Soleil Synchrotron

Epitaxial heterostructures of iron oxide thin films on oxide substrates are promising for spintronic applications. Scaling down such heterostructures into ordered nanostructures enables integration into functional devices. However, fabricating well-ordered nanostructures while retaining their structural and functional integrity remains challenging. A bottom-up approach is used to grow epitaxial Fe3O4 nanodot arrays on Nb-doped SrTiO3(Nb:STO) substrates integrating anodic aluminum oxide (AAO) templates combined with pulsed laser deposition. Following this method, the lateral confinement of Fe3O4 into 30 and 70nm nanodots with 3D long-range ordering is then confirmed by grazing-incidence small-angle X-ray scattering (GISAXS) and scanning electron microscopy (SEM). Building on this structural evidence, the Verwey transition is found to be retained, as observed in the continuous film. To explore its applicability in nanoelectronics, conductive atomic force microscopy (c-AFM) is used to probe local electrical behavior, and reveals bipolar resistive switching at room temperature in individual nanodots, consistent with behavior observed in thin films. Together, these results establish the first demonstration of ordered epitaxial Fe3O4/Nb:STO nanodots with preserved structural, magnetic, and electrical functionalities, providing a generalizable route for nanoscale integration of complexoxides.

The title coordination complex tetra-chlorido-bis-(1H-imidazo[4,5-b]pyridin-4-ium-κN 3)iron(II), [FeCl4(C6H6N3)2] or [FeCl4(LH)2], was synthesized and structurally characterized by single-crystal X-ray diffraction. The complex crystallizes in the triclinic space group P1. The iron atom (site symmetry ) is hexa-coordinated, adopting a slightly distorted octa-hedral geometry defined by two 1H-imidazo[4,5-b]pyridinium ligands and four chloride anions. In the crystal, N-H⋯Cl hydrogen bonds generate two-dimensional layers parallel to the ab plane, while the three-dimensional supra-molecular framework is further consolidated by C-H⋯Cl inter-actions. In addition, π-π stacking inter-actions contribute to the overall cohesion of the crystal structure. Hirshfeld surface analysis indicates the significance of various inter-molecular contacts in the crystal packing, with major contributions from Cl⋯H/H⋯Cl (43.2%), H⋯H (22.5%), C⋯H/H⋯C (16.4%), H⋯N/N⋯H (4.4%), N⋯C/C⋯N (3.7%), C⋯C (3.6%), Cl⋯N/N⋯Cl (3.2%), Cl⋯C/C⋯Cl (2.4%), and N⋯N (0.6%) inter-actions.

PERCIVAL, “pixellated energy-resolving CMOS imager versatile and large”, is a 2-megapixel soft X-ray imager developed for use at FELs and modern-day synchrotrons. A combination of capabilities is necessary to meet the scientific needs: a large, uninterrupted imaging area with small pixels, high dynamic range, high frame rate, and soft X-ray suitable entrance window to the sensor. A single PERCIVAL sensor offers over 4 cm × 4 cm uninterrupted imaging area (1408 × 1484 pixels of 27 × 27 μm2). Three auto-adapting gains (per pixel per image) provide the large dynamic range from 13 e- noise to over 3 Me- signal. The sensor is designed for up to 300 Hz frame rate, and can be operated faster in ROI mode.The first generation of the sensor was hampered by severe crosstalk preventing parallel operation of ADC, streamout, and pixel switches and by non-uniformity of baselines over the sensor.A revised “respin” sensor addresses these issues at the root — and good noise performance at higher frame rates as well as a more uniform baseline can now be provided to users.The first generation DAQ system — still based on existing Virtex5 hardware — had limitations that ultimately prevented handling the fast data rates from a Percival running at full speed, or other complexities such as ROI operation. A complete overhaul of the percival-specific DAQ components (FPGA with periphery and firmware) today enables acquisition at envisioned frame rates and in ROI mode.This paper summarizes first laboratory results from the respin sensors in combination with the new DAQ hardware and firmware.

We report the observation of dynamic fringe patterns in the diffuse scattering of extreme ultraviolet light from surfaces, following femtosecond optical excitation. At each point on the detector, the diffuse scattering intensity exhibits oscillations at well-defined frequencies that correspond to surface phonons with wave vectors determined by the scattering geometry, indicating that the optical excitation generates coherent surface phonons propagating in all directions and spanning a wavelength range from 60 to 300nm. This phenomenon is observed on a variety of samples, including single-layer and multilayer metal films, as well as bulk semiconductors. The measured surface phonon dispersions show good agreement with theoretical calculations. By comparing signal amplitudes from samples with different surface morphologies, we find that the excitation mechanism is linked to the natural surface roughness of the samples. However, the signal is still detectable on extremely smooth surfaces with subnanometer roughness. Our findings demonstrate a simple and effective method for optically exciting coherent surface phonons with nanoscale wavelengths on a wide range of solid samples and establish a foundation for surface phonon spectroscopy in a wave vector range well beyond the limit of conventional surface Brillouin scattering.

The effect of adding Na+ and Mg2+ metal ions on soft X-ray induced photochemistry (SXIP) is investigated. To that aim, the soft X-ray beam of the METROLOGIE beamline at the SOLEIL synchrotron was extracted through air to irradiate solutions circulating in a microfluidic cell. Benzoate was used as a sensitive profluorescent probe for hydroxyl radicals. Hydroxyl radical production yields are relatively constant in the 1.0-1.4 keV energy range, but they are significantly higher in pure benzoate solutions than in solutions supplemented with 1 M sodium or magnesium salts, both below as well as above the ion K-edges. This salt effect is not observed for cesium γ-ray irradiation. Photoelectron spectroscopy, molecular dynamics, and Kinetic Monte Carlo simulations are used to understand the origin of this effect. We conclude that it proceeds by modifying the chemistry occurring within the Auger and photoelectron tracks.

Abstract The well known version of Electrode Deposition Method, the Gas Metal Arc Welding (GMAW), has found its way from being a metal joining process to an Additive Manufacturing process. Its capability to fabricate parts of bigger dimensions has attracted manufactures particularly in the field of aeronautical industries. Further optimisations and innovations in this technique has led to the development up for Wire Arc Additive Manufacturing (WAAM). WAAM coupled with improved metal transfer mode called the Cold Metal Transfer (CMT) has improved the geometric quality of the parts produced. But the complex physics inherent to the process requires variable controls for the fabrication, generating surface irregularities on the beads which are difficult to predict. These irregularities cumulates as the fabrication is advanced from single beads to layers, and then to multiple layers forming the final part.The formation of layers involves the overlapping of adjacent beads which are spaced at an offset distance. But because of the irregular form of the beads, the offset distance also have to be controlled as a function of the form of the bead sections. Several existing models neglect the continuous variations and recommend deterministic values which is different from reality. Therefore, the current study is dedicated in developing a statistical model to predict the offset distance and its variations by considering the actual irregularities in the bead geometry.

Scanning Transmission X-ray Microscopy (STXM) and soft X-ray Ptychography (SXP) are powerful techniques for nanoscale imaging, offering high spatial resolution with chemical sensitivity. However, the interplay between spatial resolution and X-ray radiation damage remains a critical consideration for sensitive samples such as organic materials. In this study, we quantitatively compared spatial resolution and radiation damage between the two techniques. Spatial resolution is assessed using Fourier Ring Correlation (FRC), applying both the 1/2-bit threshold and a signal-to-noise ratio (SNR) threshold mathematically computed for each spatial frequency. SXP achieves superior spatial resolution due to its phase-retrieval capabilities and enhanced coherent imaging properties. In this paper, a resolution of 20-25 nm with SXP at Nitrogen K-edge (~400eV) was achieved for the first time, while STXM is limited by zone plate used, outermost zone width as 25 nm giving a theoretical resolution of 30.5 nm (1.22 x outermost zone width). Moreover, in our measurements we find that the X-ray radiation dose required for SXP is approximately 6 times lower than that for STXM, leading to a remarkably low damage level, highlighting its potential for damage-sensitive studies. These findings establish SXP as a highly efficient and minimally invasive imaging technique for nanoscale characterization of organic material.

Abstract Transition metal dichalcogenides (TMDs) are layered materials obtained by stacking two-dimensional sheets weakly bonded by van der Waals interactions. In bulk TMD, band dispersions are observed in the direction normal to the sheet plane (z-direction) due to the hybridization of out-of-plane orbitals but no kz -dispersion is expected at the single-layer limit. Using angle-resolved photoemission spectroscopy, we precisely address the two-dimensional to three-dimensional crossover of the electronic band structure of large area epitaxial WSe2 thin films. Increasing number of discrete electronic states appears in given kz -ranges while increasing the number of layers. The continuous bulk dispersion is nearly retrieved for 6-sheet films. These results are reproduced by calculations going from a relatively simple tight-binding model to a sophisticated KKR-Green’s function calculation.

Magnetic order engineeringin two-dimensional Dirac systems isof great interest for theoretical and technological exploration. Upto now, the experimental advances in this field mostly concerned graphenemonolayers. Here, we report a comprehensive study of a monolayer-thickgermanene-like sheet in contact with gadolinium atoms. Direct observationssupported by first-principles calculations reveal the fingerprintsof the Dirac fermions in the electronic structure and noncollinearantiferromagnetism. The hybridization of the germanene layer withGd atoms leads to a large and tunable gap in the Dirac states thatcarry a nonzero spin-Berry curvature. We discovered that cesium-inducedcontrolled electron doping can switch the system into a ferromagneticstate and then back to the antiferromagnetism at saturated cesiummonolayer limit. We explain these reversible magnetic transitionsby the oscillatory behavior of the Ruderman–Kittel–Kasuya–Yosidainteraction and suggest that this system could find application inmagnetoelectronics and spintronics.