HAL Portal UPHF (Université Polytechnique Hauts-de-France)
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Espace et mobilier liturgiques de la cathédrale Notre Dame de Tournai, 1566 - 1792. Essai de reconstitution et interprétation
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Addressing Machine Unavailability in Job Shop Scheduling: A Quantum Computing Approach
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Van der Waals epitaxial growth of few layers WSe2 on GaP(111) B
No full textWe acknowledge the financial support from the Tunne2D (ANR-21-CE24-0030) and ADICT (ANR-22-PEEL-0011) projects, as well as from the French technological network RENATECH and Region Hauts-de-France.International audienceAbstract 2D material epitaxy offers the promise of new 2D/2D and 2D/3D heterostructures with their own specific electronic and optical properties. In this work, we demonstrate the epitaxial growth of few layers WSe 2 on GaP(111) B by molecular beam epitaxy. Using a combination of experimental techniques, we emphasize the role of the growth temperature and of a subsequent annealing of the grown layers under a selenium flux on the polytype formed and on its structural and morphological properties. We show that a low growth temperature promotes the formation of the 1T′ and 3R phases depending on the layer thickness whereas a higher growth temperature favours the stable 2H phase. The resulting layers exhibit clear epitaxial relationships with the GaP(111) B substrate with an optimum grain disorientation and mean size of 1.1° and around 30 nm respectively for the 2H phase. Bilayer 2H WSe 2 /GaP(111) B heterostructures exhibit a staggered type II band alignment and p-doped character of the epi-layer on both p and n-type GaP substrates. This first realisation of stable p-type WSe 2 epi-layer on a large-area GaP(111) B substrate paves the way to new 2D/3D heterostructures with great interests in nanoelectronic and optoelectronic applications, especially in the development of new 2D-material p-n junctions
Thermoelectric characterization of crystalline nano-patterned silicon membranes
No full textInternational audienceResearch towards efficient and environmentally friendly thermoelectrics proposes silicon nanostructures as possible candidates through reduction of the phononic thermal conductivity. However, there is scarce literature about experimental measurements of the thermoelectric figure-of-merit zT on actual crystalline silicon devices. This article reports on the fabrication and full thermoelectric characterization of crystalline 60 nm thick membranes. To that end, an experiment with four types of built-in devices was designed using a silicon-on-insulator substrate to extract the Seebeck coefficient, electrical conductivity and thermal conductivity. The results show indeed a reduced thermal conductivity of 31 W m K for a 60 nm thick Si membrane and = 18 W m K for a porous Si membrane. This reflects an 88% reduction in thermal conductivity compared to the bulk Si material and a 42% reduction compared to plain Si membranes. In terms of power generation, the power factor of the fabricated devices surpasses that of state-of-the-art silicon thin films at room temperature. Notably, a zT figure of merit of 0.04 is reported for a 60 nm thick phonon-engineered Si membrane, which is considerably higher than that of bulk Si(0.001) but lower than previously reported results on other types of nano-objects
Étude multi-échelle de la transition induite par le champ électrique dans la phase de Mott des cristaux de GaMo4S8 et des monocouches de TaSe2
No full textIn the realm of condensed matter physics, Mott insulators are essential for exploring complex electronic phenomena, with significant implications for high-temperature superconductivity and quantum spin liquids. This thesis investigates two types of such materials, distinguished by their dimensionality : GaMo4S8 crystals and monolayer 1T-TaSe2.After presenting their properties in the first chapter, the second chapter addresses the local-scale characterization techniques used to characterize both materials, namely scanning tunneling microscopy and spectroscopy for structural and electronic studies, and multi-tip scanning tunneling microscopy for transport measurements. The latter technique was particularly employed to analyze transport in GaMo4S8. The study then delved into the material response to external electric fields, examining the threshold electric field in relation to the electrode geometry and exploring the temporal evolution of switching times in connection with inter-electrode distances. The achievement of volatile transitions opens prospects for applications such as the operation of a microneuron at room temperature.To enhance the control over phase transition properties of Mott insulators, it is beneficial to consider two-dimensional systems where the current flow is restricted within the crystal plane. The final chapter focuses on the 1T phase of TaSe2, epitaxially grown on gallium phosphide (GaP) semiconductor substrates. Low-temperature scanning tunneling microscopy studies reveal that 1T-TaSe2 monolayers exhibit not only the characteristic charge density modulation (Star of David) of the charge density wave phase but also a unique Moiré pattern due to the monolayer interaction with the GaP substrate. Scanning tunneling spectroscopy has identified a bandgap, hallmark of the Mott insulating state. This state is further substantiated by temperature-dependent transport measurements that show the persistence of the insulating phase up to 400 kelvins. Notably, spectroscopic measurements with varying tip-to-surface distances have unveiled insulator to metal transitions at low temperatures. The observation of such transitions suggests that this large-scale heterostructure could be a material of choice for neuromorphic applications.Dans le domaine de la physique de la matière condensée, les isolants de Mott sont essentiels pour explorer des phénomènes électroniques complexes, ayant des implications significatives pour la supraconductivité à haute température et les liquides de spin quantiques. Cette thèse porte sur deux types d'isolants de Mott qui se distinguent l'un de l'autre par leur dimensionalité : des cristaux de GaMo4S8 et des monocouches de 1T-TaSe2.Après avoir introduit leurs propriétés dans le premier chapitre, le second chapitre traite des techniques utilisées pour caractériser ces matériaux à l'échelle locale, d'une part la microscopie et spectroscopie à effet tunnel pour mener une étude structurale et électronique et d'autre part la microscopie à effet tunnel à pointes multiples pour effectuer des mesures de transport.Cette dernière technique a notamment servi à analyser le transport dans GaMo4S8. Nous nous sommes alors intéressés à la réponse du matériau aux champs électriques externes, examinant le champ électrique seuil en fonction de la géométrie des électrodes et explorant l'évolution temporelle des temps de commutation en relation avec les distances inter-électrodes. L'obtention de transitions volatiles ouvre la voie à des applications telles que l'opération d'un microneurone à température ambiante.Pour mieux contrôler les propriétés de transition de phase des isolants de Mott, il est intéressant de considérer des systèmes bidimensionnels dans lesquels le passage du courant est confiné dans le plan du cristal. Aussi, le dernier chapitre se rapporte à la phase 1T du TaSe2, épitaxiée sur des substrats semi-conducteurs de phosphure de gallium (GaP). Comme le révèle l'étude réalisée par microscopie à effet tunnel à basse température, les monocouches de 1T-TaSe2 ne présentent pas seulement la modulation de la densité de charge (étoile de David) caractéristique de la phase onde de densité de charge, mais aussi un motif de Moiré original dû à l'interaction de la monocouche avec le substrat de GaP. Dans cette phase, caractérisée par spectroscopie tunnel, une bande interdite a été mise en évidence, signature de l'état isolant de Mott à basse température. L'état de Mott est corroboré par des mesures de transport dépendant de la température, qui indiquent la persistance de la phase isolante jusqu'à 400 kelvins. De plus, des mesures spectroscopiques à distance pointe-surface variable ont montré l'existence de transitions isolant-métal à basse température. L'observation de telles transitions permet d'envisager l'utilisation de cette hétérostructure à grande échelle comme candidat potentiel en tant que matériau neuromorphique
Direct Electrodeposition of Electrically Conducting Ni 3 (HITP) 2 MOF Nanostructures for Micro‐Supercapacitor Integration
No full textInternational audienceAbstract Micro‐supercapacitors emerge as an important electrical energy storage technology expected to play a critical role in the large‐scale deployment of autonomous microdevices for health, sensing, monitoring, and other IoT applications. Electrochemical double‐layer capacitive storage requires a combination of high surface area and high electronic conductivity, with these being attained only in porous or nanostructured carbons, and recently found also in conducting metal–organic frameworks (MOFs). However, techniques for conformal deposition at micro‐ and nanoscale of these materials are complex, costly, and hard to upscale. Herein, the study reports direct, one step non‐sacrificial anodic electrochemical deposition of Ni 3 (2,3,6,7,10,11‐hexaiminotriphenylene) 2 – Ni 3 (HITP) 2 , a porous and electrically conducting MOF. Employing this strategy enables the growth of Ni 3 (HITP) 2 films on a variety of 2D substrates as well as on 3D nanostructured substrates to form Ni 3 (HITP) 2 nanotubes and Pt@ Ni 3 (HITP) 2 core–shell nanowires. Based on the optimal electrodeposition protocols, Ni 3 (HITP) 2 films interdigitated micro‐supercapacitors are fabricated and tested as a proof of concept
A Versatile Balun Based on a Power Divider Topology
No full textInternational audienceThis paper presents an original balun concept based on a power divider topology. The proposed concept simplifies the design compared to a Marchand balun by eliminating the interconnection problem between the two couplers forming the Marchand balun. Furthermore, the proposed concept is highly versatile and allows for the straightforward realization of a double balun, with a single input and two differential outputs, without resorting to a cascade of differential power dividers. For simplicity, the concept is demonstrated in PCB technology using transdirectional couplers to overcome dimensional constraints associated with coupled-lines backward couplers, but this concept will be highly effective for balun design in CMOS technology in millimeter-wave bands beyond the hundred GHz range. The results lead to single-to-differential insertion loss of less than 0.5 dB at the operating frequency of 2 GHz, a return loss better than 15 dB, and a 3-dB bandwidth of around 40%
Ultrafast skyrmion generation by plasmonic resonance
No full textInternational audienceThis theoretical study unveils the potential for ultrafast skyrmion generation in magnetic thin films, driven by the remarkable plasmonic properties of gold nanoparticles. By combining the plasmonic, photothermal, and micromagnetic analysis, we explore size-dependent light absorption, resonance wavelength, and electric field distribution around the nanoparticles. Our findings highlight the crucial role of the insulating layer's thickness in enhancing plasmonic effects, offering tunable absorption characteristics. Micromagnetic calculations demonstrate the efficient creation of Néel skyrmions in the range of a few tens of ps, showcasing a breakthrough in magnetic phenomena and opening thus a path for functional skyrmionic-based devices