Publications

2020

• Growth of doped epitaxial silicon at low temperature by PECVD for photovoltaic applications
  
  • Chrostowski Marta
  , 2020. This PhD thesis aims at evaluating low temperature silicon epitaxy (< 200°C) by RF-PECVD as an alternative to diffusion for the formation of the emitter layer of crystalline silicon (c-Si) solar cells. The epitaxial growth of intrinsic, n-type and p-type films grown on (100) c-Si substrates has been confirmed by ellipsometry. Surprisingly, the as-grown doped epitaxial silicon (epi-Si) films present a larger out-of-plane lattice parameter than the substrate, and are fully strained. Boron and phosphorus concentration of 3 and 3.5x1019 at/cm3, respectively, were achieved as deduced from SIMS measurements. However, in the as-grown state B-H complexes are formed and annealing is required to activate boron atoms. After annealing, we reached a doping efficiency of approximately 60%. As expected, the activation of boron leads to a drop of the mobility to ~20 cm2/Vs. Moreover, we put forward a correlation between the evolution upon annealing of the structure, electrical properties and the hydrogen content. Finally, XRD measurements have shown that by providing energy, annealing at 350°C induces the relaxation of the epi-Si structure, thus the apparition of defects, confirmed by TEM and low temperature PL.
• Hydrogen Plasma-Assisted Growth of Gold Nanowires
  
  • Gong Ruiling
  • Zheng Zhen
  • An Junyang
  • Maurice Jean-Luc
  • Azrak Edy
  • Nair Vishnu
  • Foti Antonino
  • Moldovan Simona
  • Karam Chantal
  • Duguay Sébastien
  • Pareige Philippe
  • Tian Bozhi
  • Chen Wanghua
  • Roca I Cabarrocas Pere
  Crystal Growth & Design, American Chemical Society, 2020, 20 (6), pp.4185-4192. Because of their innocuity, Au nanowires present an interesting field of applications in biology and, particularly, in cancer therapy. Since their morphology and distribution can greatly affect their performances, being able to control their mode of growth is important. Various elaboration techniques including “top-down” and “bottom-up” approaches have been developed. In this work, we propose an efficient maskless method to grow Au nanowires with the help of hydrogen plasma treatment of Au thin films. We have been able to grow Au nanowires by taking advantage of spinodal dewetting of an Au thin film and the supply of silicon radicals resulting from hydrogen plasma etching of amorphous silicon coating the walls of the reactor. A variety of techniques have been applied to study the microstructure and the optical properties of Au nanowires. A strong photothermal effect of Au nanowires has been demonstrated with the help of visible laser light. In order to study the nanowire growth, the transport of Au atoms is discussed, and a growth mechanism is proposed. (10.1021/acs.cgd.0c00480)
  DOI : 10.1021/acs.cgd.0c00480
• Depolarization metric spaces for biological tissues classification
  
  • van Eeckhout Albert
  • Garcia-Caurel Enrique
  • Ossikovski Razvigor
  • Lizana Angel
  • Rodríguez Carla
  • González-Arnay Emilio
  • Campos Juan
  Journal of Biophotonics, Wiley, 2020, 13 (8). Abstract Classification of tissues is an important problem in biomedicine. An efficient tissue classification protocol allows, for instance, the guided‐recognition of structures through treated images or discriminating between healthy and unhealthy regions (e.g., early detection of cancer). In this framework, we study the potential of some polarimetric metrics, the so‐called depolarization spaces, for the classification of biological tissues. The analysis is performed using 120 biological ex vivo samples of three different tissues types. Based on these data collection, we provide for the first time a comparison between these depolarization spaces, as well as with most commonly used depolarization metrics, in terms of biological samples discrimination. The results illustrate the way to determine the set of depolarization metrics which optimizes tissue classification efficiencies. In that sense, the results show the interest of the method which is general, and which can be applied to study multiple types of biological samples, including of course human tissues. The latter can be useful for instance, to improve and to boost applications related to optical biopsy. (10.1002/jbio.202000083)
  DOI : 10.1002/jbio.202000083
• The potentially crucial role of quasi-particle interferences for the growth of silicene on graphite
  
  • Jardali Fatme
  • Lechner Christoph
  • de Crescenzi Maurizio
  • Scarselli Manuela
  • Berbezier Isabelle
  • Castrucci Paola
  • Vach Holger
  Nano Research, Springer, 2020. A comprehensive picture of the initial stages of silicene growth on graphite is drawn. Evidence is shown that quasiparticle interferences play a crucial role in the formation of the observed silicene configurations. We propose, on one hand, that the charge modulations caused by those quantum interferences serve as templates and guide the incoming Si atoms to self-assemble to the unique (3 3 ×)R30° honeycomb atomic arrangement. On the other hand, their limited extension limits the growth to about 150 Si atoms under our present deposition conditions. The here proposed electrostatic interaction finally explains the unexpected stability of the observed silicene islands over time and with temperature. Despite the robust guiding nature of those quantum interferences during the early growth phase, we demonstrate that the window of experimental conditions for silicene growth is quite narrow, making it an extremely challenging experimental task. Finally, it is shown that the experimentally observed three-dimensional silicon clusters might very well be the simple result of the end of the silicene growth resulting from the limited extent of the quasi-particle interferences. (10.1007/s12274-020-2858-x)
  DOI : 10.1007/s12274-020-2858-x
• Deep Geometric Knowledge Distillation with Graphs
  
  • Lassance Carlos
  • Bontonou Myriam
  • Hacene Ghouthi Boukli
  • Gripon Vincent
  • Tang Jian
  • Ortega Antonio
  , 2020, pp.8484-8488. In most cases deep learning architectures are trained disregarding the amount of operations and energy consumption. However, some applications, like embedded systems, can be resource-constrained during inference. A popular approach to reduce the size of a deep learning architecture consists in distilling knowledge from a bigger network (teacher) to a smaller one (student). Directly training the student to mimic the teacher representation can be effective, but it requires that both share the same latent space dimensions. In this work, we focus instead on relative knowledge distillation (RKD), which considers the geometry of the respective latent spaces, allowing for dimension-agnostic transfer of knowledge. Specifically we introduce a graph-based RKD method, in which graphs are used to capture the geometry of latent spaces. Using classical computer vision benchmarks, we demonstrate the ability of the proposed method to efficiently distillate knowledge from the teacher to the student, leading to better accuracy for the same budget as compared to existing RKD alternatives. (10.1109/ICASSP40776.2020.9053986)
  DOI : 10.1109/ICASSP40776.2020.9053986
• Toward an automatic tool for oligoclonal band detection in cerebrospinal fluid and tears for multiple sclerosis diagnosis: lane segmentation based on a ribbon univariate open active contour
  
  • Haddad Farah
  • Boudet Samuel
  • Peyrodie Laurent
  • Vandenbroucke Nicolas
  • Hautecoeur Patrick
  • Forzy Gérard
  Medical and Biological Engineering and Computing, Springer Verlag, 2020, 58 (5), pp.967-976. The latest revision of multiple sclerosis diagnosis guidelines emphasizes the role of oligoclonal band detection in isoelectric focusing images of cerebrospinal fluid. Recent studies suggest tears as a promising noninvasive alternative to cerebrospinal fluid. We are developing the first automatic method for isoelectric focusing image analysis and oligoclonal band detection in cerebrospinal fluid and tear samples. The automatic analysis would provide an accurate, fast analysis and would reduce the expert-dependent variability and errors of the current visual analysis. In this paper, we describe a new effective model for the fully automated segmentation of highly distorted lanes in isoelectric focusing images. This approach is a new formulation of the classic parametric active contour problem, in which an open active contour is constrained to move from the top to the bottom of the image, and the x-axis coordinate is expressed as a function of the y-axis coordinate. The left and right edges of the lane evolved together in a ribbon-like shape so that the full width of the lane was captured reliably. The segmentation algorithm was implemented using a multiresolution approach in which the scale factor and the active contour control points were progressively increased. The lane segmentation algorithm was tested on a database of 51 isoelectric focusing images containing 419 analyzable lanes. The new model gave robust results for highly curved lanes, weak edges, and low-contrast lanes. A total of 98.8% of the lanes were perfectly segmented, and the remaining 1.2% had only minor errors. The computation time (1 s per membrane) is negligible. This method precisely defines the region of interest in each lane and thus is a major step toward the first fully automatic tool for oligoclonal band detection in isoelectric focusing images. (10.1007/s11517-020-02141-9)
  DOI : 10.1007/s11517-020-02141-9
• Detrimental effects of ion migration in the perovskite and hole transport layers on the efficiency of inverted perovskite solar cells
  
  • Huang Yong
  • Lopez-Varo Pilar
  • Geffroy Bernard
  • Lee Heejae
  • Bourée Jean-Eric
  • Mishra Arpit
  • Baranek Philippe
  • Rolland Alain
  • Pedesseau Laurent
  • Jancu Jean-Marc
  • Even Jacky
  • Puel Jean-Baptiste
  • Gueunier-Farret Marie-Estelle
  Journal of Photonics for Energy, Society of Photo-optical Instrumentation Engineers (SPIE), 2020, 10 (2), pp.024502. Perovskite-based solar cells (PSCs) have opened the possibility of cost-effective, high-efficiency photovoltaic conversion. However, their instabilities prevent them from commercialization. One of the instability triggers has been attributed to the mobile ions flowing into the carrier transport layer(s). To study the effect of this ionic migration, a numerical PSC model is developed, considering electronic and ionic mixed drift-diffusion transport both in the perovskite and the hole transport layer. The inverted PSC architecture, phenyl-C61-butyric acid methyl ester (PCBM)/perovskite/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with two heterojunctions, is analyzed. The effect of the ionic migration on the performance of the PSCs has been analyzed by (1) the variation of the ionic mobile concentration and (2) the modification of the local trapping density. The current–voltage (J–V) and capacitance–voltage characteristics show that the electric field in the bulk can be screened by the ionic distribution modifying the effective built-in voltage. At high ionic concentrations, the electric field at the interfaces is also affected, hindering the charge extraction. The simulations show that the short circuit current is therefore strongly modified. (10.1117/1.JPE.10.024502)
  DOI : 10.1117/1.JPE.10.024502
• Direct etching at the nanoscale through nanoparticle-directed capillary condensation
  
  • Garín M.
  • Khoury R.
  • Martín I.
  • Johnson Erik
  Nanoscale, Royal Society of Chemistry, 2020, 12 (16), pp.9240-9245. We report on a method to locally deliver at the nanoscale a chemical etchant in vapor phase by capillary condensation in a meniscus at a nanoparticle/substrate interface. The process is simple, scalable and does not require functionalization of the nanoparticles. Furthermore, it does not rely on any specific chemical properties of the materials other than the solution being aqueous and the wettability properties of the surfaces involved, which should enable its application to other materials and chemicals combinations. In particular, in this work we demonstrate the proposed process by periodically pattering a SiO2 layer using a self-assembled monolayer of polystyrene particles exposed to HF vapor. The patterned SiO2 layer is then used as a mask to etch a pattern of inverted nanopyramids in Si. The silicon nanopatterning has been demonstrated for particles sizes from 800 nm down to 100 nm, achieving pyramids with a size down to 50 nm for 100 nm nanoparticles. (10.1039/C9NR10217E)
  DOI : 10.1039/C9NR10217E
• ALD of ZnO:Ti: Growth Mechanism and Application as an Efficient Transparent Conductive Oxide in Silicon Nanowire Solar Cells
  
  • Coutancier Damien
  • Zhang Shan-Ting
  • Bernardini Simone
  • Fournier Olivier
  • Mathieu-Pennober Tiphaine
  • Donsanti Frédérique
  • Tchernycheva Maria
  • Foldyna Martin
  • Schneider Nathanaelle
  ACS Applied Materials & Interfaces, Washington, D.C. : American Chemical Society, 2020, 12, pp.21036 - 21044. In the quest for the replacement of indium tin oxide (ITO), Ti-doped zinc oxide (TZO) films have been synthesized by atomic layer deposition (ALD) and applied as an n-type transparent conductive oxide (TCO). TZO thin films were obtained from titanium (IV) i-propoxide (TTIP), diethyl zinc, and water by introducing TiO 2 growth cycle in a ZnO matrix. Process parameters such as the order of precursor introduction, the cycle ratio, and the film thickness were optimized. The as-deposited films were analyzed for their surface morphology, elemental stoichiometry, optoelectronic properties, and crystallinity using a variety of characterization techniques. The growth mechanism was investigated for the first time by in situ quartz crystal microbalance measurements. It evidenced different insertion modes of titanium depending on the precursor introduction, as well as the etching of Zn−Et surface groups by TTIP. Resistivity as low as 1.2 × 10 −3 Ω cm and transmittance >80% in the visible range were obtained for 72-nm-thick films. Finally, the first application of ALD-TZO as TCO was reported. TZO films were successfully implemented as top electrodes in silicon nanowire solar cells. The unique properties of TZO combined with conformal coverage realized by the ALD technique make it possible for the cell to show almost flat external quantum efficiency (EQE) response, surpassing the bell-like EQE curve seen in devices with a sputtered ITO top electrode. (10.1021/acsami.9b22973)
  DOI : 10.1021/acsami.9b22973
• Germanium quantum dot infrared photodetectors addressed by self-aligned silicon nanowire electrodes
  
  • Zhao Yaolong
  • Li Lingfei
  • Liu Shuaishuai
  • Wang Junzhuan
  • Xu Jun
  • Shi Yi
  • Chen Kunji
  • Roca I Cabarrocas Pere
  • Yu Linwei
  Nanotechnology, Institute of Physics, 2020, 31 (14), pp.145602. (10.1088/1361-6528/ab647e)
  DOI : 10.1088/1361-6528/ab647e
• Polarimetric analysis of a fused sphere as a model for adherent particles
  
  • Fernández-Pérez A.
  • Hyuk Yoo T. Sang
  • Fernández-Luna J.L
  • Moreno F.
  • Garcia-Caurel Enrique
  • Saiz J.M.
  Optik, Elsevier, 2020, 207, pp.164371. There are many situations of interest that are related to the geometry of soft spherical particles close – and adhering – to a surface. The case of biological cells is probably one of the most appealing ones because of their attachment/detachment processes, that are connected with their adhesion capacity and their ability to migrate. In this work, we perform imaging polarimetry on a model consisting of samples of latex spheres, or spherical caps, located on a flat transparent substrate. Different curvature degrees, achieved by gradual heating and melting, mimic the process of spreading associated to adhesion. Experiment-theory comparison allows us to identify specific states of adherence, and add some insight into experimental aspects like the contrast in the observation plane depending of the polarimetric parameter image selected, and also the effect of the numerical aperture (NA) of the microscope. (10.1016/j.ijleo.2020.164371)
  DOI : 10.1016/j.ijleo.2020.164371
• High graphene permeability for silicon atoms during deposition at room temperature: the role of defects
  
  • Ronci F.
  • Colonna S.
  • Flammini R.
  • de Crescenzi M.
  • Scarselli M.
  • Salvato M.
  • Berbezier I.
  • Jardali F.
  • Lechner C.
  • Pochet P.
  • Vach Holger
  • Castrucci P.
  Carbon, Elsevier, 2020, 158, pp.631-641. Graphene (Gr) is known to be an excellent barrier preventing atoms and molecules to diffuse through it. This is due to the carbon atom arrangement in a two-dimensional (2D) honeycomb structure with a very small lattice parameter thus forming an electron cloud that prevents atoms and molecules crossing. Nonetheless at high temperature of annealing, intercalation of atoms through graphene occurs, opening the path for formation of vertical heterojunctions formed of two-dimensional layers. In this paper, we report on the ability of silicon atoms to penetrate the graphene network, fully epitaxially grown on a Ni(111) surface, even at room temperature. Our scanning tunneling microscopy (STM) shows that defects like vacancies and dislocations of the graphene lattice favor the Si intercalation below the Gr layer forming two-dimensional, flat and disordered islands. Ab-initio molecular dynamics calculations confirm that Gr defects are necessary for Si intercalation at room temperature and show that a hypothetical intercalated silicene layer cannot be stable for more than 8 ps and that the corresponding Si atoms completely lose their in-plane order resulting in a random planar distribution and form strong covalent bonds with Ni atoms. (10.1016/j.carbon.2019.11.035)
  DOI : 10.1016/j.carbon.2019.11.035
• High graphene permeability for room temperature silicon deposition: The role of defects
  
  • Ronci F
  • Colonna S
  • Flammini R.
  • de Crescenzi M.
  • Scarselli M.
  • Salvato M.
  • Berbezier I.
  • Jardali F
  • Lechner C
  • Pochet P
  • Vach Holger
  • Castrucci P
  Carbon, Elsevier, 2020. Graphene (Gr) is known to be an excellent barrier preventing atoms and molecules to diffuse through it. This is due to the carbon atom arrangement in a two-dimensional (2D) honeycomb structure with a very small lattice parameter thus forming an electron cloud that prevents atoms and molecules crossing. Nonetheless at high an-nealing temperatures, intercalation of atoms through graphene occurs, opening the path for formation of vertical heterojunctions constituted of two-dimensional layers. In this paper, we report on the ability of silicon atoms to penetrate the graphene network, fully epitaxially grown on a Ni(111) surface, even at room temperature. Our scanning tunneling microscopy (STM) experiments show that the presence of defects like vacancies and disloca-tions in the graphene lattice favor the Si atoms intercalation, thus forming two-dimensional, flat and disordered islands below the Gr layer. Ab-initio molecular dynamics calculations confirm that Gr defects are necessary for Si intercalation at room temperature and show that: i) a hypothetical intercalated silicene layer cannot be stable for more than 8 ps and ii) the corresponding Si atoms completely lose their in-plane order resulting in a random planar distribution and form strong covalent bonds with Ni atoms. (10.1016/j.carbon.2019.11.035)
  DOI : 10.1016/j.carbon.2019.11.035
• Algorithm for the numerical calculation of the serial components of the normal form of depolarizing Mueller matrices
  
  • San José Ignacio
  • Gil José
  • Ossikovski R.
  Applied optics, Optical Society of America, 2020, 59 (8), pp.2291. The normal form of a depolarizing Mueller matrix constitutes an important tool for the phenomenological interpretation of experimental polarimetric data. Due to its structure as a serial combination of three Mueller matrices, namely a canonical depolarizing Mueller matrix sandwiched between two pure (nondepolarizing) Mueller matrices, it overcomes the necessity of making a priori choices on the order of the polarimetric components, as this occurs in other serial decompositions. Because Mueller polarimetry addresses more and more applications in a wide range of areas in science, engineering, medicine, etc., the normal form decomposition has an enormous potential for the analysis of experimentally determined Mueller matrices. However, its systematic use has been limited to some extent because of the lack of numerical procedure for the calculation of each polarimetric component, in particular in the case of Type II Mueller matrices. In this work, an efficient algorithm applicable to the decomposition of both Type II and Type I Mueller matrices is presented. (10.1364/AO.384871)
  DOI : 10.1364/AO.384871
• Mirau-based line-field confocal optical coherence tomography
  
  • Dubois Arnaud
  • Xue Weikai
  • Levecq O
  • Bulkin P
  • Coutrot Anne-Lise
  • Ogien Jonas
  Optics Express, Optical Society of America - OSA Publishing, 2020, 28 (6), pp.7918-7927. Line-field confocal optical coherence tomography (LC-OCT) is an imaging technique in which A-scans are acquired in parallel through line illumination with a broadband laser and line detection with a line-scan camera. B-scan imaging at high spatial resolution is achieved by dynamic focusing in a Linnik interferometer. This paper presents an LC-OCT device based on a custom-designed Mirau interferometer that o ers similar spatial resolution and detection sensitivity. The device has the advantage of being more compact and lighter. In vivo imaging of human skin with a resolution of 1.3 µm * 1.1 µm (lateral * axial) is demonstrated over a field of 0.9 mm * 0.4 mm (lateral * axial) at 12 frames per second. (10.1364/OE.389637)
  DOI : 10.1364/OE.389637
• Synthesis, Electronic Properties and OLED Devices of Chromophores Based on $\lambda ^5$‐Phosphinines
  
  • Pfeifer Gregor
  • Chahdoura Faouzi
  • Papke Martin
  • Weber Manuela
  • Szücs Rozsa
  • Geffroy Bernard
  • Tondelier Denis
  • Nyulászi László
  • Hissler Muriel
  • Müller Christian
  Chemistry - A European Journal, Wiley-VCH Verlag, 2020, 26 (46), pp.10534-10543. A new series of 2,4,6-triaryl-λ -phosphinines have been synthesized that contain different substituents both on the carbon backbone and the phosphorus atom of the six-membered heterocycle. Their optical and redox properties were studied in detail, supported by in-depth theoretical calculations. The modularity of the synthetic strategy allowed the establishment of structure-property relationships for this class of compounds and an OLED based on a blue phosphinine emitter could be developed for the first time. (10.1002/chem.202000932)
  DOI : 10.1002/chem.202000932
• Insights into the $\pi$ - $\pi$ interaction driven non-covalent functionalization of carbon nanotubes of various diameters by conjugated fluorene and carbazole copolymers
  
  • Benda Robert
  • Zucchi Gaël
  • Cancès Eric
  • Lebental Bérengère
  The Journal of Chemical Physics, American Institute of Physics, 2020, 152 (6), pp.064708. We investigate the interaction of polyfluorene and fluorene/carbazole copolymers bearing various functional groups and side chains with small to large diameter — from 1.7 nm to 9 nm — carbon nanotubes (CNTs) in vacuo. We use variable-charge molecular dynamics simulations based on the reactive force field ReaxFF. We show that non-covalent functionalization of nanotubes, driven by π − π interactions, is effective for all the polymers studied, thanks to their conjugated backbone and regardless of the presence of specific functional groups. The geometry at equilibrium of these polymer/CNT hybrids is analyzed in detail at the scale of each fluorene or carbazole unit. The role of both the functional groups and the alkyl chain length is analyzed in detail. Adsorption of the polymers on the nanotube sidewalls is shown to be either complete — with the whole chain physisorbed — or partial — due to intrachain coiling or interchain repulsion — depending on the initial geometry, number of polymers, and nanotube diameter. Energetic arguments supplement the described geometric features. Both energetic and geometric adsorption features are derived here for the first time for large diameter carbon nanotubes (up to 9 nm) and fluorene/carbazole copolymers having up to 30 monomers and bearing different functional groups. The force field ReaxFF and its available parameterization used for the simulations are validated, thanks to a benchmark and review on higher-level quantum calculations — for simple π − π interacting compounds made up of polycyclic aromatic molecules adsorbed on a graphene sheet or bilayer graphene. Although it is shown that the influence of the nanotube chirality on the adsorption pattern and binding strength cannot be discussed with our method, we highlight that an available force field such as ReaxFF and its parameterization can be transferable to simulate new systems without specific re-parameterization, provided that this model is validated against reference methods or data. This methodology proves to be a valuable tool for optimal polymer design for nanotube functionalization at no re-parameterization cost and could be adapted to simulate and assist the design of other types of molecular systems. (10.1063/1.5133634)
  DOI : 10.1063/1.5133634
• Electrical characterization of low temperature plasma epitaxial Si grown on highly doped Si substrates
  
  • Léon Cyril
  • Le Gall Sylvain
  • Gueunier-Farret Marie-Estelle
  • Kleider Jean-Paul
  • Roca I Cabarrocas Pere
  EPJ Photovoltaics, EDP sciences, 2020, 11, pp.4. Epitaxial silicon layers were grown on highly doped c-Si substrates using the plasma-enhanced chemical vapour deposition process (PECVD) at low temperature (175 °C). The transport and defect-related properties of these epi-Si layers were characterized by current density-voltage (J–V) and capacitance–voltage (C–V) techniques. The results show that the epi-Si layers exhibit a non-intentional n-type doping with a low apparent doping density of about 2 × 10^15 cm−3. The admittance spectroscopy technique is used to investigate the presence of deep-level defects in the structure. An energy level at 0.2 eV below the conduction band has been found with a density in the range of 10^15 cm−3 which may explain the observed apparent doping profile. (10.1051/epjpv/2020002)
  DOI : 10.1051/epjpv/2020002
• Electrical scanning probe microscopy approaches to investigate solar cell junctions and devices
  
  • Alvarez J
  • Marchat Clément
  • Morisset Audrey
  • Dai Letian
  • Kleider Jean-Paul
  • Cabal Raphaël
  • Cabarrocas Pere Roca I.
  , 2020, 11288. C-AFM and KPFM techniques have been applied to investigate advanced junctions that are currently involved in highly efficient silicon solar cells. Our first study focuses on silicon heterojunctions and notably hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) P/n or N/p heterostructures which band bending at the interface forms a 2D channel. This conductive channel was indeed evidenced for the first time by cross-sectional investigations by C-AFM confirming the analysis of macroscopic planar conductance measurements. A second example of nanoscale characterization concerns the passivating selective contacts consisting in a thin silicon oxide (SiOx) layer between the c-Si and a highly doped polysilicon (poly-Si) layer. The electrical carrier transport is here not limited by the oxide layer and it is assumed that tunnelling through the oxide and/or the presence of pinholes are the main competitive mechanisms. For this specific heterostructure KPFM reveals local surface potential drops of 15-30 mV, which do not exist on samples without SiOx. These potential drops suggest the presence of pinholes that are formed during the poly-Si annealing process performed in the range of 700-900 °C. Finally, in a third study, we concentrate on p-in radial junction (RJ) silicon nanowire (SiNW) devices that are investigated under illumination by KPFM, in the so-called surface photovoltage (SPV) technique. This work focuses on the possibility of extracting the open-circuit voltage (VOC) on single isolated SiNW RJ by local SPV measurements using different AFM tip shapes and illumination directions in order to minimize shadowing effects. (10.1117/12.2540422)
  DOI : 10.1117/12.2540422
• Maskless and contactless patterned silicon deposition using a localized PECVD process
  
  • Leal Ronan
  • Bruneau Bastien
  • Bulkin Pavel
  • Novikova Tatiana
  • Silva François
  • Habka Nada
  • Johnson Erik
  Plasma Sources Science and Technology, IOP Publishing, 2020, 29 (2), pp.025023. We present a novel technique to perform contactless and mask-free patterned plasma enhanced chemical vapour deposition and etching. When a powered electrode with narrow slits is placed very close to the substrate, plasma is selectively ignited within the slits due to the hollow cathode effect, and so deposition or etching occurs only within an area smaller than the size of the slit. This technique is demonstrated through the deposition of hydrogenated amorphous silicon using a gas mixture of hydrogen, argon and silane. Slits as small as 1 mm generate a plasma, and for this width, the lines deposited are about 750 μm wide, homogenous over their length (60 mm), and are deposited at a rate of 50 nm min −1. The phenomenon is studied using 2D Particle In Cell (PIC) modelling with a simplified argon chemistry. The electron localization observed in the PIC modelling provides an explanation of why the deposition is narrower than the slit. (10.1088/1361-6595/ab5e2c)
  DOI : 10.1088/1361-6595/ab5e2c
• The use of Stokes-Mueller polarimetry for assessment of amyloid-β progression in a mouse model of Alzheimer’s disease
  
  • Borovkova Mariia
  • Bykov Alexander
  • Popov Alexey
  • Pierangelo Angelo
  • Novikova Tatiana
  • Pahnke Jens
  • Meglinski Igor
  , 2018, 494, pp.19. (10.1117/12.2550795)
  DOI : 10.1117/12.2550795
• How to choose and optimize a classifier for your polarimetric imaging data?
  
  • Rehbinder Jean
  • Heinrich Christian
  • Pierangelo Angelo
  • Zallat Jihad
  , 2020, pp.37. Mueller polarimetry is a powerful characterization technique for a variety of samples and a promising optical-biopsy tool for early detection of cancer. Recent advances in Mueller imaging devices allow the collection of large ex-vivo and invivo image databases. Although the technique is sensitive to subtle changes in the micro-organization of tissue, the Mueller matrices of such complex media contain intertwined polarimetric effects and are difficult to interpret. To identify the polarimetric signature of a given tissue modification (cancerous or not), machine learning tools are particularly well suited. However, a statistically sound approach is needed to make the most out of these tools and avoid common pitfalls. We present a global statistical framework based on decision theory. It consists of a complete preprocessing and analysis pipeline for polarimetric bioimages. In the analysis stage, we use a loss-risk-based approach to automatically select the optimal classifier among a library of classifiers. The approach allows to determine the subset of polarimetric parameters of interest, to determine the parameters of the classifiers and to assess classifier performance using cross-validation. The proposed framework is illustrated with precancer detection on human ex-vivo cervical samples. (10.1117/12.2546032)
  DOI : 10.1117/12.2546032
• A Comparison between Nanogratings-Based and Stress-Engineered Waveplates Written by Femtosecond Laser in Silica
  
  • Tian Jing
  • Yao Heng
  • Cavillon Maxime
  • Garcia-Caurel Enric
  • Ossikovski Razvigor
  • Stchakovsky Michel
  • Eypert Celine
  • Poumellec Bertrand
  • Lancry Matthieu
  Micromachines, MDPI, 2020, 11 (2), pp.131. This paper compares anisotropic linear optical properties (linear birefringence, linear dichroism, degree of polarization) and performances (absorption coefficient, thermal stability) of two types of birefringent waveplates fabricated in silica glass by femtosecond laser direct writing. The first type of waveplate is based on birefringence induced by self-organized nanogratings imprinted in the glass. One the other hand, the second design is based on birefringence originating from the stress-field formed around the aforementioned nanogratings. In addition to the provided comparison, the manufacturing of stress-engineered half waveplates in the UV-Visible range, and with mm-size clear aperture and negligible excess losses, is reported. Such results contrast with waveplates made of nanogratings, as the later exhibit significantly higher scattering losses and depolarization effects in the UV-Visible range. (10.3390/mi11020131)
  DOI : 10.3390/mi11020131
• Effect of Strains on the Dark Current-Voltage Characteristic of Silicon Heterojunction Solar Cells
  
  • Guin Laurent
  • Roca I Cabarrocas Pere
  • Jabbour Michel E
  • Triantafyllidis Nicolas
  Solar Energy, Elsevier, 2020. Anisotropic mechanical strain as low as 0.1% modifies the electronic response of crystalline semiconductor- based devices and in particular affects the performance of solar cells. We measure the dark current-voltage characteristic of silicon heterojunction solar cells under different levels of tensile uniaxial stress and observe a reversible change of the j-V curve with applied strain. Using a two-exponential description of the j-V char- acteristic to fit our experimental data, we obtain the strain dependence of the diffusion saturation current and find a decrease of about 3% for a tensile strain level of 6.7 × 10 4 . We compare these experiments to a theoretical model that accounts for the effect of strain on the band energy levels, densities of states and mobilities of carriers. The theoretical estimation of the change in saturation current is found to be in reasonable agreement with experimental results. (10.1016/j.solener.2019.12.037)
  DOI : 10.1016/j.solener.2019.12.037
• Large-scale patterning of π-conjugated materials by meniscus guided coating methods
  
  • Richard Mélissa
  • Al-Ajaji Abdulelah
  • Ren Shiwei
  • Foti Antonino
  • Tran Jacqueline
  • Frigoli Michel
  • Gusarov Boris
  • Bonnassieux Yvan
  • Caurel Enric Garcia
  • Bulkin Pavel
  • Ossikovski Razvigor
  • Yassar Abderrahim
  Advances in Colloid and Interface Science, Elsevier, 2020, 275, pp.102080. (10.1016/j.cis.2019.102080)
  DOI : 10.1016/j.cis.2019.102080