Publications

2022

• Digital multispectral Mueller colposcopy for exploring cervical microstructure in vivo
  
  • Park Junha
  , 2022. Despite considerable advances in modern medical technology, predicting preterm births remains challenging. The cervix plays a crucial role during pregnancy and childbirth. In a full-term pregnancy, it gradually softens but remains closed to hold the fetus in the uterus for most of the gestation period. After 37 weeks of amenorrhea, it begins to shorten and dilate (cervical ripening) in preparation for delivery, which occurs at around 41 weeks of amenorrhea. The process of cervical remodeling is due to a modification in the microscopic properties of the connective tissue, in particular collagen.In preterm birth, cervical ripening occurs before 37 weeks of amenorrhea. The current clinical practice uses cervical length measured by transvaginal ultrasound to assess the risk of preterm birth. However, the predictive ability of this approach is very poor. Many imaging techniques (X-ray, MRI, OCT, SHG, etc.) have been tested to characterize cervical microstructure during pregnancy, but their clinical application remains very limited. In recent years, Mueller polarimetric imaging has shown great promise for analyzing the cervix during pregnancy.Light is an electromagnetic field. The polarization of light is defined as the space-time trajectory of the electric field. The Mueller-Stokes formalism represents the polarization as a four-dimensional vector called the Stokes vector which can be obtained by light intensity measurement. After interaction with a sample, the Stokes vector of the incident light is modified.The Mueller matrix is a real 16-component matrix that relates the Stokes vector at the input to the Stokes vector at the output of the sample. The measurement of this matrix provides a complete characterization of its optical anisotropy and scattering properties. For the cervix, the optical anisotropy is generated by the well-organized fibrous proteins of the connective tissue, such as collagen. On the other hand, the scattering properties are related to the high spatial heterogeneity of the cervical tissue at the microscopic scale.A feasibility study conducted by LPICM researchers at the Brugmann University Hospital in Brussels (Belgium) on 24 full-term pregnant patients showed that depolarization of the cervical tissue decreases as pregnancy progresses. Based on this preliminary result, the COLPOTERME research project was launched in collaboration with the Kremlin-Bicêtre University Hospital (France) to test the Mueller polarimetric imaging on a massive number of pregnant patients in a clinical trial.This thesis work enabled the launch of the clinical trial which is currently underway. The thesis manuscript is structured as follows.Chapter 1 presents the basic principles of Mueller polarimetry. Chapter 2 focuses on the description of the anatomy and microscopic structure of the cervix. In addition, previous results obtained at LPICM on the use of Mueller polarimetric imaging to probe cervical tissue are described.Chapter 3 presents the design and development of a new Mueller polarimetric colposcope (MPC) with unparalleled performance for in vivo cervical analysis. The new MPC allows the acquisition of high-resolution polarimetric images in 1 second, simultaneously at multiple wavelengths in the visible spectral range, with a macroscopic field of view and high spatial resolution. The performance and stability of the MPC, as well as the ergonomics of the system are described in detail in Chapter 4.Chapter 5 presents the preliminary results of the study. The polarimetric properties of the different types of epithelium covering the surface of the cervix were characterized. A statistical study showed that multispectral Mueller polarimetric imaging can effectively distinguish between the different types of cervical epithelium, which is very difficult to do with conventional colposcopy. Finally, polarimetric changes of each identified histological type were studied in relation to pregnancy progression.
• Polarimetric techniques for the structural studies and diagnosis of brain
  
  • Rodríguez-Núñez Omar
  • Novikova Tatiana
  Advanced Optical Technologies, Frontiers, 2022, 11 (5-6), pp.157-171. Abstract The polarimetric techniques are used in various biomedical applications for a non-contact and fast diagnosis of tissue that is known as optical biopsy approach. These optical modalities provide relevant information on micro-architecture of biological tissue and its alterations induced by different diseases, thus, helping in staging and precise delineation of the pathology zones. In this review, we summarize the work of different research groups on using polarized light for brain tissue studies. This includes the investigations of polarimetric properties of brain tissue (both scattering and optical anisotropy) for brain connectome reconstruction, the visualization of in-plane brain fiber tracts for brain tumor contrast enhancement during neurosurgery, and the histopathology analysis for disease staging in Alzheimer’s subjects. We discuss also further perspectives for the pre-clinical studies of brain with polarized light. (10.1515/aot-2022-0015)
  DOI : 10.1515/aot-2022-0015
• Nanostructuring Strategies for Silicon‐based Anodes in Lithium‐ion Batteries: Tuning Areal Silicon Loading, SEI Formation/Irreversible Capacity Loss, Rate Capability Retention and Electrode Durability
  
  • Ezzedine Mariam
  • Jardali Fatme
  • Florea Ileana
  • Zamfir Mihai‐robert
  • Cojocaru Costel‐sorin
  Batteries & Supercaps, Wiley, 2022. Silicon is one of the most promising anode materials for Lithium-ion batteries. Silicon endures volume changes upon cycling, which leads to subsequent pulverization and capacity fading. These drawbacks lead to a poor lifespan and hamper the commercialization of silicon anodes. In this work, a hybrid nanostructured anode based on silicon nanoparticles (SiNPs) anchored on vertically aligned carbon nanotubes (VACNTs) with defined spacing to accommodate volumetric changes is synthesized on commercial macroscopic current collector. Achieving electrodes with good stability and excellent electrochemical properties remain a challenge. Therefore, we herein tune the active silicon areal loading either through the modulation of the SiNPs volume by changing the silicon deposition time at a fixed VACNTs carpet length or through the variation of the VACNT length at a fixed SiNPs volume. The low areal loading of SiNPs improves capacity stability during cycling but triggers large irreversible capacity losses due to the formation of the solid electrolyte interphase (SEI) layer. By contrast, higher areal loading electrode reduces the quantity of the SEI formed, but negatively impacts the capacity stability of the electrode during the subsequent cycles. A higher gravimetric capacity and higher areal loading mass of silicon is achieved via an increase of VACNTs carpet length without compromising cycling stability. This hybrid nanostructured electrode shows an excellent stability with reversible capacity of 1330 mAh g-1 after 2000 cycles. (10.1002/batt.202200451)
  DOI : 10.1002/batt.202200451
• White light-induced halide segregation in triple-cation mixed halide perovskites studied by in-situ fast scanning nano-XRF at the NANOSCOPIUM beamline, Synchrotron SOLEIL
  
  • Loncle A.
  • Kim M.
  • Geffroy B.
  • Gautam S.
  • Plantevin Olivier
  • Jacques V.L.R.
  • Medjoubi K.
  Journal of Physics: Conference Series, IOP Science, 2022, 2380 (1), pp.012127. Abstract In-situ study of the variation of the chemical composition of triple-cation mixed halide perovskites Cs 0.05 (MA 0.17 FA 0.83 ) 0.95 Pb(I 0.83 Br 0.17 ) 3 under visible light illumination performed by Fast Scanning Nano Hard X-ray Fluorescence Imaging revealed the migration and irreversible phase separation of halide ions into micro-meter sized clusters. (10.1088/1742-6596/2380/1/012127)
  DOI : 10.1088/1742-6596/2380/1/012127
• Nanohybrids as a tool to control the dispersion of organic emitters in solution-processed electroluminescent layers
  
  • Phelipot Jonathan
  • Manzhi Payal
  • Ledos Nicolas
  • Tondelier Denis
  • Geffroy Bernard
  • Bouit Pierre- Antoine
  • Ackermann Jörg
  • Hissler Muriel
  • Margeat Olivier
  New Journal of Chemistry, Royal Society of Chemistry [1987-....], 2022, 46 (47), pp.22574-22580. Fluorescent organic-inorganic nanohybrids based on -extended hydroxyoxophosphole emitters grafted onto ZnO nanocrystals, have been introduced as an efficient way to control the spatial arrangement of the organic emitters within a host material. The homogeneous dispersion of the emissive nanohybrids within a host matrix is achieved via co-grafting of an additional surfactant, leading to very smooth films with low roughness. Interestingly, the co-grafting of this surfactant not only improves the thin film morphology but also enhances its photoluminescence quantum yield and allows for the easy solution-processing of this material as an emissive layer in a simplified OLED structure. These devices display strongly improved performances, by more than one order of magnitude, compared to OLEDs using pure nanohybrids. These promising results prove the potential of this technique to graft any type of luminophore in efficient solution-processed lightemitting devices. (10.1039/D2NJ05016A)
  DOI : 10.1039/D2NJ05016A
• Automatic pseudo-coloring approaches to improve visual perception and contrast in polarimetric images of biological tissues
  
  • Rodríguez Carla
  • van Eeckhout Albert
  • Garcia-Caurel Enrique
  • Lizana Angel
  • Campos Juan
  Scientific Reports, Nature Publishing Group, 2022, 12 (1), pp.18479. Abstract Imaging polarimetry methods have proved their suitability to enhance the image contrast between tissues and structures in organic samples, or even to reveal structures hidden in regular intensity images. These methods are nowadays used in a wide range of biological applications, as for the early diagnosis of different pathologies. To include the discriminatory potential of different polarimetric observables in a single image, a suitable strategy reported in literature consists in associating different observables to different color channels, giving rise to pseudo-colored images helping the visualization of different tissues in samples. However, previous reported polarimetric based pseudo-colored images of tissues are mostly based on simple linear combinations of polarimetric observables whose weights are set ad-hoc, and thus, far from optimal approaches. In this framework, we propose the implementation of two pseudo-colored methods. One is based on the Euclidean distances of actual values of pixels and an average value taken over a given region of interest in the considered image. The second method is based on the likelihood for each pixel to belong to a given class. Such classes being defined on the basis of a statistical model that describes the statistical distribution of values of the pixels in the considered image. The methods are experimentally validated on four different biological samples, two of animal origin and two of vegetal origin. Results provide the potential of the methods to be applied in biomedical and botanical applications. (10.1038/s41598-022-23330-6)
  DOI : 10.1038/s41598-022-23330-6
• Plasmonic Nanostructures for Enhanced Raman Spectroscopy Applications
  
  • Zhao Guili
  , 2022. Gold nanostructures have drawn considerable attention in recent decades due to their outstanding properties arising from the localized surface plasmonic resonances, which are the coherent oscillation modes of free electrons confined in nanostructures. Under the illumination of incoming light, they exhibit large absorption and scattering cross sections and large near-field enhancement. More attractively, these extraordinary properties are strongly correlated with the size, morphology, and composition of the nanostructures as well as the dielectric function of the medium surrounding them, which enables gold nanocrystals to be applied in a wide range of fields, such as plasmonic sensing and Raman spectroscopy.This thesis is an effort for expanding the use of gold nanostructures in analytical sciences in general and in the field of scanning probe microscopy (SPM) in particular, developing a facile and fast method to prepare nanometric gold trisoctahedrons as well as creating new plasmonic probes to combine Raman spectroscopy with scanning ion conductance microscopy (SICM).The investigations on the preparation of gold trisoctahedrons with high-index facets and their plasmonic performances are presented, describing a method that highlights the high control achieved over the properties of the final nanoparticle and the high uniformity of the products. With the ability to tune the size of gold trisoctahedrons, it is possible to tailor their dipolar plasmon resonance wavelength ranging from visible to near-infrared region. Furthermore, the exposed facets of the gold trisoctahedrons can be tuned by growing the nanostructures at different temperatures. Moreover, the obtained gold nanostructures with well-defined tips and edges were assessed for analytical applications exhibiting high plasmonic sensitivities and excellent surface-enhanced Raman scattering (SERS) performance.Combing plasmonic nanostructures with SICM probes is an interesting approach to bestow SPM techniques with additional SERS analytical possibilities. Towards this goal, the preparation and characterization of pipettes decorated with gold nanoparticles are presented, employing bifunctional molecules to anchor gold nanostructures on the outer surface of the nanopipettes (including borosilicate and quartz) in a very robust fashion. A set of different gold nanostructures, namely nanorods, nanospheres, trisoctahedrons, and nanobipyramids, have been used to produce SERSactive SICM nanopipettes (SERS-SICM probes). The capabilities of the SERS-SICM probes are demonstrated by being used in experiments of imaging and penetrating living cells.Finally, the preparation of SPM probes for enhanced Raman spectroscopy is taken to the limit by fixing one single nanoparticle at the tip end of a SICM nanopipette. This design has the potential to be used in tip-enhanced Raman scattering (TERS) in liquids, with evident applicability in fields such as the biology of living cells. Two different methods are presented, employing strategies of in-situ synthesis as well as post-functionalization of the nanopipettes. The probes are assessed based on their abilities for SICM imaging.
• Étude de la réduction du TiO2 en phase Magnéli TinO2n-1 par MET in situ
  
  • Schmidt Léon
  • Sharna Sharmin
  • Florea Ileana
  • Sanchez Clément
  • Ersen Ovidiu
  , 2022.
• Optical response of media and structures exhibiting spatial dispersion
  
  • Ossikovski Razvigor
  • Arteaga Oriol
  Optics Letters, Optical Society of America - OSA Publishing, 2022, 47 (21), pp.5602. We present a general method for redefining the permittivity and permeability tensors of a medium or structure exhibiting spatial dispersion (SD). The method effectively separates the electric and magnetic contributions that are intertwined in the traditional description of the SD-dependent permittivity tensor. The redefined material tensors are the ones to be used in the common methods for calculating the optical response of layered structures, thus enabling modeling of experiments in the presence of SD. (10.1364/OL.475069)
  DOI : 10.1364/OL.475069
• Study of degradation mechanisms in halide perovskite films and in perovskite solar cells using electrical and synchrotron-based characterization
  
  • Jun Haeyeon
  , 2022. Perovskite solar cells (PSCs) have become a trending technology in photovoltaic research due to a rapid increase in efficiency. However, they show degradation of their performance under operational conditions. Many researchers have studied the degradation mechanism caused by moisture, oxygen, or light to increase their long-term stability for market applications. However, understanding the intrinsic degradation attributed to the electrical field remains vague due to the complexity of these materials. In this thesis, a multitude of laboratory-based as well as synchrotron-based techniques are applied for a better understanding of the detailed mechanism of the phenomena in PSCs.Three following themes are covered in this thesis. Firstly, MAPbI3 films and solar cells were used as model systems for investigations using laboratory-based and synchrotron-based characterization. Therefore, MAPbI3 film based on thermal evaporation was optimized by varying evaporation parameters. In addition, PSCs with the optimized MAPbI3 were fabricated with various electron transport materials and hole transport materials.Secondly, we analyzed carrier dynamics in PSCs under electric field or exposure to air using electrochemical impedance spectroscopy (EIS). After applying electric bias, a second capacitance at low frequency was observed. This second capacitance indicates the presence of mobile ions. Additionally, EIS was measured periodically to study the degradation mechanism in air, and two variations of impedance at high and low frequencies were observed.Finally, synchrotron-based scanning transmission X-ray microscopy (STXM) was employed to analyze the nanoscale changes in the chemical composition of PSCs under an electric field. By applying an electric field to perovskite film with a specific in-situ electric biasing system, we observed not only halide migration but also changes in chemical structure in organic components of halide perovskites. After applying ex-situ electric biasing to PSCs, focused ion beam (FIB) sections were prepared. Halide ion migration in the bulk perovskite layer and its interface with two charge transport layers was observed with STXM. Furthermore, we proposed to explain the electric field-induced degradation mechanism in PSCs through correlation between EIS and STXM results.
• Fabrication of Crystalline Si Thin Films for Photovoltaics
  
  • An Junyang
  • Shen Ya
  • Roca i Cabarrocas Pere
  • Chen Wanghua
  physica status solidi (RRL) - Rapid Research Letters (pss RRL), Wiley-VCH Verlag, 2022, 16 (12). Crystalline Si (c‐Si) thin films have been widely studied for their application to solar cells and flexible electronics. However, their application at large scale is limited by their fabrication process. As reviewed in this paper, many approaches have been studied, but only some of them have been made into large‐scale industrial production. The standard wire sawing of Si ingots cannot be scaled down to produce thin c‐Si wafers and films due to the brittle nature of c‐Si material, the resulting significant thickness variations, and the waste of material. Therefore, techniques based on the kerf‐less processes including “top‐down” and “bottom‐up” approaches have been developed in recent decades. In this review, photovoltaic applications of thin c‐Si wafers with thicknesses ranging from 50 μm down to 1 μm are presented first. Then, methods to fabricate c‐Si thin films based on both approaches are detailed, including slim‐cut, “smart‐cut,” epi‐free, as well as various growth processes such as molecular beam epitaxy, liquid phase epitaxy, ion beam, and chemical vapor deposition processes at a wide range of growth temperatures, from 1000 °C down to 150 °C. The advantages and disadvantages of these methods are presented and compared. (10.1002/pssr.202200290)
  DOI : 10.1002/pssr.202200290
• Maskless interdigitated a-Si:H PECVD process on full M0 c-Si wafer: Homogeneity and passivation assessment
  
  • Ouaras Karim
  • Filonovich Sergej
  • Bruneau Bastien
  • Wang Junkang
  • Ghosh Monalisa
  • Johnson Erik
  Solar Energy Materials and Solar Cells, Elsevier, 2022, 246, pp.111927. (10.1016/j.solmat.2022.111927)
  DOI : 10.1016/j.solmat.2022.111927
• Silicene nanosheets intercalated in slightly defective epitaxial graphene on a 4H-SiC(0001) substrate
  
  • Fabbri Filippo
  • Scarselli Manuela
  • Shetty Naveen
  • Kubatkin Sergey
  • Lara-Avila Samuel
  • Abel Mathieu
  • Berbezier Isabelle
  • Vach Holger
  • Salvato Matteo
  • de Crescenzi Maurizio
  • Castrucci Paola
  Surfaces and Interfaces, Elsevier, 2022, 33, pp.102262. (10.1016/j.surfin.2022.102262)
  DOI : 10.1016/j.surfin.2022.102262
• Silicon nanowire solar cells : from single and double to triple and quadruple radial junctions for unassisted water splitting
  
  • Wang Chaoqi
  , 2022. Photoelectrochemical (PEC) cells are promising devices to convert solar energy to chemical energy (by splitting water and obtaining hydrogen) so that it can be stored and transported. However, according to thermodynamic calculations, a 1.23 V potential is required for water splitting, which exceeds the open-circuit voltage (VOC) of most single junction solar cells. In practice, the required potential for maximum splitting efficiency can be even higher for non-optimal catalysts and electrolytes, and would require multijunction solar cells to drive the reaction. Single and double radial junction silicon nanowire (SiNW) solar cells have been previously studied as their improved light trapping ability allows for thinner hydrogenated amorphous silicon (a-Si:H) absorber layers, and thus decreased light-induced degradation. In this thesis, radial junction SiNW solar cells are fabricated consisting of single and double junctions (1RJ, 2RJ), and for the first time, triple and quadruple junction (3RJ, 4RJ). The 3RJ solar cells – which display a VOC of more than 2 V - are fabricated using a one-pump-down plasma-enhanced chemical vapor deposition process. We investigated the 3RJ SiNW diode performance and the effect of the NW density on the triple junction solar cell performance, showing that a higher VOC correlates with a lower NW density. An efficiency optimum in NW density is found, as an S shape in the J-V curve occurs at the lowest NW density. This occurs due to a contact issue concerning the p-a-Si:H deposited at 600 °C in-between the NWs and the ZnO:Al substrate. Using a higher density of SiNWs can improve the S shape, benefiting from the superior contact between the SiNWs themselves and the substrate, but at the tradeoff of VOC. We then compare the performance of 1RJ, 2RJ and 3RJ with an eye towards water-splitting and not just absolute efficiency.In a second section, in order to know where the randomness in the performance of 3RJ solar cells comes from, the growth processes of SiNW solar cells are checked step-by-step, which includes changes in the ZnO:Al substrate, the H2 plasma treatment, and initial growth of the SiNW. We find that the ZnO:Al roughness change and the Sn droplet coalescence are the reasons. From ellipsometry measurements during NW growth, we also show a relationship between the final NW density and the position in time of the peak in the signal intensity curve. A later peak time corresponds to lower NW density.In a final section, we investigate the performance of the 4RJ SiNW solar cell for water splitting. Different scan speeds, electrolyte pH, and distances between anode and cathode for water splitting are investigated. The first RJ SiNW unassisted PEC cell is demonstrated in the thesis. The 4RJ SiNW solar cells with a VOC of 2.75 V are fabricated, and we use the earth-abundant Ni catalyst (deposited by thermal evaporation) to construct the photocathode for hydrogen evolution. With a Pt photoanode, PEC cell operation is demonstrated. Furthermore, the performance of this PEC cell with a RJ SiNW photocathode in different kinds of solution are studied. The unassisted water splitting by PEC cell runs stably for 90 min in 1M KBi electrolyte. The PEC efficiency has an initial value of 0.98% when using 0.1 M KOH as electrolyte, and a stabilized value of 0.43% when using 1 M KBi.
• Metal halide perovskite layers studied by scanning transmission X-ray microscopy
  
  • Dindault Chloé
  • Jun Haeyeon
  • Tondelier Denis
  • Geffroy Bernard
  • Bourée Jean-Eric
  • Bonnassieux Yvan
  • Schulz Philip
  • Swaraj Sufal
  RSC Advances, Royal Society of Chemistry, 2022, 12 (39), pp.25570-25577. We describe the investigation of metal halide perovskite layers, particularly CH3NH3PbI3 used in photovoltaic applications, by soft X-ray scanning transmission X-ray microscopy (STXM). Relevant reference spectra were used to fit the experimental data using singular value decomposition. The distribution of key elements Pb, I, and O was determined throughout the layer stack of two samples prepared by wet process. One sample was chosen to undergo electrical biasing. Spectral data shows the ability of STXM to provide relevant chemical information for these samples. We found the results to be in good agreement with the sample history, both regarding the deposition sequence and the degradation of the perovskite material. (10.1039/D2RA04438B)
  DOI : 10.1039/D2RA04438B
• Tin versus indium catalyst in the growth of silicon nanowires by plasma enhanced chemical vapor deposition on different substrates
  
  • Djoumi Siham
  • Kail Fatiha
  • Cabarrocas Pere Roca I
  • Chahed Larbi
  Thin Solid Films, Elsevier, 2022, 758, pp.139447. (10.1016/j.tsf.2022.139447)
  DOI : 10.1016/j.tsf.2022.139447
• Optical Constants of Titan's haze analogs particles from 3 to 10 μm
  
  • Perrin Zoé
  • Drant Thomas
  • Caurel Enrique Garcia
  • Chatain Audrey
  • Guaitella Olivier
  • Schmitt Bernard
  • Carrasco Nathalie
  , 2022, 16, pp.EPSC2022-435.
• Polarimetric observables for the enhanced visualization of plant diseases
  
  • Rodríguez Carla
  • Garcia-Caurel Enrique
  • Garnatje Teresa
  • Serra I Ribas Mireia
  • Luque Jordi
  • Campos Juan
  • Lizana Angel
  Scientific Reports, Nature Publishing Group, 2022, 12 (1), pp.14743. Abstract This paper highlights the potential of using polarimetric methods for the inspection of plant diseased tissues. We show how depolarizing observables are a suitable tool for the accurate discrimination between healthy and diseased tissues due to the pathogen infection of plant samples. The analysis is conducted on a set of different plant specimens showing various disease symptoms and infection stages. By means of a complete image Mueller polarimeter, we measure the experimental Mueller matrices of the samples, from which we calculate a set of metrics analyzing the depolarization content of the inspected leaves. From calculated metrics, we demonstrate, in a qualitative and quantitative way, how depolarizing information of vegetal tissues leads to the enhancement of image contrast between healthy and diseased tissues, as well as to the revelation of wounded regions which cannot be detected by means of regular visual inspections. Moreover, we also propose a pseudo-colored image method, based on the depolarizing metrics, capable to further enhance the visual image contrast between healthy and diseased regions in plants. The ability of proposed methods to characterize plant diseases (even at early stages of infection) may be of interest for preventing yield losses due to different plant pathogens. (10.1038/s41598-022-19088-6)
  DOI : 10.1038/s41598-022-19088-6
• Maskless interdigitated a-Si:H PECVD process on full M0 c-Si wafer: Homogeneity and passivation assessment
  
  • Ouaras Karim
  • Filonovich Sergej
  • Bruneau Bastien
  • Wang Junkang
  • Ghosh Monalisa
  • Johnson Erik
  Solar Energy Materials and Solar Cells, Elsevier, 2022, 246 (8), pp.2200248. (10.1016/j.solmat.2022.111927)
  DOI : 10.1016/j.solmat.2022.111927
• Microlayer dynamics at bubble growth in boiling
  
  • Tecchio Cassiano
  • Zhang Xiaolong
  • Cariteau B.
  • Zalczer Gilbert
  • Roca I Cabarrocas Pere
  • Bulkin Pavel
  • Charliac Jérôme
  • Vassant Simon
  • Nikolayev Vadim
  , 2022, pp.624-629. We investigate experimentally and theoretically the microscale physical phenomena occurring during the growth of a single bubble attached to the heater in nucleate boiling. The experiment is performed with water under normal conditions by using stateof- the-art high-speed (4000 fps) and microscopic scale measurements. The boiling surface consists of an indium-tin oxide (ITO) film deposited on the transparent MgF$_2$ porthole. The ITO heating is performed locally with an infrared (IR) laser directed from below. We study the liquid microlayer that can form between the heater and the bubble. The microlayer profile and macroscopic bubble shape are measured by white light interferometry (WLI) and sidewise shadowgraphy, respectively. The heater temperature is given by an IR camera. We have detected a new feature in the microlayer shape: a bump in the microlayer profile that appears at the initial stage of the bubble growth. A theory that allows us to explain such a profile is presented. We also present a 2D numerical simulation of microlayer dynamics that shows both the bump and the dewetting ridge evidenced in earlier numerical simulations. The bump in the microlayer observed in the experiments does not correspond to the dewetting ridge.
• Simplified green-emitting single-layer phosphorescent organic light-emitting diodes with an external quantum efficiency > 22%
  
  • Lucas Fabien
  • Brouillac Clément
  • Fall Sadiara
  • Zimmerman Nicolas
  • Tondelier Denis
  • Geffroy Bernard
  • Leclerc Nicolas
  • Heiser Thomas
  • Lebreton Christophe
  • Jacques Emmanuel
  • Quinton Cassandre
  • Rault-Berthelot Joëlle
  • Poriel Cyril
  Chemistry of Materials, American Chemical Society, 2022, 34 (18), pp.8345–8355. Nowadays, phosphorescent organic light-emitting diodes (PhOLEDs) is a widespread technology, in which all the high-performance devices are constructed on a stack of different organic layers called multi-layer devices (ML-PhOLEDs). Thanks to these functional layers, the injection, the transport, and the recombination of holes and electrons in the emissive layer (EML) are significantly improved, allowing to reach high performances. In this technology, the ideal devices are the single-layer PhOLEDs (SL-PhOLEDs), with a very simple stack only constituted by the electrodes and the EML. These devices are simple, very easy to fabricate, and can hence significantly decrease their costs. Nevertheless, removing the functional layers of an OLED drastically decreases the performances and there is, so far, only a few examples of high-performance SL-PhOLEDs. Thus, in SL-PhOLEDs, the role of the functional layer should be performed by the EML, which should allow an excellent injection, transport, and recombination of holes and electrons. In this work, thanks to a rational molecular design of the EML, we report a green-emitting SL-PhOLED, displaying a very high external quantum efficiency of 22.7%. The EML of this device is constructed on the barely studied Ir(ppy)2acac phosphor and a high efficiency host material possessing a Donor-spiro-Acceptor design. This performance is, to the best of our knowledge, the highest reported to date for SL-PhOLEDs (all colors considered). Through a structure/property/device performance relationship study combining morphological (AFM), photophysical (time-resolved spectroscopy) and charge transport studies, we show that the EML presents all the required characteristics such as smooth surface, quick radiative deactivation, and ambipolarity. In addition, the comparison with Ir(ppy)3, the most famous green emitter used in PhOLEDs, highlights the high potential of Ir(ppy)2acac. The impact of the phosphorescent emitter on the ambipolarity of the charge transport is particularly evidenced. (10.1021/acs.chemmater.2c01909)
  DOI : 10.1021/acs.chemmater.2c01909
• When Poor Light‐Emitting Spiro Compounds in Solution Turn into Emissive Pure Layers in Organic Light‐Emitting Diodes: The Key Role of Phosphine Substituents
  
  • Tourneur Pauline
  • Lucas Fabien
  • Brouillac Clément
  • Quinton Cassandre
  • Lazzaroni Roberto
  • Olivier Yoann
  • Viville Pascal
  • Poriel Cyril
  • Cornil Jérôme
  Advanced Photonics Research, Wiley, 2022, 3 (11), pp.2200124. (10.1002/adpr.202200124)
  DOI : 10.1002/adpr.202200124
• Triple Radial Junction Hydrogenated Amorphous Silicon Solar Cells with >2 V Open‐Circuit Voltage
  
  • Wang Chaoqi
  • Foldyna Martin
  • Johnson Erik V
  • Roca i Cabarrocas Pere
  Solar RRL, Wiley, 2022, 6 (8), pp.2200248. (10.1002/solr.202200248)
  DOI : 10.1002/solr.202200248
• Determining solar cell parameters and degradation rates from power production data
  
  • Chakar Joseph
  • Pavlov Marko
  • Bonnassieux Yvan
  • Badosa Jordi
  Energy Conversion and Management: X, Elsevier, 2022, 15, pp.100270. (10.1016/j.ecmx.2022.100270)
  DOI : 10.1016/j.ecmx.2022.100270
• Precise morphology control of in-plane silicon nanowires via a simple plasma pre-treatment
  
  • Xue Zhaoguo
  • Chen Wanghua
  • Meng Xianhong
  • Xu Jun
  • Shi Yi
  • Chen Kunji
  • Yu Linwei
  • Roca i Cabarrocas Pere
  Applied Surface Science, Elsevier, 2022, 593, pp.153435. (10.1016/j.apsusc.2022.153435)
  DOI : 10.1016/j.apsusc.2022.153435