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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I09-Surface and Interface Structural Analysis
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Rose M.
Snyder
,
Mikkel
Juelsholt
,
Curran
Kalha
,
Jason
Holm
,
Elisabeth
Mansfield
,
Tien-Lin
Lee
,
Pardeep K.
Thakur
,
Aysha A.
Riaz
,
Benjamin
Moss
,
Anna
Regoutz
,
Christina S.
Birkel
Diamond Proposal Number(s):
[29451]
Abstract: MAX phases with the general formula Mn+1AXn are layered carbides, nitrides, and carbonitrides with varying stacking sequence of layers of M6X octahedra and the A element depending on n. While “211” MAXphases (n = 1) are very common, MAX phases with higher n, especially n ≥ 3, have hardly been prepared. This work addresses open questions regarding the synthesis conditions, structure, and chemical composition of the “514” MAX phase. In contrast to literature reports, no oxide is needed to form the MAX phase, yet multiple heating steps at 1,600 °C are required. Using high-resolution X-ray diffraction, the structure of (Mo1-xVx)5AlC4 is thoroughly investigated, and Rietveld refinement suggests P-6c2 as the most fitting space group. SEM/EDS and XPS show that the chemical composition of the MAX phase is (Mo0.75V0.25)5AlC4. It was also exfoliated into its MXene sibling (Mo0.75V0.25)5C4 using two different techniques (using HF and an HF/HCl mixture) that lead to different surface terminations as shown by XPS/HAXPES measurements. Initial investigations of the electrocatalytic properties of both MXene versions show that, depending on the etchant, (Mo0.75V0.25)5C4 can reduce hydrogen at 10 mA cm–2 with an overpotential of 166 mV (HF only) or 425 mV (HF/HCl) after cycling the samples, which makes them a potential candidate as an HER catalyst.
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Jun 2023
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[29451]
Open Access
Abstract: Interdiffusion phenomena between adjacent materials are highly prevalent in semiconductor device architectures and can present a major reliability challenge for the industry. To fully capture these phenomena, experimental approaches must go beyond static and post-mortem studies to include in situ and in-operando setups. Here, soft and hard X-ray photoelectron spectroscopy (SXPS and HAXPES) is used to monitor diffusion in real-time across a proxy device. The device consists of a Si/SiO2/TixW1−x(300 nm)/Cu(25 nm) thin film material stack, with the TixW1−x film (x = 0.054, 0.115, 0.148) acting as a diffusion barrier between Si and Cu. The interdiffusion is monitored through the continuous collection of spectra whilst in situ annealing to 673 K. Ti within the TiW is found to be highly mobile during annealing, diffusing out of the barrier and accumulating at the Cu surface. Increasing the Ti concentration within the TixW1−x film increases the quantity of accumulated Ti, and Ti is first detected at the Cu surface at temperatures as low as 550 K. Surprisingly, at low Ti concentrations (x = 0.054), W is also mobile and diffuses alongside Ti. By monitoring the Ti 1s core level with HAXPES, the surface-accumulated Ti was observed to undergo oxidation even under ultra-high vacuum conditions, highlighting the reactivity of Ti in this system. These results provide crucial evidence for the importance of diffusion barrier composition on their efficacy during device application, delivering insights into the mechanisms underlying their effectiveness and limitations.
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May 2023
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I09-Surface and Interface Structural Analysis
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Maria
Basso
,
Elena
Colusso
,
Chiara
Carraro
,
Curran
Kalha
,
Aysha A.
Riaz
,
Giada
Bombardelli
,
Enrico
Napolitani
,
Yu
Chen
,
Jacek
Jasieniak
,
Laura E.
Ratcliff
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Anna
Regoutz
,
Alessandro
Martucci
Diamond Proposal Number(s):
[29451]
Open Access
Abstract: The thermochromic properties of vanadium dioxide (VO2) offer great advantages for energy-saving smart windows, memory devices, and transistors. However, the crystallization of solution-based thin films at temperatures lower than 400°C remains a challenge. Photonic annealing has recently been exploited to crystallize metal oxides, with minimal thermal damage to the substrate and reduced manufacturing time. Here, VO2 thin films, obtained via a green sol-gel process, were crystallized by pulsed excimer laser annealing. The influence of increasing laser fluence and pulse number on the film properties was systematically studied through optical, structural, morphological, and chemical characterizations. From temperature profile simulations, the temperature rise was confirmed to be confined within the film during the laser pulses, with negligible substrate heating. Threshold laser parameters to induce VO2 crystallization without surface melting were found. With respect to furnace annealing, both the crystallization temperature and the annealing time were substantially reduced, with VO2 crystallization being achieved within only 60 s of laser exposure. The laser processing was performed at room temperature in air, without the need of a controlled atmosphere. The thermochromic properties of the lasered thin films were comparable with the reference furnace-treated samples.
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May 2023
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I09-Surface and Interface Structural Analysis
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Leanne A. H.
Jones
,
Zongda
Xing
,
Jack E. N.
Swallow
,
Huw
Shiel
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Nicole
Fleck
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Laurence J.
Hardwick
,
David O.
Scanlon
,
Anna
Regoutz
,
Tim D.
Veal
,
Vinod R.
Dhanak
Diamond Proposal Number(s):
[25980]
Open Access
Abstract: A comprehensive study of bulk molybdenum dichalcogenides is presented with the use of soft and hard X-ray photoelectron (SXPS and HAXPES) spectroscopy combined with hybrid density functional theory (DFT). The main core levels of MoS2, MoSe2, and MoTe2 are explored. Laboratory-based X-ray photoelectron spectroscopy (XPS) is used to determine the ionization potential (IP) values of the MoX2 series as 5.86, 5.40, and 5.00 eV for MoSe2, MoSe2, and MoTe2, respectively, enabling the band alignment of the series to be established. Finally, the valence band measurements are compared with the calculated density of states which shows the role of p-d hybridization in these materials. Down the group, an increase in the p-d hybridization from the sulfide to the telluride is observed, explained by the configuration energy of the chalcogen p orbitals becoming closer to that of the valence Mo 4d orbitals. This pushes the valence band maximum closer to the vacuum level, explaining the decreasing IP down the series. High-resolution SXPS and HAXPES core-level spectra address the shortcomings of the XPS analysis in the literature. Furthermore, the experimentally determined band alignment can be used to inform future device work.
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Dec 2022
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[23209]
Open Access
Abstract: X-ray characterisation methods have undoubtedly enabled cutting-edge advances in all aspects of materials research. Despite the enormous breadth of information that can be extracted from these techniques, the challenge of radiation-induced sample change and damage remains prevalent. This is largely due to the emergence of modern, high-intensity X-ray source technologies and the growing potential to carry out more complex, longer duration in situ or in operando studies. The tunability of synchrotron beamlines enables the routine application of photon energy-dependent experiments. This work explores the structural stability of [Rh(COD)Cl]2, a widely used catalyst and precursor in the chemical industry, across a range of beamline parameters that target X-ray energies of 8 keV, 15 keV, 18 keV and 25 keV, on a powder X-ray diffraction synchrotron beamline at room temperature. Structural changes are discussed with respect to absorbed X-ray dose at each experimental setting associated with the respective photon energy. In addition, the X-ray radiation hardness of the catalyst is discussed, by utilising the diffraction data collected at the different energies to determine a dose limit, which is often considered in protein crystallography and typically overlooked in small molecule crystallography. This work not only gives fundamental insight into how damage manifests in this organometallic catalyst, but will encourage careful consideration of experimental X-ray parameters before conducting diffraction on similar radiation-sensitive organometallic materials.
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Nov 2022
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