Publications

2022

• Tapering-free monocrystalline Ge nanowires synthesized via plasma-assisted VLS using In and Sn catalysts
  
  • Tang Jian
  • Wang Jun
  • Maurice Jean-Luc
  • Chen Wanghua
  • Foldyna Martin
  • Yu Linwei
  • Leshchenko Egor
  • Dubrovskii Vladimir
  • Cabarrocas Pere Roca I
  Nanotechnology, Institute of Physics, 2022, 33 (40), pp.405602. Abstract In and Sn are the type of catalysts which do not introduce deep level electrical defects within the bandgap of germanium (Ge). However, Ge nanowires produced using these catalysts usually have a large diameter, a tapered morphology, and mixed crystalline and amorphous phases. In this study, we show that plasma-assisted vapor–liquid–solid (PA-VLS) method can be used to synthesize Ge nanowires. Moreover, at certain parameter domains, the sidewall deposition issues of this synthesis method can be avoided and long, thin tapering-free monocrystalline Ge nanowires can be obtained with In and Sn catalysts. We find two quite different parameter domains where Ge nanowire growth can occur via PA-VLS using In and Sn catalysts: (i) a low temperature-low pressure domain, below ∼235 °C at a GeH 4 partial pressure of ∼6 mTorr, where supersaturation in the catalyst occurs thanks to the low solubility of Ge in the catalysts, and (ii) a high temperature-high pressure domain, at ∼400 °C and a GeH 4 partial pressure above ∼20 mTorr, where supersaturation occurs thanks to the high GeH 4 concentration. While growth at 235 °C results in tapered short wires, operating at 400 °C enables cylindrical nanowire growth. With the increase of growth temperature, the crystalline structure of the nanowires changes from multi-crystalline to mono-crystalline and their growth rate increases from ∼0.3 nm s −1 to 5 nm s −1 . The cylindrical Ge nanowires grown at 400°C usually have a length of few microns and a radius of around 10 nm, which is well below the Bohr exciton radius in bulk Ge (24.3 nm). To explain the growth mechanism, a detailed growth model based on the key chemical reactions is provided. (10.1088/1361-6528/ac57d4)
  DOI : 10.1088/1361-6528/ac57d4
• Prediction of the interaction strength of an urea‐based probe toward ions in water by means of Density Functional Theory/Polarizable Continuum Model calculations
  
  • Benda Robert
  • Vezin Thomas
  • Lebental Bérengère
  International Journal of Quantum Chemistry, Wiley, 2022, 122 (12). We study numerically, by means of density functional theory (DFT) calculations complemented with an implicit solvation model, a novel chemical probe bearing urea and aromatic phenyl groups. We probe the interaction in water of the latter with a wide variety of ions relevant to water quality. We perform geometry minimizations using PBE0 functional and aug-cc-pVDZ basis set, and a polarizable continuum model (PCM) to take into account the aqueous solvent. We underline for the first time several methodological details concerning the definition of the binding or interaction energy, and the basis set superposition error definition in the context of implicit solvation models. We observe two competing interaction modes for this probe: a urea-enhanced, cation-π interaction (with cations only), and hydrogen bonding occurring between the urea group and anions, the former being more favorable than the latter. A Generalized Kohn–Sham Energy Decomposition Analysis (GKS-EDA) in implicit solvent is performed to analyze the nature of the ions–probe interactions. Magnesium and sodium ions, and respectively glyphosate and hypochlorite ions, are found as the cations (resp. anions) having the largest binding free energies with the probe. This is the first time such an exhaustive study, investigating the selectivity of an organic probe toward a wide variety of ions in water, is carried out in the context of DFT/PCM models. Computer-aided sensor design needs reliable and efficient methods. Our methodology can be used as a general way to gain a valuable insight into the sensitivity of organic ligands toward a variety of ions or pesticides in water, without the need of an explicit solvent description, but still going beyond the state-of-the-art DFT in vacuo approach. By predicting possible competitive interactions, and understanding their nature, this methodology can thus help to better design functional groups selective to specific targets. (10.1002/qua.26901)
  DOI : 10.1002/qua.26901
• Synthèse contrôlée de couches de PtSe2 par épitaxie par jets moléculaires pour les dispositifs optoélectroniques dans l’infrarouge
  
  • Verschueren Ivan
  , 2022. La découverte du graphène et de ses propriétés en 2004 a initié l'étude de très nombreux matériaux bidimensionnels (2D). Ce travail se concentre principalement sur la synthèse de PtSe2 sur différents substrats. Ce matériau 2D de la famille des dichalcogénures de métaux de transition est stable à l'air, possède une mobilité de dérive importante à Tambiante (210 cm^2/(V.s)) et un gap variable en fonction du nombre de couches le rendant capable d'absorber dans l'infrarouge et en particulier à 1,55 um. Ces différentes caractéristiques en font un matériau d'intérêt, notamment pour les photodétecteurs IR.Le problème majeur qui se pose lors de l’apparition de nouveaux matériaux présentant des propriétés intéressantes est de les synthétiser de façon contrôlée et reproductible sur des substrats de grandes tailles, compatibles avec des développements industriels.Dans ce contexte, nous avons dans un premier temps étudié la possibilité de synthétiser PtSe2 par implantation ionique. L’idée était de faire cristalliser des précurseurs implantés sous forme d’ions Pt et Se dans des substrats de saphir et d’or, en pratiquant un recuit post-implantation à haute température. Cette méthode permet une grande uniformité et un excellent contrôle de la dose implantée, donc potentiellement du nombre de couches. Les couches obtenues après recuit des substrats de saphir sont de bonne qualité, polycristallines et présentent des cristallites de petites tailles. Il est probable que la croissance des domaines de PtSe2 s’effectue à partir de germes crées de façon aléatoire au cours de l’implantation ionique, phénomène déjà observé pour MoS2. Nous n’avons pas réussi à obtenir de PtSe2 après coimplantation dans des couches minces d’or déposées sur différents substrats.Dans un deuxième temps nous avons étudié la croissance par coévaporation en MBE, méthode de croissance à l'heure actuelle bien maîtrisée. Nos travaux se sont portés sur différents substrats :- Les couches obtenues sur saphir sont de très bonne qualité cristalline, présentent une excellente homogénéité et une épaisseur contrôlée. La texture de fibre observée est qualifiée par diffraction de rayons X. Nous démontrons de plus que l'obtention de terrasses séparées par des marches atomiques sur le substrat de saphir avant croissance permet une amélioration de la qualité cristalline en imposant une orientation azimutale aux cristallites nucléant sur le bord des marches.- Les couches obtenues sur silice sont de qualité cristalline médiocre.- Les couches obtenues sur h-BN déposé sur saphir présentent une qualité cristalline exaltée par rapport au substrat.- Les couches obtenues sur SiC graphitisé sont d'excellente qualité cristalline et présentent une bonne homogénéité. Des mesures de GIXRD révèlent que l'orientation azimutale des cristallites est en partie imposée par le substrat. Deux directions particulières s'imposent, la principale étant particulièrement intense. La secondaire, correspondant à une rotation de 30° des cristallites, donne des pics de faible intensité.Dans un troisième temps nous avons étudié les performances électriques des couches obtenues sur saphir. Les caractérisations par la méthode de van der Pauw révèlent qu'une couche de surface 16 x 16 mm2 et d'épaisseur 7-8 nm présente une mobilité de Hall de 6,5 cm^2/(V.s) et une concentration de porteurs de 11,6*10^15 cm^(-2) à Tambiante. Les caractérisations sur dispositifs DC nous ont permis d'étudier la résistance par carré des canaux et les résistances de contacts. Nous obtenons une Rcarré moyenne de 1,50 kOhm avec sigma=0,35 kOhm. Les résistances de contacts sont très faibles devant la résistance du canal. Les caractérisations sur photodétecteurs RF à 1,55 um révèlent une réponse constante en fonction de la fréquence entre 2 et 30 GHz à Prf= -48 dBm (pour Popt=60 mW). Des mesures effectuées entre 2 et 67 GHz montrent une excellente fréquence de coupure (à -3 dB) de 60 GHz, soit supérieure à l'état de l'art (17 GHz).
• Rendez-vous Based Drift Diagnosis Algorithm For Sensor Networks Towards In Situ Calibration
  
  • Delaine Florentin
  • Lebental Bérengère
  • Rivano Hervé
  IEEE Transactions on Automation Science and Engineering, Institute of Electrical and Electronics Engineers, 2022. In recent years, low-cost sensors have raised strong interest for environmental monitoring applications. These instruments often suffer from degraded data quality. Notably, they are prone to drift. It can be mitigated with costly periodic calibrations. To reduce this cost, in situ calibration strategies have emerged, enabling the recalibration of instruments while leaving them in the field. However, they rarely identify which instruments actually need a calibration because of drift, so that in situ calibration may instead degrade performances. Therefore, a novel drift detection algorithm is presented in this work, exploiting the concept of rendezvous between measuring instruments. Its originality lies mainly in the comparisons of values determining the state of the instruments, for which the quality of the measurement results is taken into account. It defines the concept of compatibility between measurement results. A case study is developed, showing an accuracy of 88% for correct detection of drifting instruments. The results of the diagnosis algorithm are then combined with calibration approaches. Results show a significant improvement of the measurement results. Notably, an increase of 15% of the coefficient of determination of the linear regression between their true values and the measured values is observed with the correction and the error on the slope and on the intercept respectively is reduced by 50% and 60% at least. (10.1109/TASE.2022.3182289)
  DOI : 10.1109/TASE.2022.3182289
• XPS investigation of surface graphitized nanodiamonds: evidence of a nano effect
  
  • Ducrozet F
  • Girard H
  • Leroy J
  • Larquet E
  • Florea I
  • Brun E
  • Sicard-Roselli C
  • Arnault Jean-Charles
  , 2022.
• Strontium release from wollastonite-based brushite cement paste under semi-dynamic leaching conditions
  
  • Jdaini Jihane
  • Cau dit Coumes Céline
  • Barré Yves
  • de Noirfontaine Marie-Noëlle
  • Courtial Mireille
  • Garcia-Caurel Enrique
  • Dunstetter Frédéric
  • Gorse-Pomonti Dominique
  , 2022.
• Bulk Defects and Hydrogenation Kinetics in Crystalline Silicon Solar Cells With Fired Passivating Contacts
  
  • Lehmann Mario
  • Desthieux Anatole
  • Valle Nathalie
  • Morisset Audrey
  • Wyss Philippe
  • Eswara Santhana
  • Wirtz Tom
  • Ingenito Andrea
  • Roca i Cabarrocas Pere
  • Ballif Christophe
  • Haug Franz-Josef
  IEEE Journal of Photovoltaics, IEEE, 2022, 12 (3), pp.711-721. (10.1109/JPHOTOV.2022.3161871)
  DOI : 10.1109/JPHOTOV.2022.3161871
• Van der Waals Heteroepitaxy of Air-Stable Quasi-Free-Standing Silicene Layers on CVD Epitaxial Graphene/6H-SiC
  
  • Ben Jabra Zouhour
  • Abel Mathieu
  • Fabbri Filippo
  • Aqua Jean-Noel
  • Koudia Mathieu
  • Michon Adrien
  • Castrucci Paola
  • Ronda Antoine
  • Vach Holger
  • de Crescenzi Maurizio
  • Berbezier Isabelle
  ACS Nano, American Chemical Society, 2022, 16 (4), pp.5920-5931. (10.1021/acsnano.1c11122)
  DOI : 10.1021/acsnano.1c11122
• Metal-free Silicon-Lithium-Sulfur full cell architecture and methods of making them
  
  • Cojocaru Costel Sorin
  • Ezzedine Mariam
  • Florea Ileana
  • Jardali Fatme
  , 2022.
• Model for the depolarizing retarder in Mueller matrix polarimetry
  
  • Ossikovski Razvigor
  • Arteaga Oriol
  • Garcia-Caurel Enrique
  • Hingerl Kurt
  Journal of the Optical Society of America. A Optics, Image Science, and Vision, Optical Society of America, 2022, 39 (5), pp.873. We advance an analytical model describing the polarimetric response of a depolarizing retarder whose retardance varies spatially in magnitude or in orientation. The variation of the retarder parameters may be either of deterministic or of random nature. The model provides both the mean values and the uncertainties of the parameters. Its application is illustrated on two experimental examples, respectively covering the deterministic and the random cases. (10.1364/JOSAA.451106)
  DOI : 10.1364/JOSAA.451106
• Physical Significance of the Determinant of a Mueller Matrix
  
  • Gil José
  • Ossikovski Razvigor
  • San José Ignacio
  Photonics, MDPI, 2022, 9 (4), pp.246. The determinant of a Mueller matrix M plays an important role in both polarization algebra and the interpretation of polarimetric measurements. While certain physical quantities encoded in M admit a direct interpretation, the understanding of the physical and geometric significance of the determinant of M (detM) requires a specific analysis, performed in this work by using the normal form of M, as well as the indices of polarimetric purity (IPP) of the canonical depolarizer associated with M. We derive an expression for detM in terms of the diattenuation, polarizance and a parameter proportional to the volume of the intrinsic ellipsoid of M. We likewise establish a relation existing between the determinant of M and the rank of the covariance matrix H associated with M, and determine the lower and upper bounds of detM for the two types of Mueller matrices by taking advantage of their geometric representation in the IPP space. (10.3390/photonics9040246)
  DOI : 10.3390/photonics9040246
• Investigation of Sn-containing precursors for in-plane GeSn nanowire growth
  
  • Zheng Lulu
  • Azrak Edy
  • Gong Ruiling
  • Castro Celia
  • Duguay Sébastien
  • Pareige Philippe
  • Roca I Cabarrocas Pere
  • Chen Wanghua
  Journal of Alloys and Compounds, Elsevier, 2022, 899, pp.163273. (10.1016/j.jallcom.2021.163273)
  DOI : 10.1016/j.jallcom.2021.163273
• Soft X-ray characterization of halide perovskite film by scanning transmission X-ray microscopy
  
  • Jun Haeyeon
  • Lee Hee Ryung
  • Tondelier Denis
  • Geffroy Bernard
  • Schulz Philip
  • Bourée Jean-Eric
  • Bonnassieux Yvan
  • Swaraj Sufal
  Scientific Reports, Nature Publishing Group, 2022, 12, pp.4520. Organic-inorganic metal halide perovskites (MHPs) have recently been receiving a lot of attention due to their newfound application in optoelectronic devices, including perovskite solar cells (PSCs) which has reached power conversion efficiencies as high as 25.5%. However, the fundamental mechanisms in PSCs, including the correlation of degradation with the excellent optoelectrical properties of the perovskite absorbers, are poorly understood. In this paper, we have explored synchrotron-based soft X-ray characterization as an effective technique for the compositional analysis of MHP thin films. Most synchrotron-based studies used for investigating MHP so far are based on hard X-rays (5–10 keV) which includes various absorption edges (Pb L-edge, I L-edge, Br K-edge, etc.) but are not suited for the analysis of the organic component in MHPs. In order to be sensitive to a maximum number of elements, we have employed soft X-ray-based scanning transmission X-ray microscopy (STXM) as a spectro-microscopy technique for the characterization of MHPs. We examined its sensitivity to iodine and organic components, aging, or oxidation by-products in MHPs to make sure that our suggested method is suitable for studying MHPs. Furthermore, methylammonium triiodide with different deposition ratios of PbI$_2$ and CH$_3$ NH$_3$ I (MAI), and different thicknesses, were characterized for chemical inhomogeneity at the nanoscale by STXM. Through these measurements, we demonstrate that STXM is very sensitive to MHP chemical composition and homogeneity. Thus, we highlight the utility of STXM for an in-depth analysis of physical and chemical phenomena in PSCs. (10.1038/s41598-022-08256-3)
  DOI : 10.1038/s41598-022-08256-3
• Wet-Chemical Noncovalent Functionalization of CVD Graphene: Molecular Doping and Its Effect on Electrolyte-Gated Graphene Field-Effect Transistor Characteristics
  
  • Dieng Mbaye
  • Bensifia Mohamed
  • Borme Jérôme
  • Florea Ileana
  • Abreu Catarina
  • Jama Charafeddine
  • Léonard Céline
  • Alpuim Pedro
  • Pribat Didier
  • Yassar Abderrahim
  • Bouanis Fatima
  Journal of Physical Chemistry C, American Chemical Society, 2022, 126 (9), pp.4522-4533. Graphene sheets (mono- and multilayers) were synthesized by chemical vapor deposition and functionalized with various aromatic molecules such as Fe-/Co-porphyrin and Fe-phthalocyanine through π–π interactions. The resulting nanohybrid materials were characterized by Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) techniques. The presence of physi-adsorbed molecules (Fe-/Co-porphyrin and Fe-phthalocyanine) on the graphene sheet surface is evidenced by spectroscopic and microscopic analyses, which confirm that these molecules are immobilized through electrostatic and π–π interactions. RS confirmed the n- or p-type doping of graphene, according to the chemical nature of those physi-adsorbed molecules. The electrical characteristics of electrolyte-gated graphene field-effect transistors (GFETs) based on nanohybrid materials were subsequently evaluated and demonstrated a charge transfer between the physi-adsorbed molecules and the graphene. All of these results suggest that the electronic structure of graphene can be tailored by doping with aromatic molecules. Density functional theory (DFT) calculations were performed to confirm these observations. (10.1021/acs.jpcc.1c10737)
  DOI : 10.1021/acs.jpcc.1c10737
• Negative differential resistance in photoassisted field emission from Si nanowires
  
  • Choueib M.
  • Derouet A.
  • Vincent P.
  • Ayari A.
  • Perisanu S.
  • Poncharal P.
  • Cojocaru Costel Sorin
  • Martel R.
  • Purcell S.
  Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics, AVS through the American Institute of Physics, 2022, 40 (2), pp.022802. Field emission (FE) from semiconducting nanowires (NWs) is studied for expanding electron gun performances and functionality in terms of stability, brightness, and pulsed emission. Here, we report on a pronounced and robust double negative differential resistance (NDR) in the FE IV characteristics measured during photoassisted field emission experiments on highly crystalline p-type silicon NWs. The main feature is a double NDR in the current saturation regime, which can be modulated by both temperature and light intensity. These results contrast with previous FE studies in which only a barely noticeable single NDR was reported. Several mechanisms for the physical explanation of the NDR are currently under consideration: photogenerated carrier instabilities in the depletion region, which give rise to a pulsed space-charge current in the nanowire or tunneling through a double quantum well formed by confinement at the NW apex. Because NDRs are signatures of pulsed currents, these results suggest new functionalities for which pulsed electron sources can potentially be achieved at high repetition rates. (10.1116/6.0001650)
  DOI : 10.1116/6.0001650
• Thermal Evolution of C–Fe–Bi Nanocomposite System: From Nanoparticle Formation to Heterogeneous Graphitization Stage
  
  • Rusu Mihai
  • Vulpoi Adriana
  • Maurin Isabelle
  • Cotet Liviu
  • Pop Lucian
  • Fort Carmen
  • Baia Monica
  • Baia Lucian
  • Florea Ileana
  Microscopy and Microanalysis, Cambridge University Press, 2022, 28 (2), pp.317-329. Carbon xerogel nanocomposites with integrated Bi and Fe particles (C–Bi–Fe) represent an interesting model of carbon nanostructures decorated with multifunctional nanoparticles (NPs) with applicability for electrochemical sensors and catalysts. The present study addresses the fundamental aspects of the catalyzed growth of nano-graphites in C–Bi–Fe systems, relevant in charge transport and thermo-chemical processes. The thermal evolution of a C–Bi–Fe xerogel is investigated using different pyrolysis treatments. At lower temperatures (~750°C), hybrid bismuth iron oxide (BFO) NPs are frequently observed, while graphitization manifests under more specific conditions such as higher temperatures (~1,050°C) and reduction yields. An in situ heating TEM experiment reveals graphitization activity between 800 and 900°C. NP motion is directly correlated with textural changes of the carbon support due to the catalyzed growth of graphitic nanoshells and nanofibers as confirmed by HR-TEM and electron tomography (ET) for the graphitized sample. An exponential growth model for the catalyst dynamics enables the approximation of activation energies as 0.68 and 0.29–0.34 eV during reduction and graphitization stages. The results suggest some similarities with the tip growth mechanism, while oxygen interference and the limited catalyst–feed gas interactions are considered as the main constraints to enhanced growth. (10.1017/S1431927622000241)
  DOI : 10.1017/S1431927622000241
• Ultrathin Ge epilayers on Si produced by low-temperature PECVD acting as virtual substrates for III-V / c-Si tandem solar cells
  
  • Ghosh Monalisa
  • Bulkin Pavel
  • Silva François
  • Johnson Erik
  • Florea Ileana
  • Funes-Hernando Daniel
  • Tanguy Alexandre
  • Renard Charles
  • Vaissiere Nicolas
  • Decobert Jean
  • García Iván
  • Rey-Stolle Ignacio
  • Roca i Cabarrocas Pere
  Solar Energy Materials and Solar Cells, Elsevier, 2022, 236, pp.111535. (10.1016/j.solmat.2021.111535)
  DOI : 10.1016/j.solmat.2021.111535
• Comparing Commercial Metal-Coated AFM Tips and Home-Made Bulk Gold Tips for Tip-Enhanced Raman Spectroscopy of Polymer Functionalized Multiwalled Carbon Nanotubes
  
  • Foti Antonino
  • Venkatesan Suriya
  • Lebental Bérengère
  • Zucchi Gaël
  • Ossikovski Razvigor
  Nanomaterials, MDPI, 2022, 12 (3), pp.451. Tip-enhanced Raman spectroscopy (TERS) combines the high specificity and sensitivity of plasmon-enhanced Raman spectroscopy with the high spatial resolution of scanning probe microscopy. TERS has gained a lot of attention from many nanoscience fields, since this technique can provide chemical and structural information of surfaces and interfaces with nanometric spatial resolution. Multiwalled carbon nanotubes (MWCNTs) are very versatile nanostructures that can be dispersed in organic solvents or polymeric matrices, giving rise to new nanocomposite materials, showing improved mechanical, electrical and thermal properties. Moreover, MWCNTs can be easily functionalized with polymers in order to be employed as specific chemical sensors. In this context, TERS is strategic, since it can provide useful information on the cooperation of the two components at the nanoscale for the optimization of the macroscopic properties of the hybrid material. Nevertheless, efficient TERS characterization relies on the geometrical features and material composition of the plasmonic tip used. In this work, after comparing the TERS performance of commercial Ag coated nanotips and home-made bulk Au tips on bare MWCNTs, we show how TERS can be exploited for characterizing MWCNTs mixed with conjugated fluorene copolymers, thus contributing to the understanding of the polymer/CNT interaction process at the local scale. (10.3390/nano12030451)
  DOI : 10.3390/nano12030451
• Polarization-Based Histopathology Classification of Ex Vivo Colon Samples Supported by Machine Learning
  
  • Ivanov Deyan
  • Dremin Viktor
  • Genova Tsanislava
  • Bykov Alexander
  • Novikova Tatiana
  • Ossikovski Razvigor
  • Meglinski Igor
  Frontiers in Physics, Frontiers, 2022, 9. In biophotonics, novel techniques and approaches are being constantly sought to assist medical doctors and to increase both sensitivity and specificity of the existing diagnostic methods. In such context, tissue polarimetry holds promise to become a valuable optical diagnostic technique as it is sensitive to tissue alterations caused by different benign and malignant formations. In our studies, multiple Mueller matrices were recorded for formalin-fixed, human, ex vivo colon specimens containing healthy and tumor zones. The available data were pre-processed to filter noise and experimental errors, and then all Mueller matrices were decomposed to derive polarimetric quantities sensitive to malignant formations in tissues. In addition, the Poincaré sphere representation of the experimental results was implemented. We also used the canonical and natural indices of polarimetric purity depolarization spaces for plotting our experimental data. A feature selection was used to perform a statistical analysis and normalization procedure on the available data, in order to create a polarimetric model for colon cancer assessment with strong predictors. Both unsupervised (principal component analysis) and supervised (logistic regression, random forest, and support vector machines) machine learning algorithms were used to extract particular features from the model and for classification purposes. The results from logistic regression allowed to evaluate the best polarimetric quantities for tumor detection, while the use of random forest yielded the highest accuracy values. Attention was paid to the correlation between the predictors in the model as well as both losses and relative risk of misclassification. Apart from the mathematical interpretation of the polarimetric quantities, the presented polarimetric model was able to support the physical interpretation of the results from previous studies and relate the latter to the samples’ health condition, respectively. (10.3389/fphy.2021.814787)
  DOI : 10.3389/fphy.2021.814787
• Towards plasma jet controlled charging of a dielectric target at grounded, biased, and floating potential
  
  • Slikboer Elmar
  • Guaitella Olivier
  • Garcia-Caurel Enrique
  • Sobota Ana
  Scientific Reports, Nature Publishing Group, 2022, 12 (1), pp.1157. Electric field and surface charge measurements are presented to understand the dynamics in the plasma-surface interaction of a plasma jet and a dielectric surface. The ITO coated backside of the dielectric allowed to impose a DC bias and thus compare the influence of a grounded, biased and floating potential. When imposing a controlled potential at the back of the target, the periodical charging is directly dependent on the pulse length, irrespective of that control potential. This is because the plasma plume is sustained throughout the pulse. When uncontrolled and thus with a floating potential surface, charge accumulation and potential build-up prevents a sustained plasma plume. An imposed DC bias also leads to a continuous surface charge to be present accumulated on the plasma side to counteract the bias. This can lead to much higher electric fields (55 kV/cm) and surface charge (200 nC/cm 2) than observed previously. When the plasma jet is turned off, the continuous surface charge decreased to half its value in 25 ms. These results have implications for surface treatment applications. (10.1038/s41598-022-05075-4)
  DOI : 10.1038/s41598-022-05075-4
• Quantification of surface charging memory effect in ionization wave dynamics
  
  • Viegas Pedro
  • Slikboer Elmar
  • Bonaventura Zdenek
  • Garcia-Caurel Enric
  • Guaitella Olivier
  • Sobota Ana
  • Bourdon Anne
  Scientific Reports, Nature Publishing Group, 2022, 12 (1), pp.1181. The dynamics of ionization waves (IWs) in atmospheric pressure discharges is fundamentally determined by the electric polarity (positive or negative) at which they are generated and by the presence of memory effects, i.e. leftover charges and reactive species that influence subsequent IWs. This work examines and compares positive and negative IWs in pulsed plasma jets (1 [Formula: see text]s on-time), showing the difference in their nature and the different resulting interaction with a dielectric BSO target. For the first time, it is shown that a surface charging memory effect is produced, i.e. that a significant amount of surface charges and electric field remain in the target in between discharge pulses (200 [Formula: see text]s off-time). This memory effect directly impacts IW dynamics and is especially important when using negative electric polarity. The results suggest that the remainder of surface charges is due to the lack of charged particles in the plasma near the target, which avoids a full neutralization of the target. This demonstration and the quantification of the memory effect are possible for the first time by using an unique approach, assessing the electric field inside a dielectric material through the combination of an advanced experimental technique called Mueller polarimetry and state-of-the-art numerical simulations. (10.1038/s41598-022-04914-8)
  DOI : 10.1038/s41598-022-04914-8
• Mirau-based line-field confocal optical coherence tomography for three-dimensional high-resolution skin imaging
  
  • Xue Weikai
  • Ogien Jonas
  • Bulkin Pavel
  • Coutrot Anne-Lise
  • Dubois Arnaud
  , 2022, pp.73. (10.1117/12.2608747)
  DOI : 10.1117/12.2608747
• Is a complete Mueller matrix necessary in biomedical imaging?
  
  • Novikova Tatiana
  • Ramella-Roman Jessica
  Optics Letters, Optical Society of America - OSA Publishing, 2022, 47 (21), pp.5549. The advent of imagers with integrated linear polarization selectivity opens new opportunities for researchers interested in the polarization properties of biological tissues. In this Letter, we explore the mathematical framework necessary to obtain common parameters of interest: azimuth; retardance; and depolarization with reduced Mueller matrices that can be measured with the new instrumentation. We show that in the case of acquisition close to the tissue normal, simple algebraic analysis of the reduced form of the Mueller matrix yields results very close to those obtained with more complex decomposition algorithms applied to a complete Mueller matrix. (10.1364/OL.471239)
  DOI : 10.1364/OL.471239
• Visualizing the effects of plasma-generated H atoms <i>in situ</i> in a transmission electron microscope
  
  • Maurice Jean-Luc
  • Bulkin Pavel
  • Ngo Éric
  • Wang Weixi
  • Foldyna Martin
  • Florea Ileana
  • Roca I Cabarrocas Pere
  • Béjaud Romuald
  • Hardouin Duparc Olivier
  European Physical Journal: Applied Physics, EDP Sciences, 2022, 97, pp.7. The radicals and atoms generated by a plasma have the effect, among others, of changing the surface energies of materials, which allows one to prepare nano-objects that would not stabilise in other conditions. This is the case of the Sn catalysed silicon nanowires (NWs) we present in this paper: without plasma, the liquid Sn at the top of NWs is unstable (because Sn naturally wets the Si) so that no growth is allowed, while in presence of the H atoms generated by the plasma, the balance of surface energies is drastically changed; the Sn droplet stabilises and can be used efficiently by the vapour-liquid-solid (VLS) mechanism of growth. Thus, if one wants to study the growth mechanisms of such NWs in situ in the transmission electron microscope (TEM), one has to adapt a plasma system on the TEM. This is precisely what was done at École polytechnique on the NanoMAX environmental TEM. The paper reports on the plasma effects, on the catalyst and on NW growth, recorded in situ in real time, at atomic resolution. The results are discussed in the light of density functional calculations of bare and hydrogenated Si surface energies. (10.1051/epjap/2022210276)
  DOI : 10.1051/epjap/2022210276
• Synthesis, crystal structure, tropicity and charge transport properties of diindenothienothiophene derivatives
  
  • Jousselin-Oba Tanguy
  • Mamada Masashi
  • Wright Karen
  • Marrot Jérôme
  • Adachi Chihaya
  • Yassar Abderrahim
  • Frigoli Michel
  Journal of Materials Chemistry C, Royal Society of Chemistry, 2022. A set of π-conjugated diindenothienothiophene derivatives (DITTs) which formally possess an extended as-indacene core with 16 π-electrons has been synthesised and their closed-shell configuration has been confirmed by X-ray structure analysis. Bond lengths analysis provides insight into the peculiar bond lengths observed for diindenoacene diradicaloids. The annellation mode at the outer rings has a great impact on the tropicity, optoelectrochemical properties and molecular packing. The featured molecules exhibit low energy band gap with values up to 1.30 eV and have high electron affinities with LUMO energies up to 3.86 eV. Their optical properties are similar to those of benzo-fused indeno[2,1-c]fluorene (BIFs) counterparts possessing formally the as-indacene core. Analysis of the molecule tropicity using NICS and ACID plot shows that the central rings of DITTs are weakly antiaromatic and should be regarded as quinoidal molecules bridged by two sulphur atoms. Three out of four molecules show ambipolar behavior in OFETs with moderate mobilities (10.1039/D2TC01324J)
  DOI : 10.1039/D2TC01324J