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Aluminum Nanoparticles for Photobleaching Resistance of Quantum Dots in Solution
No full textInternational audienceWe report on the optical properties of aluminum spherical nanoparticles exhibiting diameters ranging between 2 and 20 nm made by the reduction of aluminum ions in alkane solvents. In the UV-range, the extinction spectroscopy measurements unveiled well-defined surface plasmon resonances corresponding to the calculations performed using Mie theory. Furthermore, a photobleaching resistance effect appears for semiconductor quantum dots (QDs) in a solution containing aluminum nanoparticles. The particles allowed for a global increase in the number of photons emitted by a factor of up to 1.75 compared to QDs alone. Our investigation led us to the conclusion that the aluminum nanoparticles initially absorb a part of the emitted light and prevent the photobleaching of the QDs. Thus, these nanoparticles have the potential to be used as elementary building blocks for making more complex aluminum nanostructures for nanophotonics and also to protect emitters from photobleaching.</div
Resilient stepped transmission and control for nonlinear systems against DoS attacks
No full textInternational audienc
Quantum Coherent Transport of 1D ballistic states in second order topological insulator BiBr
No full textMain text and Supplemental materialWe investigate quantum transport in micrometer-sized single crystals of BiBr, a material predicted to be a second-order topological insulator. 1D topological states with long phase coherence times are revealed via the modulation of quantum interferences with magnetic field and gate voltage. In particular, we demonstrate the existence of Aharanov-Bohm interference between 1D ballistic states several micrometers long, that we identify as phase-coherent hinge modes on neighbouring step edges at the crystal surface. These Aharanov-Bohm interferences are made possible by a disordered phase-coherent contact region, the existence of which is confirmed by STEM/EDX imaging of FIB lamellae. Their coherent nature modulates the transmission of the 1D edge states, leading to weak antilocalization and universal conductance fluctuations with surprisingly large characteristic fields and a strongly anisotropic behavior. These complementary experimental results provide a comprehensive, coherent description of quantum transport in BiBr, and establishes the material as belonging to the class of second-order topological insulators with topologically protected 1D ballistic states
Biosensors integrated within wearable devices for monitoring chronic wound status
No full textInternational audienceSlowly healing wounds significantly affect the life quality of patients in different ways, due to constant pain, unpleasant odor, reduced mobility up to social isolation, and personal frustration. While remote wound management has become more widely accepted since the COVID-19 pandemic, delayed treatment remains frequent and results in several wound healing related complications. As inappropriate management of notably diabetic foot ulcers is linked to a high risk of amputation, effective management of wounds in a patient-centered manner remains important to be implemented. The integration of diagnostic devices into wound bandages is under way, owing to advancements in materials science and nanofabrication strategies as well as innovation in communication technologies together with machine learning and data-driven assessment tools. Leveraging advanced analytical approaches around local pH, temperature, pressure, and wound biomarker sensing is expected to facilitate adequate wound treatment. The state-of-the-art of time-resolved monitoring of the wound status by quantifying key physiological parameters as well as wound biomarkers' concentration is presented herewith. A special focus will be given to smart bandages with on-demand delivery capabilities for improved wound management.</div
Null controllability of a highly coupled fourth-order parabolic system with one internal control
No full textControlling systems of partial differential equations with fewer controls than states has been a central topic in the last decades. The nature of the equations and existing couplings are key factors to consider. Even if we can find several works for parabolic systems, there are only a few for fourth-order equations. In this paper, we use the fictitious control method and the algebraic resolution method, as introduced by Coron and Lissy, in order to prove the null controllability of a highly coupled fourth-order parabolic system with only one control input.</div
Phenomena, Ideas & Mechanisms: Introducing the Essays in History of Physics and Mathematics
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Étude de la linéarité et de la fiabilité de composants HEMT GaN pour des applications en gamme d’ondes millimétriques
No full textGaN HEMTs have already demonstrated outstanding RF performance at millimeter-wavefrequencies, establishing them as the leading technology for high-power and high-efficiencyapplications such as radar, space systems, and 5G/6G communications. With these capabilitiesnow largely validated, research attention is increasingly directed toward other remainingbottlenecks such as reliability and linearity at the device level. Reliability is a critical concernfor short gate length devices around 100 nm, where degradation mechanisms and limitsremain insufficiently understood and device qualification is still lacking. In parallel, linearityhas become a stringent requirement alongside high efficiency, since modern communicationsystems employ complex modulation schemes that demand highly linear amplification.Trapping effects are widely recognized as central to these challenges, as they impact nearly allkey figures of merits, including output power, efficiency, reliability, and potentially linearity, making their thorough understanding essential.In this thesis, on-wafer short-term HTOL measurements using active load pull were used toevaluate the early reliability of different mmWave GaN HEMT technologies. To enable linearitystudies, a two-tone active load-pull bench operating at 40 GHz designed and implemented.Such experimental setups are exceptionally rare in the literature at millimeter-wavefrequencies, making this contribution particularly distinctive. For trapping investigations, adedicated drain current transient (DCT) spectroscopy system was likewise developed,enabling accurate characterization of trap dynamics.Experimental measurements were further combined with TCAD-calibrated simulations to provide deeper physical insights on selected phenomena.The experimental work focused primarily on state-of-the-art GaN HEMTs operating at 40GHz.carbon-doped AlN/GaN devices with an AlGaN back-barrier, and promising buffer-freeQuanFINE structures. For trapping investigations, however, a broader range of devicetechnologies was examined, thereby overcoming a limitation of many prior works that focuson a single platform. Particular attention was given to the influence of bias conditions on thetrap time constants and on the full kinetics of the detrapping process.Several important findings emerged from this research. Carbon-related deep levels wereidentified in both GaN and AlGaN, with carbon doping shown to introduce similar trapcharacteristics in both materials. The origin of the non-Arrhenius behavior observed in thecarbon related traps was investigated and explained. In devices with an AlGaN back-barrier, aparasitic channel was identified, and its physical origin determined. The mechanismresponsible for the kink effect in carbon-doped devices was also clarified. In QuanFine devices,traps located at the GaN channel/AlN nucleation layer interface were revealed andsuccessfully suppressed through stack engineering.Concerning reliability, degradation mechanisms were identified in carbon-doped devices, witha direct correlation established between trapped charge accumulation and performancedegradation. A clear temperature-dependent degradation was also observed. In buffer-freeQuanFINE devices, distinct degradation mechanisms were identified, and correspondingmitigation strategies were proposed.Finally, preliminary linearity measurements were performed using the developed load-pullbench, providing the first insights into the intrinsic nonlinear behavior of short-gate-lengthGaN HEMTs at millimeter-wave frequencies.Les transistors HEMT à base de nitrure de gallium (GaN) ont déjà démontré d’excellentes performances RF aux ondes millimétriques, s’imposant comme une technologie clé pour les applications à forte puissance et à haut rendement telles que le radar et les systèmes spatiaux, et constituant un candidat potentiel pour les communications 5G/6G. Ces capacités étant désormais largement validées, les travaux de recherche se concentre de plus en plus sur d’autres verrous, comme la fiabilité et la linéarité au niveau du transistor. La fiabilité est une préoccupation critique pour les dispositifs à courte longueur de grille autour de 100 nm, où les mécanismes de dégradation restent insuffisamment compris et où des technologies qualifiées sont très rare. En parallèle, la linéarité est devenue une exigence stricte, en plus d’un haut rendement, car les systèmes de communication modernes utilisent des modulations complexes qui demandent une amplification très linéaire.Les effets de piégeage sont reconnus comme centraux dans ces défis, car ils impactent presque toutes les figures de mérites, y compris la puissance de sortie, le rendement, la fiabilité et potentiellement la linéarité, rendant leur compréhension approfondie essentielle.Dans cette thèse, des mesures HTOL sous pointes, ont été employées pour évaluer la fiabilité à court termes de différentes technologies HEMT GaN aux ondes millimétriques. Pour permettre des études de linéarité, un banc load-pull actif 2-tons à 40 GHz a été conçu et réalisé. De tels bancs sont rares dans la littérature aux ondes millimétriques, ce qui rend cette contribution particulièrement notable. Pour l’étude du piégeage, un système de spectroscopie du courant de drain transitoire (DCT) a également été développé, permettant la caractérisation approfondie despièges.Des mesures expérimentales ont été combinées à des simulations TCAD afin d’apporter des clarifications physiques plus profondes sur certains phénomènes physiques.Les travaux de caractérisation se sont concentrés sur des HEMT GaN à l’état de l’art : des transistors AlN/GaN dopés carbone, ainsi que des structures QuanFINE prometteuses sans couche tampon (buffer-free). Pour l’investigation des phénomènes de piégeage, un éventail plus large de technologies a toutefois été examiné, dépassant la limite de nombreux travaux antérieurs focalisés sur une seule plate-forme. Une attention particulière a été portée à l’influence des conditions de polarisation sur les constantes de temps des pièges et la cinétique du dépiégeage.Plusieurs résultats importants ont émergé de ces travaux. Des pièges liés au carbone ont été identifiés dans le GaN et dans l’AlGaN, et il a été montré que le carbone introduit des pièges de caractéristiques similaires dans les deux matériaux. L’origine du comportement non-Arrhenius observé pour les pièges liés au carbone a été étudiée et expliquée. Dans les dispositifs avec back-barrière AlGaN, un canal parasite a été identifié et son origine physique déterminée. Le mécanisme responsable de l’effet « kink » dans les transistors dopés au carbone a également été clarifié. Dans les dispositifs QuanFINE, des pièges situés à l’interface entre le canal GaN et la couche de nucléation AlN ont été mis en évidence et supprimés avec succès par ingénierie de l’épitaxie.Concernant la fiabilité, des mécanismes de dégradation ont été identifiés dans les dispositifs dopés au carbone, avec l’établissement d’une corrélation directe entre les phénomènes de piégeage et la dégradation. Un phénomène de dégradation dépendant clairement de la température a également été observée. Dans les transistors QuanFINE, des mécanismes de dégradation distincts ont été identifiés et des stratégies de mitigation ont été proposées.Enfin, des mesures préliminaires de linéarité ont été réalisées à l’aide du banc load-pull 2-tons développé, fournissant de premières indications sur le comportement non linéaire des HEMT GaN aux ondes millimétriques
Inverted BER Trends for Energy-Detected GRSM-MQAM Massive MIMO Downlink
No full textNational audienceThis work investigates Generalized Receiver Spatial Modulation (GRSM) in a massive MIMO downlink scenario over millimetre wave channels. While GRSM enhances spectral efficiency (SE) and reduces power consumption, indexing additional bits using the spatial dimension increases the vulnerability to detection errors. These errors primarily stem from thresholddependent spatial detection. We propose a novel predefined threshold computation method minimizing spatial detection errors, rigorously validated through the Maximum A Posteriori (MAP) criterion. Furthermore, we derive an analytical Average Bit Error Probability (ABEP) expression tailored for energy detection, exploiting inherent constellation energy distributions. The analytical derivation was validated via link-level simulations under two scenarios: (i) perfect spatial detection, and (ii) practical spatial detection. The results show spatial errors dominating overall performance, shifted from theoretical values by practical spatial detection using multiple thresholds for different energy levels in 16QAM. Crucially, an inverted error trend revealed between GRSM-4QAM and GRSM-16QAM, highlighting a tradeoff between error resilience, complexity, and energy efficiency