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Graphene assisted III-V epitaxy towards substrate recycling
No full textInternational audienceRe-using the substrate is identified as a method for reducing the cost of high efficiency III-V solar cells. The approach investigated here consists in inserting a graphene layer onto a (001)GaAs substrate prior to the epitaxial growth of GaAs. To obtain a monocrystalline GaAs grown layer, the graphene layer is patterned, followed by a two-step epitaxial growth, here performed by molecular beam epitaxy (MBE). The first step is a selective area growth of GaAs in graphene openings, followed by a lateral overgrowth, under a modulated Ga flux. The second step, after reaching coalescence, consists in a regular growth under continuous Ga supply. It is observed that the pattern orientations relative to the crystallographic direction of the GaAs substrate below the graphene have an influence on GaAs morphology and quality. The best result was obtained for patterns oriented along [1̅10]+22.5° with a graphene coverage of 50%, with a significantly reduced roughness down to 3.3 nm
Multifunctional quantum dot-decorated drug-loaded magnetite nanosystem for dual optical-magnetic resonance imaging and drug delivery
No full textInternational audienceEarly detection of cancer plays a significant role in the effective prognosis, treatment regimen planning, and patient recovery. The aim of this study was to combine a near-infrared (NIR) contrast agent, a magnetic resonance imaging (MRI) contrast agent and a therapeutic agent in an all-in-one nanosystem. In particular, owing to their excellent properties, Fe3O4 magnetic nanoparticles (an MRI contrast agent), CdTe quantum dots (an NIR optical fluorescence agent), and curcumin (an anticancer drug) were incorporated in the nanosystem using carboxymethyl chitosan as the coating polymer. The nanosystem was characterized using DLS, zeta potential analysis, Fourier transform infrared spectroscopy, fluorescence spectroscopy, EDX analysis and TEM analysis. The nanoparticles exhibited average sizes ranging from 100 nm to 170 nm in DI water, PBS and DMEM, with zeta potential in the range of -40 to -64 mV, indicating good stability. The nanoplatform demonstrated potential as a positive MRI contrast agent, exhibiting an r2 relaxivity of 78.33 mM -1 s -1 and an r2/r1 ratio of 470.95 ± 15.11 at 7 T, attributed to second-sphere water interactions. The multifunctional nanoplatform showed great in vitro stability and drug encapsulation over two-month period. The MR and NIR optical imaging efficiencies were evaluated in vitro and in vivo on CT26-bearing mice. The ex vivo signal acquisition was also studied for the tumor, liver, spleen, lung and kidney in the mouse model. Results demonstrated the potential of the prepared multifunctional nanosystem in dual optical MR imaging and passive drug delivery applications
Encoding and Expressing the Handedness of a Möbius π System in a Totemic Architecture
No full textInternational audienceThe efficient control of the chirality of Möbius π systems remains a challenging task that hinders the development of such molecules into information processing systems. Achieving such control through a redox process would thus open new opportunities. In this context, redox behaviors of Ni(II) and Pd(II) complexes of a Möbius aromatic [28]hexaphyrin doubly linked to an α-cyclodextrin have been investigated. This totemic architecture embedding three types of chirality elements generates two pseudoenantiomers after coordination with either metal. These isomeric pairs possess marked and opposite chiroptical signatures resulting from the P and M configurations of the Möbius π systems. Chemical oxidation to 26-π systems led to behaviors reminiscent to The Oak and the Reeds fable, due to a N3C coordination sphere of Ni(II) being more robust than that of Pd(II). Oxidized Ni(II) complexes (the Oak) maintain a Möbius-type conformation at the expense of the π-systems, which undergo an interruption due to inevitable water insertion. In contrast, oxidation of Pd(II) complexes (the Reeds) converts the Möbius aromatic systems into Hückel (rectangular) aromatic ones that are maintained in the chiral environment provided by the linking pattern with the cyclodextrin. This constitutes an effective chiral instructing site, as reduction back to their original Möbius configuration occurs with high stereoselectivity. Such a reversible shape-shifting process corresponds to a chiral memory phenomenon where the handedness of a cyclic π system is encoded in a scaffold and expressed upon changing an electronic state. For both metals, spectroelectrochemical studies ultimately revealed robust ON-OFF chiroptical switches, which is unprecedented with Möbius π-systems
Analysis of the mechanical damage of a solid-state recycled aluminium alloy under tensile loading
No full textInternational audienceSolid state recycling of aluminium chips by hot extrusion allows to produce dense profiles, but the former chips result in the presence of a meso-scale oxide network in the parts, referred to as prior chips boundaries. This study links the detailed characterization of this oxide network structure and the alloy microstructure with the damage evolution in the material during tensile loading. The chips flow, due to the die geometry, results in a prior chips boundary network made of planes mostly aligned along the extrusion direction. Depending on their thickness and number, these planes can have low impact on the microstructure, with even crystalline continuity on both sides, indicating perfect chips welding, or be correlated to grain boundaries. Tensile tests in the transverse and longitudinal directions confirm highly ductile plastic behavior (above 10 % of uniform engineering strain) and reveal a fracture comprised of delamination and ductility. Combining fracture surface analyses and damage nucleation and growth followed by X-ray tomography, this study reveals that pores, or cracks, develop in the prior chip boundaries planes. Their nucleation and growth is similar, in size, number and evolution with strain, to what is conventionally observed in non-recycled materials. They contribute, at most, to a loss of 1 %, or 1.5 MPa for an ultimate tensile strength of about 150 MPa, to the material’s mechanical resistance when the prior chip boundary planes are oriented parallel to the tensile axis, and thus have a very limited impact. However, it is shown that planes perpendicular to the tensile axis, mostly found in specimens with tensile direction perpendicular to the extrusion axis, lead to a significant decrease in ductility, up to the absence of post-necking behavior. This study therefore reveals the details of damage evolution in solid state recycled materials, proving, in favorably oriented cases, the absence of damage induced by the oxide network, but points out the major importance of its orientation
Visible‐Light Photocatalyzed Selective Synthesis of 1,2‐ or 1,3‐Dithianes From Thietanes: An Experimental and Theoretical Study
No full textInternational audienceUnlike other sulfur-containing heterocycles, the potential applications of functionalized dithianes have been less explored to date due to their challenging synthesis. To address this issue, we herein leverage the straightforward access to functionalized thietanes and describe a selective photochemical ring enlargement of the latter to 1,2-or 1,3-dithianes using thiocarbonyl substrates, which are in situ generated via a Norrish-type II fragmentation reaction. The library of dithianes obtained by this photocatalyzed domino sequence between diversely substituted thietanes and various thiocarbonyls revealed regioselectivity rules: excited thioketones lead exclusively to 1,2-dithianes, while excited thioaldehydes selectively yield 1,3-dithianes, where 1,2-dithianes serve as precursors to their regioisomers. The ring expansion reaction leading to 1,2-dithianes was also integrated into a triple photochemical cascade, where the thietane intermediates were obtained via a thia-Paternò _ Büchi reaction between Norrish-II thiocarbonyl products and various alkene partners. These experimental results were complemented with time-dependent density functional theory calculations, which support the complex chemical pathway, rationalize the observed regioselectivity, and further substantiate mechanistic proposals related to the photolysis of disulfide bridges in peptides.</div
Strongly vs. weakly associating anions: transport–structure relationship in LiTFSI–LiNO3 electrolytes
No full textInternational audienceLiquid battery electrolytes based on mixtures of salts with weakly and strongly associating anions have emerged as a promising route toward high-performance, sustainable battery technologies. Their success is primarily attributed to the unique influence of salt composition on the solvation structure. Here, we employ classical molecular dynamics simulations, corroborated by experimental data, to study mixed lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/lithium nitrate (LiNO3) in diglyme electrolytes, a formulation of particular interest for lithium–sulfur and lithium–oxygen batteries. We investigate how the ratio of weakly associating anions (TFSI ) to strongly associating anions (NO3) affects ion transport within the electrolyte. Our findings reveal that the anion ratio significantly impacts both the solvation structure and the solvation dynamics, which together contribute to the distinct transport behavior observed in these systems. These findings underscore the tunability of battery electrolyte transport properties through careful mixing of anions
From Formation to Reactivation of Inactive Lithium in Lithium Metal Anodes
No full textInternational audienceInactive lithium (Li), often referred to as dead or isolated Li, consists of electrochemically disconnected metallic Li and Li‐containing compounds trapped within or beneath the solid–electrolyte interphase (SEI). It is widely recognized as a primary failure mode in lithium‐metal batteries (LMBs), contributing to performance degradation, safety concerns, and limited scalability. This review outlines the sequential processes of Li nucleation, growth of high‐surface‐area Li, and the formation of inactive Li, while identifying the key physicochemical factors influencing each stage. Li nucleation is governed by current density, temperature, electrolyte formulation, and interfacial properties, which collectively dictate the uniformity of Li plating. High‐surface‐area Li growth introduces mechanical and chemical instabilities, fractures and uneven stripping of these filamentous structures lead to Li isolation and inactive Li accumulation. To address these challenges, advanced characterization techniques, including solid‐state nuclear magnetic resonance spectroscopy, titration gas chromatography, inductively coupled plasma optical emission spectroscopy, and operando synchrotron X‐ray diffraction, offer critical insights into the formation and progression of inactive Li. Emerging reactivation strategies, such as redox mediators and tailored cycling protocols, show promise in recovering lost capacity. This review presents key mechanistic factors, advanced diagnostic tools, and emerging reactivation strategies to support a deeper understanding and control of failure mechanisms in LMBs systems
Advanced approach for phosphor recovery and characterization of LED components
No full textInternational audienceThis study introduces a novel approach for characterizing Light Emitting Diode (LED) devices by isolating their individual components—specifically the phosphor, housing, and LED chips—and analyzing each separately
SPARC is a new driver of early breast tumor progression via TGF-β -dependent mechanism
No full textAbstract Ductal carcinoma in situ (DCIS) is a pre-invasive lesion that is thought to be a precursor of invasive ductal carcinoma (IDC). The challenge lies in discriminating between DCIS progressors and DCIS non-progressors, often resulting in over- or under-treatment in many cases. Membrane type 1 (MT1)-matrix metalloproteinase (MMP) has been previously identified as an essential gene involved in DCIS progression. Here, RNA-sequencing analysis of MT1-MMP high subpopulation derived from invasive breast tumors in the intraductal xenograft model was compared against a dataset of human high-grade DCIS, and Secreted Protein Acidic and Cysteine Rich (SPARC) has emerged as a master candidate involved in early breast tumor progression. We report that SPARC is up-regulated in DCIS as compared to normal breast epithelial tissues, and further increased in IDC relative to synchronous DCIS foci. We found a positive correlation between SPARC and MT1-MMP expression in DCIS lesions. At the mechanistic level, depletion of SPARC reduced MT1-MMP expression, the degradative capacity of the cells and the activation of the TGF-β signalling canonical pathway. Pharmacological inhibition of the TGF-β signalling pathway decreased SPARC and MT1-MMP at the mRNA and protein level, and concomitantly the cell degradative capacity and 3D cell migration. Strikingly, inhibition of the TGF-β signalling pathway limits the invasive transition of breast tumors in a new triple-negative mouse intraductal syngeneic xenograft model. Moreover, high SPARC expression was positively correlated with both, TGF-β and its receptor, TGFBRI, in a basal type of breast cancer collection supporting our findings. This study identifies SPARC as a new driver of early breast tumor progression via a TGF-β-dependent mechanism, suggesting TGF-β signaling pathway as a potential target for patients with high SPARC expression
III-V growth on patterned graphene covered substrates towards thin film exfoliation and substrate recycling
No full textInternational audienceThis work aims at reducing the cost of III V solar cell by substrate recycling investigating growth on graphene covered substrates It was shown in the literature that the graphene layer allowed the growth of monocrystalline layers with the same orientation as the substrate, while still allowing the exfoliation thanks to the mechanically weak graphene plane. Two possible underlying physical mechanism s could play a role in obtaining a crystallographic alignment of the epi layer: a remote interaction through the graphene, or a nucleation at graphene holes followed by a lateral growth. With our developed process, we have not observed remote interactions. We have therefore investigated the possibility of optimizing growth on patterned graphene. We show that a crucial parameter in obtaining a good quality III V is the graphene opening orientation relative to the substrate. Stripes oriented along <100 > directions on (001) substrates provided the smoothest nanostructures prior coalescence. Surprisingly, afterwards, higher index directions, e.g. 120 4° resulted in the smoothest surfaces, with RMS roughness down to 3.3 nm, and the highest luminescence emission. First exfoliation tests have been carried out, showing a dependance on the peel off direction relative to the stripes orientation, which will be further studied in coming works