I09-Surface and Interface Structural Analysis
|
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.
|
Mar 2026
|
|
I09-Surface and Interface Structural Analysis
|
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).
|
Feb 2026
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Jan 2026
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Dec 2025
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Sep 2025
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Aug 2025
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[30534]
Open Access
Abstract: A comprehensive understanding of the solid electrolyte interphase (SEI) is crucial for ensuring long-term battery stability. This is particularly pertinent in sodium-ion batteries (NIBs), where the SEI remains poorly understood, and investigations are typically undertaken in half-cell configurations with sodium metal as the counter electrode. Na metal is known to be highly reactive with common carbonate-based electrolytes; nevertheless, its effects on SEI formation at the working electrode are largely unexplored. This work investigates the evolution of the SEI in NIBs during cycling, with an emphasis on the consequences of using a sodium metal counter electrode. Advanced analytical techniques, including hard X-ray photoelectron spectroscopy (HAXPES) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), are used to obtain depth-resolved insights into the chemical composition and structural changes of the SEI on hard carbon anodes during cycling. The findings demonstrate that the cell configuration has a significant impact on SEI evolution and, by extension, battery performance. These findings suggest that full-cell studies are necessary to better simulate practical operating conditions, challenging traditional half-cell experiments.
|
Jun 2025
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[34325]
Abstract: MAX phase carbides have attracted much attention due to their unique combination of metallic and ceramic properties, making them promising materials for high-temperature applications. Understanding how the materials fail is a crucial step in working toward implementing them into devices outside of the laboratory setting. Their stability toward oxidation at high temperatures, while also being electronically and thermally conductive, sets MAX phases apart from other materials. Some aluminum-containing compounds form a protective alumina layer that contributes to the oxidation resistance of the respective MAX phase. However, a broader understanding of how other MAX phases, especially those with M-elements beyond titanium and A-elements beyond aluminum, oxidize is lacking. Therefore, we synthesized two A-site solid solutions (gallium and germanium as the A-elements) based on chromium and vanadium as M-elements by high-temperature solid-state syntheses. Their composition, structural properties, and bonding characteristics are investigated by synchrotron powder X-ray diffraction, electron microscopy with elemental analysis, and Raman and X-ray photoelectron spectroscopy. Thermal analysis reveals the influence of the M- and A-elements on the oxidation behavior: phases with Cr on the M-site have higher oxidation stability than with V, and solid solutions Cr2Ga1–xGexC have improved oxidation resistance compared to the individual phases Cr2GaC and Cr2GeC.
|
Jun 2025
|
|
B18-Core EXAFS
I09-Surface and Interface Structural Analysis
|
Muhammad
Ans
,
Gaurav C.
Pandey
,
Innes
Mcclelland
,
Naresh
Gollapally
,
Harry
Gillions
,
Beth I. J.
Johnston
,
Matthew J. W.
Ogley
,
James A.
Gott
,
Eleni
Fiamegkou
,
Veronica
Celorrio
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Serena A.
Cussen
,
Ashok S.
Menon
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[30104, 33553]
Open Access
Abstract: Single-crystalline LiNiO2 (SC-LNO), a high-energy-density Li-ion cathode material, suffers from poor long-term electrochemical performance when cycled above 4.2 V (vs Li+/Li). In this study, this degradation is evaluated using SC-LNO–graphite pouch cells electrochemically aged within a stressful voltage window (2.5–4.4 V) using a constant-current constant-voltage (CC-CV) protocol. Notable capacity fade is observed after one hundred cycles at C/3 rate, in addition to an increase in the overall electrochemical cell impedance. Operando X-ray diffraction data reveal that, despite no significant long-range bulk structural changes, (de-)lithiation of the aged SC-LNO becomes kinetically hindered after 100 cycles. Aging-induced changes in the short-range structure and charge compensation are evaluated through a multi-model quantitative analysis of the operando X-ray absorption spectroscopy data. While the electrochemical aging does not result in particle cracking, soft X-ray absorption spectroscopy data revealed the reconstruction of the cathode surface to a dense rock salt-like layer after long-term cycling, which acts as a kinetic trap for Li+ diffusion. Therefore, even under stressful conditions, it is the surface reconstruction that dominates the overall cathode degradation by reducing the Li+ mobility and leading to the capacity fade. Cathode surface engineering will therefore be key to improving the long-term electrochemical performance of SC-LNO cathodes.
|
May 2025
|
|
|
|
Open Access
Abstract: Multi-walled carbon nanotubes (MWCNTs), synthesized using the microwave plasma-enhanced chemical vapor deposition (MPCVD) technique, have been examined to elucidate their electronic and magnetic structures through near-edge X-ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD) spectroscopy. NEXAFS analysis at the Fe and Co L-edges reveals the presence of Fe-metal nanoparticles embedded within the CNT lattice, along with divalent Co ions coordinated to the matrix in an octahedral symmetry. Furthermore, the appearance of two distinct NEXAFS peaks between the π* and σ* transitions indicates 1s to sp3 hybridization, attributed to the interaction of Fe and Co2+ ions with the carbon nanotube structure. Additionally, XMCD spectra confirm that MWCNTs exhibit room temperature ferromagnetism, primarily driven by Fe–C and Co–C bonding within the nanotubes. This intrinsic ferromagnetic behavior, along with the high aspect ratio and unique electronic properties of MWCNTs, highlights their promising potential for applications in spintronic storage devices.
|
Mar 2025
|
|
