I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[36180]
Abstract: Cr2GaC/C and V2PC/C MAX phase composites were synthesized via a free-radical polymerization–pyrolysis route, achieving > 87 wt% crystalline MAX phase content. SEM/EDS confirms the expected 2:1 atomic ratios of Cr:Ga and V:P, while BET analysis reveals structures with specific surface areas of 344 and 282 m2 g−1 for the Cr2GaC/C and V2PC/C composites, respectively, which are attributed to the porous carbonaceous network. HAXPES verifies core-level signatures consistent with the targeted MAX phases. This approach demonstrates the versatility of sol–gel-derived free-radical polymer networks as reactive precursors for MAX phase formation. The method further provides a foundation for advanced processing strategies, including vat photopolymerization-based additive manufacturing of high-surface-area and complex MAX phase architectures.
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Sep 2026
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[36180]
Abstract: A correlation between depth-resolved defect chemistry and operando electrochemical response is established for compositionally graded gadolinia-doped ceria (GDC)/yttria-stabilized zirconia (YSZ) thin film electrodes. Integration of operando high-temperature scanning surface potential microscopy (HT-SSPM) with depth-resolved hard X-ray photoelectron spectroscopy (HAXPES) enables the relationship between bias-induced contact potential difference (CPD) evolution and spatially resolved Ce3+ distributions across the active film depth. While homogeneous GDC confines oxygen vacancies predominantly near the surface, compositionally graded architectures sustain a subsurface vacancy population extending toward the electrolyte interface. The fully graded structure exhibits steeper and more symmetric CPD gradients under both anodic and cathodic bias, consistent with balanced oxygen reduction and evolution kinetics. Depth-dependent HAXPES indicates that this electrochemical response correlates with enrichment of subsurface Ce3+ states rather than surface composition alone. These findings identify subsurface defect continuity as a key materials parameter influencing ionic transport and interfacial electrochemical behaviour in solid oxide electrodes.
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Aug 2026
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I09-Surface and Interface Structural Analysis
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Uday
Kushwah
,
Shiyang
Lu
,
Prajna
Bhatt
,
Aysha A.
Riaz
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Marco
Kirm
,
Vitali
Nagirnyi
,
Tanel
Käämbre
,
Johannes
Lischner
,
Anna
Regoutz
,
Juhan Matthias
Kahk
Diamond Proposal Number(s):
[36189]
Open Access
Abstract: Ultrafast scintillators based on ternary hexafluorides are promising for next-generation radiation detectors, which can be used in time-of-flight positron emission tomography. To gain a detailed understanding of the scintillation mechanism in these materials, accurate knowledge of the electronic band structure is required. In this study, photoelectron spectroscopy, density-functional theory, and G0W0 calculations were used to investigate the electronic structure of K2SiF6. The G0W0 calculations predict a wide band gap of 12.4 eV reflecting the strongly ionic character of the bonding. In contrast to predictions from semi-local or hybrid density-functional theory calculations, the large band gap predicted by G0W0 suggests that Auger-Meitner decay of K 3p holes is energetically not allowed and that scintillation via cross-luminescence is possible in this material. However, the poor light-yield observed experimentally indicates that the exclusion of Auger-Meitner decay is not sufficient for good scintillation performance, and cross-luminescence competes with other decay channels.
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Jul 2026
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I09-Surface and Interface Structural Analysis
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Galo J.
Paez Fajardo
,
Daniela E.
Dogaru
,
Hrishit
Banerjee
,
Muhammad
Ans
,
Matthew J. W.
Ogley
,
Veronika
Majherova
,
Gerard
Bree
,
Innes
Mcclelland
,
Shohei
Hayashida
,
Pascal
Puphal
,
Masahiko
Isobe
,
Bernhard
Keimer
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Dave C.
Grinter
,
Pilar
Ferrer
,
Serena A.
Cussen
,
Matthias
Hepting
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[33459, 35075, 36917, 30201]
Open Access
Abstract: Describing lithium-based battery positive electrodes based on different transition metal or oxygen-redox regimes can cause confusion in understanding metal–ligand hybridization, oxygen dimerization and degradation processes. Therefore, it is urgent to investigate the electronic structure of these materials and identify the role each cation and anion has in charge compensation at the subnanoscale. Here, using X-ray resonance photoemission spectroscopy, single-impurity Anderson models, spectral simulations and theoretical calculations, we examine redox mechanisms in positive electrodes during lithium-based battery operation. This approach reconciles the redox description of two positive electrode active materials—LiMn0.6Fe0.4PO4 and LiNiO2—in terms of varying degrees of charge transfer using the Zaanen–Sawatzky–Allen framework. In LiMn0.6Fe0.4PO4, the lack of strong hybridization indicates that the capacity results from the depopulation of metal 3d states, that is, conventional metal redox. However, in cells with LiNiO2-based positive electrodes, negative charge transfer dominates, and redox occurs through the formation and elimination of ligand-hole states. These results clarify the role of oxygen in Ni-rich systems and provide a framework to explain how the charge/discharge capacities are linked to oxygen-dominated states in highly covalent systems, without the need to consider oxygen dimerization.
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Jun 2026
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I09-Surface and Interface Structural Analysis
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Muhammad
Ans
,
Eleni
Fiamegkou
,
Ashok S.
Menon
,
Gaurav C.
Pandey
,
Gaolo J.
Paez Fajardo
,
Harry
Gillions
,
Paolo
Melgari
,
Calum
Clenahan
,
Satish
Bolloju
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Serena A.
Cussen
,
Beth I. J.
Johnston
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[38340]
Open Access
Abstract: Lithium nickel oxide (LNO) cathodes offer high capacity for high-energy-density applications but suffer rapid degradation above 4.2 V due to surface and bulk instabilities. Here, we apply an ultrathin aluminum oxide coating using powder atomic layer deposition to improve surface stability. Pouch cell testing shows that coated LNO delivers improved cycling behavior, retaining 91.2% capacity after 100 cycles at C/3. Operando X-ray diffraction reveals that after aging, coated LNO undergoes a less kinetically hindered delithiation, indicating that the surface coating further provides a surface-to-bulk stabilization effect. Postmortem surface sensitive spectroscopy confirms that the aluminum oxide layer (1) scavenges hydrofluoric acid and (2) suppresses surface reconstruction, reducing impedance growth and improving the surface integrity. Overall, the results demonstrate that ultrathin aluminum oxide coatings effectively mitigate interfacial degradation and enhance bulk electrochemical kinetics, providing an effective and scalable approach toward improving the long-term performance of ultra-Ni-rich cathodes.
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Mar 2026
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I09-Surface and Interface Structural Analysis
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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
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Arya
Loloee
,
Manuel
Scharrer
,
Tullio S.
Geraci
,
Hui-Fei
Zhai
,
Matt S.
Flores
,
Prajna
Bhatt
,
Aysha A.
Riaz
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Anna
Regoutz
,
Jakoah
Brgoch
,
Jason F.
Khoury
,
Alexandra
Navrotsky
,
Christina S.
Birkel
Diamond Proposal Number(s):
[34325]
Abstract: MAX phases are a class of compounds known for having both metallic and ceramic properties, such as good electrical conductivity, oxidation resistance, and high hardness. The bulk of the research on their properties focuses on those with titanium at the M-site and metals from groups 13 to 15, e.g., aluminum, at the A-site. Here, we expand the properties repertoire with new arsenic-containing A-site solid solutions, V2(As1–xPx)C and V2(As1–xGex)C. The structure and elemental composition of the solid solutions were resolved with powder X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and hard X-ray photoelectron spectroscopy. The electrical resistivity measurements show that both full series are metallic with the parent phases being the most conductive. Thermal analyses show V2GeC is the most oxidation resistant and V2AsC is the least, while substitutions decrease thermal stability, as oxidation resistance of the intermediate compositions shifts toward that of V2AsC. The V2(As1–xGex)C series shows little variation in hardness across compositions, while the incorporation of phosphorus noticeably increases hardness.
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Jan 2026
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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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I09-Surface and Interface Structural Analysis
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Anna A.
Wilson
,
Benjamin
Moss
,
Aysha A.
Riaz
,
Curran
Kalha
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Anna
Regoutz
,
Tsuyoshi
Takata
,
Takashi
Hisatomi
,
Kazunari
Domen
,
James R.
Durrant
Diamond Proposal Number(s):
[29451]
Open Access
Abstract: Photocatalytic water splitting offers a scalable and potentially low-cost route for the production of renewable hydrogen. Recently, a state-of-the-art system based on flux-mediated Al3+-doped SrTiO3, modified with Rh–Cr-based proton reduction and CoOOH water oxidation cocatalysts, achieved apparent quantum yields for unassisted water splitting of up to 93%. Herein, we focus on the role of Al3+ doping and Rh–Cr-based cocatalyst deposition on the accumulation and reaction dynamics of the long-lived holes required to drive water oxidation. We employ in situ and operando photoinduced absorption spectroscopy (PIAS) under water splitting conditions complemented by X-ray photoelectron spectroscopy (XPS). XPS data indicate that Al3+ doping suppresses surface Ti3+ defect states, coinciding with a 5-fold increase in the accumulation of long-lived SrTiO3 holes observed by PIAS. Rh–Cr-based cocatalyst addition is observed to further enhance the yield and lifetime (s–10 s time scales) of these photoaccumulated holes, assigned to the efficient electron extraction by this cocatalyst. These photoaccumulated holes exhibit fast (ca. 1 s) and slow (ca. 10 s) decay phases. While the dominant fast phase is assigned to the desired water oxidation reaction, the slow phase is assigned to deeply trapped unreactive holes; the yield of these unreactive holes is suppressed by facet-selective photodeposition of cocatalysts or preillumination. These results provide key insights into how Al:SrTiO3 functionalized by Rh–Cr-based cocatalysts accumulates oxidizing holes with lifetimes long enough to drive the kinetically challenging water oxidation reaction, thus achieving remarkably high quantum efficiencies for overall water splitting, insights which can be applied in the design of future photocatalytic materials.
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Sep 2025
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I09-Surface and Interface Structural Analysis
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Stefania
Riva
,
Fredrik O. L.
Johansson
,
Sergei M.
Butorin
,
Corrado
Comparotto
,
Olivier
Donzel-Gargand
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Henry
Nameirakpam
,
M. Venkata
Kamalakar
,
Soham
Mukherjee
,
Jonathan J. S.
Scragg
,
Hakan
Rensmo
Open Access
Abstract: The chalcogenide perovskite BaZrS3 is a semiconductor that exhibits a high absorption coefficient and is composed of earth-abundant elements, making it a promising candidate for sustainable optoelectronic devices. To integrate BaZrS3 thin films into devices, one needs to obtain clean surfaces and characterize them thoroughly. Herein, we report a sputtering-annealing method to produce clean surfaces of prefabricated BaZrS3 thin films with varying metal ratios (Ba-rich, stoichiometric, and Zr-rich). This method combines Ar sputtering with high-temperature annealing (600 and 750 °C) in ultra-high vacuum. Depth-profiling via photoelectron spectroscopy with soft (950 eV) and hard X-rays (6.6 keV) confirms that this processing route substantially mitigates undesired surface oxidation of the films, revealing predominantly core level peaks characteristic of the BaZrS3 perovskite. As a drawback, the sputtering process also produces Zr0, which persists in the Zr-rich sample even after the annealing treatment. In contrast, the Ba-rich and stoichiometric BaZrS3 samples converge to similar surface compositions free of Zr0, and the low roughness of the Ba-rich thin film indicates its preference for device integration. While the thermal treatment modifies the surface chemistry, the bulk characteristics, e.g., nominal metal-ratio, orthorhombic structure, and crystallite sizes, remain unaffected. However, high-temperature annealing affects band realignment with respect to the Fermi level, resulting in n-type doping characteristics. By correlating the experimentally measured valence band to the density functional theory calculated molecular orbital picture, we assign the valence band features to specific elemental orbitals and their interactions. The proposed cleaning procedure has the potential to advance the application of BaZrS3 in layered devices, such as photovoltaic cells and photodetectors.
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Aug 2025
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