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Open Access
Abstract: Synthetic antiferromagnets consist of two ferromagnetic layers that are antiferromagnetically coupled. These systems support complex dynamical magnetic excitations, where interlayer coupling gives rise to both in-phase (acoustic) and anti-phase (optical) magnonic modes. Typically, simultaneous excitation of both modes requires breaking the symmetry between the ferromagnetic layers – commonly achieved through slight misalignment of the experimental setup or by modifying the intrinsic magnetic properties. In our approach, we utilize a pinned synthetic antiferromagnet, where one of the ferromagnetic layers is exchange-coupled to an antiferromagnet. We demonstrate that by tuning the thickness of the antiferromagnet and slightly enhancing the magnetic anisotropy of the pinned layer, both acoustic and optical modes can be efficiently excited – without the need for experimental misalignment or changes to the intrinsic material properties. Under specific conditions, the magnon dispersion relations exhibit anti-crossing behavior, resulting in the emergence of a magnonic bandgap – a clear signature of strong magnon-magnon coupling. The coupling efficiency
, defined as the ratio between the bandgap and the characteristic frequency, reaches
, well in the ultrastrong and approaching the deep-strong coupling regime of
. The combination of strong mode hybridization, a sizable magnonic bandgap, and high ferromagnetic resonance coherence over large areas – all achieved at room temperature without cryogenic cooling – underscores the potential of these systems for quantum magnonic applications, including quantum computing.
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Dec 2025
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I09-Surface and Interface Structural Analysis
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Abstract: Superconducting microwave circuits are a promising physical implementation of quantum computing. A significant challenge with the development of superconducting qubits is the materials source of loss leading to qubit decoherence. Much of this loss is dielectric loss or quasiparticle dissipation at superconductor surfaces and interfaces. In order to understand the loss mechanisms microscopically, it is necessary to have an accurate picture of the atomic structure and microstructure. In this work, we explore the structure of three interfaces. First, we present non- destructive X-ray characterization of the NbH surface precipitation in Nb thin films. Unwanted hydride precipitation in niobium-based superconducting circuits is a side effect of hydrofluoric acid etching of the Nb surface oxide. The precipitate microstructure is challenging to probe because of the high mobility of hydrogen in niobium. Using X-rays diffraction, we show evidence supporting phase-field simulations that the nucleation of NbH occurs at free surfaces. Using darkfield X-ray nanoprobe microscopy, we identify a complex microstructure suggesting a martensitic nucleation that transitions to a dendritic growth. Next, we present X-ray standing wave excited X-ray photoelectron spectroscopy of the annealed, Nb(110) ordered oxide surface layer. We discover the existence of an oxygen interstitial rich subsurface layer and identify the origin of two distinct oxygen chemical states at the surface: one coming from this subsurface layer, and the other from the surface NbO termination. Last, we present the heteroepitaxy of single crystal Al2O3 with a TiN. We identify TiN as an ideal substrate for the epitaxial growth of Al2O3 in a capacitor geometry based on the high degree of crystallinity and sharp interfaces with minimal diffusion and
3
we measure the two-level-state loss of the Al2O3 junction dielectric layer. We present this interface as an alternative to the commonly used amorphous alumina in Josephson Junctions.
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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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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Diamond Proposal Number(s):
[33956]
Abstract: Multiwavelength light emission was observed in undoped tin oxide thin films deposited by metal-organic chemical vapor deposition at temperatures ranging from 700°C to 800°C. This work presents the relationship between the presence and nature of defects in undoped SnO2 thin films and their emission properties. Blue and orange emissions were observed on SnO2 thin films using a He-Cd laser and an Xe lamp at an excitation wavelength of 325 nm. Systematic characterization and analysis techniques, including low-temperature photoluminescence at temperatures ranging from 77K to 298K and surface-sensitive techniques using brilliant synchrotron radiation facilities, were applied to elucidate the features and origin of emission in undoped SnO2 layers. Based on our results, surface and bulk oxygen and interstitial tin defects play an important role in multi-wavelength emission processes and can be separately activated by controlling the applied light source.
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Dec 2025
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DIAD-Dual Imaging and Diffraction Beamline
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Loris
Chavée
,
Emile
Haye
,
Jochen M.
Schneider
,
Stanislav
Mráz
,
Andreas
Pflug
,
Dennis
Barton
,
Armel
Descamps
,
Claudie
Josse
,
Jérôme
Müller
,
Pavel
Moskovkin
,
James
Marrow
,
Amael
Caillard
,
Stephane
Lucas
Diamond Proposal Number(s):
[34010]
Abstract: The deposition of functional coatings on open-cell foam substrates using magnetron
sputtering is gaining popularity, particularly for applications like Oxygen Evolution
Reaction (OER)/Hydrogen Evolution Reaction (HER) catalysis, batteries, and
supercapacitors. While most research focuses on performance, little attention has
been paid to the coating growth mechanisms or properties within the foam, which could
significantly impact device performance. This work investigates the properties and
growth mechanisms of TiO₂ coatings inside porous foams, using experimental and
modeling techniques.
The structure, composition and thickness of the coating on the outermost surface of
the foam are studied using Focused Ion Beam (FIB), Scanning Transmission Electron
Microscopy (STEM), Energy-Dispersive X-Ray Spectroscopy (EDS), Selected Area
Electron Diffraction (SAED) and High-Resolution Transmission Electron Microscopy
(HRTEM). The experimental results reveal the formation of a dense, (quasi-
)stoichiometric and crystalline coating.
Numerical simulations and experiments highlight the transport of plasma particles in
the foam. Interestingly, Direct Simulation Monte Carlo (DSMC)/Particle-In-Cell Monte
Carlo (PICMC) models, coupled with Mass-Energy Analyzer (MEA) experiments,
demonstrate that the particle flux is reduced, but the particle energy distribution is not
Accepted Manuscript affected while traveling inside the foam. Using kinetic Monte Carlo (kMC) thin film
growth models provided by Virtual CoaterTM, the physical properties of the coating
inside the foam have been modeled, and the drop in coating thickness as well as the
impact of bias voltage on densification, resistivity, and optical absorption are
confirmed. Synchrotron X-Ray Diffraction (SXRD) analyses of the foam demonstrate
that the same crystalline phase is obtained along the foam thickness, but it can be
tailored with bias voltages. The decrease in the recorded SXRD signal with increasing
depth inside the foam also suggests a drop in coating thickness.
The new insights on the properties of coatings inside open-cell foams presented in this
study can be used to improve future foam-based devices.
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Dec 2025
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B18-Core EXAFS
I09-Surface and Interface Structural Analysis
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Abstract: Hydrogen shows promise as the energy vector of the future, but problems with storage and transport are significant. Storage of hydrogen as ammonia has the potential to solve these problems, but current catalysts for its cracking are not efficient enough to enable the large-scale application of ammonia. Carbon materials, such as carbon nanotubes (CNTs), have shown potential as supports for ammonia decomposition catalysts. This thesis investigates the use of graphitised nanofibers (GNFs), which offer high purity and graphitisation, as a support material for Ru catalysts. Ru/GNF was synthesised using magnetron sputtering and tested for catalytic activity in ammonia decomposition and the catalyst exhibited self-improvement over the course of the reaction. The evolution of the Ru nanoclusters on GNF was studied by Identical Location Scanning Transmission Electron Microscopy (IL-STEM). The analysis revealed that the Ru nanoclusters undergo significant morphological changes during the reaction - transforming from flat and amorphous structures to more three-dimensional crystalline nanoclusters. The step-edges on the GNF surface help to stabilise the Ru nanoclusters, preventing excessive growth and maintaining a high density of active sites. Spectroscopic analysis using in-operando EXAFS and ex-situ XPS provide further insights into the mechanism behind the self-improvement. EXAFS data suggest that the Ru nanoparticles undergo bulk nitridation during the reaction. This is supported by XPS analysis, which confirms the formation of a metal nitride species. It is proposed that the formation of bulk nitrided Ru nanoclusters leads to a change in the reaction mechanism, increasing the number of active sites and enhancing the catalyst’s activity. This thesis highlights the importance of studying the dynamic behaviour of catalysts and provides an understanding of the self-improvement mechanism in Ru/GNF. This knowledge can contribute to the design of more efficient and stable catalysts for low-temperature ammonia cracking, advancing sustainable hydrogen production technologies.
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Dec 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Diamond Proposal Number(s):
[34919, 37955]
Open Access
Abstract: A combination of experimental methods and computational techniques have been used to investigate the composition of the zinc ferrite (ZnFe2O4) (1 1 1) single crystal surface under different preparation methods. Surface-sensitive XPS and NEXAFS measurements show that upon annealing in ultra-high vacuum (UHV), Zn depletion occurs, leading to the formation of an iron-rich (1 1 1) surface, whereas annealing in the presence of O2 gas maintains a more bulk-like ZnFe2O4 surface composition. Analysis of the Fe 2p photoemission (XPS) and Fe L edge X-ray absorption signals shows a clear difference in iron oxidation state and distribution between the two different preparation conditions. After annealing in UHV, a mixed Fe2+/Fe3+ oxidation state and a cation distribution like that of a magnetite (Fe3O4) structure is observed, whereas after annealing in oxygen gas only Fe3+, mostly in octahedral coordination, is observed, as expected for a ZnFe2O4 structure. Temperature-dependent XPS confirms significant Zn depletion in the near-surface region above 500 °C under UHV, with almost no Zn remaining at 600 °C; under an O2 atmosphere no zinc depletion is observed up to 600 °C. A theoretical model based on DFT simulations illustrates how reduction from ZnFe2O4 to Fe3O4 with formation of O2 and Zn gas is thermodynamically feasible under UHV conditions, whereas the same reaction is not favourable at higher oxygen partial pressures. Our findings demonstrate the strong impact that UHV treatment has on zinc ferrite surfaces, and cautions that UHV environments, routinely employed for surface analysis, can themselves induce substantial modifications to the surface, thereby complicating the interpretation of measurements in the context of catalytically relevant conditions.
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Dec 2025
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I05-ARPES
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Diamond Proposal Number(s):
[34246]
Open Access
Abstract: Magnetic van der Waals materials are an important building block to realize spintronic functionalities in heterostructures of two-dimensional (2D) materials. However, establishing their magnetic and electronic properties and the interrelationship between the magnetic ground state and electronic structure is often challenging because only a limited number of techniques can probe magnetism and electronic structure on length scales of tens to hundreds of nanometers. Chromium chalcogenides are a class of 2D magnetic materials for which a rich interplay between structure and magnetism has been predicted. Here, we combine angle-resolved photoemission and quasiparticle interference imaging to establish the electronic structure of a monolayer of CrTe2 on graphite. From a comparison of model calculations with spectroscopic mapping using angle-resolved photoemission spectroscopy and scanning tunneling microscopy we establish the magnetic ground state and the low-energy electronic structure. We demonstrate that the band structure of monolayer CrTe2 is captured well by density functional theory (DFT) in a DFT+𝑈 framework when a Coulomb repulsion of 𝑈=2.5eV is accounted for.
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Dec 2025
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I07-Surface & interface diffraction
I15-Extreme Conditions
I19-Small Molecule Single Crystal Diffraction
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Yang
Lu
,
Young-Kwang
Jung
,
Milos
Dubajic
,
Xinjuan
Li
,
Shabnum
Maqbool
,
Qichun
Gu
,
Xinyu
Bai
,
Yorrick
Boeije
,
Xian Wei
Chua
,
Alessandro J.
Mirabelli
,
Taeheon
Kang
,
Lars
Sonneveld
,
Youcheng
Zhang
,
Thomas A.
Selby
,
Capucine
Mamak
,
Kan
Tang
,
Zhongzheng
Yu
,
Tianjun
Liu
,
Miguel
Anaya
,
Stephen
Barlow
,
Seth R.
Marder
,
Bruno
Ehrler
,
Caterina
Ducati
,
Richard H.
Friend
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[32266, 38601, 30043, 33123, 36628, 38508]
Abstract: Halide perovskites exhibit superior optoelectronic properties but lack precise thickness and band offset control in heterojunctions, which is critical for modular multilayer architectures such as multiple quantum wells. We demonstrate vapor-phase, layer-by-layer heteroepitaxial growth exemplified by CsPbBr3 deposition on single crystals of PEA2PbBr4 (PEA: 2-phenylethylammonium). Angstrom-level thickness control and subangstrom smooth layers enable quantum-confined photoluminescence of CsPbBr3 from monolayer, bilayer, and through to bulk. The interfacial structure controls the electronic structure from a Cs‒PEA-terminated interface (type II heterojunction) to a PEA‒PEA-terminated interface (type I heterojunction), with a layer-tunable band offset shift exceeding 0.5 electron volts. Electron transfer from CsPbBr3 to PEA2PbBr4 for a type II Cs‒PEA heterojunction results in delayed electron-hole recombination beyond 10 microseconds. Precise quantum confinement control and large band offset tunability unlock perovskite heterojunctions as platforms for scalable, superlattice-based optoelectronic applications.
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Nov 2025
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[16967, 37411]
Open Access
Abstract: Atomic-scale wetting governs material formation at the nanoscale but remains poorly understood under confinement, where classical capillarity models fail. The growth of metallic nanowires within multi-wall carbon nanotubes (MWCNTs) exemplifies this challenge, requiring precise control over wetting, nucleation, and vapour-phase condensation. Here we show that nanowire formation proceeds through a two-stage mechanism: curvature-driven nucleation at open tube ends followed by capillary-driven elongation sustained by continuous vapour condensation. Using in situ atomic-resolution transmission electron microscopy (ARTEM) coupled with a deep learning convolutional neural network (CNN) capable of classifying liquid, solid and intermediate SnxO phase transitions, we directly capture the cascade of thermally induced nanowire growth within CNTs. Growth requires a wetting interface (contact angle, θ <90°) between liquid SnxO and the nanotube wall—conditions not described by Kelvin or Lucas–Washburn models. These results establish a predictive framework for vapour-phase nanowire encapsulation, linking nanoscale wetting dynamics to the fabrication of advanced nanomaterials.
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Nov 2025
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