Publications

2024

• Synthèse d'hétérostructures hybrides TMDs@SWCNTs à haute cristallinité : Vers des photodétecteurs et des capteurs de gaz de nouvelle génération
  
  • Taoum Haifa
  , 2024. The evolution of Si-based technologies is approaching intrinsic limits, driving the need for innovative materials and architectures that support advanced miniaturization, high sensitivity, and low-power operation in electronic devices. Among the promising candidates are transition metal dichalcogenides (TMDs), whose atomic-scale thickness and unique optoelectronic properties, have garnered attention for applications such as photodetection and gas sensing. However, achieving high-crystallinity TMDs synthesis, with controlled growth parameters, via molecular beam epitaxy (MBE), remains challenging, often limiting performance in practical applications. In parallel, single-walled carbon nanotubes (SWCNTs) offer unique properties, such as high specific surface area, tunable conductivity, and mechanical stability, that can enhance device functionality when integrated with TMDs. Combining the merit of these two classes of materials in a hierarchical arrangement can unlock a new realm of multifunctional devices with enhanced performance.This thesis explores the synthesis and characterization of high crystalline TMDs@SWCNTs van der Waals (vdW) hybrid heterostructures and their implementation in device structures.TMDs (molybdenum disulfide (MoS2) and tungsten disulfide (WS2) growth by MBE were investigated. The van der Waals epitaxial growth of these TMDs (MoS2 and WS2) has demonstrated high crystalline structures on large lattice-mismatched substrates (quartz and C-sapphire) without compromising material integrity. We explored a novel approach based on ultra-high vacuum techniques (UHV), in a home-built reactor, through sequential Hot-filament chemical vapor deposition (HF-CVD) /MBE offering highly controlled growth on quartz substrates. We achieved the synthesis of TMDs@SWCNTs hybrid structures that exhibit high crystallinity, uniform thickness up to 10 nm, and precise interfacial bonding. The fundamental role of SWCNTs in the growth mechanisms of WS2 and MoS2 is elucidated through comprehensive in-situ/operando and ex-situ characterizations, leading to a proposed growth mechanism based on the obtained experimental results.Detailed material characterization, including Raman spectroscopy, surface electron spectroscopy techniques, and transmission electron microscopy (TEM), demonstrates the structural integrity and high crystallinity of the TMD layers grown on SWCNT templates, while also confirming the charge transfer between these materials. Integrated as an active channel into a device, the as-grown heterostructures have proven remarkable optical properties, achieving high Responsivity (~8.1 × 103 A/W) and Detectivity (~2.91 × 1013 Jones) for detecting near-ultraviolet light. Additionally, the synthesized TMDs@SWCNTs exhibit a high density of exposed edge sites on TMD nanoflakes, that enhance the adsorption of target gas molecules and facilitate faster response in sensing applications. Environmental humidity exposure testing further demonstrated the stability of these heterostructures, which is attributed to the distinctive electronic interactions at the TMD-SWCNT interface. Moreover, the heterostructures display contrasting intrinsic electronic properties and tunable doping effects (p and n doping), underscoring their versatility and possibility to be integrated into multifunctional devices.The work presented here underscores the potential of TMDs@SWCNTs heterostructures as scalable, high-performance materials for next-generation gas sensors and photodetectors. By advancing the understanding of nucleation and growth dynamics of hybrid nanostructures, this research paves the way for integrating TMDs and SWCNTs into versatile sensing platforms with superior response characteristics, laying a foundation for applications spanning environmental monitoring and optoelectronics.
• Advanced Photovoltaic Degradation Analysis using Physics Modeling and Bayesian Machine Learning
  
  • Chakar Joseph
  , 2024. The forecast for solar energy is bright. However, ensuring this prediction holds in the real world depends on our capacity to understand and limit the impact of degradation on performance. Indeed, established solar cell technologies like silicon and emerging ones like perovskites are susceptible to a wide array of internal and external factors that can impair their performance and, thereby, their commercial viability. Although experimental techniques exist for studying degradation, their accessibility is limited by their costly, time-consuming, and expert-dependent implementation. Fortunately, with today's computing advancements, the coupling of physical modeling with artificial intelligence offers a swift way to analyze degradation from readily available performance data. Nonetheless, the complex and multifaceted nature of this task is unsuitable for traditional machine learning techniques designed to find a single optimal solution. In this context, probabilistic Bayesian approaches stand out by offering a framework to explore the range of possible solutions, quantify prediction uncertainty, understand parameter interdependencies, and update conclusions as additional data becomes available. This work presents a set of open-access Python-based Bayesian tools for photovoltaic degradation analysis, showcasing their superior effectiveness and flexibility compared to existing solutions across diverse applications at the solar cell and module levels.
• Solution-processed functionalized MoS2 for room temperature NO2 chemiresistive sensors
  
  • Ni Pingping
  , 2024. In response to environmental and public health issues, sensors for toxic and/or polluting gases are at the core of extensive research and innovation. Therefore, their development is important and also a major challenge for society. Up to date for gas sensing applications, metal oxide chemiresistive sensors are the most widely investigated devices thanks to their ease in fabrication, simplicity of operation, and facile integration in miniaturization. However, their high working temperature restricts their implementation in the wearable, flexible devices. Two-dimensional (2D) materials possess great potential in serving as a gas-sensing layer in wearable gas sensors due to their excellent mechanical flexibility, large specific surface areas, strong surface activities with a high gas sensitivity. Among this family, transition metal chalcogenides (TMDs), such as molybdenum disulfides (MoS2), exhibit outstanding properties thanks to its tunable band gap, and are also promising candidates for the detection of toxic gas at room temperature.This thesis aims to fabricate and optimize nitrogen dioxide (NO2) chemiresistive gas sensors based on solution-processed 2D MoS2. The first step in the work involved the development and the optimization of liquid phase exfoliation process to produce colloidal suspensions of MoS2 nanosheets on a large scale. In parallel, we assessed vacuum-assisted filtration and liquid/liquid interfacial self-assembly as two thin film fabrication techniques from individual nanosheets. Besides 2D MoS2 dispersion production and thin film processing, a multiscale physicochemical characterization of the produced MoS2 through microscopic and spectroscopic techniques, coupled with electrical measurements was conducted to determine the optimal exfoliation conditions to obtain MoS2 nanosheets and the morphologies of thin films produced by two distinct deposition processes. Then, MoS2 thin film fabricated by vacuum-assisted filtration with gold interdigitated electrodes on top were assessed for NO2 gas sensing, which exhibited a moderate sensitivity to a low NO2 concentration down to 1 ppm at room temperature. However, full recovery of NO2 sensing cannot always be achieved due to the MoS2 NSs atom vacancies generated during liquid shear exfoliation. To solve this issue, we passivated these vacancies on MoS2 nanosheets with gold nanoparticles (Au NPs). The functionalization of MoS2 nanosheets with Au NPs improved the sensitivity towards NO2 and lowered the recovery time compared to bare MoS2 sensor.
• Selective Passivation of 2D MoS2 Nanosheets Surface Defects by Spontaneous Growth of Au Nanoparticles for Full Response-Recovery NO2 Detection at Room Temperature
  
  • Ni Pingping
  • Maina Elmehdi Ould
  • Dembélé Kassiogé
  • Dragoe Diana
  • Bouanis Fatima Zahra
  • Yassar Abderrahim
  Surfaces and Interfaces, Elsevier, 2024, 55, pp.105372. Full recovery at RT is quite challenging for two dimensional transition metal dichalcogenides chemiresistive gas sensors. The main reason for the incomplete recovery is the strong bonding of gas molecules onto sensing layer defects. Here, we show that the recovery rate of MoS2 chemiresistive NO2 sensors can be improved by selective passivation of MoS2 nanosheets (NSs) defects with Au nanoparticles (NPs) via a simple spontaneous reduction method. MoS2 NSs were produced by liquid shear exfoliation. Pristine and Au NPs functionalized MoS2 were characterized using ς-potential, UV-Visible spectroscopy, TEM, SEM, AFM, EDS, XRD, XPS and Raman spectroscopy. The analyses confirm the presence of Au NPs on the edges of MoS2 NSs at defective sites with NP sizes of 1-4 nm and 5-30 nm. Both pristine MoS2 and Au-decorated MoS2 NSs were employed to fabricate NO2 chemiresistive devices. Au-decorated MoS2 sensors showed an improved performance (for 1 ppm NO2, Au-MoS2 sensor exhibited a response of 5.6% instead of 2.2% for MoS2 sensor), and gave faster response and better recovery time. Concurrently, the functionalization is independent of the adsorption and desorption of NO2. Most importantly, the functionalization of MoS2 NSs helps to full responserecovery within one hour, without either thermal or UV irradiation treatment. (10.1016/j.surfin.2024.105372)
  DOI : 10.1016/j.surfin.2024.105372
• Full-field multispectral Mueller polarimetric imaging to explore microscopic properties of post-caesarian healed uterine tissue
  
  • Courilleau A.
  • Vanel J.C.
  • Debras Elodie
  • Pierangelo A.
  , 2024, pp.1-2. We present the preliminary results obtained using a Mueller polarimetric imaging technique to characterize uterine specimens to extend the understanding of microscopic mechanisms involved in post-caesarian uterine healing, and to determine predictive parameters correlated to associated risks with future pregnancies, based on polarimetric signatures. (10.1109/IPC60965.2024.10799668)
  DOI : 10.1109/IPC60965.2024.10799668
• Simulating organic thin film transistors using multilayer perceptron regression models to enable circuit design
  
  • Calvet Laurie E
  • El-Nakouzi Sami
  • Li Zonglong
  • Kim Yerin
  • Zaibi Amer
  • Golec Patryk
  • Bhattacharyya Mei
  • Bonnassieux Yvan
  • Kadura Lina
  • Iniguez Benjamin
  , 2024. <div><p>There is increasing interest in using specialized circuits based on emerging technologies to develop a new generation of smart devices. The process and device variability exhibited by such materials, however, can present substantial challenges for designing circuits. We consider the use of three models: a physical compact model, an empirical look up table and an empirical surrogate model based on a multilayer perceptron (MLP) regression. Each is fit to measured discrete organic thin film transistors in the low voltage regime. We show that the models provide consistent results when designing artificial neuron circuits, but that the MLP regression provides the highest accuracy and is much simpler to fit compared to the compact model. The targeted technology exhibits non-ideal behavior such as variable threshold voltage and hysteresis. Using the multiplayer perceptron model, we compare the effect of such variability on the performance of the neuron circuit. We find that these effects alter the neuron firing rate and change the time spent in the on/off states but do not change the basic operation. V g V d V g 2 V d 2 Input Output HL1 HL2 V g V d ln(|I d |)</p></div>
• Roadmap for Schottky barrier Transistors
  
  • Bestelink Eva
  • Galderisi Giulio
  • Golec Patryk
  • Han Yi
  • Iniguez Benjamin
  • Kloes Alexander
  • Knoch Joachim
  • Matsui Hiroyuki
  • Mikolajick Thomas
  • Niang Kham M
  • Richstein Benjamin
  • Schwarz Mike
  • Sistani Masiar
  • Sporea Radu A
  • Trommer Jens
  • Weber Walter M
  • Zhao Qing-Tai
  • Calvet Laurie E
  , 2024. <div><p>In this roadmap we consider the status and challenges of technologies that use the properties of a rectifying metal-semiconductor interface, known as a Schottky barrier, as an asset for device functionality. We discuss source gated transistors, which allow for excellent electronic characteristics for low power, low frequency environmentally friendly circuits. Also considered are reconfigurable field effect transistors, where the presence of two or more independent gate electrodes can be used to program different functionalities at the device level, providing an important option for ultra-secure embedded devices. Both types of transistors can be used for neuromorphic systems, notably by combining them with ferroelectric Schottky barrier transistors with an increased number analog states. At cryogenic temperatures SB transistors can advantageously serve for the control electronics in quantum computing devices. If the source/drain of the metallic contact becomes superconducting, Josephson junctions with a tunable phase can be realized for scalable quantum computing applications. Developing applications using Schottky barrier devices require physics-based and compact models that can be used for circuit simulations. The roadmap reveals that the main challenges for these technologies are improving processing, access to industrial technologies and modeling tools for circuit simulations.</p></div>
• III-V epitaxy by RP-CVD : from thin film growth to solar cell devices
  
  • Watrin Lise
  , 2024. Solar cells based on III-V materials have reached the highest efficiency of any technology available today, i.e. up to 47% under concentration. However, their production cost is approximately a hundred times higher than that of c-Si solar cell, the technology that dominates the market (95% in 2023) but currently cap at around 26.8% of efficiency. Reducing the cost of III-V semiconductors would represent a major advancement towards increasing the share of solar energy in the energy mix. Specifically, combining III-V with low-cost silicon in tandem configuration would maximize energy conversion from the solar spectrum. The high price of this technology is mainly due to the III-V solar cell processing, the III-V substrate and the III-V epitaxy. This PhD thesis specifically addresses this third challenge. To this end, we have developed a new approach for the epitaxial growth of III-V materials by using a Remote Plasma Chemical Vapor Deposition (RP-CVD) reactor. The addition of a plasma in the reactor proves advantageous, as it allows (i) low pressure growth (~1 mbar vs. ~500 mbar for CVD) which contribute to a reduction of frequently toxic and expensive gases consumption, (ii) effective precursor dissociation leading to reduced growth temperature, and (iii) effective in-situ surface treatments, reducing the number and complexity of processing steps. We have developed and optimized this innovative reactor, entirely built in the laboratory (LPICM, Ecole Polytechnique), for the growth of III-V materials, namely gallium nitride (GaN) and then gallium arsenide (GaAs). For GaN, we have achieved epitaxial growth on sapphire and highly (0002) oriented growth on c-Si at a low temperature of 500°C. We have proposed an innovative solution for the direct growth of GaN on c-Si and addressed the challenges associated with using standard techniques to analyze the composition of materials produced through non-conventional processes. For GaAs, we have obtained high-quality homoepitaxial growth at 400°C and 3 µm/h, optimized doping, and developed proof-of-concept solar cells. Our work also tackles the issue of substrate cost by achieving heteroepitaxial growth on virtual substrates, all at low pressure (~ 0.5 mbar), proposing a set of viable solutions for producing high-efficiency, low-cost solar cells.
• Self-Assembled Ti3C2TX MXene Thin Films for High-Performance Ammonia Sensors
  
  • Maina Elmehdi Ould
  • Ni Pingping
  • Dembélé Kassiogé
  • Dragoe Diana
  • Yassar Abderrahim
  • Bouanis Fatima
  Applied Surface Science, Elsevier, 2024, 672, pp.160864. MXenes have emerged as a fascinating material for RT gas-sensing applications due to their outstanding properties. This work reports the design and fabrication of a high-performance ammonia sensor based on MXenes material. To improve its sensing performance, a MXenes nanosheets thin film with a thickness of ≈ 10 nm was prepared using a scalable self-assembled method. Specifically, we employed the controlled and enhanced interfacial self-assembled method to fabricate a continuous and conductive MXene ultra-thin film. The morphology and the structure of the produced MXene materials and their films were characterized by combining multi-characterization tools. Altoghether, these highlight the uniform and continuous deposition of the MXene nanosheets film on the glass substrate. The electrical characterization indicates a sheet resistance value of 4.82 × 105 Ω/sq. The fabricated devices present good RT sensing performances for NH3 detection, ranging from 1 to 20 ppm. This demonstrates the outstanding sensitivity of MXene with a value of 1.92 % for the lowest concentration (1 ppm), a fast response (179 s) and a recovery time of (612 s), which is related to the high quality of the ultra-thin MXene sensiting layer. Moreover, the sensors demonstrate high degree of stability and excellent reproducibility, make them suitable candidate for practical applications like environmental monitoring (10.1016/j.apsusc.2024.160864)
  DOI : 10.1016/j.apsusc.2024.160864
• Insights into the growth of GaN thin films through liquid gallium sputtering: A plasma-film combined analysis
  
  • Srinivasan Lakshman
  • Gazeli Kristaq
  • Prasanna Swaminathan
  • Invernizzi Laurent
  • Roca i Cabarrocas Pere
  • Lombardi Guillaume
  • Ouaras Karim
  The Journal of Chemical Physics, American Institute of Physics, 2024, 161 (15). This study presents the detailed characterization of a magnetron-based Ar–N2 plasma discharge used to sputter a liquid Ga target for the deposition of gallium nitride (GaN) thin films. By utilizing in situ diagnostic techniques including optical emission spectroscopy and microwave interferometry, we determine different temperatures (rotational and vibrational of N2 molecules, and electronic excitation of Ar atoms) and electron density, respectively. Beyond providing insights into fundamental plasma physics, our research establishes a significant correlation between gas-phase dynamics, particularly those of gallium atoms (flux and average energy at the substrate) and deposited GaN thin film properties (growth rate and crystalline fraction). These findings underscore the role of plasma conditions in enhancing thin film quality, highlighting the importance of plasma characterization in understanding and optimizing GaN thin film growth processes. (10.1063/5.0226028)
  DOI : 10.1063/5.0226028
• Insights into the growth of GaN thin films through liquid gallium sputtering: A plasma-film combined analysis
  
  • Srinivasan Lakshman
  • Gazeli Kristaq
  • Prasanna Swaminathan
  • Invernizzi Laurent
  • Roca i Cabarrocas Pere
  • Lombardi Guillaume
  • Ouaras Karim
  The Journal of Chemical Physics, American Institute of Physics, 2024, 161, pp.154709. This study presents the detailed characterization of a magnetron-based Ar–N2 plasma discharge used to sputter a liquid Ga target for the deposition of gallium nitride (GaN) thin films. By utilizing in situ diagnostic techniques including optical emission spectroscopy and microwave interferometry, we determine different temperatures (rotational and vibrational of N2 molecules, and electronic excitation of Ar atoms) and electron density, respectively. Beyond providing insights into fundamental plasma physics, our research establishes a significant correlation between gas-phase dynamics, particularly those of gallium atoms (flux and average energy at the substrate) and deposited GaN thin film properties (growth rate and crystalline fraction). These findings underscore the role of plasma conditions in enhancing thin film quality, highlighting the importance of plasma characterization in understanding and optimizing GaN thin film growth processes. (10.1063/5.0226028)
  DOI : 10.1063/5.0226028
• Electrochemical and Spectro-Microscopic Analyses of Charge Accumulation and Ion Migration in Dry Processed Perovskite Solar Cells under Electrical Biasing
  
  • Jun Haeyeon
  • Tondelier Denis
  • Geffroy Bernard
  • Florea Ileana
  • Bouree Jean-Eric
  • Lopez-Varo Pilar
  • Schulz Philip
  • Bonnassieux Yvan
  • Swaraj Sufal
  Journal of Physical Chemistry Letters, American Chemical Society, 2024, 16 (3), pp.835-847. We study the influence of the electrical biasing on the modification of the chemical composition and the electrical performance of perovskite solar cells (PSCs) by coupling Electrochemical impedance spectroscopy (EIS) and scanning transmission X-ray microscopy (STXM) techniques. EIS reveals the formation of charge accumulation at the interfaces and changes in resistive and capacitive properties. STXM study on PSCs after applying strong electric field for a long biasing time indicates the break-down of methylammonium (MA + ) cation promoting iodide ions to migrate and create defects at the interface. This complementary EIS and STXM study allows to suggest a degradation mechanism that includes the migration of iodide ions that leads to interface defects and subsequent degradation of solar cell performance. In addition, we study the evolution of the performance of PSCs under air. We observe an increased hysteresis index on current-voltage curves and fill factor reduction of the perovskite solar cells with ageing in air. EIS measurements show the formation of a capacitive layer resulting from accumulation of iodide ions through modification of the mobile ion concentration and ion mobility. (10.26434/chemrxiv-2024-mgq6l)
  DOI : 10.26434/chemrxiv-2024-mgq6l
• Microlayer evaporation during bubble growth in nucleate boiling
  
  • Tecchio Cassiano
  • Cariteau Benjamin
  • Houedec Corentin Le
  • Bois Guillaume
  • Saikali Elie
  • Zalczer Gilbert
  • Vassant Simon
  • Roca i Cabarrocas Pere
  • Bulkin Pavel
  • Charliac Jérôme
  • Nikolayev Vadim
  International Journal of Heat and Mass Transfer, Elsevier, 2024, 231, pp.125860. We experimentally investigate the near-wall heat transfer at single bubble growth in nucleate saturated pool boiling of water at atmospheric pressure. Our focus is on the evaporation of the micro-metric thin film of liquid (microlayer) that is formed between the heating wall and the bubble. High speed and high resolution optical techniques are employed. Synchronous and simultaneous measurements of the microlayer thickness, wall temperature and bubble macroscopic shape are performed by white light interferometry, infrared thermography and side-wise shadowgraphy, respectively. We measure the wall temperature of an ITO heating film through a transparent to the infrared waves porthole. The heating is provided by an infrared laser. The wall heat flux is numerically reconstructed by using the experimental wall temperature data. We reveal a temporal rise of the thermal resistance of the liquid–vapor interface during the microlayer evaporation, which corresponds to a decrease of the accommodation coefficient. We attribute it to the progressive accumulation of impurities at the interface during evaporation. The contribution of microlayer evaporation to the overall bubble growth is about 18%. (10.1016/j.ijheatmasstransfer.2024.125860)
  DOI : 10.1016/j.ijheatmasstransfer.2024.125860
• Liquid-phase shear exfoliation of graphite and its application as corrosion protection coating on aluminum substrate
  
  • El Hajj Inass
  • Laïk Barbara
  • Gassama Adama
  • Bensifia Mohamed
  • Dembélé Kassiogé
  • Jama Charafeddine
  • Monnier Judith
  • Léonard Céline
  • Yassar Abderrahim
  • Bouanis Fatima Zahra
  Surface and Coatings Technology, Elsevier, 2024, 494 (2), pp.131412. Although aluminum (Al) or its alloys are moderately protected by a native oxide layer, the presence of chloride ions in aqueous media in direct contact causes pitting attacks and accelerates corrosion. Using graphene as a coating protector can obstruct corrosion due to its numerous chemical and physical properties. This study investigates corrosion protection of Al using graphene nanosheets (GNSs) produced by liquid phase shear exfoliation method (LPE). To do so, few layer-thick graphene nanosheet colloidal solutions were produced by a scalable eco-friendlier lower cost approach. The GNSs were thoroughly characterized using complementary characterization techniques to determine its quality. Spectroscopic and microscopic analyses indicate the synthesis of few-layers graphene (≤ 5 layers) with a high quality. Once approved, the colloidal solution of GNSs was spread over Al substrate by spray coating method, widely used in industrial manufacturing. Raman and near infrared spectroscopies, X-ray diffraction, microscopy techniques including scanning electron, transmission electron and atomic force microscopies were used to investigate morphological and structural behavior of coated GNSs films either on glass or Al substrates. Density functional theory (DFT) calculations revealed the interaction between the two materials is of the physisorption type, with almost no charge transfer and almost no effect of the number of graphene layers. Electrochemical measurements enabled to investigate the corrosion resistance of GNSs films and its stability over time in a 0.5 M sodium chloride (NaCl) solution, similar to marine surroundings. It was found that introducing a GNSs film can indeed reduce the corrosion rate and preserve Al substrate for an extended period. (10.1016/j.surfcoat.2024.131412)
  DOI : 10.1016/j.surfcoat.2024.131412
• Towards a Unified Formalism of Multivariate Coefficients of Variation: Application to the Analysis of Polarimetric Speckle Time Series
  
  • Colin Elise
  • Ossikovski Razvigor
  Journal of the Indian Society of Remote Sensing, Springer India, 2024. The main aim of this article is to unify the different formalisms of multivariate coefficients of variation, based on the advanced concepts of generalized averages - weighted or unweighted - applied to the eigenvalues of covariance matrices. We highlight the existence of an infinite number of these coefficients and demonstrate that they are bounded. Furthermore, we link the various coefficients of variation identified in the literature to specific instances within our unified formalism. We illustrate the utility of our method by applying it to a time series of polarimetric radar imagery, where the coefficient of variation emerges as a key tool for detecting changes or identifying permanent scatterers characterized by remarkable temporal stability. Multidimensionality arises from the diversity of polarizations. The introduction of various possible coefficients shows how their selection impacts the detection of samples exhibiting specific temporal behaviors, underlining the contribution of polarimetry to dynamic speckle analysis. (10.1007/s12524-024-02005-x)
  DOI : 10.1007/s12524-024-02005-x
• Maximizing the Electromagnetic Efficiency of Spintronic Terahertz Emitters
  
  • Koleják Pierre
  • Lezier Geoffrey
  • Vala Daniel
  • Mathmann Baptiste
  • Halagačka Lukáš
  • Gelnárová Zuzana
  • Dusch Yannick
  • Lampin Jean‐françois
  • Tiercelin Nicolas
  • Postava Kamil
  • Vanwolleghem Mathias
  Advanced Photonics Research, Wiley, 2024. Optically pumped spintronic terahertz emitters (STEs) have, in less than a decade, strongly impacted terahertz (THz) source technology, by the combination of their Fourier‐limited ultrafast response, their phononless emission spectrum and their wavelength‐independent operation. However, the intrinsic strength of the inverse spin Hall effect governing these devices introduces a challenge: the optical‐to‐terahertz conversion efficiency is considerably lower than traditional sources. It is therefore primordial to maximize at least their electromagnetic efficiency independently of the spin dynamics at play. Using a rigorous time‐domain treatment of the electromagnetic generation and extraction processes, an optimized design is presented and experimentally confirmed. With respect to the strongest reported spintronic THz emitters it achieves a 250% enhancement of the emitted THz field and therefore an 8 dB increase of emitted power. This experimental achievement brings STE close to the symbolic barrier of mW levels. The design strategy is generically applicable to any kind of ultrafast spin‐to‐charge conversion (S2C) system. On a broader level, our work highlights how a rigorous handling of the purely electromagnetic aspects of THz spintronic devices can uncover overlooked aspects of their operation and lead to substantial improvements. (10.1002/adpr.202400064)
  DOI : 10.1002/adpr.202400064
• Three Terminal Organic-Silicon Tandem Models
  
  • Connolly James P.
  • Alvarez J
  • Kleider Jean-Paul
  • Chambon Sylvain
  • Hirsch Lionel
  • Vignau Laurence
  • Wantz Guillaume
  • Gueunier-Farret Marie-Estelle
  • Roca I Cabarrocas Pere
  • Nejim Ahmed
  • Plews Andrew
  , 2024. The search for ever higher efficiency solar cells is at present focussed on multijunction devices. In this field, there is enormous research on tandems consisting of a high bandgap top sub-cell coupled to a Si bottom sub-cell . An emerging top cell candidate is the organic solar cell, given recent impressive breakthroughs in efficiency and stability , thanks in part to non-fullerene ac-ceptors. In this context, we report on approaches to modelling organic solar cells for silicon / organic tandems. The device studied is the three-terminal selective band-offset tandem cell . This innovative design shown in figure 1a is based on the Si interdigitated back contact solar cell , which features a number of fabrication and operating advantages over four terminal and two terminal tandems . The higher gap organic top sub-cell consists of donor and acceptor organic phases in an absorber blend, contacted to hole and electron transport layers, which is in devel-opment within the French ANR project ORGANIST. The modelling of the organic sub-cell is the main focus of this presentation, and is investigated with increasing levels model complexity. The modelling of the complete tandem is first described with a simple first approximation which only considers idealised classic drift-diffusion phenomena of inorganic semiconductors, with optical and band structure data from current best estimates of suitable non-fullerene high bandgap organic solar cell materials . It is shown that this approach is sufficient to quantitatively predict tandem efficiencies with suitable approximations for optical and transport parameters. Figure 1b shows the resulting quantum efficiency of a preliminary 26% tandem without device optimisation, and with a non-textured Si IBC. Organic modelling is then developed from stand-ard open access models , by moving from the widespread effective medium approach treating the absorber blend as a homogeneous material, to a bulk heterojunction model where the accep-tor and donor organic phases are simulated separately. We conclude with lessons learned on the comparative benefits of the modelling approaches for the design and development of high effi-ciency organic solar cells.
• Evidence of different positron annihilation quantum states in Methylammonium Lead Iodide depending on Preparation
  
  • Aversa P.
  • Helm R.
  • Jun H.
  • Cai Y.
  • Nahdi H.
  • Desgardin P.
  • Tondelier D.
  • Bourée J.E
  • Begin S.
  • Oswald F.
  • Bonnassieux Y.
  • Fischer T.
  • Mitteneder J.
  • Liedke M.O.
  • Madaan K.
  • Roma G.
  • Pochet P.
  • L. Liszkay J.
  • Butterling Maik
  • Dickmann M.
  • Wagner A.
  • Barthe M.F.
  • Egger W.
  • Geffroy B.
  • Corbel C.
  , 2024, 4, pp.13-14. (10.4028/b-JwTbe6)
  DOI : 10.4028/b-JwTbe6
• Near-wall heat transfer phenomena during bubble growth in nucleate boiling
  
  • Tecchio Cassiano
  • Le Houedec Corentin
  • Cariteau Benjamin
  • Bois Guillaume
  • Saikali Elie
  • Zalczer Gilbert
  • Roca I Cabarrocas Pere
  • Bulkin Pavel
  • Charliac Jérôme
  • Vassant Simon
  • Nikolayev Vadim
  , 2024, pp.94-96. We experimentally investigate the near-wall heat transfer at single bubble growth in nucleate saturated pool boiling of water at atmospheric pressure. Our focus is on the evaporation of the micro-metric thin film of liquid (microlayer) that is formed between the heating wall and the bubble. Synchronous and simultaneous measurements of the microlayer thickness, wall temperature and bubble macroscopic shape are performed by white light interferometry, infrared thermography and side-wise shadowgraphy, respectively. We measure the wall temperature of an ITO heating film through a transparent to the infrared waves porthole. The heating is provided by an infrared laser. The wall heat flux is numerically reconstructed by using the experimental wall temperature data. We reveal a temporal rise of the thermal resistance of the liquid-vapor interface during the microlayer evaporation, which corresponds to a decrease of the accommodation coefficient. We attribute it to the progressive accumulation of impurities at the interface during evaporation.
• 3D Shape Reconstruction of Ge Nanowires during Vapor–Liquid–Solid Growth under Modulating Electric Field
  
  • Erofeev Ivan
  • Saidov Khakimjon
  • Baraissov Zhaslan
  • Yan Hongwei
  • Maurice Jean-Luc
  • Panciera Federico
  • Mirsaidov Utkur
  ACS Nano, American Chemical Society, 2024, 18 (34), pp.22855-22863. <div><p>Bottom-up growth offers precise control over the structure and geometry of semiconductor nanowires (NWs), enabling a wide range of possible shapes and seamless heterostructures for applications in nanophotonics and electronics. The most common vapor-liquid-solid (VLS) growth method features a complex interaction between the liquid metal catalyst droplet and the anisotropic structure of the crystalline NW, and the growth is mainly orchestrated by the triple-phase line (TPL). Despite the intrinsic mismatch between the droplet and the NW symmetries, its discussion has been largely avoided because of its complexity, which has led to the situation when multiple observed phenomena such as NW axial asymmetry or the oscillating truncation at the TPL still lack detailed explanation. The introduction of an electric field control of the droplet has opened even more questions, which cannot be answered without properly addressing three-dimensional (3D) structure and morphology of the NW and the droplet. This work describes the details of electric-field-controlled VLS growth of germanium (Ge) NWs using environmental transmission electron microscopy (ETEM). We perform TEM tomography of the droplet-NW system during an unperturbed growth, then track its evolution while modulating the bias potential. Using 3D finite element method (FEM) modeling and crystallographic considerations, we provide a detailed and consistent mechanism for VLS growth, which naturally explains the observed asymmetries and features of a growing NW based on its crystal structure. Our findings provide a solid framework for the fabrication of complex 3D semiconductor nanostructures with ultimate control over their morphology.</p></div> (10.1021/acsnano.4c00087)
  DOI : 10.1021/acsnano.4c00087
• Microlayer in nucleate boiling seen as Landau–Levich film with dewetting and evaporation
  
  • Tecchio Cassiano
  • Zhang Xiaolong
  • Cariteau Benjamin
  • Zalczer Gilbert
  • Roca i Cabarrocas Pere
  • Bulkin Pavel
  • Charliac Jérôme
  • Vassant Simon
  • Nikolayev Vadim
  Journal of Fluid Mechanics, Cambridge University Press (CUP), 2024, 989, pp.A4. Both experimental and theoretical studies of fast and microscale physical phenomena occurring during the growth of vapour bubbles in nucleate pool boiling are reported. The focus is on the liquid film of micrometric thickness (a ‘microlayer’) that can form between the heater and the liquid–vapour interface of a bubble. The microlayer strongly affects the macroscale heat transfer and is thus important to be understood. The microlayer appears as a result of the inertial forces that cause the hemispherical bubble shape. It is shown that the microlayer can be seen as the Landau–Levich film deposited by the bubble foot edge during its receding. Paradoxically, the deposition is controlled by viscosity and surface tension. The microlayer profile measured with white-light interferometry, the temperature distribution over the heater, and the bubble shape are observed with synchronised high-speed cameras. According to the numerical simulations, the microlayer consists of two regions: a dewetting ridge near the contact line, and a longer and flatter bumped part. It is shown that the ridge cannot be measured by interferometry because of its intrinsic limitation on the interface slope. The ridge growth is linked to the contact line receding. The simulated dynamics of both the bumped part and the contact line agrees with the experiment. The physical origin of the bump in the flatter part of microlayer is explained. (10.1017/jfm.2024.488)
  DOI : 10.1017/jfm.2024.488
• Uterine healing after cesarean, Development of a rabbit model
  
  • Debras Elodie
  • Maudot Constance
  • Allain Jean-Marc
  • Pierangelo Angelo
  • Courilleau A.
  • Rivière Julie
  • Dahirel Michèle
  • Richard Christophe
  • Gelin Valerie
  • Morin Gwendoline
  • Capmas Perrine
  • Chavatte-Palmer Pascale
  , 2024.
• Optoelectronic properties of perovskite thin films derived from lead sulfide via radio frequency magnetron sputtering: effect of the substrate temperature
  
  • Wongcharoen Sittan
  • Raifuku Itaru
  • Yu Xianhuan
  • Kawanishi Hidenori
  • Bonnassieux Yvan
  • Cabarrocas Pere Roca I
  • Uraoka Yukiharu
  Japanese Journal of Applied Physics, Japan Society of Applied Physics, 2024, 63 (7), pp.070903. Abstract Methylammonium lead iodide (CH 3 NH 3 PbI 3 ; MAPbI 3 ) films were fabricated from sputtered lead sulfide (PbS) films prepared at various substrate temperatures according to the Thornton structural zone model. PbS films were converted to lead iodide (PbI 2 ) and finally to MAPbI 3 in a two-step gas-phase reaction. The increase in substrate temperature caused the morphology to change to fibrous interconnected grains, which played an important role in improving the optoelectrical properties of perovskite films. Moreover, enhanced charge transport of MAPbI 3 films was observed owing to the fibrous interconnected PbI 2 precursor, which was confirmed by a higher absorption coefficient and longer carrier lifetime. (10.35848/1347-4065/ad55c0)
  DOI : 10.35848/1347-4065/ad55c0
• Noncovalent functionalization of carbon nanotubes with new conjugated aromatic ligands for selective detection of water pollutants
  
  • Nasiri Aram
  , 2024. Nanotechnology has significantly addressed global issues, notably improving access to clean drinking water. Climate change exacerbates water quality decline, necessitating innovative solutions. Nanotech-driven sensors offer remote water quality analysis, crucial for decision-making in crisis management. These advancements aim to alleviate the ongoing drinking water scarcity worldwide, with potential long-term benefits.The first part of this work explores carbon nanotubes (CNTs) as 2D nanomaterials for enhancing the reliability of resistive devices. It emphasizes the importance of understanding and treating CNTs in thin film to ensure electronic and chemical reliability. A new purification process is introduced to eliminate unwanted amorphous matter, enhancing the effectiveness of wet processes and solvent-based depositions of CNTs. This approach aims to restore trust in these cost-effective and scalable methods, addressing previous concerns about poor quality and high amorphous content.In the second experimental chapter, CNTs underwent extensive studies for their parallel electronic and chemical capability to create nanohybrids with conjugated molecules, referred to as noncovalent π-π functionalization. Different methods of noncovalent functionalization were thoroughly compared, and finally incubation method was chosen both for its more promising results in terms of functionalization and its perfect compatibility with the thin-film treatment method developed in the first part.Thanks to a process development mindset, the resulting nanohybrids were accessible in thin-films and proven for their highly electronic and chemical performances. Finally, these prepared thin-films were integrated into different resistive device concepts, and were characterized against different analytes in water. The results of the devices are preliminary, but promising in the domain of water quality analysis to inspire more studies on the development of sensors.
• Optical techniques for near-wall phenomena in nucleate boiling
  
  • Tecchio Cassiano
  • Cariteau Benjamin
  • Zalczer Gilbert
  • Vassant Simon
  • Roca I Cabarrocas Pere
  • Bulkin Pavel
  • Charliac Jérôme
  • Nikolayev Vadim
  , 2024, pp.31. We report an experimental method consisting of high-speed and high-resolution optical techniques to investigate the near-wall phenomena in nucleate pool boiling. Our focus is on the micrometric liquid layer (microlayer) that can be formed between the wall and the vapor-liquid interface during the bubble growth. We also investigate the wall dewetting dynamics: the dry spot spreading. The installation performs simultaneous and synchronous measurements of the microlayer thickness profile, the wall temperature distribution and the bubble macroscopic shape by white-light interferometry, infrared thermography and sidewise shadowgraphy, respectively, at 4000 frames per second. The novelty is the white light interferometry, which provides precise data on microlayer thickness. The calibration and validation procedures of these optical techniques are discussed along with the post-processing techniques used for image treatment. We also show the results obtained for a nucleate boiling experiment on single bubble growth. These advanced techniques aim at understanding the fundamental aspects of the near-wall phenomena in nucleate boiling heat transfer, in particular the physics of microlayer formation, its evaporation, the dewetting dynamics and the associated heat transfer. The experimental data can be used to support the development of novel physical models.