I09-Surface and Interface Structural Analysis
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Bhavya
Rakheja
,
Adam
Hultqvist
,
Rahul Mahavir
Varma
,
Natalia M.
Martin
,
Karen
Radetzky
,
Stefania
Riva
,
Evelyn
Johannesson
,
Ute B.
Cappel
,
Hakan
Rensmo
,
Erik M. J.
Johansson
,
Tobias
Torndahl
Diamond Proposal Number(s):
[35209]
Open Access
Abstract: Tin oxide (SnOx) by atomic-layer deposition (ALD), in combination with fullerene, is widely employed as an electron transport layer in p–i–n perovskite solar cells. This study investigates the direct deposition of ALD SnOx on top of formamidinium (FA)-based perovskites, as a step toward the elimination of the fullerene interlayer and its poor effect on solar cell’s long-term stability. The interfacial chemistry between FA-based perovskites (FAPbI3 and FAPbBr3) and ALD SnOx was studied using soft and hard X-ray photoelectron spectroscopy (SOXPES and HAXPES) with a focus on investigating the separate roles FA and different halides play during interface formation. FAPbI3 and FAPbBr3 solar cell structures solely containing ALD SnOx resulted in s-shaped current–voltage characteristics, indicating the formation of a transport barrier at the interface. Both SOXPES and HAXPES measurements revealed the emergence of additional nitrogen states at the interface during the ALD SnOx deposition on FAPbI3 and FAPbBr3, where these states are linked to the decomposition of FA+. The FAPbI3/ALD SnOx interface also showed the presence of lead iodide (PbI2) through additional lead states other than that from FAPbI3 by using SOXPES measurements. Concerning the FAPbBr3/ALD SnOx interface, no additional lead states were observed; however, measurements instead revealed the formation of Sn–Br bonds at the interface along with the migration of bromine ions into the bulk of the ALD SnOx. Thus, FAPbI3 and FAPbBr3 undergo distinct reaction pathways upon direct deposition of ALD SnOx on top of them. We reason that the decomposition of FA+ in both perovskites and the formation of PbI2 at the FAPbI3/ALD SnOx interface and the incorporation of Br in SnOx at the FAPbBr3/ALD SnOx interface prove detrimental toward device performance. Therefore, careful interfacial engineering that can mitigate the formation of these products should be utilized to enhance the performance of perovskite solar cells.
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Jun 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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I09-Surface and Interface Structural Analysis
I10-Beamline for Advanced Dichroism - scattering
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Naina
Kushwaha
,
Olivia
Armitage
,
Brendan
Edwards
,
Liam
Trzaska
,
Jennifer
Rigden
,
Peter
Bencok
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Charlotte
Sanders
,
Gerrit
Van Der Laan
,
Peter
Wahl
,
Phil D. C.
King
,
Akhil
Rajan
Diamond Proposal Number(s):
[33239, 38049]
Open Access
Abstract: Chromium ditelluride, CrTe2, is an attractive candidate van der Waals material for hosting 2D magnetism. However, how the room-temperature ferromagnetism of the bulk evolves as the sample is thinned to the single-layer limit has proved controversial. This, in part, reflects its metastable nature, vs. a series of more stable self-intercalation compounds with higher relative Cr:Te stoichiometry. Here, exploiting a recently developed method for enhancing nucleation in molecular-beam epitaxy growth of transition-metal chalcogenides, we demonstrate the selective stabilisation of high-coverage CrTe2 and Cr2+εTe3 epitaxial monolayers. Combining X-ray magnetic circular dichroism, scanning tunnelling microscopy, and temperature-dependent angle-resolved photoemission, we demonstrate that both compounds order magnetically with a similar TC. We find, however, that monolayer CrTe2 forms as an antiferromagnetic metal, while monolayer Cr2+εTe3 hosts an intrinsic ferromagnetic semiconducting state. This work thus demonstrates that control over the self-intercalation of metastable Cr-based chalcogenides provides a powerful route for tuning both their metallicity and magnetic structure, establishing the CrxTey system as a flexible materials class for future 2D spintronics.
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May 2025
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I09-Surface and Interface Structural Analysis
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Qianhui
Liu
,
Tove
Ericson
,
Robert
Temperton
,
Ida
Kallquist
,
Fredrik
Lindgren
,
Laura
King
,
Alenka
Križan
,
Katie L.
Browning
,
Ethan
Crumlin
,
Gabriel M.
Veith
,
Maria
Hahlin
Diamond Proposal Number(s):
[36581]
Open Access
Abstract: The real-time interface chemistry between the lithium cobalt oxide (LCO) working electrode and the LiClO4/propylene carbonate (PC) electrolyte is investigated during lithiation/delithiation using dip-and-pull ambient pressure photoelectron spectroscopy (APXPS). The APXPS results appear to exhibit the seldom discussed Co2+ state in the LCO structure, where the operando measurements indicate electron transfer among Co2+, Co3+, and Co4+ states. Specifically, the lithiation of LCO reduces the Co4+ state to both Co3+ and Co2+ states, where, as a function of voltage, reduction to Co2+ state is initially more pronounced followed by Co3+ formation. In addition, a delay in surface delithiation is observed during the reverse potential steps. This is discussed in terms of overpotential at the interface measurement position as a consequence of the dip-and-pull setup for this experiment. Finally, the shifts in the apparent binding energies of the spectral features corresponding to the electrolyte and LCO at their interface shows that the electrochemical potentials at delithiation voltage steps are different from the lithiation steps at the same applied voltages. This further explains the non-responsive delithiation. The BE shift observed from the LCO surface is argued to be dominantly due to the semi-conductive nature of the sample. Overall, this article shows the importance of operando APXPS for probing non-equilibrium states in battery electrodes for understanding electron transfer in the reactions.
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May 2025
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I09-Surface and Interface Structural Analysis
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Francesco
Offi
,
Francesco
Borgatti
,
Pasquale
Orgiani
,
Vincent
Polewczyk
,
Sandeep Kumar
Chaluvadi
,
Shyni
Punathum Chalil
,
Aleksandr
Petrov
,
Federico
Motti
,
Gian Marco
Pierantozzi
,
Giancarlo
Panaccione
,
Bogdan
Rutkowski
,
Paolo
Mengucci
,
Gianni
Barucca
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Emiliano
Marchetti
,
Alberto
Martinelli
,
Davide
Peddis
,
Gaspare
Varvaro
Diamond Proposal Number(s):
[32921]
Open Access
Abstract: Epitaxial heterostructures integrating thin Fe3O4 films hold great potential for spintronics, magnetoionics, and multifunctional device development. In this work, the morpho-structural and magnetic properties of all-spinel Fe3O4/MgCr2O4/Fe3O4 trilayers grown on a MgCr2O4 buffer-layer, exhibiting very close lattice matching, were investigated by using both surface and bulk sensitive techniques. The close lattice match between Fe3O4 and MgCr2O4 enables the growth of epitaxial heterostructures with magnetically decoupled Fe3O4 layers for spacer thicknesses ≥ 1.6 nm, while reducing the formation of antiphase boundaries. Despite localized interphase diffusion, which leads to the formation of a mixed Cr/Fe spinel oxide with magnetically polarized Cr ions at the Fe3O4/MgCr2O4 interfaces, the overall magnetic properties remain largely consistent with those of the individual Fe3O4 layers. This study sheds light on the magnetic interactions within Fe3O4 layers mediated by a MgCr2O4 spacer, and demonstrates the feasibility of the approach in preserving the properties of thin Fe3O4 films, in complex heterostructures, thus offering a promising pathway for designing advanced all-spinel oxide devices.
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May 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Abstract: This article presents the synthesis and evaluation of a novel double perovskite Dy2NiRu0.5Ir0.5O6, as a promising catalyst precursor for the oxygen evolution reaction (OER) in acidic electrolyte. In this perovskite, which was synthesised by a simple sol-gel process, there are two different B sites, one with Ni2+ atoms, and the other in which half of the Ir4+ atoms are replaced by Ru4+.
Electrochemical measurements revealed and exceptional OER activity, with an Ir-normalised mass activity 5–7 times higher than the state-of-the-art IrO2 benchmarks. The catalyst also exhibited remarkable stability, maintaining a stable performance for at least 36,000 OER cycles. Structural and compositional analyses during cycling revealed a transformation of the pristine double perovskite structure into a 3D-hollow Ir0.9Ru0.1Ox framework. The reconstruction, which is driven by the dissolution of Dy3+, Ni2+ and part of Ru4+, results in a highly active and durable electrocatalyst. The enhanced OER performance is attributed to the composition and increased surface area of the reconstructed Ir0.9Ru0.1Ox hollow structure.
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May 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[35796]
Open Access
Abstract: Two-dimensional (2D) transition metal dichalcogenides have emerged as a promising platform for next-generation optoelectronic and spintronic devices. Mechanical exfoliation using adhesive tape remains the dominant method for preparing 2D materials of highest quality, including transition metal dichalcogenides, but always results in small-sized flakes. This limitation poses a significant challenge for investigations and applications where large scale flakes are needed. To overcome these constraints, we explored the preparation of 2D
WS
2
and
WSe
2
using a recently developed kinetic in situ single-layer synthesis method (KISS). In particular, we focused on the influence of different substrates, Au and Ag, and chalcogen atoms, S and Se, on the yield and quality of the 2D films. The crystallinity and spatial morphology of the 2D films were characterized using optical microscopy and atomic force microscopy, providing a comprehensive assessment of exfoliation quality. Low-energy electron diffraction verified that there is no preferential orientation between the 2D film and the substrate, while optical microscopy revealed that
WSe
2
consistently outperformed
WS
2
in producing large monolayers, regardless of the substrate used. Finally, X-ray diffraction and X-ray photoelectron spectroscopy demonstrate that no covalent bonds are formed between the 2D material and the underlying substrate. These results identify KISS method as a non-destructive method for a more scalable approach of high-quality 2D transition metal dichalcogenides.
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May 2025
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
B18-Core EXAFS
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Diamond Proposal Number(s):
[32514]
Open Access
Abstract: Fe/N/C based catalysts are the best positioned ones to replace the state-of-the-art Pt-based catalysts for the oxygen reduction reaction (ORR) in Proton Exchange Membrane Fuel Cells (PEMFCs). Here, a Fe/N/C catalyst characterized by a high N/C ratio, has been synthesized from the pyrolysis of a N-rich imine-based polymer. In acidic electrolyte (0.1 M HClO4). The catalyst demonstrates notable ORR activity with Eonset and E1/2 values of 1.09 and 0.77 V vs. RHE, respectively. Furthermore, the catalyst’s performance has been assessed in a single cell PEMFC setup. The optimization of the membrane electrode assembly (MEA) with the Fe/N/C catalyst entails examining various ionomer to catalyst ratios (I/C) as well as two coating methods: spray coating and drop casting. The optimized MEA achieved a cell performance of 725 mA cm-2 at 0.3 V and a power density close to 220 mW cm-2. In order to understand the factors influencing PEMFC polarisation curves, electrochemical impedance spectroscopy (EIS) was performed under potentiostatic conditions. The effect of operational parameters, such as ionomer to catalyst ratios (I/C) and the use of either O2 or air at the anode feed, has been investigated. EIS spectra allow the calculation of the distribution of relaxation times (DRT), providing insights into the rate and resistance of the ORR process occurring at the MEA. Notably, the cathode with an I/C=2, prepared by drop casting, exhibited superior performance attributed to reduced ORR resistances. The current density and power density reached with the 25 cm2 MEA are comparable to those obtained with the 5 cm2 MEA using O2 as cathode reactant.
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Apr 2025
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[34784]
Open Access
Abstract: Plasmonic nanocavities offer exceptional confinement of light, making them effective for energy conversion applications. However, limitations with stability, materials, and chemical activity have impeded their practical implementation. Here we integrate ultrathin palladium (Pd) metal films from sub- to few- atomic monolayers inside plasmonic nanocavities using underpotential deposition. Despite the poor plasmonic properties of bulk Pd in the visible region, minimal loss in optical field enhancement is delivered along with Pd chemical enhancement, as confirmed by ab initio calculations. Such synergistic effects significantly enhance photocatalytic activity of the plasmonic nanocavities as well as photostability by suppressing surface atom migration. We show the atomic alchemical-glazing approach is general for a range of catalytic metals that bridge plasmonic and chemical catalysis, yielding broad applications in photocatalysis for optimal chemical transformation.
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Apr 2025
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I06-Nanoscience (XPEEM)
I09-Surface and Interface Structural Analysis
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Yiru
Zhu
,
Zhepeng
Zhang
,
Ye
Wang
,
Soumya
Sarkar
,
Yang
Li
,
Han
Yan
,
Larissa
Ishibe-Veiga
,
Anita
Bagri
,
Ziwei J.
Yang
,
Hugh
Ramsden
,
Goki
Eda
,
Robert L. Z.
Hoye
,
Yan
Wang
,
Manish
Chhowalla
Diamond Proposal Number(s):
[36685, 33391]
Open Access
Abstract: Chalcogen vacancy defects in monolayer transition metal dichalcogenides form in-gap states that can trap excitons, leading to defect-mediated photoluminescence (PL) emission. Here, we show that room-temperature (RT, 300 K) PL from sulfur vacancies in defective monolayer MoS2 is sensitive to doping from dielectric substrates such as SiO2 and HfO2. The defect-mediated PL is observed for monolayer MoS2 on untreated HfO2 but is quenched on untreated SiO2, which is attributed to electron doping of MoS2 on SiO2. Electron doping of MoS2 is confirmed by Raman and synchrotron X-ray photoelectron spectroscopy. Annealing of the SiO2 substrate modifies its surface states, which is reflected in the recovery of the defect-mediated PL emission. The role of substrate-induced doping on sulfur vacancy-mediated PL is further supported by gate-dependent PL measurements. Our results suggest that excess electrons fill the defect energy states from sulfur vacancies in MoS2, reducing the probability of photoexcited carrier occupation and subsequent defect-mediated emission.
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Apr 2025
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