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Conception de films photomagnétiques ultra-minces par électrodéposition de complexes Fe 4 Co 4 pontés au cyanure commutables
No full textInternational audiencePreparing thin-films of molecular polymetallic materials remains one of the current limitations in the implementation of polymetallic complexes into devices. The hurdle was tackled here using an electrochemical route for depositing the cyanido-bridged polymetallic complex {Tl[Fe II (2-TPhTp)(CN) 3 ] 4 [Co III (Tp)] 3 [Co II (Tp)]}(1) (where 2-TPhTp = [4-(2thienyl)Phenyl]tris(pyrazol-1-yl)borate ; and Tp = hydrotris(pyrazol-1-yl)borate), functionalized with thiophene groups, on conductive surface (Pt/mica). Cyclic voltammograms show that the electrochemical pattern of the cubic units is maintained in the electropolymerized film, notably with four quasi reversible successive Fe III /Fe II redox events. Assessing the morphology and the chemical composition of the resulting thin-film by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) experiments respectively, reveal a homogenous deposition (thickness of ca. 20 nm) showing the expected metallic ratio. More importantly, X-ray Absorption Spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD) measurements demonstrate that the photo-induced metal-metal electron transfer is preserved in the film. XMCD signals of Fe and Co atoms at their L 2,3 absorption edges both indicate an equivalent conversion of Fe II -CN-Co III diamagnetic pairs into Fe III -CN-Co II paramagnetic ones under laser light irradiation below 62 K. As for the photomagnetic complex, the phenomenon is reversible: the metastable Fe III -CN-Co II paramagnetic pairs thermally relax to the diamagnetic ground state upon heating to room temperature.La préparation de couches minces de matériaux polymétalliques moléculaires reste l'une des limitations actuelles dans la mise en œuvre de complexes polymétalliques dans des dispositifs. Cet obstacle a été abordé ici en utilisant une voie électrochimique pour déposer le complexe polymétallique ponté cyanido {Tl[Fe II (2-TPhTp)(CN) 3 ] 4 [Co III (Tp)] 3 [Co II (Tp)]}(1) (où 2-TPhTp = [4-(2thiényl)phényl]tris(pyrazol-1-yl)borate ; et Tp = hydrotris(pyrazol-1-yl)borate), fonctionnalisé avec des groupes thiophène, sur une surface conductrice (Pt/mica). Les voltampérogrammes cycliques montrent que le motif électrochimique des unités cubiques est maintenu dans le film électropolymérisé, notamment avec quatre événements redox Fe III /Fe II successifs quasi réversibles. L'évaluation de la morphologie et de la composition chimique du film mince obtenu, par microscopie à force atomique (AFM) et spectroscopie de photoélectrons X (XPS), révèle un dépôt homogène (épaisseur d'environ 20 nm) présentant le rapport métallique attendu. Plus important encore, les mesures de spectroscopie d'absorption des rayons X (XAS) et de dichroïsme circulaire magnétique des rayons X (XMCD) démontrent que le transfert d'électrons métal-métal photo-induit est préservé dans le film. Les signaux XMCD des atomes de Fe et de Co à leurs seuils d'absorption L 2,3 indiquent tous deux une conversion équivalente des paires diamagnétiques Fe II -CN-Co III en paires paramagnétiques Fe III -CN-Co II sous irradiation laser à une température inférieure à 62 K. Concernant le complexe photomagnétique, le phénomène est réversible : les paires paramagnétiques métastables Fe III -CN-Co II se relaxent thermiquement et reviennent à l'état fondamental diamagnétique lors du chauffage à température ambiante
Spin properties of NV ensembles in phosphorus doped diamond
No full textInternational audienceNitrogen-vacancy (NV) color centers in diamond have demonstrated their full potential in various applications, ranging from highly-sensitive nanoscale magnetometers [1], high-pressure sensors [2] and diamond-based quantum applications [3]. As a solid-state spin, the properties of these color centers strongly depend on the host material. Recent works nicely demonstrated this point: isotopic purification has shown to improve the spin coherence time of low impurity concentration diamond [4], while phosphorous doping allows to improve NV charge stability [5] and lead to record spin coherence [6].In this work, we investigate the spin properties of native NV ensembles in phosphorus-doped diamond layers, homoepitaxially grown on (100) Ib HPHT substrates with either natural or isotopically purified methane. The concentrations of phosphorus, nitrogen and NV centers, [P], [N] and [NV], are quantified by different techniques including SIMS, absorption and photoluminescence (PL) at low temperature. First, low temperature PL confirms phosphorus doping (7x1013 – 7x1015 P.cm-3) stabilizes the negative charge state of the NV center with a NV0 population that remains below 10% even at 1 mW laser power. Then, the dephasing time of spin ensemble (T2*) is characterized by Optical Detected Magnetic Resonance (ODMR) under continuous excitation. We investigate the T2* dependence with [N], which is the majority impurity in the samples. We found results that are consistent with a dipolar coupling of NVs with a bath spins made of nuclear 13C and/or substitutional nitrogen. We found T2* around 0.5 μs for natural isotopic composition, and up to ~3 μs for 12C purified diamond with [N] = 6.3x1016 cm-3. These results are promising for diamond quantum magnetometers with NV centers.References1. G. Balasubramanian, et al. Nature 455 (2008), 7213.2. M. Lesik, et al. Science 366 (2019), 6471.3. L. Childress et al. Science 314 (2006), 5797.4. G. Balasubramanian et al. Nature Materials 8 (2009), 383.5. Y. Doi et al. Physical Review B 93 (2016), 081203.6. E.D. Herbschleb, et al. Nature Communications 10 (2019), 3766
Commutation moléculaire multivoie dans des réseaux hexagonaux 2D : une stratégie d'ingénierie moléculaire pour la conception de matériaux bistables à température ambiante
No full textInternational audienceMagnetic materials exhibiting bistability at ambient condition are appealing for application in high-density memory, data storage, sensing and switches devices. Octacyanometallates have been extensively studied as building blocks for constructing novel molecular magnetic materials with exciting physical properties. Here, we have designed and synthesized two cyanide bridged 2D hexagonal networks using octacyanotungstate(V) building block where {[W(CN)8]2[Co(V-im)4]3}n(1) undergoes a single-crystal to single-crystal (SC-SC) structural transformation to form {[W(CN)8]2[Co(V-im)4]2[Co(V-im)2(DMF)2].4H2O}n (2). Complex 1 exhibits reversible thermo-induced metal-to-metal electron transfer (MMET) (T1/2 = 176 K) with a 12 K thermal hysteresis width while complex 2 exhibits near ambient temperature two-step MMET (heating: T1/2(1) 324 K, T1/2(2) 340 K; cooling: T1/2(1) 286 K, T1/2(2) 232 K) with a hysteresis width of 4 and 15 K respectively. Interestingly, light-induced reversible ON/OFF MMET has also been observed for both complexes (1 and 2) using 808 nm and 900 nm lights (ON mode) and 405 and 635 (OFF mode) respectively, converting the low-temperature diamagnetic {WIVLS-CN-CoIIILS} ground-state into the metastable paramagnetic {WVLS-CN-CoIIHS} phase and vice-versa . X-ray absorption spectroscopy was performed in order to investigate the local electronic structure and magnetization associated with the MMET between the W and Co metal centres.Les matériaux magnétiques bistables en conditions ambiantes sont prometteurs pour les applications dans les mémoires haute densité, le stockage de données, les capteurs et les commutateurs. Les octacyanométallates ont été largement étudiés comme éléments constitutifs de nouveaux matériaux magnétiques moléculaires aux propriétés physiques intéressantes. Nous avons conçu et synthétisé ici deux réseaux hexagonaux 2D pontés au cyanure en utilisant l'élément constitutif octacyanotungstate(V) où {[W(CN)8]2[Co(V-im)4]3}n(1) subit une transformation structurale monocristalline-monocristalline (SC-SC) pour former {[W(CN)8]2[Co(V-im)4]2[Co(V-im)2(DMF)2].4H2O}n(2). Le complexe 1 présente un transfert d'électrons métal-métal (MMET) thermo-induit réversible (T1/2 = 176 K) avec une largeur d'hystérésis thermique de 12 K tandis que le complexe 2 présente un MMET en deux étapes à température ambiante (chauffage : T1/2(1) 324 K, T1/2(2) 340 K ; refroidissement : T1/2(1) 286 K, T1/2(2) 232 K) avec une largeur d'hystérésis de 4 et 15 K respectivement. Il est intéressant de noter qu'un MMET ON/OFF réversible induit par la lumière a également été observé pour les deux complexes (1 et 2) en utilisant des lumières de 808 nm et 900 nm (mode ON) et de 405 et 635 (mode OFF) respectivement, convertissant l'état fondamental diamagnétique à basse température {WIVLS-CN-CoIIILS} en phase paramagnétique métastable {WVLS-CN-CoIIHS} et vice-versa. Une spectroscopie d'absorption des rayons X a été réalisée afin d'étudier la structure électronique locale et la magnétisation associées au MMET entre les centres métalliques W et Co
Protection of Stainless Steels by Mo against Cl Attack: A DFT Study
No full textInternational audienceWe report a DFT study of (0001)-oriented Cr 2 O 3 and Fe 2 O 3 surfaces addressing the beneficial effects of Mo on the passivity breakdown of stainless steels in Cl-rich environments. Compared to Cr-rich zones, Fe-rich zones of the oxide barrier layer of the passive film are more prone to adsorbing Cl ions. Mo substitutes preferentially in these Fe-rich zones and favors the cationic vacancy formation to promote selective dissolution, thus curing the weak sites, sensitive to localized corrosion attack. In the Fe-rich weak sites with adsorbed Cl, Mo increases the barrier of O vacancy formation, thus mitigating passivity breakdown by inhibiting Cl penetration
Alteration markers of green copper bimetallic pigments in easel paintings by an inter-comparison of analogues and historical samples
No full textInternational audienceThis paper investigates the alteration of copper acetate (verdigris) and resinate green pigments widely used in oil paintings during the Middle Ages and Renaissance periods. These are bimetallic Cu(II) complexes. Their alteration consists in a color change of these bimetallic pigments from green into brown resulting in a darkening.By combining micro-analysis of both historical painting samples and analogue mock-ups this study elucidates the interactions between pigments and organic oily matrix and the chemical changes leading to the long-term degradation of copper acetate and resinate.Different analytical techniques were combined to characterize browning and identify degradation markers. The use of multimodal micro- spectroscopic techniques with a high lateral resolution (such as scanning electron microscopy, infrared micro spectroscopy, synchrotron photoluminescence, synchrotron micro-X-ray absorption near edge spectroscopy at the Cu K-edge) proved to be successful for the characterization of paint stratigraphy. The study shows the development of the pigment degradation from the surface to the inner painted layers, its facilitated propagation through defects (as cracks) and the influence of light and oxygen.The reproduced alteration in model samples fits with the ageing of masterpiece paintings. Finally, the browning mechanism is attributed to the formation of new copper complexes resulting from the ageing of organic binder and its interaction with copper bimetallic, without any detected structural modification of pigments in altered and non-altered areas
Translocation of cell-penetrating peptides involving calcium-dependent interactions between anionic glycosaminoglycans and phosphocholine bilayer
No full textInternational audienceCell-penetrating peptides can internalize ubiquitously in many, if not all, cell types. To explore the specific targeting issue of cell-penetrating peptides (CPPs), we studied glycosaminoglycan (GAG)-binding peptides previously identified in Otx2 and En2 homeoproteins (HPs), alone or extended with the penetratin-like third helix (H3) of En2. HPs are indeed known to internalize in specific cells, thanks to their GAG-targeting sequence (Joliot et al. 2022; Cardon et al. 2023). We quantified the capacity of these peptides to enter into various cell lines known to express different levels and types of heparan sulfates (HS) and chondroitin sulfates (CS) GAGs. We also analyzed by calorimetry (DSC, ITC) and fluorescence spectroscopy, the binary and ternary interactions between heparin (HI), (4S, 6S)CS (CS-E), zwitterionic phosphocholine (PC) model membranes and those peptides. Altogether, our results demonstrate the existence of Ca2+-dependent interactions between CS-E or HI and PC lipid bilayers, the major phospholipid found in animal cell plasma membrane. Importantly, we show that CS-E can act as a Ca2+-dependent bridge with PC membranes that can be exploited by a chimeric CS-E-recognition motif-H3 peptide to bind and cross the membrane lipid bilayer and get access directly to the cytosol of cells. Altogether, this study brings further information uncovering the molecular mechanism of the translocation process of CPPs that implies specific GAGs at the cell-surface. It also shed light on the role of GAGs in the paracrine activity and cell specificity of HPs
Towards Efficient coupling of single nanodiamonds to an optical fibers for single photons emission
No full textInternational audienceThe development of integrated quantum technologies relies on efficient single-photon sources and deterministic quantum operations. Solid-state quantum emitters coupled to nanophotonic structures present a promising solution. This work investigates color centers in nanodiamonds,particularly Germanium Vacancy (GeV) [1], Silicon Vacancy (SiV), and Magnesium Vacancy (MgV) centers, a novel, understudied emitter [2], at both room and cryogenic temperatures. These nanodiamonds are chosen for their stability and superior coherence properties at cryogenic conditions. To collect their emission we have successfully deposited a single GeV- nanodiamond on tapered optical nanofibers by gently contacting a diluted droplet to the nanofiber [3], demonstrating an average coupling of 15% into a conventional optical fiber through the confined evanescent field of the nanofiber mode and single photon emission. Building on this achievement, we aim to study the system at cryogenic temperatures, which should enable the demonstration of efficient and indistinguishable single photons coupling to conventional optical fibers.Current collection efficiencies are intrinsically limited to 30% with the nanofiber[4], and improving light-matter coupling efficiency remains a key goal for high-performance single-photon sources and more advanced applications.To achieve this, we are investigating a newly developed technique [5]: the deterministic fabrication of dielectric and plasmonic nanostructures directly on the nanofiber surface using an “electron beam induced deposition” (EBID). The precision and versatility of this technique openthe way to different applications: Purcell enhancement of the quantum emitter emission using metallic nanoantennas and efficient light-matter coupling using dielectric structures. Our first calculation shown that optimizing the composition, geometry, and placement of these nanostructures a simple pattern of carbon pillars around the emitter should increase coupling efficiency up to 69% while maintaining high transmission in the nanofiber. We also demonstratethe fabrication of those nanostructures on top of the nanofiber.This work advances integrated nanophotonic devices for single-photon sources.[1] M. Nahra et al.,Single germanium vacancy centers in nanodia-monds with bulk-like spectral stability, AVS Quantum Science3(1), (2021).[2] E. Corte et al, Magnesium-Vacancy Optical Centers in Diamond, ACS Photonics, 10(1), p101-110, (2023)[3] Pierini et al. Highly Photostable Perovskite Nanocubes : TowardIntegrated Single Photon Sources Based on Tapered Nanofibers.ACS Photonics, 7(8), p.2265-2272, (2020).[4] Fujiwara et al., Highly efficient coupling of photons from na-noemitters into single-mode optical fibers, Nano Letters, 11(10),4362–4365, (2011).[5] A.Balena et al, Deterministic Bottom-Up Fabrication of Plasmonic Nanostructures on OpticalNanofibers via Blurred Electron Beam Deposition (soon to be published in Advance Material)
Decoding Mono- and Dual- Molecular Passivation behaviors for High-Efficiency Inverted Perovskite Solar Cells
No full textInternational audienceIn recent years, inverted (p-i-n) perovskite solar cells (PSCs) employing self-assembled monolayers (SAMs) at their bottom interface have been widely investigated owing to their low-temperature processing, high fabrication reproducibility, ever-increasing power conversion efficiency (PCE) and long-term damp-heat stability.[1,2] In comparison to the functionalization of the bottom contact interface by SAMs, the top interface presents more challenging issues because solution-processed perovskite thin films tend to lost volatile species from the upward side during high-temperature annealing. These compositional variations lead to defect generation and, in turn, to non-ideal charge carrier dynamics. This, in addition to the formation of energetic barriers due to poor energy level alignment, hinder efficient electron extraction from the perovskite to the electron transport layer (ETL). Therefore, tailored interlayers at the top interface between the perovskite and the ETL, C60 or its derivatives (e.g., [6,6]-phenyl-C₆₁-butyric acid methyl ester, PCBM), are crucial for improving the performance and stability of inverted perovskite solar cells (PSCs). Indeed, surface modification plays a pivotal role in developing state-of-the-art inverted perovskite solar cells (PSCs).[3-5] However, the functional specificity of amine-based compounds often results in selective passivation, leading to inconsistent device performance improvements. In this study, by combining the analysis of the quasi-Fermi level splitting (QFLS) [6] and surface photovoltage (SPV) by absolute photoluminescence and Kelvin probe measurements, we systematically investigate three cyclic-structured amine salts (benzene-, thiophene-, and piperazine-based) to elucidate their distinct enhancement mechanisms via defect passivation and thus suppression of non-radiative recombination. Our results reveal that the benzene and thiophene functional groups effectively passivate defects at grain interiors and boundaries owing to their conjugated structure, thereby improving the interfacial contact and reducing the defect density. Meanwhile, the piperazine-based molecules exhibit a superior hole-blocking capability, effectively repelling minority carriers back into the perovskite bulk and thus improving charge transfer kinetics. These mechanistic insights inspired the development of a bimolecular passivation strategy that simultaneously addresses surface defect mitigation and charge carrier management. By implementing this bifunctional approach combining piperazine- and thiophene- iodate, we achieved a champion device efficiency exceeding 25% (mask area: 0.152 cm²) with exceptional operational stability. The encapsulated devices maintained over 85% of their initial performance after 600 hours of continuous operation at 50°C under ambient conditions (ISOS-L-1 protocol)
Bifunctional Chiral ImPy‐Carbene Ligands. H‐Bonding Controlled Reactivity and Enantioselectivity in Au(I)‐Catalysis
No full textInternational audienceBifunctional chiral N‐heterocyclic carbene ligands have been devised for enantioselective gold(I) catalysis. Based on a single C ‐stereogenic center derived from chiral pool α‐aminoacids and connecting an imidazopyridine core to an arylurea motif, enantioselective gold(I)‐catalyzed cycloisomerization reactions could be achieved. High enantioselectivities were notably observed for substrates presenting a pendant propargyl alcohol on 2‐naphthol and 1,6‐enyne scaffolds. In the latter case, the catalyst shows a high degree of selectivity for the unprecedented 6‐ endo‐dig biscyclization of these substrates to give cyclopropyl‐fused 6‐ring heterocycles with a free OH functionality instead of the previously reported furan‐fused products. This unusual selectivity was investigated by DFT studies, which suggested the dual role of the carbonyl group of the urea moiety: first as an H‐bond acceptor in the catalytic cycle to direct the enantioselectivity and second as a cooperative group in the hydrogen shift leading to deauration