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We demonstrate the possibility of using a CMOS 2D sensor for time-resolved pump–probe XUV FEL experiments. We gained a factor of 30 in acquisition time compared to the use of a commercial CCD-BSI., The latest Complementary Metal Oxide Semiconductor (CMOS) 2D sensors now rival the performance of state-of-the-art photon detectors for optical application, combining a high-frame-rate speed with a wide dynamic range. While the advent of high-repetition-rate hard X-ray free-electron lasers (FELs) has boosted the development of com­plex large-area fast CCD detectors in the extreme ultraviolet (EUV) and soft X-ray domains, scientists lacked such high-performance 2D detectors, principally due to the very poor efficiency limited by the sensor processing. Recently, a new generation of large back-side-illuminated scientific CMOS sensors (CMOS-BSI) has been developed and commercialized. One of these cost-efficient and com­petitive sensors, the GSENSE400BSI, has been implemented and characterized, and the proof of concept has been carried out at a synchrotron or laser-based X-ray source. In this article, we explore the feasibility of single-shot ultra-fast ex­peri­ments at FEL sources operating in the EUV/soft X-ray regime with an AXIS-SXR camera equipped with the GSENSE400BSI-TVISB sensor. We illustrate the detector capabilities by performing a soft X-ray magnetic scattering experiment at the DiProi end-station of the FERMI FEL. These measurements show the possibility of integrating this camera for collecting single-shot images at the 50 Hz operation mode of FERMI with a cropped image size of 700 × 700 pixels. The efficiency of the sensor at a working photon energy of 58 eV and the linearity over the large FEL intensity have been verified. Moreover, on-the-fly time-resolved single-shot X-ray resonant magnetic scattering imaging from prototype Co/Pt multilayer films has been carried out with a time collection gain of 30 com­pared to the classical start-and-stop acquisition method performed with the conventional CCD-BSI detector available at the end-station.

When designing sound packages, often fully filling the available space with acoustic materials is not the most absorbing solution. Better solutions can be obtained by creating cavities of air pockets, but determining the most optimal shape and topology that maximises sound absorption is a computationally challenging task. Many recent topology optimisation applications in acoustics use heuristic methods such as solid-isotropic-material-with-penalisation (SIMP) to quickly find near-optimal solutions. This study investigates seven heuristic and metaheuristic optimisation approaches including SIMP applied to topology optimisation of acoustic porous materials for absorption maximisation. The approaches tested are hill climbing, constructive heuristics, SIMP, genetic algorithm, tabu search, covariance-matrix-adaptation evolution strategy (CMA-ES), and differential evolution. All the algorithms are tested on seven benchmark problems varying in material properties, target frequencies, and dimensions. The empirical results show that hill climbing, constructive heuristics, and a discrete variant of CMA-ES outperform the other algorithms in terms of the average quality of solutions over the different problem instances. Though gradient-based SIMP algorithms converge to local optima in some problem instances, they are computationally more efficient. One of the general lessons is that different strategies explore different regions of the search space producing unique sets of solutions.

The use of Pt-based cathode catalyst materials hinders the widespread application of anion exchange membrane fuel cells (AEMFCs). Herein, we present a non-precious metal catalyst (NPMC) material based on pyrolysed Fe and Co co-doped electrospun carbon nanofibres (CNFs). The prepared materials are studied as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts in alkaline and acidic environments. High activity towards the ORR in alkaline solution indicated the suitability of the prepared NPMCs for the application at the AEMFC cathode. In the AEMFC test, the membrane-electrode assembly bearing a cathode with the nanofibre-based catalyst prepared with the ionic liquid (IL) (Fe/Co/IL–CNF–800b) showed the maximum power density (Pmax) of 195 mW cm−2, which is 78% of the Pmax obtained with a commercial Pt/C cathode catalyst. Such high ORR electrocatalytic activity was attributed to the unique CNF structure, high micro-mesoporosity, different nature of nitrogen species and metal-Nx active centres.

Replacing scarce and expensive platinum (Pt) with metal–nitrogen–carbon (M–N–C) catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells has largely been impeded by the low oxygen reduction reaction activity of M–N–C due to low active site density and site utilization. Herein, we overcome these limits by implementing chemical vapour deposition to synthesize Fe–N–C by flowing iron chloride vapour over a Zn–N–C substrate at 750 °C, leading to high-temperature trans-metalation of Zn–N4 sites into Fe–N4 sites. Characterization by multiple techniques shows that all Fe–N4 sites formed via this approach are gas-phase and electrochemically accessible. As a result, the Fe–N–C catalyst has an active site density of 1.92 × 1020 sites per gram with 100% site utilization. This catalyst delivers an unprecedented oxygen reduction reaction activity of 33 mA cm−2 at 0.90 V (iR-corrected; i, current; R, resistance) in a H2–O2 proton exchange membrane fuel cell at 1.0 bar and 80 °C. Replacing platinum with metal–nitrogen–carbon catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells has been impeded by low activity. These limitations have now been overcome by the trans-metalation of Zn–N4 sites into Fe–N4 sites.

The open porosity of air-saturated acoustical porous materials is estimated from the low-frequency or high-frequency asymptotes of the real part of the dynamic bulk modulus. Combining this technique with the estimation of the static air-flow resistivity from the low-frequency asymptote of the imaginary part of the dynamic mass density and the analytical inversions of the remaining parameters from the dynamic mass density and bulk modulus [methods introduced by Panneton and Olny, J. Acoust. Soc. Am. 119(4), 2027-2040 (2006) and Olny and Panneton 123(2), 814-824 (2008)], this work estimates all six parameters of a Johnson-Champoux-Allard-Lafarge model from impedance tube measurements. A classical two-microphone impedance tube, as well as three- or four-microphone tubes, can be used for these measurements and estimations. Examples of applications and limits of the method are presented and a tool to estimate the open porosity and the static air-flow resistivity is made available online.

Two-dimension (2D) magnets have recently developed into a class of stoichiometric materials with prospective applications in ultra-compact spintronics and quantum computing. Their functionality is particularly rich when different magnetic orders are competing in the same material. Metalloxenes REX2 (RE = Eu, Gd; X = Si, Ge), silicene or germanene — heavy counterparts of graphene — coupled with a layer of rare-earth metals, evolve from three-dimension (3D) antiferromagnets in multilayer structures to 2D ferromagnets in a few monolayers. This evolution, however, does not lead to fully saturated 2D ferromagnetism, pointing at a possibility of coexisting/competing magnetic states. Here, REX2 magnetism is explored with element-selective X-ray magnetic circular dichroism (XMCD). The measurements are carried out for GdSi2, EuSi2, GdGe2, and EuGe2 of different thicknesses down to 1 monolayer employing K absorption edges of Si and Ge as well as M and L edges of the rare-earths. They access the magnetic state in REX2 and determine the seat of magnetism, orbital, and spin contributions to the magnetic moment. High-field measurements probe remnants of the bulk antiferromagnetism in 2D REX2. The results provide a new platform for studies of complex magnetic structures in 2D materials.

The biocompatibility and very high specific area of cellulose nanofibrils (CNF) are properties of high interest for the development of active substrates for new medical device development. Enzyme pretreated CNF (CNF-e) can be self-organized into nanostructured membranes that are suitable for active principle ingredients (API) encapsulation through adsorption phenomena. In addition, tunable surface chemistry of CNF-e, allow for covalent immobilization of API. In this work, ciprofloxacin is integrated to CNF-e membranes according to two different strategies. The first one relies only on adsorption mechanisms; ciprofloxacin is encapsulated in the bulk before the membrane formation by solvent casting. The influence of the membrane properties and preparation parameters such as grammage, thickness and drying technique, are assessed with water uptake measurements and API release experiments. The second strategy deals with the covalent immobilization of ciprofloxacin directly onto CNF-e membrane. The two kinds of membranes are then compared in terms of antibacterial activity, in both static and dynamic conditions. Thick CNF-e membranes loaded with adsorbed ciprofloxacin that were overdried (2 h, 150 °C) prove to be more resistant in liquid medium and present a more prolonged drug release. However, these membranes rapidly lost their antibacterial activity, while CNF-e membranes with covalently immobilized ciprofloxacin remain contact active for several days. These 100% CNF active nanostructured membranes can be used as new wound dressing for topical application.

The incorporation of Pt into an iron-nitrogen-carbon (FeNC) catalyst for the oxygen reduction reaction (ORR) was recently shown to enhance catalyst stability without Pt directly contributing to the ORR activity. However, the mechanistic origin of this stabilisation remained obscure. It is established herein with rotating ring disc experiments that the side product, H2O2, which is known to damage FeNC catalysts, is suppressed by the presence of Pt. The formation of reactive oxygen species is additionally inhibited, independent of intrinsic H2O2 formation, as determined by electron paramagnetic resonance. Transmission electron microscopy identifies an oxidised Fe-rich layer covering the Pt particles, thus explaining the inactivity of the latter towards the ORR. These insights develop understanding of FeNC degradation mechanisms during ORR catalysis, and crucially establish the required properties of a precious metal free protective catalyst to improve FeNC stability in acidic media.

Electrocatalytic conversion of nitrogen oxides to value-added chemicals is a promising strategy for mitigating the human-caused unbalance of the global nitrogen-cycle, but controlling product selectivity remains a great challenge. Here we show iron–nitrogen-doped carbon as an efficient and durable electrocatalyst for selective nitric oxide reduction into hydroxylamine. Using in operando spectroscopic techniques, the catalytic site is identified as isolated ferrous moieties, at which the rate for hydroxylamine production increases in a super-Nernstian way upon pH decrease. Computational multiscale modelling attributes the origin of unconventional pH dependence to the redox active (non-innocent) property of NO. This makes the rate-limiting NO adsorbate state more sensitive to surface charge which varies with the pH-dependent overpotential. Guided by these fundamental insights, we achieve a Faradaic efficiency of 71% and an unprecedented production rate of 215 μmol cm−2 h−1 at a short-circuit mode in a flow-type fuel cell without significant catalytic deactivation over 50 h operation., Electrocatalytic conversion of nitrogen oxides to value-added chemicals is a promising strategy for mitigating the imbalance in the global nitrogen cycle. Here, the authors present iron–nitrogen-doped carbon as an efficient and durable electrocatalyst for selective nitric oxide reduction to hydroxylamine.

International audience; Precious metal-free catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells are gaining momentum, with Fe-N-C catalysts comprising atomic FeN x sites the most promising candidate. Research and development is shifting from activity targets to improved stability of Fe-N-C catalysts in fuel cells. Their durability has hitherto been extensively studied using accelerated stress tests (AST) performed at room temperature and in inert-gas saturated acidic pH electrolyte. Here, we reveal stronger degradation of the Fe-N-C structure and four times higher ORR activity loss when performing load cycling AST in O2-vs. Ar-saturated pH 1 electrolyte. Raman spectroscopy results point towards strong carbon corrosion after AST in O2 , even when cycling at low potentials of 0.3-0.7 V vs. the reversible hydrogen electrode, while no corrosion occurred after any load cycling AST in Ar. The load cycling AST in O2 leads to the loss of a significant fraction of FeN x sites, as shown by energy dispersive X-ray spectroscopy analyses, and to the formation of Fe oxides. The results support that the unexpected carbon corrosion occurring at such low potential in the presence of O2 is due to reactive oxygen species produced between H 2 O 2 and Fe sites via Fenton reactions.

International audience; We report a comprehensive analysis of the catalytic oxygen reduction reaction (ORR) reactivity of four of today's most active benchmark platinum group metal-free (PGM-free) iron/nitrogen doped carbon electrocatalysts (Fe-N-Cs). Our analysis reaches far beyond previous such attempts in linking kinetic performance metrics, such as electrocatalytic mass-based and surface area-based catalytic activity with previously elusive kinetic metrics such as the active metal site density (SD) and the catalytic turnover frequency (TOF). Kinetic ORR activities, SD and TOF values were evaluated using in situ electrochemical NO 2 À reduction as well as an ex situ gaseous CO cryo chemisorption. Experimental ex situ and in situ Fe surface site densities displayed remarkable quantitative congruence. Plots of SD versus TOF (''reactivity maps'') are utilized as new analytical tools to deconvolute ORR reactivities and thus enabling rational catalyst developments. A microporous catalyst showed large SD values paired with low TOF, while mesoporous catalysts displayed the opposite. Trends in Fe surface site density were linked to molecular nitrogen and Fe moieties (D1 and D2 from 57 Fe Mössbauer spectroscopy), from which pore locations of catalytically active D1 and D2 sites were established. This cross-laboratory analysis, its employed experimental practices and analytical methodologies are expected to serve as a widely accepted reference for future, knowledge-based research into improved PGM-free fuel cell cathode catalysts. Broader context Polymer electrolyte membrane fuel cells (PEMFC) have reached the commercial stage and ever wider deployment is imminent. To further reduce the loading of platinum group metal (PGM) catalysts in PEMFC electrodes, PGM-free, iron and nitrogen-doped carbon oxygen reduction (ORR) electrocatalysts (Fe-N-C) were developed over past decades. Recent advances in activity and stability of Fe-N-C are impressive, yet methods to evaluate the number of catalytic active Fe sites at the surface and intrinsic turn over frequency remained elusive. This changed with the advent of CO cryo-sorption and in situ nitrite stripping techniques that yielded these intrinsic reactivity descriptors. Never before, however, have these two complementary specific adsorption/stripping techniques been compared and combined with other chemical and spectroscopic analytics for an in-depth analysis of catalytic reactivity of Fe-N-C ORR electrocatalysts. The present study addresses this issue and presents a comprehensive analysis of the reactivity of the four state-of-the-art Fe-N-C PEMFC electrocatalysts. The study provides a deeper understanding of the origin and difference in catalytic performance through the combination of a host of different surface sensitive and bulk analysis methods. The methodologies and analyses of this benchmark catalyst study will benefit future developments in Fe-N-C catalysis.

International audience; M-N-C electrocatalysts (where M is Fe or Co) have been investigated for mitigating the dependence on noble metals when catalyzing the oxygen reduction reaction (ORR) for fuel cell technologies in acidic or alkaline conditions. Rotating disc and rotating ring-disk electrodes measurements for Fe-N-C and CoN -C catalysts demonstrate promising performances and stability for the ORR, while the activity of main suspected active sites (M-NxCy and M@N-C) has been discussed on the basis of the known physical-chemical properties of the catalysts in acid and alkaline media. Thereupon, it is observed that atomically-dispersed Fe-NxCy sites reach the highest ORR activity in acid media when amplified by an adequate energy binding between the metallic center and the oxygenated reaction intermediates. In contrast, Fe@N-C core-shell sites reach a maximum ORR mass activity in alkaline media through a synergistic effect involving catalyst particles with metallic iron in the core and nitrogen-doped carbon in the shell.

Iron- and nitrogen-doped carbon-based catalysts are one of the most promising alternatives to platinum-group metal-based ones currently used in the fuel cell industry. Here, we study the effect of ...

Metal–nitrogen–carbon catalysts have emerged as the most promising platinum group metal-free catalysts toward oxygen reduction reaction for proton exchange membrane fuel cell (PEMFC) applications. ...

We propose a new method for the progressive enhancement of images degraded by noise and blur using shock filters. The originality of our approach lies in the iterative exploitation of nonconservative edge-based force fields normally designed for segmentation to determine both locations and amplitudes of the sharpening action. The proposed nonconservative shock filter (NCSF) produces images with strong discontinuities that can be used as an additional pre-processing step to facilitate higher level tasks such as edge detection or segmentation. NCSF is especially useful when coupled with an anisotropic diffusion equation in noisy configurations. Using the proposed method, edges that are not well defined prior to filtering can be iteratively recovered. We show processing results on various types of images, focusing on medical transrectal ultrasound and brain PET imaging.

The number of catalytically active sites (site density, SD) and the catalytic turnover frequency (TOF) are critical for meaningful comparisons between catalytic materials and their rational improvement. SD and TOF numbers have remained elusive for PGM-free, metal/nitrogen-doped porous carbon electrocatalysts (MNC), in particular, FeNC materials that are now intensively investigated and widely utilized to catalyze the oxygen reduction reaction (ORR) in fuel cell cathodes. Here, we apply CO cryo sorption and desorption to evaluate SD and TOF numbers of a state-of-art FeNC ORR electrocatalyst with atomically dispersed coordinative FeNx (x ≤ 4) sites in acid and alkaline conditions. More specifically, we study the impact of thermal pretreatment conditions prior to assessing the number of sorption-active FeNx sites. We show that the pretreatment temperature sensitively affects the CO sorption uptake through a progressive thermal removal of airborne adsorbates, which, in turn, controls the resulting catalytic S...

International audience; The electrochemical behavior of osmociphenol (3, Oc-OH), an organometallic osmium-based anticancer drug candidate, has been investigated by cyclic voltammetry in the absence and presence of lutidine used as a base model. Osmociphenol exhibited spontaneous deprotonation of the phenol function upon oxidation of the osmocene moiety due to its high acidity. In the presence of lutidine, a base-dependent and different electrochemical behavior was observed at low scan rates indicating a second oxidation step leading to the corresponding cationic quinone methide precursor (3b +). However, compared to ruthenocene derivatives, the stability of 3b + prevented its conversion into quinone methide as the final and stable complex. Despite differences in their oxidative processes, osmociphenol and ruthenociphenol derivatives exhibit similar biological activities.

International audience; Fe phthalocyanine was coordinated to pyridine-modified carbon nanotubes and studied as a catalyst for the oxygen reduction (ORR) and oxygen evolution reactions (OER). X-ray Photoelectron Spectroscopy (XPS), Mössbauer, and Electron Paramagnetic Resonance spectroscopy (EPR) analysis supported that pyridine acts as an axial ligand to yield penta-coordinated catalytic active Fe sites. The impedance analyses show an increase in the double-layer capacitance (Cdl) value, corroborating the adsorption of the complexes to give FePc-Py-CNT. The evaluation of the electrocatalytic activity for the ORR was performed in both acid (0.1 M H2SO4) and basic (0.1 M KOH) media, while the evaluation of the OER activity was investigated only in alkaline medium. DFT studies revealed an increased length in the Fe-N binding of the pentacoordinate Fe-based site, leading to a decreased O2-Fe binding energy, explaining the higher ORR and OER activity of FePc-Py-CNT relative to FePc-CNT.

We have examined the electrocatalytic activity of iron phthalocyanine (FePc) and perchlorinated iron phthalocyanine 16(Cl)FePc for the oxygen reduction reaction (ORR) in alkaline medium with the two molecules either adsorbed on the external surface of single-wall carbon nanotubes (SWCNT) or covalently anchored via an axial pyridine ligand on pyridine-functionalized single-wall carbon nanotubes (py-SWCNT). Regardless of the particular phthalocyanine type, the ORR activity is higher when the substrate is py-SWCNT rather than SWCNT. The Tafel slopes for ORR are very similar for the two Fe macrocyclic complexes attached to SWCNTs in the two different configurations, suggesting a common rate-determining step for the ORR for all four catalysts. It is also observed that, for both the SWCNT and py-SWCNT supports, the ORR activity is higher for 16(Cl)FePc than for FePc. This is attributed to the electron-withdrawing effect of the peripheral and non-peripheral chlorine atoms in the macrocyclic ligand. While FeN4 macrocycles are known to be located on the strong binding side of a volcano correlation including several MN4 species, the chlorine substituents decrease the binding energy of O2 on the central Fe cation, thereby moving up the macrocycle catalyst towards the apex of the volcano correlation. Both the carbon surface and macrocyclic ligand effects were optimized with 16(Cl)FePc attached to py-SWCNT, which is more active than both FePc on SWCNT and FePc on py-SWCNT. Here we show that both the axial ligand and the electron withdrawing groups (-Cl) have a combined collaborative effect in increasing the catalytic activity for ORR of Fe-phthalocyanines confined on the external walls of single-wall carbon nanotubes.

International audience; The Big Data era requires new processing architectures, among which streaming systems which have become very popular. Those systems are able to summarize infinite data streams with aggregates on the most recent data. However, up to now, only point events have been considered and spanning events, which come with a duration, have been let aside, restricted to the persistent databases world only. In this paper, we propose a unified framework to deal with such stream mechanisms on spanning events. To this end, we formally define a spanning event stream with new stream semantics and events properties, particularly considering how the event is received. We then review and extend usual stream windows to meet the new spanning event requirements. Eventually, we validate the soundness of our new framework with a set of experiments, based on a straightforward implementation, showing that aggregation of spanning event stream is providing as much new insight on the data as effectiveness in several use cases.

Noncollinear chiral spin textures in ferromagnetic multilayers are at the forefront of recent research in nano-magnetism with the promise for fast and energy-efficient devices. The recently demonstrated possibilities to stabilize such chiral structures in synthetic antiferromagnets (SAF) has raised interests as they are immune to dipolar field, hence favoring the stabilization of ultra small textures, improve mobility and avoid the transverse deflections of moving skyrmions limiting the efficiency in some foreseen applications. However, such systems with zero net magnetization are hence difficult to characterize by most of the standard techniques. Here, we report that the relevant parameters of a magnetic SAF texture, those being its period, its type (N\'eel or Bloch) and its chirality (clockwise or counterclockwise), can be directly determined using the circular dichroism in x-ray resonant scattering (CD-XRMS) at half integer multilayer Bragg peaks in reciprocal space. The analysis of the dependence in temperature down to 40K allows us moreover to address the question of the temperature stability of a spin spiral in a SAF sample and of the temperature scaling of the symmetric and antisymmetric exchange interactions.

The electrochemical reduction of CO2 (eCO2RR) using renewable energy is an effective approach to pursue carbon neutrality. The eCO2RR to CO is indispensable in promoting C-C coupling through bifunctional catalysis and achieving cascade conversion from CO2 to C2+. This work investigates a series of M/N-C (M = Mn, Fe, Co, Ni, Cu, and Zn) catalysts, for which the metal precursor interacted with the nitrogen-doped carbon support (N-C) at room temperature, resulting in the metal being present as (sub)nanosized metal oxide clusters under ex situ conditions, except for Cu/N-C and Zn/N-C. A volcano trend in their activity toward CO as a function of the group of the transition metal is revealed, with Co/N-C exhibiting the highest activity at -0.5 V versus RHE, while Ni/N-C shows both appreciable activity and selectivity. Operando X-ray absorption spectroscopy shows that the majority of Cu atoms in Cu/N-C form Cu0 clusters during eCO2RR, while Mn/, Fe/, Co/, and Ni/N-C catalysts maintain the metal hydroxide structures, with a minor amount of M0 formed in Fe/, Co/, and Ni/N-C. The superior activity of Fe/, Co/, and Ni/N-C is ascribed to the phase contraction and the HCO3- insertion into the layered structure of metal hydroxides. Our work provides a facile synthetic approach toward highly active and selective electrocatalysts to convert CO2 into CO. Coupled with state-of-the-art NiFe-based anodes in a full-cell device, Ni/N-C exhibits >80% Faradaic efficiency toward CO at 100 mA cm-2., The research leading to these results has received funding from the A-LEAF Project, which is funded by the European Union’s H2020 Programme under grant agreement no. 732840. ICN2 and ICIQ acknowledge funding from the FEDER/Ministerio de Ciencia e Innovación, Agencia Estatal de Investigación (projects ENE2017-85087-C3 and RTI2018-095618-B-I00) and the Generalitat de Catalunya (2017 SGR 327 and 2017- SGR-1406) and by the CERCA Programme / Generalitat de Catalunya. ICN2 and ICIQ are supported by the Severo Ochoa program from Spanish MINECO (grants no. SEV-2017-0706 and CEX2019-000925-S).

Black phosphorus is a quasi-two-dimensional layered semiconductor with a narrow direct band gap of 0.3 eV. A giant surface Stark effect can be produced by the potassium doping of black phosphorus, leading to a semiconductor to semimetal phase transition originating from the creation of a strong surface dipole and associated band bending. By using time- and angle-resolved photoemission spectroscopy, we report the partial photoinduced screening of this band bending by the creation of a compensating surface photovoltage. We further resolve the detailed dynamics of this effect at the pertinent timescales and the related evolution of the band structure near the Fermi level. We demonstrate that after a fast rise time, the surface photovoltage exhibits a plateau over a few tens of picoseconds before decaying on the nanosecond timescale. We support our experimental results with simulations based on drift-diffusion equations., 18 pages, 12 figures

Structural dynamics 8(3), 034305 (1-9) (2021). doi:10.1063/4.0000109, During the last two decades, a variety of models have been developed to explain the ultrafast quenching of magnetization following femtosecond optical excitation. These models can be classified into two broad categories, relying either on a local or a non-local transfer of angular momentum. The acquisition of the magnetic depth profiles with femtosecond resolution, using time-resolved x-ray resonant magnetic reflectivity, can distinguish local and non-local effects. Here, we demonstrate the feasibility of this technique in a pump–probe geometry using a custom-built reflectometer at the FLASH2 free-electron laser (FEL). Although FLASH2 is limited to the production of photons with a fundamental wavelength of 4 nm (≃310 eV), we were able to probe close to the Fe $L_3$ edge (706.8 eV) of a magnetic thin film employing the third harmonic of the FEL. Our approach allows us to extract structural and magnetic asymmetry signals revealing two dynamics on different time scales which underpin a non-homogeneous loss of magnetization and a significant dilation of 2 Å of the layer thickness followed by oscillations. Future analysis of the data will pave the way to a full quantitative description of the transient magnetic depth profile combining femtosecond with nanometer resolution, which will provide further insight into the microscopic mechanisms underlying ultrafast demagnetization, Published by AIP Publishing LLC, Melville, NY

We present a combined angle-resolved photoemission spectroscopy and low-energy electron diffraction (LEED) study of the prominent transition metal dichalcogenide ${\mathrm{IrTe}}_{2}$ upon potassium (K) deposition on its surface. Pristine ${\mathrm{IrTe}}_{2}$ undergoes a series of charge-ordered phase transitions below room temperature that are characterized by the formation of stripes of Ir dimers of different periodicities. Supported by density functional theory calculations, we first show that the K atoms dope the topmost ${\mathrm{IrTe}}_{2}$ layer with electrons, therefore strongly decreasing the work function and shifting only the electronic surface states towards higher binding energy. We then follow the evolution of its electronic structure as a function of temperature across the charge-ordered phase transitions and observe that their critical temperatures are unchanged for K coverages of 0.13 and 0.21 monolayer. Using LEED we also confirm that the periodicity of the related stripe phases is unaffected by the K doping. We surmise that the charge-ordered phase transitions of ${\mathrm{IrTe}}_{2}$ are robust against electron surface doping, because of its metallic nature at all temperatures, and due to the importance of structural effects in stabilizing charge order in ${\mathrm{IrTe}}_{2}$.

This work presents a prediction model for rolling noise in multi-story buildings, such as that generated by a rolling delivery trolley. Until now, mechanical excitation in multi-story buildings has been limited to impact sources such as the tapping machine. Rolling noise models have been limited to outdoor sources such as trains and automotive vehicles. The model presented here is able to represent the physical phenomena unique to indoor rolling noise, taking into account influencing factors such as the roughness of the wheel and the floor, the material and geometric properties of the wheel and the floor, the rolling velocity of the trolley, and the load on the trolley. The model may be used as a tool to investigate how different flooring systems (including multi-layer systems) respond to rolling excitation, for the purpose of developing multi-story building solutions which are better equipped to combat this kind of noise source.

We present a numerical algorithm for the simulation of resonant x-ray magnetic scattering in reflection geometry for an arbitrary three-dimensional magnetization distribution over a multilayer sample utilizing the distorted-wave Born approximation. Our approach takes the medium boundary matrix approach for specular reflection, and the Born approximation typically used for off-specular reflection, combines the two, and adds the contribution from transmission through the sample before and after a reflection event. The algorithm is then tested on experimental data from an ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$/Co/Pt multilayer sample with hybrid N\'eel/Bloch/N\'eel domain walls at incidence angles at and near multilayer Bragg angles, and photon energies near the Co ${L}_{3}$ absorption edge, achieving high levels of agreement with experimental data. Incorporating the transmission components into the algorithm was found to explain the dichroism observed in scattering from Bloch-type domain walls, and uncovered the likely importance of diffuse scattering in transmission from the polycrystalline grain walls along the optical path of the x rays in the sample---a theme which deserves further investigation.

Simple Summary One of the primary causes of chemotherapy failure is the occurrence of cancer multidrug resistance (MDR). Uncontrolled growth of resistant tumor cells leads to metastasis and recurrence, associated with high mortalities. Ferrocifens have been shown to possess anticancer properties via an original mechanism dependent on redox properties and generation of active metabolites that can cause disruption of cell metabolism. However, these molecules are highly insoluble in water, requiring a formulation stage before being administered in vivo. Lipid nanocapsules (LNCs) have already demonstrated their ability to successfully encapsulate various hydrophobic therapeutic agents, such as ferrocifens, and offer the option of surface modification, making it possible to adapt the pharmacological behavior of the nanocarrier. The aim of this review is to give, for the first time, an overview of the in vitro and in vivo studies performed with ferrocifen-loaded LNCs on several MDR cancers. Abstract Resistance of cancer cells to current chemotherapeutic drugs has obliged the scientific community to seek innovative compounds. Ferrocifens, lipophilic organometallic compounds composed of a tamoxifen scaffold covalently bound to a ferrocene moiety, have shown very interesting antiproliferative, cytotoxic and immunologic effects. The formation of ferrocenyl quinone methide plays a crucial role in the multifaceted activity of ferrocifens. Lipid nanocapsules (LNCs), meanwhile, are nanoparticles obtained by a free organic solvent process. LNCs consist of an oily core surrounded by amphiphilic surfactants and are perfectly adapted to encapsulate these hydrophobic compounds. The different in vitro and in vivo experiments performed with this ferrocifen-loaded nanocarrier have revealed promising results in several multidrug-resistant cancer cell lines such as glioblastoma, breast cancer and metastatic melanoma, alone or in combination with other therapies. This review provides an exhaustive summary of the use of ferrocifen-loaded LNCs as a promising nanomedicine, outlining the ferrocifen mechanisms of action on cancer cells, the nanocarrier formulation process and the in vivo results obtained over the last two decades.

The SOLEIL synchrotron radiation source is regularly operated in special filling modes dedicated to pump–probe experiments. Among others, the low-α mode operation is characterized by shorter pulse duration and represents the natural bridge between 50 ps synchrotron pulses and femtosecond experiments. Here, the capabilities in low-α mode of the experimental set-ups developed at the TEMPO beamline to perform pump–probe experiments with soft X-rays based on photoelectron or photon detection are presented. A 282 kHz repetition-rate femtosecond laser is synchronized with the synchrotron radiation time structure to induce fast electronic and/or magnetic excitations. Detection is performed using a two-dimensional space resolution plus time resolution detector based on microchannel plates equipped with a delay line. Results of time-resolved photoelectron spectroscopy, circular dichroism and magnetic scattering experiments are reported, and their respective advantages and limitations in the framework of high-time-resolution pump–probe experiments compared and discussed. Fil: Silly, Mathieu G.. Synchrotron Soleil; Francia Fil: Ferte, Tom. Synchrotron Soleil; Francia Fil: Tordeux, Marie Agnes. Synchrotron Soleil; Francia Fil: Pierucci, Debora. Synchrotron Soleil; Francia Fil: Beaulieu, Nathan. Synchrotron Soleil; Francia Fil: Chauvet, Christian. Synchrotron Soleil; Francia Fil: Pressacco, Federico. Synchrotron Soleil; Francia Fil: Sirotti, Fausto. Synchrotron Soleil; Francia Fil: Popescu, Horia. Synchrotron Soleil; Francia Fil: Lopez Flores, Victor. Synchrotron Soleil; Francia Fil: Tortarolo, Marina del Carmen. Synchrotron Soleil; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sacchi, Maurizio. Universite de Paris Vi. Institut des Nanosciences de Paris; Francia Fil: Jaouen, Nicolas. Synchrotron Soleil; Francia Fil: Hollander, Philippe. Synchrotron Soleil; Francia Fil: Ricaud, Jean Paul. Synchrotron Soleil; Francia Fil: Bergeard, Nicolas. Synchrotron Soleil; Francia Fil: Boeglin, Christine. Synchrotron Soleil; Francia Fil: Tudu, Bharati. Synchrotron Soleil; Francia Fil: Delaunay, Renaud. Universite de Paris VI; Francia Fil: Luning, Jan. Universite de Paris VI; Francia Fil: Malinowski, Gregory. Synchrotron Soleil; Francia Fil: Hehn, Michel. Synchrotron Soleil; Francia Fil: Baumier, Cedric. Université Paris Sud; Francia Fil: Fortuna, Franck. Université Paris Sud; Francia Fil: Krizmancic, Damjan. Elettra - Synchrotron Light Laboratory; Italia Fil: Stebel, Luigi. Elettra - Synchrotron Light Laboratory; Italia Fil: Sergo, Rudi. Elettra - Synchrotron Light Laboratory; Italia Fil: Cautero, Giuseppe. Elettra - Synchrotron Light Laboratory; Italia

Non-collinear spin textures in ferromagnetic ultrathin films are attracting a renewed interest fueled by possible fine engineering of several magnetic interactions, notably the interfacial Dzyaloshinskii-Moriya interaction. This allows the stabilization of complex chiral spin textures such as chiral magnetic domain walls (DWs), spin spirals, and magnetic skyrmions. We report here on the ultrafast behavior of chiral DWs after optical pumping in perpendicularly magnetized asymmetric multilayers, probed using time-resolved circular dichroism in x-ray resonant magnetic scattering (CD-XRMS). We observe a picosecond transient reduction of the CD-XRMS, which is attributed to the spin current-induced coherent and incoherent torques within the continuously dependent spin texture of the DWs. We argue that a specific demagnetization of the inner structure of the DW induces a flow of hot spins from the interior of the neighboring magnetic domains. We identify this time-varying change of the DW textures shortly after the laser pulse as a distortion of the homochiral N'eel shape toward a transient mixed Bloch-N\'eel-Bloch textures along a direction transverse to the DW. Our study highlights how time-resolved CD-XRMS can be a unique tool for studying the time evolution in other systems showing a non-collinear electric/magnetic ordering such as skyrmion lattices, conical/helical phases, as well as the recently observed antiskyrmion lattices, in metallic or insulating materials.

International audience; Fe–N–C aerogel catalysts were prepared by sol–gel polycondensation of resorcinol, melamine and formaldehyde precursors in the presence of FeCl3 salt, followed by supercritical drying and thermal treatments. The effect of the mass ratio of precursors on the microstructure, iron speciation and oxygen reduction reaction (ORR) performance of the Fe–N–C aerogels was investigated by N2 sorption, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, X-ray absorption spectroscopy, CO chemisorption and rotating disk electrode in acidic medium. The best ORR performance (activity and mass transport) was obtained by an optimum balance between pore structure and active Fe-Nx species. Through acid washing, the durability of the catalyst was further improved by eliminating unstable and inactive species, particularly iron nanoparticles and iron carbide. From the CO chemisorption and turnover-frequency value, the surface sites were comparable with the highest values reported in literature. Finally, Fe–N–C aerogel catalyst was implemented a in membrane–electrode assembly with an active area of 25 cm2 and tested in single cell, emphasizing the importance of the ink formulation on the performance.

International audience; One of the most important needs for the future of low-cost fuel cells is the development of highly active platinum group metal (PGM)-free catalysts. For the oxygen reduction reaction, Fe–N–C materials have been widely studied in both acid and alkaline media. However, reported catalysts in the literature show quite different intrinsic activity and in-cell performance, despite similar synthesis routes and precursors. Here, two types of Fe–N–C are prepared from the same precursor and procedure – the main difference is how the precursor was handled prior to use. It is shown that in one case Fe overwhelmingly existed as highly active single-metal atoms in FeN4 coordination (preferred), while in the other case large Fe particles coexisting with few single metal atoms were obtained. As a result, there were drastic differences in the catalyst structure, activity, and especially in their performance in an operating anion exchange membrane fuel cell (AEMFC). Additionally, it is shown that catalyst layers created from single-atom-dominated Fe–N–C can have excellent performance and durability in an AEMFC using H2/O2 reacting gases, achieving a peak power density of 1.8 W cm−2 – comparable to similar AEMFCs with a Pt/C cathode – and being able to operate stably for more than 100 h. Finally, the Fe–N–C cathode was paired with a low-loading PtRu/C anode electrode to create AEMFCs (on H2/O2) with a total PGM loading of only 0.135 mg cm−2 (0.090 mgPt cm−2) that was able to achieve a very high specific power of 8.4 W mgPGM−1 (12.6 W mgPt−1)

International audience; The membrane electrode assembly (MEA) is a core component of low-temperature fuel cells. The first step of MEA manufacturing is the preparation of a catalyst ink suspension in which the catalyst powder is homogeneously dispersed in a liquid solvent through mechanical or sonic agitation. In this work, we have studied the effects of catalyst dispersion in water or alcohol solutions and subsequent drying processes on the physicochemical properties of Fe-N-C catalysts and their electrocatalytic oxygen reduction activities. We find that dispersing the model Fe-N-C catalyst comprising only FeNxCy moieties in water and subsequent drying treatment change neither its bulk structure nor surface composition, as indicated by various spectroscopic measurements before and after treatment. However, zeta potential measurements, which are very sensitive to the chemistry of functionalities present on the carbon surface, reveal that the Fe-N-C catalyst becomes slightly more acidic, and that the change in their acido-basicity is magnified with a) increasing treatment temperature and b) repetitions of a same wetting/drying treatment. This small change in the surface acido-basicity of the Fe-N-C catalyst results in a measurable and reproducible decrease in its electrocatalytic activity, which shows a positive correlation with the zeta potential changes measured at pH = 1. Observed on the Fe-N-C catalyst but not on Pt/C, it is surmised that the electrocatalytic activities of the oxygen-reducing FeNxCy moieties are influenced by the surface chemistry of the carbonaceous support. Since catalyst wetting and drying processes are essential for MEA fabrication for fuel cells, these results suggest that careful attention should be paid to the conditions employed to prepare and dry catalytic inks for the family of Fe-N-C catalysts in order to obtain their highest possible ORR activity.

Equivalent or condensed plate models are being used in various industries to reduce the computation time in finite element modelling. Out of the available equivalent plate models, the model developed by J.L. Guyader in 1978 exhibits high agreement with Lamb wave theory but it requires some time for implementation. Therefore, in this paper, a simple model is proposed to quickly compute the dynamic equivalent parameters of a three-layer sandwich panel. Although the model is formulated from only four parameters, which could be easily computed via the asymptotic and transition behaviours of the sandwich panel, it is shown to be able to capture the equivalent dynamic response for the entire frequency range.

International audience; Iron and nitrogen doping of carbon materials is one of the promising pathways towards replacing Pt/C in polymer electrolyte fuel cell cathodes. Here, we show a synthesis method to produce highly active non-precious metal catalysts and study the effect of synthesis parameters on the oxygen reduction reaction (ORR) activity in high-pH conditions. The electrocatalysts are prepared by functionalizing silicon carbide-derived carbon (SiCDC) with 1,10-phenanthroline, iron(II)acetate and, optionally polyvinylpyrrolidone, by ball-milling with ZrO2 in dry or wet conditions, followed by pyrolysis at 800 °C. The catalysts are characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, N2 physisorption and inductively coupled plasma mass spectrometry. By optimizing the ball-milling conditions, we achieved a reduction in the size of SiCDC grains from >1 μm to 200 nm without negatively affecting the high BET area of catalysts derived from SiCDC. This resulted in increased ORR activity in both rotating disk electrode and anion exchange membrane fuel cell (AEMFC) environments, and improved mass-transport properties of the cathode layer in fuel cell. The ORR activity at 0.9 V in AEMFC of the optimized iron and nitrogen-doped SiCDC reaches 52 mA cm−2, exceeding that of a Pt/C cathode at 36.5 mA cm−2.

The impressive progress in the performance of synchrotron radiation sources is nowadays driven by the so-called `ultimate storage ring' projects which promise an unprecedented improvement in brightness. Progress on the detector side has not always been at the same pace, especially as far as soft X-ray 2D detectors are concerned. While the most commonly used detectors are still based on microchannel plates or CCD technology, recent developments of CMOS (complementary metal oxide semiconductor)-type detectors will play an ever more important role as 2D detectors in the soft X-ray range. This paper describes the capabilities and performance of a camera equipped with a newly commercialized backside-illuminated scientific CMOS (sCMOS-BSI) sensor, integrated in a vacuum environment, for soft X-ray experiments at synchrotron sources. The 4 Mpixel sensor reaches a frame rate of up to 48 frames s−1 while matching the requirements for X-ray experiments in terms of high-intensity linearity (>98%), good spatial homogeneity (−), and low readout noise (down to 2 e− r.m.s.) and dark current (3 e− per second per pixel). Performance evaluations in the soft X-ray range have been carried out at the METROLOGIE beamline of the SOLEIL synchrotron. The quantum efficiency, spatial resolution (24 line-pairs mm−1), energy resolution (

International audience; Transition metal dichalcogenides (TMDs) display a rich variety of instabilities such as spin and charge orders, Ising superconductivity, and topological properties. Their physical properties can be controlled by doping in electric double‐layer field‐effect transistors (FET). However, for the case of single layer NbSe2, FET doping is limited to ≈1 × 1014 cm−2, while a somewhat larger charge injection can be obtained via deposition of K atoms. Here, by performing angle‐resolved photoemission spectroscopy, scanning tunneling microscopy, quasiparticle interference measurements, and first‐principles calculations it is shown that a misfit compound formed by sandwiching NbSe2 and LaSe layers behaves as a NbSe2 single layer with a rigid doping of 0.55–0.6 electrons per Nb atom or ≈6 × 1014 cm−2. Due to this huge doping, the 3 × 3 charge density wave is replaced by a 2 × 2 order with very short coherence length. As a tremendous number of different misfit compounds can be obtained by sandwiching TMDs layers with rock salt or other layers, this work paves the way to the exploration of heavily doped 2D TMDs over an unprecedented wide range of doping.

While the Anion Exchange Membrane Fuel Cell (AEMFC) is gaining interest due to high power performance recently achieved with platinum-group-metal (PGM) catalysts, its implementation will require high-performing PGM-free cathodes. FeNC catalysts have shown high activity and stability for the Oxygen Reduction Reaction (ORR) in alkaline electrolyte; however, the production of hydrogen peroxide during ORR can lead to premature degradation of FeNC and ionomer. In order to minimize the amount of peroxide formed on FeNC, α-MnO2, β-MnO2, δ-MnO2 and α-Mn2O3 were investigated as co-catalysts, with the aim of increasing the apparent activity of FeNC-based cathodes for the hydrogen peroxide reduction reaction (HPRR). The specific activity of α-Mn2O3 for the HPRR was distinctly superior to the other Mn-oxides. The four Mn-oxides were mixed with a FeNC catalyst comprising atomically-dispersed FeNx sites, showing higher HPRR activity and higher four-electron ORR selectivity than FeNC alone. The stability of α-Mn2O3/FeNC was studied operando by on-line inductively-coupled plasma mass spectrometry, to evaluate the potential and time dependent leaching of Mn and Fe. Finally, FeNC and α-Mn2O3/FeNC were applied at the cathode of AEMFCs, both achieving similar or higher current density at 0.9 V than a Pt/C commercial cathode, and peak power densities of ca. 1 W·cm−2.

While Fe-N-C materials are a promising alternative to platinum for catalyzing oxygen reduction in acidic polymer fuel cells, limited understanding of their operando degradation restricts rational approaches towards improved durability. Here we show that Fe-N-C catalysts initially comprising two distinct FeNx sites (S1 and S2) degrade via the transformation of S1 into iron oxides while the structure and number of S2 were unmodified. Structure-activity correlations drawn from end-of-test 57Fe Mössbauer spectroscopy reveal that both sites initially contribute to the ORR activity but only S2 significantly contributes after 50 h of operation. From in situ 57Fe Mössbauer spectroscopy in inert gas coupled to calculations of the Mössbauer signature of FeNx moieties in different electronic states, we identify S1 to be a high-spin FeN4C12 moiety and S2 a low- or intermediate spin FeN4C10 moiety. These insights lay the ground for rational approaches towards Fe-N-C cathodes with improved durability in acidic fuel cells.

Electrocatalysts for the oxygen reduction reaction within polymer electrolyte membrane fuel cells based on iron, nitrogen, and carbon elements (Fe–N–C) have received significant research attention ...

This paper shows how the detailed dispersion of the giant Rashba split surface states in the ferroelectric \ensuremath{\alpha}--GeTe(111) can be resolved by static ARPES and surface potassium doping. The authors further confirm the Rashba mechanism for these states by moving them into the occupied part of the band structure, in good agreement with state of the art DFT calculations.

PGM-free catalysts have high initial activity for O2 reduction reaction, but they suffer from low stability in acid medium in proton exchange membrane fuel cells (PEMFC) and direct methanol fuel ce...

Morphology and porosity are crucial aspects for designing electrodes with facile transport of electrons, ions and matter, which is a key parameter for electrochemical energy storage and conversion. Carbon nanofibers (CNFs) prepared by electrospinning are attractive for their high aspect ratio, inter-fiber macroporosity and their use as self-standing electrodes. The present work compares several strategies to induce intra-fiber micro-mesoporosity in self-standing CNF webs prepared by electrospinning polyacrylonitrile (PAN). Two main strategies were investigated, namely i) a templating method based on the addition of a porogen (polymethyl methacrylate, polyvinylpyrrolidone, Nafion&reg, or ZnCl2) in the electrospinning solution of PAN, or ii) the activation in ammonia of previously formed CNF webs. The key result of this study is that open intra-fiber porosity could be achieved only when the strategies i) and ii) were combined. When each approach was applied separately, only closed intra-fiber porosity or no intra-fiber porosity was observed. In contrast, when both strategies were used in combination all CNF webs showed high mass-specific areas in the range of 325 to 1083 m2&middot, g&minus, 1. Selected webs were also characterized for their carbon structure and electrical conductivity. The best compromise between high porosity and high electrical conductivity was identified as the fibrous web electrospun from PAN and polyvinylpyrrolidone.

Anion-exchange membrane fuel cells (AEMFCs) show remarkable and rapid progress in performance, significantly increasing the relevance for research on electrocatalysis of the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) for this technology. Since much of the recent progress in AEMFC performance can be tied to the improved interface between anion-exchange ionomers (AEIs) and catalysts, this topic deserves specific attention. This work reports the ORR and HOR activity measured in rotating disk electrodes for several ionomer–catalyst combinations, involving five different AEIs and Nafion® and four ORR and HOR catalysts selected from the best-in-class PGM-based and PGM-free catalytic materials. The results show little impact of the ionomers on the ORR and HOR activity of Pt/C and PtRu/C catalysts, respectively; however, the choice of the AEI has critical importance on the ORR activity of Fe–N–C and significant effect on the HOR activity of Pd–CeO2/C.

International audience; Since the ban on the use of asbestos due to its carcinogenic properties, the removal of asbestos cement, representing the major asbestos-containing waste, has proven to be a challenge in most industrial countries. Asbestos-containing products are mainly disposed of in landfills and have remained untreated. Bioremediation involving bacteria previously reported the ability of Pseudomonas aeruginosa to release iron from flocking asbestos waste through a siderophore-driven mechanism. We examined the involvement of siderophore-producing Pseudomonas in the biodeterioration of asbestos cement. Iron and magnesium solubilization were evaluated by specific siderophore-producing mutants. The absence of one of the two siderophores affected iron extraction, whereas equivalent dissolution as that of the control was observed in the absence of siderophore. Both pyoverdine and pyochelin biosynthesis was repressed in the presence of asbestos cement, suggesting iron bioavailability from the waste. We compared the efficiency of various pyoverdines to scavenge iron from asbestos cement waste that revealed the efficiency of all pyoverdines. Pyoverdines were efficient in iron Revised Manuscript Texte removal extracted continuously, with no evident extraction limit, in long-term weathering experiments with these pyoverdines. The optimization of pyoverdine-asbestos weathering may allow the development of a bioremediation process to avoid the disposal of such waste in landfills.

The emergence of magnetic skyrmions, topological spin textures, has aroused tremendous interest in studying the rich physics related to their topology. While skyrmions promise high-density and energy-efficient magnetic memory devices for information technology, the manifestation of their nontrivial topology through single skyrmions and ordered and disordered skyrmion lattices could also give rise to many fascinating physical phenomena, such as chiral magnon and skyrmion glass states. Therefore, generating skyrmions at designated locations on a large scale, while controlling the skyrmion patterns, is the key to advancing topological magnetism. Here, a new, yet general, approach to the "printing" of skyrmions with zero-field stability in arbitrary patterns on a massive scale in exchange-biased magnetic multilayers is presented. By exploiting the fact that the antiferromagnetic order can be reconfigured by local thermal excitations, a focused electron beam with a graphic pattern generator to "print" skyrmions is used, which is referred to as skyrmion lithography. This work provides a route to design arbitrary skyrmion patterns, thereby establishing the foundation for further exploration of topological magnetism.

International audience; Chirality, a foundational concept throughout science, may arise at ferromagnetic domain walls 1 22 and in related objects such as skyrmions 2. However, chiral textures should also exist in other types 23 of ferroics such as antiferromagnets for which theory predicts that they should move faster for 24 lower power 3 , and ferroelectrics where they should be extremely small and possess unusual 25 topologies 4,5. Here we report the concomitant observation of antiferromagnetic and electric chiral 26 textures at domain walls in the room-temperature ferroelectric antiferromagnet BiFeO 3. 27 Combining reciprocal and real-space characterization techniques, we reveal the presence of 28 periodic chiral antiferromagnetic objects along the domain walls as well as a priori energetically 29 unfavorable chiral ferroelectric domain walls. We discuss the mechanisms underlying their 30 formation and their relevance for electrically controlled topological oxide electronics and 31 spintronics. 32 33 Metallic ferromagnets have been the elemental bricks of spintronics for the last three decades and 34 continue to hold promises on the basis of non-collinear chiral spin textures such as skyrmions. These 35 topologically protected objects are envisioned to be the future of magnetic data storage thanks to 36 their specific stability, dynamics, and scalability 2. In parallel, antiferromagnets (AFs) are emerging as a 37 new paradigm for spintronics 6. They are intrinsically stable (being insensitive to spurious magnetic 38 fields), scalable (no cross talk between neighbouring memory cells), and fast (switching frequencies 39 in the THz regime). The opportunity of gathering the best of these two worlds and realize 40 "antiferromagnetic skyrmions" is then tremendously appealing but faces at least two major 41 challenges. The first one is to achieve antiferromagnetic chirality and the second one is to identify 42 appropriate control stimuli to create, annihilate and move these chiral objects. 43 On one hand, chirality may naturally emerge at domain walls. The antiferromagnetic domain wall 44 structure is a virtually uncharted territory but this is where translational symmetry is broken and spin 45 rotation favoured. On the other hand, AF manipulation is hampered by the intrinsic lack of net 46 magnetization, which prevents a straightforward magnetic actuation. This fundamental issue may be 47

A new instrument named COMET for COherent Magnetic scattering Experiments in Transmission using polarized soft X-rays has been designed and built. This high-vacuum setup is placed at the intermediate focal point of the elastic branch of the SEXTANTS beamline at Synchrotron SOLEIL. The main application is in solid state physics, the instrument being optimized for studying material properties using coherent scattering of soft X-rays with an emphasis on imaging, with chemical selectivity, the magnetic domains of artificially nano-structured materials. The instrument's principal features are presented and illustrated through recently performed experiments.

The tensile strain is a promising tool for creation and manipulation of magnetic solitonic textures in the chiral helimagnets via tunable control of magnetic anisotropy and Dzyaloshinskii-Moriya interaction. Here, by using the in-situ resonant small-angle x-ray scattering we demonstrate that the skyrmion and chiral soliton lattices can be achieved as metastable states in FeGe lamella as distinct states or even simultaneously by combining the tensile strain and magnetic fields in various orientations with respect to the deformation. The small-angle scattering data are discussed in the frame of the analytical model which is sufficient to describe the experimental results for soliton lattice. By using the experimental results and analytical theory, unwinding of the metastable skyrmions in the perpendicular magnetic field as seen by small-angle scattering experiment was analyzed by the micromagnetic simulation.

International audience