I09-Surface and Interface Structural Analysis
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H. J.
Elmers
,
O.
Tkach
,
Y.
Lytvynenko
,
H.
Agarwal
,
D.
Biswas
,
J.
Liu
,
A.-A.
Haghighirad
,
M.
Merz
,
S.
Pakhira
,
G.
Garbarino
,
T.-L.
Lee
,
J.
Demsar
,
G.
Schönhense
,
M.
Le Tacon
,
O.
Fedchenko
Diamond Proposal Number(s):
[37580]
Abstract: This study uses angle-resolved photoemission spectroscopy to examine the low-temperature electronic structure of Cs(V0.95Nb0.05)3Sb5, demonstrating that partially substituting V atoms with isoelectronic Nb atoms results in an increase of the bandwidth and enhanced gap opening at the Dirac-like crossings due to the resulting chemical pressure. This increases the magnetic circular dichroism signal in the angular distribution compared to CsV3Sb5, enabling detailed analysis of magnetic circular dichroism in several bands near the Fermi level. These results substantiate the predicted coupling of orbital magnetic moments to three van Hove singularities near the Fermi level at 𝑀 points. Previous studies have observed that Nb doping lowers the charge density transition temperature and increases the critical temperature for superconductivity. This article demonstrates that Nb doping concomitantly increases the magnetic circular dichroism signal attributed to orbital moments.
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Dec 2025
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I09-Surface and Interface Structural Analysis
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G.
Cicconi
,
M.
Bosi
,
F.
Mezzadri
,
A.
Ugolotti
,
I.
Cora
,
L.
Seravalli
,
H.
Tornatzky
,
J.
Lähnemann
,
M. R.
Wagner
,
P.
Bhatt
,
P. K.
Thakur
,
T.-L.
Lee
,
A.
Regoutz
,
A.
Baraldi
,
D.
Bersani
,
L.
Cademartiri
,
A.
Parisini
,
B.
Pécz
,
L.
Miglio
,
R.
Fornari
,
P.
Mazzolini
Diamond Proposal Number(s):
[36180]
Open Access
Abstract: The ultra-wide bandgap semiconductor rutile germanium oxide (r-GeO2, Eg ≈ 4.6 eV) is gaining momentum in the quest for novel materials for power electronics. In this work, we experimentally and theoretically investigate the physical mechanisms behind the nucleation and growth of epitaxial (001) r-GeO2 on isostructural r-TiO2 substrates via metalorganic vapor phase epitaxy (MOVPE) using isobutylgermane and O2 precursors. In the identified deposition window, the thin film growth seems to be affected by partial GeO suboxide desorption, and we observe that the layers are always composed of r-GeO2 islands embedded and/or surrounded by amorphous material. Ge/Ti interdiffusion at the epilayer-substrate interface is found at the base of each r-GeO2 island; combining experimental analysis and multiscale theoretical simulations we discuss how such a process is fundamental to achieve partial strain mitigation allowing for the nucleation of epitaxial r-GeO2 and suggest in this regard a limiting threshold to avoid the formation of amorphous material. Moreover, we shed light on the formation of different facets in r-GeO2 at early stages of growth and after merging of islands.
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Dec 2025
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B18-Core EXAFS
E01-JEM ARM 200CF
I09-Surface and Interface Structural Analysis
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Thomas J.
Liddy
,
Benjamin J.
Young
,
Emerson C.
Kohlrausch
,
Andreas
Weilhard
,
Gazi N.
Aliev
,
Yifan
Chen
,
Manfred E.
Schuster
,
Mohsen
Danaie
,
Luke L.
Keenan
,
Donato
Decarolis
,
Diego
Gianolio
,
Siqi
Wang
,
Mingming
Zhu
,
Graham J.
Hutchings
,
David M.
Grant
,
Wolfgang
Theis
,
Tien-Lin
Lee
,
David A.
Duncan
,
Alberto
Roldan
,
Andrei N.
Khlobystov
,
Jesum
Alves Fernandes
Diamond Proposal Number(s):
[38764]
Open Access
Abstract: Ammonia is an attractive hydrogen carrier, yet its practical use is limited by the need for efficient catalytic decomposition. We demonstrate that in-situ N-doping of Ru nanoparticles and graphitized carbon nanofiber supports during reaction produces a sharp increase in hydrogen production during the first 40 h, followed by stable activity. Spectroscopic and microscopic analyses, together with density functional theory simulations, reveal that Ru nitridation is rapid and support-independent, resulting in a mechanistic shift from the traditional Langmuir–Hinshelwood to a Mars–van Krevelen pathway, further confirmed by isotopic labelling experiments. In contrast, the progressive nitridation of the carbon support, observed via X-ray photoelectron spectroscopy, modulates the electronic environment of Ru and functions as a dynamic nitrogen reservoir that enables reversible N atoms exchange with the Ru particles, facilitating N desorption from the Ru surface and thereby governing the catalytic activity enhancement. These new findings provide new mechanistic insight into ammonia decomposition and establish progressive nitrogen doping of carbon supports as a strategy for designing efficient metal-based catalysts for hydrogen production.
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Dec 2025
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I09-Surface and Interface Structural Analysis
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Han
Yan
,
Yan
Wang
,
Yang
Li
,
Dibya
Phuyal
,
Lixin
Liu
,
Hailing
Guo
,
Yuzheng
Guo
,
Tien-Lin
Lee
,
Minhyuk
Kim
,
Hu Young
Jeong
,
Manish
Chhowalla
Diamond Proposal Number(s):
[30105, 33391, 32963, 38086]
Open Access
Abstract: Two-dimensional transition metal dichalcogenide semiconductors possess ideal attributes for meeting industry scaling targets for transistor channel technology. However, the development of scaled field-effect transistors (FETs) requires industry-compatible gate dielectrics with low equivalent oxide thicknesses. Here we show that zirconium oxide (ZrO2)—an industry-compatible high-dielectric-constant (k) oxide—can form a clean interface with two-dimensional molybdenum disulfide (MoS2). Photoelectron spectroscopy analysis shows that although silicon dioxide and hafnium oxide substrates introduce the doping of MoS2, ZrO2 exhibits no measurable interactions with MoS2. Back-gated monolayer MoS2 FETs using ZrO2 as a dielectric exhibit stable and positive threshold voltages of 0.36 V, subthreshold swings of 75 mV dec−1 and ON currents of more than 400 µA. We also use ZrO2 dielectrics to fabricate p-type tungsten diselenide FETs with ON-state currents of more than 200 µA µm−1. Atomic-resolution imaging of ZrO2 deposited on top of MoS2 reveals a defect-free interface, which leads to top-gated FETs with an equivalent oxide thickness of 0.86 nm and subthreshold swing values of 80 mV dec−1. The clean interface between ZrO2 and monolayer MoS2 allows the effective modulation of threshold voltage in top-gated FETs via gate metal work-function engineering.
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Oct 2025
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I09-Surface and Interface Structural Analysis
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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
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Wenjing
Xu
,
Hailing
Guo
,
Zhenni
Yang
,
Yihong
Chen
,
Xiangyu
Xu
,
Tien-Lin
Lee
,
Duanyang
Chen
,
Xinxin
Yu
,
Yuzheng
Guo
,
Zhaofu
Zhang
,
Hongji
Qi
,
Kelvin H. I.
Zhang
Diamond Proposal Number(s):
[37428]
Abstract: In this work, we investigate the electronic structure and interfacial band alignment of β-(Al𝑥Ga1−𝑥)2O3/Ga2O3 heterojunctions using a combination of synchrotron-based hard x-ray photoemission spectroscopy (HAXPES) and first-principles hybrid density functional theory calculations. β-(Al𝑥Ga1−𝑥)2O3 films with Al compositions of x = 0.12, 0.19, and 0.29 were grown on Fe-doped β-Ga2O3 (010) substrates via pulsed laser deposition. The band gap of β-(Al𝑥Ga1−𝑥)2O3 increases from (4.83 ± 0.05) eV (x = 0) to (5.37 ± 0.08) eV (x = 0.29), primarily driven by an upward shift of the conduction band edge due to hybridization between Al 3s and Ga 4s states, while the valence band edge exhibits a slight downward shift. Both experimental HAXPES data and theoretical calculations confirmed the formation of a “type I” (straddling) band alignment in the β-(Al𝑥Ga1−𝑥)2O3/Ga2O3 heterojunctions. For instance, at x = 0.29, the conduction band offset and valence band offset are approximately 0.33 and 0.21 eV, respectively. These findings provide valuable insights for designing modulation-doped β-(Al𝑥Ga1−𝑥)2O3/Ga2O3 heterostructures, enabling the realization of a two-dimensional electron gas and its application in high-frequency electronic devices.
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Oct 2025
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I09-Surface and Interface Structural Analysis
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Ali
Sufyan
,
Tyler
James
,
Connor
Fields
,
Shabnam
Naseri
,
Filipe L. Q.
Junqueira
,
Sofia
Alonso Perez
,
Sally
Bloodworth
,
Gabriella
Hoffman
,
Mark C.
Walkey
,
Elizabeth S.
Marsden
,
Richard J.
Whitby
,
Yitao
Wang
,
David A.
Duncan
,
Tien-Lin
Lee
,
James N.
O'Shea
,
Andreas
Larsson
,
Brian
Kiraly
,
Philip
Moriarty
Diamond Proposal Number(s):
[31574]
Open Access
Abstract: Core-level and tunnelling spectroscopies applied to noble gas endofullerenes offer complementary insights into electron transfer rates, addressing both intramolecular and extramolecular processes. Elastic and inelastic tunnelling spectroscopy of empty C60 and Kr@C60 on Pb/Cu(111) each show that the encapsulated atom is essentially invisible to scanning probes. We interpret the lineshape of the lowest unoccupied molecular orbital (LUMO) of Pb-adsorbed (endo)fullerenes in tunnelling spectra as a signature of the dynamic Jahn-Teller (DJ-T) effect. This effect persists in electronically decoupled second-layer molecules, which also display distinct vibronic progressions in on-resonance tunnelling. DFT calculations reproduce the LUMO alignment and low density of states at the Fermi level seen in experimental tunnelling spectra for (endo)fullerenes on Pb, and, in line with submolecular resolution STM images, also predict that an atom-down orientation of the fullerene cage is energetically most favourable (although other adsorption geometries differ only by tens of meV at most). In contrast to the tunnelling data, core-level-focussed techniques -namely, photoemission, X-ray absorption, and resonant Auger-Meitner electron spectroscopy -of Ar@C60/Pb(111) indicate that the encapsulated atom is heavily coupled to the molecular environment, with both a clear influence of substrate screening on the core-level lineshape and the absence of spectator signal in decay spectra.
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Oct 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[36085]
Open Access
Abstract: For establishing a fundamental understanding of the emerging properties of two-dimensional (2D) materials, a reliable determination of the crystallographic structure is essential, as we demonstrate in this work for the specific case of the quantum spin Hall insulator bismuthene. Diffraction-based methods are widely used for structure determination, however, they suffer from a fundamental shortcoming, the phase retrieval problem, that is the inability to directly measure the phase of scattered waves. The (normal incidence) X-ray standing wave (NIXSW) technique circumvents this problem by introducing a Bragg-generated X-ray standing wave field throughout the sample, relative to which any atomic species can be localized. In essence, a single NIXSW measurement captures the complex scattering factor (amplitude and phase) corresponding to one single Bragg reflection. Collecting data for multiple reflections enables a three-dimensional reconstruction of the scattering density as the Fourier sum of all measured scattering factors. Here, we utilize this technique to reveal the mechanism of a reversible switching process that has been reported for a 2D Bi layer recently (Tilgner et al., Nat. Commun. 16, 6171, 2025). In this prominent example, the Bi layer is confined between a 4H-SiC substrate and an epitaxial graphene layer, and can be reversibly switched between an electronically inactive precursor state and the bismuthene state. In our NIXSW imaging experiment, we clearly identify the change of the adsorption site of the Bi atoms, caused by H-saturation of one out of three Si dangling bonds per unit cell, as the key feature leading to the formation of the characteristic band structure of the 2D bismuthene honeycomb.
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Oct 2025
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E02-JEM ARM 300CF
I09-Surface and Interface Structural Analysis
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Benedikt P.
Klein
,
Matthew A.
Stoodley
,
Joel
Deyerling
,
Luke A.
Rochford
,
Dylan B.
Morgan
,
David G.
Hopkinson
,
Sam
Sullivan-Allsop
,
Henry
Thake
,
Fulden
Eratam
,
Lars
Sattler
,
Sebastian M.
Weber
,
Gerhard
Hilt
,
Alexander
Generalov
,
Alexei
Preobrajenski
,
Thomas
Liddy
,
Leon B. S.
Williams
,
Mhairi A.
Buchan
,
Graham A
Rance
,
Tien-Lin
Lee
,
Alex
Saywell
,
Roman
Gorbachev
,
Sarah J.
Haigh
,
Christopher S.
Allen
,
Willi
Auwärter
,
Reinhard
Maurer
,
David A.
Duncan
Diamond Proposal Number(s):
[25379, 30875, 31695, 31165, 33709]
Open Access
Abstract: Chemical vapour deposition enables large-domain growth of ideal graphene, yet many applications of graphene require the controlled inclusion of specific defects. We present a one-step chemical vapour deposition procedure aimed at retaining the precursor topology when incorporated into the grown carbonaceous film. When azupyrene, the molecular analogue of the Stone–Wales defect in graphene, is used as a precursor, carbonaceous monolayers with a range of morphologies are produced as a function of the copper substrate growth temperature. The higher the substrate temperature during deposition, the closer the resulting monolayer is to ideal graphene. Analysis, with a set of complementary materials characterisation techniques, reveals morphological changes closely correlated with changes in the atomic adsorption heights, network topology, and concentration of 5-/7-membered carbon rings. The engineered defective carbon monolayers can be transferred to different substrates, potentially enabling applications in nanoelectronics, sensorics, and catalysis.
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Sep 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[30105, 33391, 38086]
Open Access
Abstract: The clean and reliable transfer of two-dimensional (2D) materials is critical for preserving their intrinsic properties and enabling high-performance device applications. This study presents a method utilizing UV-ozone treated polydimethylsiloxane (UV-PDMS) as a transfer medium to achieve residue-free 2D materials. The UV-PDMS transfer method increases surface rigidity, reduces surface polymeric residues, and ensures intimate contact between 2D materials and target substrates. This is translated into cleaner samples as confirmed by atomic force microscopy (AFM), photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Field-effect transistors (FETs) based on monolayer MoS2 fabricated with UV-PDMS transferred method exhibit lower subthreshold swing, reduced hysteresis, and higher carrier mobility compared to devices fabricated with PDMS transfer. Additionally, vertical solar cells based on multilayer WSe2 prepared with UV-PDMS method demonstrate enhanced fill factor and power conversion efficiency.
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Sep 2025
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