I09-Surface and Interface Structural Analysis
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Rajesh
Dutta
,
Prajwal M.
Laxmeesha
,
Tarush
Tandon
,
Tessa D.
Tucker
,
Sharup
Sheikh
,
Uditha M.
Jayathilake
,
Wei
Tian
,
Adam A.
Aczel
,
Tien-Lin
Lee
,
Alexander X.
Gray
,
Steven J.
May
Abstract: We have investigated the electronic and magnetic structures of topological kagome Fe1−𝑥Mn𝑥Sn (0≤𝑥≤0.3) thin films via neutron diffraction, electronic transport measurements, and ab initio density functional theory (DFT) to understand the interplay between hole doping, magnetism, and the electronic structures. Temperature-dependent neutron diffraction measurements on parent FeSn reveal the Néel temperature to be 𝑇N∼355 K and the underlying A-type antiferromagnetic ordering is associated with a wave vector 𝒒=(001/2). Upon Mn doping to 𝑥=0.15, 𝑇N decreases slightly while the magnetic ordering vector remains the same. Resistivity measurements show metallic characteristics and in-plane anisotropy down to 10 K for all the investigated samples. The effects of hole doping are mapped in terms of electronic ground state calculations via DFT which show that the Dirac point is moved closer to the Fermi level (𝐸F) and the flat bands get pushed away from 𝐸F upon hole doping. However, a comparison between hole-doped Fe1−𝑥Mn𝑥Sn and electron-doped Fe1−𝑥Co𝑥Sn indicates that the Néel temperature does not scale with the position of 𝐸F relative to the flat band. Our results establish the antiferromagnetic state of FeSn and Fe1−𝑥Mn𝑥Sn films at room temperature, laying the groundwork for future studies of magnetism in kagome heterostructures.
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Jul 2025
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I09-Surface and Interface Structural Analysis
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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.
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Jun 2025
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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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I07-Surface & interface diffraction
I09-Surface and Interface Structural Analysis
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Alessandro J.
Mirabelli
,
Birgit
Kammlander
,
Yang
Lu
,
Rahul Mahavir
Varma
,
Qichun
Gu
,
Karen
Radetzky
,
Thomas A.
Selby
,
Tianjun
Liu
,
Stefania
Riva
,
Zimu
Wei
,
Tien-Lin
Lee
,
Jonathan
Rawle
,
Hakan
Rensmo
,
Miguel
Anaya
,
Ute B.
Cappel
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[30043, 32266, 30838, 33096]
Open Access
Abstract: To commercialize lead halide perovskites as light-emitting diodes (LEDs), the operational device lifetime needs to be drastically improved. For this to be achieved, an understanding of degradation behavior under bias is crucial. Herein, we perform operando measurements of the structural, chemical, and electronic changes using synchrotron-based grazing-incidence wide-angle X-ray scattering and hard X-ray photoelectron spectroscopy on full-stack deep blue mixed bromide/chloride lead halide perovskite LEDs. While a clear drop in optoelectronic performance is recorded under electrical bias, the accompanying X-ray scattering data reveals only minor changes in structural properties. However, photoelectron spectroscopy reveals substantial chemical changes at the electron-injecting interface after bias is applied, including the formation of unwanted metallic lead and a new chlorine species that is not in the perovskite structure. These operando approaches give important structural and interfacial perspectives to reveal the degradation mechanisms in these LEDs and highlight the need to address the top electron-injecting interface to realize step-changes in operational stability.
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Jun 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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I09-Surface and Interface Structural Analysis
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Open Access
Abstract: The development of analog resistive non-volatile memory elements is of great interest for future information storage technology. These devices can be used to emulate the electronic behaviour of biological synapses and neurons for neuromorphic computing or sensing applications. Hafnia is a promising material to use in resistive memory systems due to its high industrial compatibility. Both the migration of oxygen ions and ferroelectricity are two mechanisms actively being explored to drive resistance change in hafnia based devices. This thesis explores the interplay between interfacial redox chemistry and ferroelectricity and how these influence the resistance switching behaviour in epitaxial hafnia films. A device stack is engineered to elicit large resistance changes through both ferroelectricity and interfacial redox reactions. Ultra-thin epitaxial Y doped HfO2 (YHO) is grown with a controlled oxygen stoichiometry. To stabilise the polar phase in YHO and provide a resistance-tuneable bottom interface, YHO is grown on La0.66Sr0.33MnO3 (LSMO) buffered Nb doped SrTiO3 substrates. In-depth X-Ray diffraction based structural analysis identified the polar nature of the film and a strain induced rhombohedral distortion. Ferroelectricity in the film was confirmed by piezoresponse force microscopy. In device configuration, using an Au top electrode with an ultra-thin Ti adhesion layer, a resistance switching mode with large on-off ratio was observed. The pristine device was stabilised in an intermediate resistance state and did not need an electro-forming process. The mode reversibly switched between a purely capacitive (Schottky) and resistive (Ohmic) state, a Schottky-to-Ohmic transition (SOT). A series of voltage pulse trains were used to explore the intermediate resistance states of the system. Both analog and integration behaviour was demonstrated, depending on the pulse profile. The SOT may therefore find application as both a synapse and a neuron respectively in neuromorphic applications. Capacitance-voltage measurements were employed to correlate the ferroelectric polarisa- tion reversal with the SET process and not the RESET process. Therefore, ferroelectricity was indicated to only be partially responsible for the observed resistance change. Electrode area dependent current measurements suggested that in the low resistance state, current transport occurred through a localised conductive filament. A detailed analysis of the inter- face chemistry suggested the importance of precisely designed oxygen scavenging at both interfaces to stabilise the SOT. Furthermore, interface stoichiometry changes were observed during resistance switching by a combined hard photo-electron spectroscopy and electron energy loss spectroscopy study. Impedance spectroscopy measurements were used to correlate the stoichiometry changes at the LSMO|YHO interface to resistance changes during the SOT. The conductive pristine resistance state was shown to predominantly be limited by the LSMO|YHO interface and was proposed to occur due to oxygen scavenging at the top electrode, by-passing through-grain conduction. Analysis of the SOT analog switching behaviour showed that both the YHO layer and the LSMO|YHO interface switch separately during the RESET operation, but simultaneously during the SET process. Furthermore, stack modifications demonstrated the importance of using an ultra-thin LSMO to stabilise the SOT. It was hypothesised to occur due to interface strain enhanced defect formation, oxygen transfer or symmetry changes at the LSMO|YHO interface.
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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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Abstract: Cobalt ferrite is of great interest due to its promising properties, such as its semiconducting transport behavior and high Curie temperature of 793K. Consequently, cobalt ferrite is used in various applications, including magnetic sensors and magnetic tunnel junctions. Particularly, ultrathin cobalt ferrite films are considered interesting candidates for efficient spin filters in spintronics. This is a significant field in physics that utilizes spin-dependent charge transport in solids. Unlike conventional electronics, spintronics exploits not only charge but also electron spin for information transfer, enabling faster and more energy-efficient devices.
The spin-filter effect relies on the exchange splitting of energy levels in the conduction band of a magnetic insulator. As a result, the tunnel barriers in spin filters differ for spin-up and spin-down electrons, leading to a higher tunneling probability for one type, thereby generating a spin-polarized current. In theory, spin filters can reach 100% efficiency, but cobalt ferrites have so far only achieved spin polarization of -8%, indicating an excess of spin-down electrons. Improving spin-filter efficiency requires a deep understanding of the electronic, optical, and transport properties of the material.
Therefore, this work investigates the properties of ultrathin cobalt ferrite films. Magnesium oxide (MgO) is used as a substrate due to its minimal lattice mismatch with cobalt ferrite. Since cobalt ferrite’s properties strongly depend on stoichiometry, this study examines how its characteristics vary with cobalt content.
Synchrotron radiation was employed for sample measurements, as it offers advantages over conventional laboratory-based X-ray sources. Its extremely high intensity, small beam size, and adjustable energy range provide enhanced capabilities for thin film characterization. Moreover, it provides the excitation energy required for HAXPES experiments. The measurements had already been conducted prior to this work, and this study focuses on analyzing the results.
The theoretical foundations are explained in Chapter 2. Before discussing measurement results in Chapter 5, Chapter 3 introduces the material system, and Chapter 4 presents the experimental background. Finally, Chapter 6 provides a summary and an outlook.
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Feb 2025
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I09-Surface and Interface Structural Analysis
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Scott A.
Chambers
,
Enrique
Ramerez
,
Deepa
Guragain
,
Joseph H.
Ngai
,
Peter V.
Sushko
,
Krishna P.
Koirala
,
Yingge
Du
,
Niranjan
Govind
,
Mark E.
Bowden
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Conan
Weiland
,
Joseph C.
Woicik
Diamond Proposal Number(s):
[25314]
Abstract: We have investigated the structural and electronic properties of 3 at. % Yb-doped SrTiO3/Si(001) grown by molecular beam epitaxy. Other rare-earth dopants that result in 𝑛-type conductivity typically substitute for Sr at the 𝐴 sites in the 𝐴𝐵O3 perovskite lattice. In contrast, Yb is shown to substitute predominantly for Ti at the perovskite 𝐵 sites based on data from atomically resolved scanning transmission electron microscopy and energy dispersive spectroscopy, as well as extended x-ray absorption fine structure measurements. An atom beam flux (Θ) mismatch was present during film growth because it was assumed that Yb would occupy 𝐴 sites. As a result of this assumption, the fluxes were set such that ΘYb+ΘSr=ΘTi. The formation of YbTi rather than YbSr results in Sr vacancies and extraneous (i.e., nonlattice) Ti atoms in the films. Yb exhibits two distinct charge states as determined by x-ray absorption spectroscopy and associated theoretical modeling, +2.7 and +2.1. These aliovalent dopants are compensated by donor electrons from oxygen vacancies that form during film growth. The defect complexes resulting from the flux mismatch, together with oxygen vacancies, lead to deep-level electron traps that were detected by resonant photoemission and predicted to be stable by ab initio theory, as well as much higher sheet resistance than that associated with, for instance, La-doped SrTiO3 (STO) films. Ab initio calculations show that the preference for 𝐵-site occupancy is driven by low oxygen chemical potential at the growth front as required to deposit STO on Si without SiO2 formation.
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Jan 2025
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