lattices, typically hosting metals or trivial insulators. Here, we conceive and realize “indenene”, a triangular monolayer of indium on SiC exhibiting non-trivial valley physics driven by local spin-orbit coupling, which prevails over inversion-symmetry breaking terms. By means of tunneling microscopy of the 2D bulk we identify the quantum spin Hall phase of this triangular lattice and unveil how a hidden honeycomb connectivity emerges from interference patterns in Bloch px ± ipy-derived wave functions.
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Sep 2021
|
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