HAL Portal IOGS (nstitut d'Optique Graduate School)
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VO2 by Pulsed-laser Deposition : controlling thin films nature and properties
No full textInternational audienceThis work investigates the synthesis of vanadium dioxide (VO2) thin films and nanoparticles, a material well-known for switching from a dielectric to a metallic state at 68 °C, with applications in various domains such as electronics, thermal imaging, smart windows, etc.We used Pulsed Laser Deposition (PLD) from vanadium pentoxide and pure vanadium targets, and Rapid Thermal Annealing (RTA) in an oxygen atmosphere to produce thermoswitching films. We explored their properties through various characterization techniques, including Raman spectroscopy, Grazing-Incidence X-Ray Diffraction (GIXRD) in temperature, profilometry, four-point conductivity measurement, atomic force microscopy (AFM), and scanning electron microscopy (SEM) to assess their structural, optical, and electrical properties. We used an ultrashort pulsed laser, with THz and GHz burst capabilities, allowing us to play around with the specificities of femtosecond and nanosecond PLD. We also explored different RTA processing paths, modifying the oxygen pressure, duration, heating rate, etc. We observed significant changes in the global nature of the deposited material; in particular, nanoparticles or partially dewetted films were obtained, allowing us to limit the thermo-optical transition to the near-infrared domain without affecting longer wavelengths and with good control of the electrical conductivity. This is achieved while maintaining a remarkable transmission in the visible domain. These findings could impact a range of selected applications, especially in optical and thermal detection for microelectonics
Multiscale characterization of the wettability of thin film metallic glasses surfaces: Effect of a fs-laser treatment
No full textInternational audienceWith the absence of crystalline defects and their amorphous structure, metallic glasses (MGs) exhibit very interesting mechanical and chemical properties. They have been studied since the 60s in their bulk state (BMGs), but are size limited and complex to synthesize due to their high needed number of elements. More recently, it was proved that PVD processes exhibit high cooling rate of the deposited atoms to allow the formation of metastable amorphous metallic phases [1]. Thus, metallic glasses are easier to obtain by PVD in thin film form than bulk ones. In addition, the thin film approach allows a great freedom in the films’ chemistry.From pure metallic targets, the magnetron sputtering process has already shown its ability to synthesize binary Zr-Cu thin film metallic glasses (TFMGs) over a wide range of chemical compositions (from 13 to 85 at.% of Cu [2]). These films exhibited a very low surface roughness together with the absence of grain boundaries, making them suitable for a femtosecond laser treatment [3], in order to still improve their properties. The laser irradiation process allows a one-step modification with a great repeatability, and gives rise to localized topographic and chemical modifications at the surface of the thin film.The work proposed here considers the formation of laser induced periodic surface structures (LIPSS) at the surface of two ternary magnetron sputtered TFMGs (ZrCuAg and ZrTiAg, with interesting biological properties [4-5]) using infrared ultrashort laser treatment. Several surface texturations are created by controlling the parameters of the laser (fluence, recovering of the pulses, etc…). These surfaces are first studied in terms of topographic (through scanning electron microscopy and atomic force microscopy) and chemical modifications, then a focus on the wettability modification of the textured surfaces (hydro-phily/phoby) is proposed. Wettability is studied first at the macroscale from the conventional measurement of the water contact angle of small water droplets. On the other hand, the condensation process of water onto the surface is also measured at the microscale by in situ measurements conducted in an environmental scanning electron microscope. Such a complementary small-scale method gives key information on the interaction of very small water droplets with the textured surface. Wetting behaviour is then discussed in light of the surface chemical nature and texture.[1] C.-Y. Chuand, et al., Surface and Coatings Technology, 215, 2013[2] M. Apreutesei, et al., Journal of Alloys and Compounds, 619, 2015[3] M. Prudent, et al., Nanomaterials, 11(5), 2021[4] A. Etiemble, et al., Journal of Alloys and Compounds, 707, 2019[5] A. Jabed, et al., Surface and Coatings Technology, 372, 201
Photobleaching Effect on the Sensitivity Calibration at 638 nm of a Phosphorus-Doped Single-Mode Optical Fiber Dosimeter
No full textInternational audienceWe investigated the influence of the photobleaching (PB) effect on the dosimetry performances of a phosphosilicate single-mode optical fiber (core diameter of 6.6 µm) operated at 638 nm, within the framework of the LUMINA project. Different irradiation tests were performed under ~40 keV mean energy fluence X-rays at a 530 µ Gy(SiO2)/s dose rate to measure in situ the radiation-induced attenuation (RIA) growth and decay kinetics while injecting a 638 nm laser diode source with powers varying from 500 nW to 1 mW. For injected continuous power values under 1 µW, we did not measure any relevant influence of the photobleaching effect on the fiber radiation sensitivity coefficient of ~140 dB km−1 Gy−1 up to ~30 Gy. Above 1 µW, the fiber radiation sensitivity is significantly reduced due to the PB associated with the signal and can decrease to ~80 dB km−1 Gy−1 at 1 mW, strongly affecting the capability of this fiber to serve as a dosimeter-sensitive element. Higher power values up to 50 µW can still be used by properly choosing a pulsed regime with periodic injection cycles to reduce the PB efficiency and maintain the dosimetry properties. Basing on the acquired data, a simple model of the photobleaching effect on a coil of the investigated fiber is proposed in order to estimate its sensitivity coefficient evolution as a function of the cumulated dose and its fiber length when injecting a certain laser power. Additional studies need to investigate the influence of the temperature and the dose rate on the PB effects since these parameters were fixed during all the reported acquisitions
14 MeV and Atmospheric Neutron Monitoring Through Optical Fiber Dosimeters
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Sensitivity Enhancement of Tapered Cerium-Doped Optical Fibers for Dosimetry Applications
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AuNPs amplification in surface plasmon resonance imaging for the detection of micro-RNAs in the context of organ donation
No full textInternational audienceWe present a Surface Plasmon Resonance Imaging (SPRI) biochip system to quantitatively detect micro-RNAs involved in the cytokine storm during an inflammatory response. The thiol composition of the self-assembled monolayer on the biochip gold surface was tuned to maximize the capture of RNAs at low concentrations. To further amplify this signal, we have developed a sandwich-like assay using oligonucleotides functionalized gold nanoparticles (AuNPs), synthesized at ambient temperature and optimized to have a high solubility in saline solutions. Sub-picomolar detection limit of those small RNAs was achieved with all these combined improvements
Derby LLM : Évaluation comparative des approches RAG et fine-tuning
No full textNational audienceLes grands modèles de langage ont récemment été largement exploités dans les agents conversationnels, où l’injection de connaissances pour des domaines d’applications spécifiques est un enjeu crucial. Nous comparons deux approches : le fine-tuning et la génération augmentée de récupération. Nous évaluons ces techniques pour deux cas d’usage différents avec des métriques automatiques et la préférence humaine. Bien que la pertinence des réponses soit proche, la fidélité et la préférence humaine avantagent la génération augmentée de récupération
Unveiling nature and consequences of tungsten oxidation upon ultrafast laser irradiation
No full textInternational audienceDespite ultrafast laser-induced topography modification becoming a recognized surface texturing technique inthe recent years, comparatively little work has focused on the accompanying chemical alterations. This studyaims to fill that gap by investigating the oxidation induced by ultrafast laser irradiation of metals, with a specificfocus on tungsten, in different environments: ambient and high vacuum (10-7 mbar). Laser irradiating conditionswere chosen to generate so-called High Spatial Frequency Laser Induced Periodic Surface Structures with a sub-100 nm period and sub-20 nm amplitude, as they are supposed to arise in a non-ablative regime. Contact anglemeasurements, Scanning Transmission electron microscopy cross-sectional images, and x-ray photoelectronspectroscopy analyses were used to investigate the surface chemistry of these structures and reveal significantstructural differences between the laser-generated oxides and those accumulated over time from ambientexposure. To establish an oxidation mechanism during laser interaction with tungsten, Two Temperature Modeland Molecular Dynamics simulations (TTM-MD) were conducted to determine the temperature evolution overtime. The simulation results, complemented by oxygen diffusion data, provide a predictive insight into thedevelopment of a thin oxide layer induced by laser irradiation, a conclusion substantiated by the STEM images.These findings suggest that oxidation can occur mostly by solid-state diffusion while the surface is still in theprocess of cooling down to room temperature following ultrafast photoexcitation
Evaluation of liver viability for transplantation by fluorescence spectroscopy
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Multi-Terminal GaInP/GaInAs/Ge Solar Cells for Subcells Characterization
No full textInternational audienceImprovement of triple-junction (3J) III-V/Ge solar cells efficiency is hindered by the low current produced by the top and middle cells relative to the bottom cell (Ge). This can be explained by the difficulty of characterizing, on an individual basis, the subcells. We investigate the fabrication process of multi-terminal multi-junction solar cells (MTMJSC) and its potential as a promising architecture to independently characterize subcells of multi-junction solar cells. Here, we study monolithic triple-junction solar cells, with an InGaP top cell, an InGaAs middle cell and a Ge bottom cell interconnected by tunnel junctions. We demonstrate a fabrication process for MTMJSC on commercial wafers for characterization applications purposes. I-V measurements, under illumination, of two-terminals and MTMJSC were compared to validate that the MTMJSC fabrication process does not degrade the cells’ performance. The dark current of each subcell was also measured and an ideal-diode model used to determine the subcells electrical parameters. The results suggest a method to measure the relative absorption and the opto-electrical couplings between the subcells unambiguously, through EQE and electroluminescence measurements, based on basic micro-fabrication processes