Publications

2020

• Nanosensor technology for road pavements monitoring
  
  • Barriera Maria
  , 2020. The road network is one of the major assets in our countries. The assessment of pavement conditions and their evolution with time is essential for the establishment of cost-effective maintenance plans. In this respect, pavement instrumentation allows remote and continuous monitoring with no traffic disruption. However it remains a major scientific and technological challenge in terms of devices resilience to the harsh road environment as well as of strategies for sensor data interpretation. The overall goal of this thesis is to prove the feasibility of embedded pavement monitoring by demonstrating the exploitability of embedded sensor data to assess road ageing, and by providing a high performance, low intrusiveness technology. We propose, via an accelerated pavement test, a validation of asphalt strain gauges as monitoring method for fatigue prediction in a road pavement. Thus, we further explored the use of embedded sensors for inverse calculation of pavement mechanical conditions via the instrumentation of an existing road with a network of asphalt strain gauges. The same trial section was the environment for a first validation of a novel sensing technology based on the use of nanocarbon-based flexible strain sensors, later tested under an accelerated pavement test. Thereby we demonstrated how the proposed nanotechnology can overcome some of the drawbacks of existing sensing devices in terms of geometry, compatibility with the road environment, and sensitivity.
• Reinforcement Learning application for Energy Management of Microgrids
  
  • Levent Tanguy
  , 2020. The thesis project is about the application of reinforcement learning methods to develop an Energy Management System, managing the electricity flows of microgrids. Based on the observation, end of 2017, that this subject wasn’t well studying, we have started our research by an exhaustive bibliography and possible methods in order to have a better strategy to define the thesis goals. We have defined hypothesis in this thesis:• No use a forecaster• Having a data distribution of weather, PV produced and consumptions as wide as possible (integrating seasonality, holidays...)• Develop algorithms capable of generalization over unseen and new dataset• Compare performances with traditional methodsAll the experiences are based on simulation and can be divided in 4 parts:• Manage an islanded hybrid Microgrid with a new algorithm combining Q Learning and CART Decision Tree. A new method is also developed in order to accelerate the learning performance.• Manage the same aforementioned Microgrid, integrating rare events in the problem. An enhanced Double Deep Q Network (DDQN) was developed in order to manage this rare events and the overall Microgrid.• Manage six Microgrids: islanded, connected and weak-grid (with lot of perturbations) based on 2 locations: France (Ecole Polytechnique) and Tahiti (Museum). The goal was to develop a single and unique DDQN, capable to manage all the microgrids without modify its architecture and hyper-parameters (this idea is inspired by DeepMind work with Atari games)• Improving the learning performance in term of computation time by using Transfer Learning
• 2,2′-Bipyrimidine as a Building Block for the Design of Emissive Conjugated Polymers for Hybrid LED Lighting
  
  • Lin Qiqiao
  • Huang Xiaoguang
  • Ramachandran Sasikumar
  • Wang Xinyang
  • Boonsin Rachod
  • Khendriche Yasmine
  • Valleix Rodolphe
  • Roblin Jean-Philippe
  • Boyer Damien
  • Chadeyron Geneviève
  • Zucchi Gaël
  ACS Applied Polymer Materials, American Chemical Society, 2020, 2 (12), pp.5581-5591. This work introduces 2,2′-bipyrimidine as an acceptor unit in the design of donor−acceptor conjugated polymers. Regularly alternating this moiety with the electron-rich 2,7-dihexyl fluorene and 3,6-carbazole units lead to polymers P1 and P2, respectively, which both showed a red-shifted emission with respect to the parent polyfluorene and polycarbazole derivatives. Investigations on the thermal properties showed that P1 and P2 both possess decomposition temperatures higher than 250°C under a mixture of N 2 and O 2. P1 was used as a representative example of this family of conjugated polymers to design white-emitting materials, both in solution and in the solid state. P1 and P2 were investigated as phosphors for LED lighting. Two composite films elaborated with P1 and P2 embedded into a PMMA matrix labeled P1c and P2c, respectively, were irradiated with a 375 nm-LED at a power as high as 48 W/m 2. P1c was found to show a lower photostability. Two ways to improve the stability under UV exposure were investigated. On the one hand, replacing 2,7-dihexyl fluorene by 3,6-hexyl carbazole approximately improved the photostability by a factor of 2, while on the other hand, embedding the polymers into a liquid sol−gel hybrid matrix allowed an improvement of the stability by a factor of 3. We could obtain a stabilization of the intensity of P2c at ∼half of its initial intensity, thus showing an improvement of the photostability of more than five times with respect to pure P1. (10.1021/acsapm.0c00915)
  DOI : 10.1021/acsapm.0c00915
• 2,2′-Bipyrimidine as a Building Block for the Design of Emissive Conjugated Polymers for Hybrid LED Lighting
  
  • Lin Qiqiao
  • Huang Xiaoguang
  • Ramachandran Sasikumar
  • Wang Xinyang
  • Boonsin Rachod
  • Khendriche Yasmine
  • Valleix Rodolphe
  • Roblin Jean-Philippe
  • Boyer Damien
  • Chadeyron Geneviève
  • Zucchi Gaël
  ACS Applied Polymer Materials, American Chemical Society, 2020, 2 (12), pp.5581-5591. (10.1021/acsapm.0c00915)
  DOI : 10.1021/acsapm.0c00915
• In situ calibration of low-cost instrumentation for the measurement of ambient quantities : evaluation methodology of the algorithms and diagnosis of drifts
  
  • Delaine Florentin
  , 2020. In various fields going from agriculture to public health, ambient quantities have to be monitored in indoors or outdoors areas. For example, temperature, air pollutants, water pollutants, noise and so on have to be tracked. To better understand these various phenomena, an increase of the density of measuring instruments is currently necessary. For instance, this would help to analyse the effective exposure of people to nuisances such as air pollutants.The massive deployment of sensors in the environment is made possible by the decreasing costs of measuring systems, mainly using sensitive elements based on micro or nano technologies. The drawback of this type of instrumentation is a low quality of measurement, consequently lowering the confidence in produced data and/or a drastic increase of the instrumentation costs due to necessary recalibration procedures or periodical replacement of sensors.There are multiple algorithms in the literature offering the possibility to perform the calibration of measuring instruments while leaving them deployed in the field, called in situ calibration techniques.The objective of this thesis is to contribute to the research effort on the improvement of data quality for low-cost measuring instruments through their in situ calibration.In particular, we aim at 1) facilitating the identification of existing in situ calibration strategies applicable to a sensor network depending on its properties and the characteristics of its instruments; 2) helping to choose the most suitable algorithm depending on the sensor network and its context of deployment; 3) improving the efficiency of in situ calibration strategies through the diagnosis of instruments that have drifted in a sensor network.Three main contributions are made in this work. First, a unified terminology is proposed to classify the existing works on in situ calibration. The review carried out based on this taxonomy showed there are numerous contributions on the subject, covering a wide variety of cases. Nevertheless, the classification of the existing works in terms of performances was difficult as there is no reference case study for the evaluation of these algorithms.Therefore in a second step, a framework for the simulation of sensors networks is introduced. It is aimed at evaluating in situ calibration algorithms. A detailed case study is provided across the evaluation of in situ calibration algorithms for blind static sensor networks. An analysis of the influence of the parameters and of the metrics used to derive the results is also carried out. As the results are case specific, and as most of the algorithms recalibrate instruments without evaluating first if they actually need it, an identification tool enabling to determine the instruments that are actually faulty in terms of drift would be valuable.Consequently, the third contribution of this thesis is a diagnosis algorithm targeting drift faults in sensor networks without making any assumption on the kind of sensor network at stake. Based on the concept of rendez-vous, the algorithm allows to identify faulty instruments as long as one instrument at least can be assumed as non-faulty in the sensor network. Across the investigation of the results of a case study, we propose several means to reduce false results and guidelines to adjust the parameters of the algorithm. Finally, we show that the proposed diagnosis approach, combined with a simple calibration technique, enables to improve the quality of the measurement results. Thus, the diagnosis algorithm opens new perspectives on in situ calibration.
• Visualization of White Matter Fiber Tracts of Brain Tissue Sections With Wide-Field Imaging Mueller Polarimetry
  
  • Schucht Philippe
  • Lee Hee Ryung
  • Mezouar Hachem Mohammed
  • Hewer Ekkehard
  • Raabe Andreas
  • Murek Michael
  • Zubak Irena
  • Goldberg Johannes
  • Kovari Eniko
  • Pierangelo Angelo
  • Novikova Tatiana
  IEEE Transactions on Medical Imaging, Institute of Electrical and Electronics Engineers, 2020, 39 (12), pp.4376-4382. (10.1109/TMI.2020.3018439)
  DOI : 10.1109/TMI.2020.3018439
• Studies of scattering and anisotropic media with Mueller polarimetry : towards digital histology and optical biopsy of tissue
  
  • Lee Hee Ryung
  , 2020. Imaging Mueller polarimetry represents an emerging optical technique for a non-invasive diagnostics of tissue. This optical modality explores the extreme sensitivity of polarized light to the microstructure of a sample under study and provides the most complete information on sample polarimetric properties.First, the potential of the transmission Mueller microscope operating in the visible wavelength range for digital histology analysis was studied on the unstained histological sections of human skin equivalents. Logarithmic decomposition of the experimental Mueller matrices was combined with the statistical density-based clustering algorithm for the applications with noise (DBSCAN) for diagnostic segmentation of the microscope images of human skin models. The validity of the differential Mueller matrix formalism for fluctuating homogenous depolarizing media was confirmed experimentally for biological tissue. An original method was suggested to mitigate the impact of thickness variation that could affect the accuracy of polarimetric diagnostics of thin tissue sections. A new version of the DBSCAN algorithm was developed to reduce the calculation time and, thus, to allow clustering of large size datasets. When dataset outliers (noise) were effectively filtered out, the contrast between the dermal and epidermal zones of human skin equivalents was significantly increased. Polarized Monte Carlo modeling of the experimental Mueller matrices of thin sections of human skin equivalents confirmed that both linear dichroism and anisotropy of depolarization detected within the dermal zone are due to the presence of well-aligned collagen fibers.The ex-vivo proof-of-principle studies of the sensitivity of backscattered polarized light to the highly ordered structure of healthy brain white matter are presented in the second part. The thick sections of the formalin-fixed human brain and fresh calf brain were imaged in reflection configuration using wide-field imaging Mueller polarimeter operating in the visible wavelength range. It is known that brain tumors break the highly ordered structure of brain white matter because tumor cells grow in a chaotic way. However, this difference in structural complexity is hardly detectable with a state-of-the-art operative microscope during neurosurgery because of low visual contrast between tumor and healthy brain tissue. We studied the capability of the wide-field imaging Mueller polarimetry to visualize the fiber tracts of healthy brain white matter by detecting the anisotropy of its refractive index (i.e. birefringence of brain white matter that will be erased by tumor). The experimental Mueller matrices of brain specimens were processed using the algorithm of Lu-Chipman polar decomposition. The maps of the azimuth of the optical axis of uniaxial linear birefringent medium demonstrated the compelling correlation with the microscopy images of silver-stained histological sections of brain tissue that is a gold standard technique for the visualization of brain white matter fiber tracts ex-vivo. These results show the potential of wide-field imaging Mueller polarimetry to provide information on the relative spatial orientation of brain fiber tracts, which can help to detect the exact border between the tumor and surrounding brain tissue, guide neurosurgeon during tumor resection and improve patient outcomes.
• Polarizer calibration method for Mueller matrix polarimeters
  
  • Ossikovski Razvigor
  • Al Bugami Bandar
  • Garcia-Caurel Enrique
  • Cloude Shane
  Applied optics, Optical Society of America, 2020, 59 (33), pp.10389. We advance what we believe is a novel eigenvalue-based method for calibrating Mueller matrix polarimeters employing a single calibration optical component: a polarizer. The method is potentially advantageous in high numerical aperture imaging or wide spectral range spectroscopic polarimetric configurations restricting or even prohibiting the standard use of a retarder as a second calibration component. (10.1364/AO.409799)
  DOI : 10.1364/AO.409799
• Improvement of carrier collection in Si/a-Si:H nanowire solar cells by using hybrid ITO/silver nanowires contacts
  
  • Mathieu-Pennober Tiphaine
  • Foldyna Martin
  • Zhang Shan-Ting
  • Julien François H
  • Schneider Nathanaelle
  • Tchernycheva Maria
  Nanotechnology, Institute of Physics, 2020, 31 (43), pp.435408. Optoelectronic devices based on high aspect ratio nanowires bring new challenges for transparent electrodes, which can be well addressed by using hybrid structures. Here we demonstrate that a composite contact to radial junction nanowire solar cells made of a thin indium-tin oxide (ITO) layer and silver nanowires greatly improves the collection of charge carriers as compared to a single thick ITO layer by reducing the series resistance losses while improving the transparency. The optimization is performed on p-in solar cells comprising of dense non-vertical nanowires with a p-doped c-Si core and an ultra-thin a-Si:H absorption layer grown by plasma-enhanced chemical vapor deposition on glass substrates. The optimal hybrid contact developed in this work is demonstrated to increase the solar cell conversion efficiency from 4.3% to 6.6%. (10.1088/1361-6528/aba4ce)
  DOI : 10.1088/1361-6528/aba4ce
• Reduced Lasing Thresholds in GeSn Microdisk Cavities with Defect Management of the Optically Active Region
  
  • Elbaz Anas
  • Arefin Riazul
  • Sakat Emilie
  • Wang Binbin
  • Herth Etienne
  • Patriarche Gilles
  • Foti Antonino
  • Ossikovski Razvigor
  • Sauvage Sebastien
  • Checoury Xavier
  • Pantzas Konstantinos
  • Sagnes Isabelle
  • Chrétien Jérémie
  • Casiez Lara
  • Bertrand Mathieu
  • Calvo Vincent
  • Pauc Nicolas
  • Chelnokov Alexei
  • Boucaud Philippe
  • Boeuf Frederic
  • Reboud Vincent
  • Hartmann Jean-Michel
  • El Kurdi Moustafa
  ACS photonics, American Chemical Society, 2020, 7 (10), pp.2713-2722. GeSn alloys are nowadays considered as the most promising materials to build Group IV laser sources on silicon (Si) in a full complementary metal oxide semiconductor-1 arXiv:submit/3525756 [physics.app-ph] 21 Dec 2020 compatible approach. Recent GeSn laser developments rely on increasing the band structure directness, by increasing the Sn content in thick GeSn layers grown on germanium (Ge) virtual substrates (VS) on Si. These lasers nonetheless suffer from a lack of defect management and from high threshold densities. In this work we examine the lasing characteristics of GeSn alloys with Sn contents ranging from 7 % to 10.5 %. The GeSn layers were patterned into suspended microdisk cavities with different diameters in the 4-8 µm range. We evidence direct band gap in GeSn with 7 % of Sn and lasing at 2-2.3 µm wavelength under optical injection with reproducible lasing thresholds around 10 kW cm −2 , lower by one order of magnitude as compared to the literature. These results were obtained after the removal of the dense array of misfit dislocations in the active region of the GeSn microdisk cavities. The results offer new perspectives for future designs of GeSn-based laser sources. (10.1021/acsphotonics.0c00708)
  DOI : 10.1021/acsphotonics.0c00708
• Investigation of microstructure evolution and mechanical properties in cardiac tissue
  
  • Tueni N.
  • Vizet J.
  • Pierangelo A.
  • Allain J.-M.
  • Genet Martin
  Computer Methods in Biomechanics and Biomedical Engineering, Taylor & Francis, 2020, 23 (sup1), pp.S297-S299. (10.1080/10255842.2020.1816296)
  DOI : 10.1080/10255842.2020.1816296
• Modélisation numérique des transistors à effet de champ organiques basé sur la densité d’états Gaussienne
  
  • Lee Yongjeong
  , 2020. Although the device physics of organic field-effect transistors (OFETs) has been widely studied, the analysis with energetic distribution of the density-of-states (DOS) is still lacking in spite of the disordered nature of organic semiconductors. Because charge transport and injection take place at the Gaussian DOS, this distinctive energetic structure of organic semiconductors could make the charge-accumulation process, and hence the device operation, different. This thesis is dedicated to understanding the effect of Gaussian DOS on device parameters of OFETs, the threshold voltage, charge-carrier mobility and injection barrier via numerical finite-element based 2D simulations and experimental validation. The threshold voltage is comprehended by the charge trapping into the secondary Gaussian trap DOS as well as the intrinsic Gaussian DOS. We show that the overlap of two Gaussian DOSs due to the disorder induces specific threshold behaviors of OFETs. Second, the hopping transport is studied via Gaussian disordered model (GDM) on random spatial sites of organic semiconductors. This model can offer a precise result over GDM with cubic lattice. Also, we propose a correct parametrization of the model for wide range of materials from polymers to small molecules. Lastly, charge-based and transport-based injection barrier are studied and compared with Gaussian DOS. The advantages and limits of each model are evaluated.
• Characterization of plasma jets interacting with dielectric and metallic targets: comparison between simulations and experiments
  
  • Bourdon Anne
  • Viegas Pedro
  • Slikboer Elmar
  • Hofmans Marlous
  • van Rooij Olivier
  • Obrusník Adam
  • Klarenaar Bart
  • Bonaventura Zdenek
  • Garcia-Caurel Enric
  • Guaitella Olivier
  • Sobota Ana
  , 2020.
• Observation of photovoltaic effect within locally doped silicon nanojunctions using conductive probe AFM
  
  • Khoury R.
  • Alvarez J
  • Ohashi T.
  • Martín I.
  • Ortega P.
  • Lopez G.
  • Jin C.
  • Li Z.
  • Rusli -
  • Bulkin P.
  • Johnson E.V. V
  Nano Energy, Elsevier, 2020, 76, pp.105072. Localized p-doped nanojunctions (200-300 nm in diameter) were formed in n-type crystalline silicon substrates and were characterized using scanning electron microscopy (SEM) and conductive-probe atomic force microscopy (C-AFM). Localized doping was performed by diffusion through sub-micron sized holes in a silicon-oxide mask defined using self-organized polystyrene nanoparticles. After oxide removal, a significant brightness contrast in the SEM top and side view images strongly suggested the successful local doping of these areas. Furthermore, local current-voltage measurements performed by C-AFM revealed an open circuit voltage and a short-circuit current only in the areas defined as nanojunctions. This photovoltaic effect is driven by the laser used to control cantilever deflection in the AFM. (10.1016/j.nanoen.2020.105072)
  DOI : 10.1016/j.nanoen.2020.105072
• Load and Demand Side Flexibility Forecasting
  
  • Merce Rocio Alvarez
  • Grover-Silva Etta
  • Le Conte Johanna
  , 2020. Recent developments in energy metering technologies have allowed electric load data to be more easily accessible. Services that use this data to inform customers can raise awareness about electricity consumption and provide suggestions to encourage energy efficient behavior. Quantifying the flexibility of the demand combined with accurate predictions of the total electric load allow information services to provide suggestions to end-users on how to reduce electric consumption that are appliance and time specific. With the arrival of new electric generation technologies, such as photovoltaic or wind energy, demand side flexibility will play an important role in the optimization of the future electric system. The accurate prediction of demand flexibility at a building level, therefore can contribute to the optimization of load scheduling. This study presents an effective multi-step technique to forecast the average hourly demand flexibility for a household, using neural networks, unsupervised clustering techniques and an optimization algorithm, combined with statistical studies. The model is mainly based on the historical electric use of a building and does not require significant computational capacity, thus making it widely applicable and informative for residential customers, helping them improve their behavior to be more energy efficient in the future.
• From latent ferroelectricity to hyperferroelectricity in alkali lead halide perovskites
  
  • Roma Guido
  • Marronnier Arthur
  • Even Jacky
  Physical Review Materials, American Physical Society, 2020, 4 (9). (10.1103/PhysRevMaterials.4.092402)
  DOI : 10.1103/PhysRevMaterials.4.092402
• Robustesse structurelle des architectures d'apprentissage profond
  
  • Lassance Carlos
  • Gripon Vincent
  • Tang Jian
  • Ortega Antonio
  , 2020. Les réseaux de neurones profonds sont devenus les références dans beaucoup de problèmes d'apprentissage machine. Malheureuse-ment, ils sont sensibles à divers types de bruits ou à des déformations des entrées. Dans ce travail, nous introduisons une nouvelle définition de robustesse caractérisant la constante de Lipschitz de la fonction du réseau dans un sous-ensemble restreint de son domaine de définition. Nous comparons cette définition à celles existantes, et discutons des liens avec différentes méthodes introduites dans la littérature afin accroître la robustesse des réseaux. Abstract-Deep Networks have been shown to provide state-of-the-art performance in many machine learning challenges. Unfortunately, they are susceptible to various types of noise, including adversarial attacks and corrupted inputs. In this work we introduce a formal definition of robustness which can be viewed as a localized Lipschitz constant of the network function, quantified in the domain of the data to be classified. We compare this notion of robustness to existing ones, and study its connections with methods in the literature. We evaluate this metric by performing experiments on various competitive vision datasets.
• Transmission electron microscopy characterization of low temperature boron doped silicon epitaxial films
  
  • Noircler Guillaume
  • Chrostowski Marta
  • Larranaga Melvyn
  • Drahi Etienne
  • Roca I Cabarrocas Pere
  • de Coux Patricia
  • Warot-Fonrose Bénédicte
  CrystEngComm, Royal Society of Chemistry, 2020, 22 (33), pp.5464-5472. Transmission electron microscopy (TEM) techniques can provide a complementary understanding of the physico-chemical mechanisms of the growth and the annealing behavior of boron-doped hydrogenated silicon epitaxial films grown at low temperatures (<200 °C) by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). Compared to the standard boron diffusion or ion implantation, the PECVD process ensures a lower thermal budget and the realization of a sharper doping profile. The complexity of this epi-layer process lies on the fact that many impurities are incorporated during growth and their analysis requires the use of advanced characterization methods. Particular attention is paid to defects by combining high resolution transmission electron microscopy (HRTEM) and an image processing routine called geometric phase analysis (GPA) which allows the strain field to be studied. For the as-grown epitaxial layer, we will show how the non-conventional PECVD growth process influences its microstructure and gives it a non-uniform strain-field. In the annealed epitaxial layer, no strain is measured but nanotwins have been detected and analyzed through a geometric model. Scanning TEM (STEM) techniques are also applied to analyze chemical variation at the interface. A darker contrast is observed at the interface of the annealed sample most likely due to the migration of hydrogen atoms during annealing. (10.1039/D0CE00817F)
  DOI : 10.1039/D0CE00817F
• Colon cancer detection by using Poincaré sphere and 2D polarimetric mapping of ex vivo colon samples
  
  • Ivanov Deyan
  • Dremin Viktor
  • Bykov Alexander
  • Borisova Ekaterina
  • Genova Tsanislava
  • Popov Alexey
  • Ossikovski Razvigor
  • Novikova Tatiana
  • Meglinski Igor
  Journal of Biophotonics, Wiley, 2020, 13 (8), pp.1. (10.1002/jbio.202000082)
  DOI : 10.1002/jbio.202000082
• Colon cancer detection by using Poincaré sphere and 2D polarimetric mapping of ex vivo colon samples
  
  • Ivanov Deyan
  • Dremin Viktor
  • Bykov Alexander
  • Borisova Ekaterina
  • Genova Tsanislava
  • Popov Alexey
  • Ossikovski Razvigor
  • Novikova Tatiana
  • Meglinski Igor
  Journal of Biophotonics, Wiley, 2020, 13 (8). Abstract This work is dedicated to the diagnosis and grading of colon cancer by a combined use of Poincaré sphere and 2D Stokes vector polarimetry mapping approaches. The major challenge consists in exploring the applicability of polarized light for noninvasive screening of the histological abnormalities within the samples of biological tissues. Experimental studies were conducted in ex vivo colon sample, excised after surgical procedure for colon tumor removal of G2‐adenocarcinoma lesion. Polarimetric measurements in linear and circular regime were carried via personally developed polarimetric, optical set‐up, using supercontinuous fiber laser with irradiation fixed at 635 nm. We apply the Poincaré sphere and two‐dimensional Stokes vector scanning approach for screening the corresponding tissue samples. A comparison between linear and circular polarization states is made both for quantitative and qualitative evaluations. It is shown that circular polarization has better diagnostic capabilities than linear polarization, with higher dynamic ranges of the polarimetric parameters and better values of the diagnostic quantities. In addition to the standard polarimetry parameters, utilized as essential diagnostic markers, we apply statistical analysis to obtain more detailed information in frame of the applied diagnostic approach. (10.1002/jbio.202000082)
  DOI : 10.1002/jbio.202000082
• Front Cover
  
  • Ivanov Deyan
  • Dremin Viktor
  • Bykov Alexander
  • Borisova Ekaterina
  • Genova Tsanislava
  • Popov Alexey
  • Ossikovski Razvigor
  • Novikova Tatiana
  • Meglinski Igor
  Journal of Biophotonics, Wiley, 2020, 13 (8), pp.4509. (10.1002/jbio.202070019)
  DOI : 10.1002/jbio.202070019
• Area selective deposition of silicon by plasma enhanced chemical vapor deposition using a fluorinated precursor
  
  • Akiki Ghewa
  • Suchet Daniel
  • Daineka Dmitri
  • Filonovich Sergej
  • Bulkin Pavel
  • Johnson Erik
  Applied Surface Science, Elsevier, 2020, 531, pp.147305. An Area Selective Deposition (ASD) process using Plasma-Enhanced Chemical Vapour Deposition (PECVD) is demonstrated. Using a plasma chemistry containing a fluorinated silicon precursor (SiF 4), no deposition is observed on an aluminum oxide (AlO X) surface area, whereas a thin film of silicon is deposited on a silicon nitride (SiN X) surface area, while both areas are located on the same crystalline silicon substrate. The thin film deposition is characterized using spectroscopic ellipsometry, scanning electron microscopy, and atomic force microscopy, showing that 10 nm of silicon is deposited on the SiN x in 4 min. The growth on the SiN X is characterized by small grains and a rough surface, consistent with microcrystalline silicon, while no deposition or etching is observed for the AlO X surface. (10.1016/j.apsusc.2020.147305)
  DOI : 10.1016/j.apsusc.2020.147305
• Reversible Photo-Induced Phase Segregation and Origin of Long Carrier Lifetime in Mixed-Halide Perovskite Films
  
  • Gautam Subodh K
  • Kim Minjin
  • Miquita Douglas R
  • Bourée Jean-Eric
  • Geffroy Bernard
  • Plantevin Olivier
  Advanced Functional Materials, Wiley, 2020, 30 (28), pp.2002622. Mixed-halide based hybrid perovskite semiconductors have attracted tremendous attention as a promising candidate for high efficient photovoltaic and light-emitting devices. However, these advanced perovskite materials may undergo phase segregation under light illumination due to halide ion migration, affecting their optoelectronic properties. Here, we report photo-excitation induced phase segregation in triple-cation mixed-halide perovskite films that yields to red-shift in photoluminescence response. We demonstrate that photo-excitation induced halide ion migration leads to the formation of smaller-bandgap iodide-rich and larger-bandgap bromide-rich domains in the perovskite film, where the phase segregation rate is found to follow the excitation power-density as a power law. Results confirm that charge carrier lifetime increases with redshift in photoluminescence due to the trapping of photo-excited carriers in the segregated smaller-bandgap iodide-rich domains. Interestingly, we found that these photo-induced changes are fully reversible and thermally activated when the excitation power is turned off. A significant difference in activation energies for halide ion migration is observed during phase segregation and recovery process under darkness. Additionally, we have investigated the emission linewidth broadening as a function of temperature which is governed by the exciton-optical phonon coupling. The mechanism of photo-induced phase segregation is interpreted based on excitonphonon coupling strength in both mixed and demixed (segregated) states of perovskite film. (10.1002/adfm.202002622)
  DOI : 10.1002/adfm.202002622
• Interfacial hydrogen incorporation in epitaxial silicon for layer transfer
  
  • An Junyang
  • Zheng Zhen
  • Gong Ruilin
  • Nguyen Thi Bao Tran
  • Jun Haeyeon
  • Chrostowki Marta
  • Maurice Jean-Luc
  • Chen Wanghua
  • Roca I Cabarrocas Pere
  Applied Surface Science, Elsevier, 2020, 518, pp.146057. Recently, epitaxial Si layers have attracted strong attention, particularly in photovoltaics. This successful application depends mainly on the easiness of their transfer to a foreign carrier substrate. Therefore, developing a simple and efficient method to realize the transfer is a key issue. A most delicate point is the lift-off of the epitaxial layer from its parent substrate. In this work, we present a method to weaken the interface based on hydrogen incorporation. We have been able to control the hydrogen content at the interface between the crystalline silicon substrate and the epitaxial films by changing the epitaxial growth conditions. Several bonding techniques have been tested and epitaxial Si films have been transferred successfully via anodic bonding. A hydrogen-assisted transferring mechanism is presented. (10.1016/j.apsusc.2020.146057)
  DOI : 10.1016/j.apsusc.2020.146057
• Wide-Field Mueller Polarimetry of Brain Tissue Sections for Visualization of White Matter Fiber Tracts
  
  • Schucht Philippe
  • Lee Hee Ryung
  • Mezouar Mohammed Hachem
  • Hewer Ekkehard
  • Raabe Andreas
  • Murek Michael
  • Zubak Irena
  • Goldberg Johannes
  • Kovari Eniko
  • Pierangelo Angelo
  • Novikova Tatiana
  , 2020. Identification of white matter fiber tracts of the brain is crucial for delineating the tumor border during neurosurgery. A custom-built Mueller polarimeter was used in reflection configuration for the wide-field imaging of thick section of fixed human brain and fresh calf brain. The experimental images of azimuth of the fast optical axis of linear birefringent medium showed a strong correlation with the silver-stained sample histology image, which is the gold standard for ex-vivo brain fiber tract visualization. The polarimetric images of fresh calf brain tissue demonstrated the same trends in depolarization, scalar retardance and azimuth of the fast optical axis as seen in fixed human brain tissue. Thus, label-free imaging Mueller polarimetry shows promise as an efficient intra-operative modality for the visualization of healthy brain white matter fiber tracts, which could improve the accuracy of tumor border detection and, ultimately, patient outcomes.