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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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[19420]
Open Access
Abstract: Theoretical calculations of materials have in recent years shown promise in facilitating the analysis of convoluted experimental data. This is particularly invaluable in complex systems or for materials subject to certain environmental conditions, such as those exposed to X-ray radiation during routine characterisation. Despite the clear benefit in this use case to shed further light on intermolecular damage processes, the use of theory to study radiation damage of samples is still not commonplace, with very few studies in existing literature. In this paper, we demonstrate the potential of density functional theory for modelling the electronic structure of two industrially important organometallic systems of the formula [M(COD)Cl]2 where M=Ir/Rh and COD=1,5-cyclooctadiene, which are subject to X-ray irradiation via X-ray Diffraction and X-ray Photoelectron Spectroscopy. Our approach allows calculated spectra to be compared directly to experimental data, in this case, the X-ray photoelectron valence band spectra, enabling the valuable correlation of individual atomic states to the electronic structure.
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Oct 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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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.
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Jun 2025
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[18324]
Open Access
Abstract: With the advent of ever more intense and focused X-ray sources, including in laboratories, at synchrotrons, and at X-ray free electron lasers, radiation-induced sample change and damage are becoming increasingly challenging. Therefore, the exploration of possible mitigation strategies is crucial to continue to allow the collection of robust and repeatable data. One mitigation approach is the introduction of short, X-ray-free “dark” periods. However, it is unclear whether this strategy minimises damage or, in actuality, promotes it through a phenomenon called “dark progression”, i.e. the increase or progression of radiation damage that occurs after the X-ray beam is turned off. This work discusses the influence of introducing dark periods and their duration on the radiation-induced changes in two model small-molecule catalysts, [Ir(COD)Cl]2 and [Rh(COD)Cl]2, exposed to X-ray radiation in synchrotron powder diffraction (PXRD) and laboratory photoelectron spectroscopy (XPS) experiments. This provides, for the first time, insights into how damage progresses under varying radiation regimes and allows the distinction between the processes that affect the unit cell itself, the individual molecular units, and the respective atomic chemical environments. Furthermore, it provides the basis for informed decision-making in the design of future experiments where the need to minimise radiation-induced damage is crucial.
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Apr 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[36180]
Abstract: The delamination of hydrothermally etched V2CTx has presented challenges, with limited reports of an effective delamination process. X-ray diffraction data indicate that excess lithium and lithium salts in the reaction mixture interact with the multilayered MXene surfaces in the interlayer space, impeding intercalants that would separate the nanosheets. The removal of this salt with a dilute acid solution is the key step to enable the synthesis of a delaminated MXene with a markedly higher yield in comparison to that of traditional HF-etched (and delaminated) V2CTx. Because this yield is substantial, the sample can be centrifuged to produce 20 mL of a concentrated (25 mg mL–1) sample. Due to the removal of excess water and dissolved O2, this concentrated sample shows improved stability toward oxidation and can withstand ambient conditions over the course of a year.
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Mar 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[36180]
Abstract: MAX phases are a large and growing family of transition metal-based ternary carbides and (carbo)nitrides, that have also attracted significant attention as precursors for a class of two-dimensional materials referred to as MXenes. The ability to partially substitute elements on the M-, A-, and X-sites of the layered crystal structure has expanded MAX phases to over 340 members known to date. They can be exfoliated to form single- and few-layer MXene sheets by removal of the A-element while maintaining the M- and X-elements of the precursor MAX phase. MXenes are extremely interesting materials with properties that are, among other factors, dependent on their chemical composition and offer a wide array of potential applications, for example for energy conversion. Here, we synthesize hitherto unknown solid solution MAX phases, (V1–yMoy)2AlC (y = 0.0–0.5) and exfoliate all compounds with varying V/Mo ratios into the respective MXenes by hydrothermal treatment with in situ-formed hydrofluoric acid. The delaminated MXenes can be utilized for electrocatalytic reactions, here demonstrated for the hydrogen evolution reaction (HER). As the Mo content within the MXenes increases, electrocatalytic activity for HER improves, peaking at an overpotential of 394 mV at 10 mA cm–2 and a Tafel slope of 129 mV dec–1 for (V0.5Mo0.5)2CTx.
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Jan 2025
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B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
E01-JEM ARM 200CF
I09-Surface and Interface Structural Analysis
I20-EDE-Energy Dispersive EXAFS (EDE)
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Xuze
Guan
,
Rong
Han
,
Hiroyuki
Asakura
,
Bolun
Wang
,
Lu
Chen
,
Jay Hon Cheung
Yan
,
Shaoliang
Guan
,
Luke
Keenan
,
Shusaku
Hayama
,
Matthijs A.
Van Spronsen
,
Georg
Held
,
Jie
Zhang
,
Hao
Gu
,
Yifei
Ren
,
Lun
Zhang
,
Zhangyi
Yao
,
Yujiang
Zhu
,
Anna
Regoutz
,
Tsunehiro
Tanaka
,
Yuzheng
Guo
,
Feng Ryan
Wang
Diamond Proposal Number(s):
[23759, 24450, 29092, 31852]
Open Access
Abstract: Single-atom catalysts have garnered significant attention due to their exceptional atom utilization and unique properties. However, the practical application of these catalysts is often impeded by challenges such as sintering-induced instability and poisoning of isolated atoms due to strong gas adsorption. In this study, we employed the mechanochemical method to insert single Cu atoms into the subsurface of Fe2O3 support. By manipulating the location of single atoms at the surface or subsurface, catalysts with distinct adsorption properties and reaction mechanisms can be achieved. It was observed that the subsurface Cu single atoms in Fe2O3 remained isolated under both oxidation and reduction environments, whereas surface Cu single atoms on Fe2O3 experienced sintering under reduction conditions. The unique properties of these subsurface single-atom catalysts call for innovations and new understandings in catalyst design.
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Jul 2024
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I09-Surface and Interface Structural Analysis
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Niels
Kubitza
,
Isabel
Huck
,
Hanna
Pazniak
,
Curran
Kalha
,
David
Koch
,
Bo
Zhao
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Aysha A.
Riaz
,
Wolfgang
Donner
,
Hongbin
Zhang
,
Benjamin
Moss
,
Ulf
Wiedwald
,
Anna
Regoutz
,
Christina S.
Birkel
Diamond Proposal Number(s):
[29451]
Abstract: MAX phases are almost exclusively known as carbides, while nitrides and carbonitrides form a significantly underrepresented subgroup even though they have been shown to possess enhanced properties in comparison to their carbide counterparts. One example is the nitride phase Cr2GaN which exhibits a spin density wave magnetic state below T = 170 K, while the metallic carbide phase Cr2GaC follows the MAX phase-typical Pauli-paramagnetic behavior. To investigate the influence on the materials/functional properties of mixing carbon and nitrogen on the X-site, this study aims to synthesize and comprehensively characterize the hitherto unknown carbonitride phase Cr2GaC1-xNx and compare it to the parent phases. Due to the challenging synthesis of (carbo)nitrides in general, a sol-gel-assisted approach is applied which was recently developed by our group. This process was further improved by using time-efficient microwave heating, leading to a highly phase pure product. STEM-EDX analyses reveal a C/N ratio of roughly 2:1. Temperature-dependent XRD measurements confirm the literature-known magnetic phase transition of the parent nitride phase Cr2GaN, while the incorporation of carbon suppresses the latter. Nonetheless, magnetic characterization of the phases reveals that the magnetic behavior can be specifically influenced by changing the composition of the X site, resulting in an increase of the susceptibility by increasing the nitrogen amount. Overall, these findings further substantiate the big potential in nitrogen-containing MAX phases, which will also serve as starting materials for future doping studies, i.e. on the M- and A-site, and as precursors for novel 2D MXenes.
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Apr 2024
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I09-Surface and Interface Structural Analysis
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Curran
Kalha
,
Laura E.
Ratcliff
,
Giorgio
Colombi
,
Christoph
Schlueter
,
Bernard
Dam
,
Andrei
Gloskovskii
,
Tien-Lin
Lee
,
Pardeep K.
Thakur
,
Prajna
Bhatt
,
Yujiang
Zhu
,
Jürg
Osterwalder
,
Francesco
Offi
,
Giancarlo
Panaccione
,
Anna
Regoutz
Diamond Proposal Number(s):
[29451]
Open Access
Abstract: Metal hydrides are potential candidates for applications in hydrogen-related technologies, such as energy storage, hydrogen compression, and hydrogen sensing, to name just a few. However, understanding the electronic structure and chemical environment of hydrogen within them remains a key challenge. This work presents a new analytical pathway to explore these aspects in technologically relevant systems using hard x-ray photoelectron spectroscopy (HAXPES) on thin films of two prototypical metal dihydrides:
YH
2
−
δ
and
Ti
H
2
−
δ
. By taking advantage of the tunability of synchrotron radiation, a nondestructive depth profile of the chemical states is obtained using core-level spectra. Combining experimental valence-band (VB) spectra collected at varying photon energies with theoretical insights from density functional theory (DFT) calculations, a description of the bonding nature and the role of
d
versus
s
p
contributions to states near the Fermi energy are provided. Moreover, a reliable determination of the enthalpy of formation is proposed by using experimental values of the energy position of metal
s
-band features close to the Fermi energy in the HAXPES VB spectra.
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Nov 2023
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