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Localized spin textures stabilized by geometry induced strain in 2D magnet Fe3GeTe2
Get PDFStrain engineering promises to enable manipulation and control of the properties of exfoliated flakes of 2D van der Waals vdW ferromagnets for spintronic applications. However, while previous studies of strain effects have focused on global properties, the impact on local magnetic spin textures remains unexplored. Here, manipulation of magnetism in the 2D ferromagnet Fe3GeTe2 FGT is demonstrated using geometry induced strain. Employing scanning transmission X ray microscopy STXM , the effects of spatially varying strain profiles on the magnetic order of FGT sheets stamped onto micropillar arrays are directly visualized. It is found that the in plane strain components, with magnitudes lt;0.5 , locally elevate the Curie temperature of FGT by 10 K, stabilizing magnetic domains near the pillar corners. These domains include skyrmions and higher order topological spin textures such as skyrmioniums and skyrmion bags. The possibility to locally seed and control topological spin textures via strain opens new avenues for future spin based information technologie
In situ NAP XPS and electrochemical impedance characterisation of La0.31Sr0.58Ti0.97Ni0.03O3 delta thin film model electrodes
No full textLaxSr0.9 xTiyNi1 yO3 amp; 948; LSTN has been proposed as a promising group of mixed ionic electronic MIEC perovskites for solid oxide fuel and electrolysis cell applications. In this study thin film as prepared before redox treatment La0.31Sr0.58Ti0.97Ni0.03O3 amp; 948; LSTN3 pulsed laser deposited PLD electrodes were characterised electrochemically and using in situ near ambient pressure X ray photoelectron spectroscopy NAP XPS at different H2 H2O ratios and electrode potentials at 650 C. The electrochemical activity of LSTN3 gas surface increased with water content in a hydrogen environment. Ti XPS spectra revealed rutile like coordinated Ti surface termination of LSTN3 and Ti3 Ti4 ratio changes in the surface layer as a function of oxygen activity in LSTN3. Change in the kinetics of the electrochemical process at amp; 8764;0.3 V in H2 with 1.6 H2O was observed and explained as oxidation of exsolved Ni. La and Sr XPS spectra were independent of polarisation and depended only on water content in the gas. The changes in La OH 3 concentration at the surface influenced by water content in the gas match with the changes in the electrochemical activit
Structural Insights Into Phase Formation of Sodium Layered Cathodes Materials with Prominent Electrochemical Performances
No full textThe electrochemical performances of layered cathodes for sodium ion batteries SIBs are intimately dependent on their structural characteristics. However, realizing accurate regulation of structure by phase engineering is challenging, primarily due to constrained synthesis methods and the existing gaps in understanding of specialized phase structures. Herein, a series of P amp; 8242;2 Na0.67Fe0.05Ti0.1Mn0.85O2 cathode material with prominent electrochemical performances were successfully synthesized, based on an in depth understanding of structural insights into P amp; 8242;2 phase. By analyzing the structural evolution and Mn valence changes during synthesis, we found that oxygen vacancies play a significant role in determining the P amp; 8242;2 P2 phase transition. Moreover, these insights not only identified the oxygen release and uptake behaviors in phase formation but also expanded synthesis strategy with enhanced operational feasibility. Benefits from expanded Mn redox range and stable oxygen vacancies during cycling, the obtained P amp; 8242;2 Na0.67Fe0.05Ti0.1Mn0.85O2 demonstrated a capacity increase of over amp; 8764;40 mAh g amp; 8722;1 at 0.1 C, maintaining amp; 8764;93 mAh g amp; 8722;1 even after 1000 cycles at 10 C, with an impressive retention rate of 87.5 . This research significantly advances the comprehension of both synthesis mechanism and electrochemical properties optimization mechanisms of P amp; 8242;2 phase materials, offering a pragmatic strategy for elevating the performance of SIB material
Hard carbon from a sugar derivative for next generation sodium ion batteries
No full textSodium ion batteries have emerged as a promising secondary battery system due to the abundance of sodium resources. One of the boosters for accelerating the practical application of sodium ion batteries is the innovation in anode materials. This study focuses on developing a high performance hard carbon anode material derived from hydroxymethylfurfural, produced from carbohydrates, using a straightforward thermal condensation method. The process results in a unique pseudo graphitic material with abundant microporosity. Electrochemical evaluations demonstrate excellent sodium storage performance by maintaining the plateau capacity even at higher current densities. This translates to a promising energy density when coupled with the cathode material. However, we also discuss the influence of electrolyte composition on the performance of the hydroxymethylfurfural derived hard carbon, emphasizing the critical role of electrolyte optimization for the development of efficient and sustainable carbonaceous anode materials for next generation sodium based batterie
Degradation mechanisms of LiNi0.5Mn0.3Co0.2O2 graphite battery in real life driving scenarios
Get PDFUnderstanding the aging mechanisms of lithium ion batteries LIBs in real life driving scenarios is the key to advancing battery design and management for electric vehicles. This work studies in detail the aging modes of commercial LIBs under real life driving scenarios with a standardized World Harmonized Light Vehicle Test Cycle WLTC discharging procedure. Combined results from electrochemical analyses, post mortem, and operando characterization show that a large depth of DOD 100 leads to significant structural changes, especially Ni O bond length and coordination number, of NMC532 cathode materials and hence rapid degradation related to active material loss, while a low DOD level 45 results in intensified interfacial degradation, both leading to a limited battery cycle life lt;900 and lt;1600 equivalent full cycles EFCs , respectively, under 45 and 100 DoDs . In contrast, a medium DOD 75 results in balanced electrode and interface degradations and significantly enhanced cycling stability gt;2200 EFCs under 75 DoDs . Besides, we also emphasized that in real life driving, the loss of active materials primarily originates from the cathode. These findings reveal that balancing the electrode and interfacial degradations are crucial for extending battery lifetime in practical applications. This work provides mechanistic insights into the degradation of LIBs under real life operating conditions, guiding the rational design and optimization of cycling protocols in battery management systems BMSs for advanced battery developmen
The effect of non stoichiometry in Sb2Se3 films on their phonon and electronic properties in the infrared range
Get PDFDue to the noticeable part of Sb2Se3 films in solar cell technology, the deposition of Sb2Se3 films with the desirable content and improved crystalline perfection is of crucial importance. Therefore, extensive experimental and theoretical studies of the electronic and phonon properties of these materials are of interest. In this work, the stoichiometry and morphology of antimony selenide films are correlated to their optical properties in the far infrared regime and compared to theoretically calculated properties for an ideal crystal. For this study, the reflectance of a series of 1.4 1.7 amp; 956;m thick SbxSey layers, produced on soda lime glass substrates by molecular beam chemical deposition, was measured in the spectral range of 25 5000 cm amp; 8315; using an FT IR spectrometer and synchrotron radiation. The nearsurface and bulk crystallographic structure and phase composition were previously determined using grazing incidence X ray diffraction GIXRD under varying incident angles. The chemical composition and morphology were investigated using scanning electron microscopy SEM and energy dispersive X ray spectroscopy EDX . It was shown that the spectral positions of numerous maxima of the reflectance of SbxSey layers for various x y indices in the phonon excitation range of 25 230 cm amp; 8315; are consistent with the positions of the maxima of the imaginary part of the dielectric function of Sb2Se3 crystals, calculated within the framework of density functional theory. A significant increase in the reflectance values was observed for SbxSey layers containing the largest relative amount of antimony x y, which may be due to the increased content of the metallic form of antimony compared to the amount of the pure Sb2Se3 semiconducting phase. A correlation was found between the technological parameters of production temperature and the final chemical composition and morphology of the SbxSey layers. To explain the observed relationships, calculations of the cohesive energy of Sb2Se3 and Sb crystals and the binding energy of the residual antimony atom inside and on the surface of the antimony selenide supercell were performed. The main conclusions of the theoretical calculations are consistent with the results of EDX and XRD measurements of the SbxSey layer
A framework for evaluating the chemical knowledge and reasoning abilities of large language models against the expertise of chemists
Get PDFLarge language models LLMs have gained widespread interest owing to their ability to process human language and perform tasks on which they have not been explicitly trained. However, we possess only a limited systematic understanding of the chemical capabilities of LLMs, which would be required to improve models and mitigate potential harm. Here we introduce ChemBench, an automated framework for evaluating the chemical knowledge and reasoning abilities of state of the art LLMs against the expertise of chemists. We curated more than 2,700 question answer pairs, evaluated leading open and closed source LLMs and found that the best models, on average, outperformed the best human chemists in our study. However, the models struggle with some basic tasks and provide overconfident predictions. These findings reveal LLMs impressive chemical capabilities while emphasizing the need for further research to improve their safety and usefulness. They also suggest adapting chemistry education and show the value of benchmarking frameworks for evaluating LLMs in specific domain
Initial Stages of Palladium Growth on Vicinal Si 001 2x1 Surfaces
Get PDFThe early growth stages of Palladium Pd on Si 001 have been studied in situ by Reflectance Anisotropy Spectroscopy RAS and Raman spectroscopy in UHV. Two vicinal Si 001 samples with different degrees of surface ordering are investigated, revealing a distinct Volmer Weber type growth behavior. Ex situ Atomic Force Microscopy AFM shows an inhomogeneous surface covered with islands on the less ordered substrate, while a complex layer with circular structures related to a nucleation controlled phase transition as previously reported is found on the well ordered sample. By Raman spectroscopy, a silicide like reacted phase at the Si Pd interface is identified which is promoted by annealing up to 600 C. The appearance of several additional phonon modes due to the interface reaction is in very good agreement with vibrational modes obtained from ab initio calculations for Pd incorporation into Si surface layer
Structured Multilayer Thin Films for Catalytic Applications A Novel Approach on Catalyst Design Utilizing Microfabrication Techniques
Get PDFThe metal metal oxide interface is key to establishing catalytic performance, selectivity, and stability in heterogeneous systems. In this proof of concept study, a systematic methodology is introduced for the preparation of multilayer catalysts that combines Radio Frequency RF magnetron sputtering with laser microstructuring for the synthesis of high density Cu ZnO interfaces. By means of a specifically designed split target, alternating few nanometer thick layers of Cu and ZnO are deposited under precise control and with high reproducibility. Laser scribing is then employed to create defined microstructures that reveal buried interfaces, improving access to catalytically active interfaces. As deposited and laser scribed multilayer s structural and chemical stability is confirmed through Atomic Force Microscopy AFM , X Ray Fluorescence XRF , X Ray Diffraction XRD , X Ray Photoelectron Spectroscopy XPS , and Scanning Electron Microscope SEM characterizations. Catalytic activity is evaluated under gradient free, continuous stirring conditions for CO2 hydrogenation to methanol where the catalyst produces methanol and CO under laboratory scale conditions. The strategy addresses specific design bottlenecks such as limited control over interfacial geometry and exposure while acknowledging the inherent limitations of thin film systems in terms of surface area and scalability. While demonstrated for CO2 to methanol conversion, the method is generally applicable to other interface dependent reactions. Building on this initial demonstration, forthcoming efforts will focus on detailed mechanistic analysis, long duration testing, and performance benchmarking against conventional powder based catalyst
Correlation Effects in van der Waals CrXTe3 Materials X Si, Ge from X ray Spectroscopy Studies
No full textThe recently discovered CrXTe3 X Si, Ge layered ferromagnets are under increased attention for the demonstration of low dimensional ferromagnetism down to the monolayer limit. In the present study, we employ near edge X ray absorption fine structure spectroscopy NEXAFS and resonant photoelectron spectroscopy ResPES at the Cr L2,3 absorption edge accompanied by DFT calculations to gain insights into the electronic structure and electron correlation effects for these compounds. It is found that the 3dn 1 final state in the photoemission spectra is located at the top of the valence band, thus assigning CrXTe3 to the Mott Hubbard state. Moreover, as revealed in NEXAFS and ResPES, significant hybridization between Cr 3d and Te 5p valence band states is found in both compounds, leading to the slightly weaker electron localization in CrGeTe3 as compared to CrSiTe3. Our results bring new insight into the deep understanding of the correlation phenomena in these vdW materials allowing us to draw further ways on the modulation of the correlation effects and magnetic structures in different layered compound