Publications

2023

• Preparation of Dye Semiconductors via Coupling Polymerization Catalyzed by Two Catalysts and Application to Transistor
  
  • Ren Shiwei
  • Zhang Wenqing
  • Wang Zhuoer
  • Yassar Abderrahim
  • Chen Jinyang
  • Zeng Minfeng
  • Yi Zhengran
  Molecules, MDPI, 2023, 29 (1), pp.71. Organic dye semiconductors have received increasing attention as the next generation of semiconductors, and one of their potential applications is as a core component of organic transistors. In this study, two novel diketopyrrolopyrrole (DPP) dye core-based materials were designed and separately prepared using Stille coupling reactions under different palladium catalyst conditions. The molecular weights and elemental compositions were tested to demonstrate that both catalysts could be used to successfully prepare materials of this structure, with the main differences being the weight-average molecular weight and the dispersion index. PDPP-2Py-2Tz I with a longer conjugation length exhibited better thermodynamic stability than the counterpart polymer PDPP-2Py-2Tz II. The intrinsic optical properties of the polymers were relatively similar, while the electrochemical tests showed small differences in their energy levels. The polymers obtained with different catalysts displayed similar and moderate electron mobility in transistor devices, while PDPP-2Py-2Tz I possessed a higher switching ratio. Our study provides a comparison of such dye materials under different catalytic conditions and also demonstrates the great potential of dye materials for optoelectronic applications. (10.3390/xxxxx)
  DOI : 10.3390/xxxxx
• Organic materials modelling in three terminal Organic/Si tandem solar cells
  
  • Connolly James P.
  • Alvarez J
  • Kleider Jean-Paul
  • Chambon Sylvain
  • Hirsch Lionel
  • Vignau Laurence
  • Wantz Guillaume
  • Gueunier-Farret Marie-Estelle
  • Roca I Cabarrocas Pere
  • Nejim Ahmed
  , 2023.
• Development of Wide Bandgap Organic Solar Cells for an Integration in Organic/Silicon Tandem Cells
  
  • Waiprasoet S.
  • Chambon Sylvain
  • Gueunier-Farret Marie-Estelle
  • Wantz Guillaume
  • Hirsch Lionel
  • Vignau Laurence
  • Alvarez J
  • Connolly James P.
  • Kleider Jean-Paul
  • Roca I Cabarrocas Pere
  • Pattanasattayavong Pichaya
  , 2023.
• Boron activation in silicon thin films grown by PECVD under epitaxial and microcrystalline conditions
  
  • Olivares Antonio
  • Zamchiy A.
  • Nguyen V.S.
  • Roca I Cabarrocas P.
  Applied Surface Sciences Advances, Elsevier, 2023, 18, pp.100508. (10.1016/j.apsadv.2023.100508)
  DOI : 10.1016/j.apsadv.2023.100508
• Ultrasmall and tunable TeraHertz surface plasmon cavities at the ultimate plasmonic limit
  
  • Aupiais Ian
  • Grasset Romain
  • Guo Tingwen
  • Daineka Dmitri
  • Briatico Javier
  • Houver Sarah
  • Perfetti Luca
  • Hugonin Jean-Paul
  • Greffet Jean-Jacques
  • Laplace Yannis
  Nature Communications, Nature Publishing Group, 2023, 14 (1), pp.7645. Abstract The ability to confine THz photons inside deep-subwavelength cavities promises a transformative impact for THz light engineering with metamaterials and for realizing ultrastrong light-matter coupling at the single emitter level. To that end, the most successful approach taken so far has relied on cavity architectures based on metals, for their ability to constrain the spread of electromagnetic fields and tailor geometrically their resonant behavior. Here, we experimentally demonstrate a comparatively high level of confinement by exploiting a plasmonic mechanism based on localized THz surface plasmon modes in bulk semiconductors. We achieve plasmonic confinement at around 1 THz into record breaking small footprint THz cavities exhibiting mode volumes as low as $${V}_{cav}/{\lambda }_{0}^{3} \sim 1{0}^{-7}-1{0}^{-8}$$ V c a v / λ 0 3 ~ 1 0 − 7 − 1 0 − 8 , excellent coupling efficiencies and a large frequency tunability with temperature. Notably, we find that plasmonic-based THz cavities can operate until the emergence of electromagnetic nonlocality and Landau damping, which together constitute a fundamental limit to plasmonic confinement. This work discloses nonlocal plasmonic phenomena at unprecedentedly low frequencies and large spatial scales and opens the door to novel types of ultrastrong light-matter interaction experiments thanks to the plasmonic tunability. (10.1038/s41467-023-43394-w)
  DOI : 10.1038/s41467-023-43394-w
• Development of an in-situ effective electron lifetime measurement device
  
  • Poplawski Mateusz
  , 2023. As technology progresses through Technology Readiness Levels (TRLs), it moves from theoretical concepts and basic research, towards practical applications and refined prototypes. In-situ lifetime measurements, provide valuable insights into the quality of the semiconductor fabrication process, enabling real-time monitoring and analysis of dynamic processes. By analysing minority carrier lifetimes, researchers can assess the effectiveness of various passivation techniques and surface treatments aimed at reducing recombination losses and enhancing the efficiencies of solar cell devices. This thesis focuses on the development of hardware, theory, and experimental application of an in-situ minority carrier lifetime measurement (in-situ lifetime) device. This involved the inclusion of non-imaging optics and beam shaping for a design which has an ease of installation. Moreover, decreasing measurement time facilitates the detection of rapid changes that may be critical to understanding complex systems while switching from indirect to direct measurement technique for a lifetime measurement using a Gaussian could open new avenues.Amorphous Aluminium oxide (AlOx) has gained significant attention as an important material in surface passivation for crystalline silicon solar cells in recent years. Utilizing the developed device, potential avenues using a PECVD reactor were highlighted such as optimizing the fabrication process through annealing procedures, and analysis base material properties.
• Conjugated molecules for the elaboration of optical sensors for water monitoring
  
  • Murga Cotrina Christian
  , 2023. Anthropogenic activity has had the consequence of deeply modifying the environmental conditions on Earth. One of the main causes of this effect has been the indiscriminate release of chemicals into the air, soil and water that disturbs ecosystems and also poses a significant public health concern. In particular, measuring the quality of tap water that is received by individuals is a problem that needs to be tackled effectively and efficiently.A first family of chemicals that has toxic effects on humans are heavy metals. While most of them are essential to life in very small quantities because they regulate enzymatic processes in the body, they become extremely dangerous when their concentration exceeds certain thresholds. Moreover, they form stable aquo-ions which promotes an increased bioavailability and their intake by plants or animals is greatly facilitated.A second family of contaminants are pesticides. It is not possible to neglect the enormous societal and economic benefits of using these chemicals; however, it is their unmethodical release in soil and water that has promoted them to be found at concentrations that represent a danger to human health. In particular, the herbicide glyphosate, widely widespread in North America and Europe, has been subject to scrutiny in the last decade.Besides these families of harmful chemicals, there are compounds which presence is generally indicative of a healthy environment. The hypochlorite anion, for example, is used as a pipeline disinfectant, meaning that its presence is taken as a guarantee of bacterial absence in household water systems. Nonetheless, its concentration must be controlled as it can produce toxic compounds when reacting with organic matter. Finally, dissolved oxygen is another parameter of importance to be controlled as it is a testament of a healthy aquatic life.Evidently, several analytical techniques exist to detect and monitor the aforementioned species and they are mostly based on spectroscopic measurements like GC-MS or HPLC. These techniques provide great sensitivity as their detection limits can reach the ppb level, but they require heavy and expensive instrumentation, and highly skilled people to operate them.Hence, there is a need for developing simple and fast techniques that accomplish the same goals, and one of the most powerful ones is luminescence spectroscopy. this technique provides several advantages over the classic techniques such as being not invasive, it either does not consume the fluorophore or the analyte if the interaction is reversible, nor requires any references, it allows real-time in-situ mesuremets thanks to the portability of the devices, it can be sensitive enough, and, very importantly, luminesent molecules can be designed to specifically interact with the targeted species.The main goal of this project is thus to design and synthesize novel conjugated molecules with adequate optical properties. These molecules are such that, upon interacting with a target analyte, a change in their emission is observed in a way that identification and/or quantification of such species can be made.Within the scope of this thesis work, 11 new compounds with sensing capabilities have been developed using molecules belonging to the pyrene (compounds M1, M2 and M3), benzazole (compounds M4, M5 and M6), coumarin (compound M7) and porphyrin (compounds M8-Pd, M8-Pt, M9-Pd and M9-Pt) chemical families. Sensing studies with these compounds have shown that they can effectively detect Al3+, Fe2+, Fe3+, Cu2+, Zn2+, OCl-, glyphosate and dissolved O2 in aqueous environments, making them interesting candidates for real-life water quality assessment.
• Polarized Light
  
  • Novikova Tatiana
  • Ramella-Roman Jessica
  , 2023, pp.1-23. (10.1007/978-3-031-04741-1_1)
  DOI : 10.1007/978-3-031-04741-1_1
• Mueller Polarimetric Imaging for Cervical Intraepithelial Neoplasia Detection
  
  • Pierangelo Angelo
  • Novikova Tatiana
  • Rehbinder Jean
  • Nazac André
  • Vizet Jérémy
  , 2023, pp.149-177. (10.1007/978-3-031-04741-1_6)
  DOI : 10.1007/978-3-031-04741-1_6
• Polarization-Sensitive Monte Carlo
  
  • Novikova Tatiana
  • Ramella-Roman Jessica
  , 2023, pp.105-131. (10.1007/978-3-031-04741-1_4)
  DOI : 10.1007/978-3-031-04741-1_4
• The Impact of X-Ray Radiation on Chemical and Optical Properties of Triple Cation Lead Halide Perovskite
  
  • Guillaume Vidon
  • Pia Dally
  • Mirella Al-Katrib
  • Daniel Ory
  • Minjin Kim
  • Etienne Soret
  • Eva Rangayen
  • Marie Legrand
  • Alexandre Blaizot
  • Philip Schulz
  • Jean-Baptiste Puel
  • Daniel Suchet
  • Arnaud Etcheberry
  • Muriel Bouttemy
  • Stefania Cacovich
  • Jean-François Guillemoles
  , 2023.
• Synthetic approaches to p-conjugated diradicaloid materials for transistors
  
  • Yassar Abderrahim
  , 2023.
• Selective ion sensing in aqueous media with ESIPT active fluorescent probes – A particular case for hypochlorite detection
  
  • Murga Cotrina Christian Julio
  • Bhattacharyya Arghyadeep
  • Wang Shenming
  • Amouroux Baptiste
  • Casaretto Nicolas
  • Bourcier Sophie
  • Leray Isabelle
  • Zucchi Gaël
  Dyes and Pigments, Elsevier, 2023, 218. We report two ESIPT active novel fluorescent probes, 1 and 2, based on benzoxazole and benzimidazole units, respectively. Their sensing aptitude towards metal ions in aqueous media is reported. A specific response of 1 to Al 3+ and, to a lesser extent, Zn 2+ , was found, while the emission of 2 is highly impacted by the Al 3+ , Cu 2+ , Fe 2+ and Fe 3+ metal ions by either a blue shift or a quenching of the emission. Emission of 2 also shows a relative sensitivity to the Ni 2+ and Hg 2+ cations. Anions sensing studies on 2 revealed a unique emission in presence of hypochlorite ions, while glyphosate and aminomethylphosphonic acid have the effect to decrease the emission intensity by 40% and 75%, respectively. Investigations on the recognition mechanism led to the conclusion that Al 3+ was inhibiting the ESIPT process by deprotonation of the phenol group, and that a fast but weak interaction was taking place between the hypochlorite ion and 2. (10.1016/j.dyepig.2023.111524)
  DOI : 10.1016/j.dyepig.2023.111524
• Polarimetric imaging for cervical pre-cancer screening aided by machine learning: ex vivo studies
  
  • Robinson Demelza
  • Hoong Kevin
  • Kleijn Willem Bastiaan
  • Doronin Alexander
  • Rehbinder Jean
  • Vizet Jeremy
  • Pierangelo Angelo
  • Novikova Tatiana
  Journal of Biomedical Optics, Society of Photo-optical Instrumentation Engineers, 2023, 28 (10). (10.1117/1.JBO.28.10.102904)
  DOI : 10.1117/1.JBO.28.10.102904
• Investigation of LSPR Coupling Effects toward the Rational Design of Cs x WO 3– δ Based Solar NIR Filtering Coatings
  
  • Daugas Louise
  • Lahlil Khalid
  • de Langavant Capucine Cleret
  • Florea Ileana
  • Larquet Eric
  • Henry Hervé
  • Kim Jongwook
  • Gacoin Thierry
  Advanced Functional Materials, Wiley, 2023, 33 (43). Abstract The optical range of localized surface plasmon resonance (LSPR) is extended into the infrared region, thanks to the development of highly doped semiconductor nanocrystals. Particularly, the near‐infrared (NIR) range holds a significant interest in managing solar radiation. However, practical applications necessitate the arrangement of particles, which is known to possibly impact their optical properties through LSPR coupling effects. How such coupling modifies the LSPR response in semiconductor hosts remains largely unexplored. In this study, a protocol for producing composite coatings composed of cesium‐doped tungsten bronze nanocrystals embedded in a silica matrix is presented. Achieving individual dispersion of nanocrystals is made possible through careful selection of a surface polyglycerol ligand exchange. This allows to tune the interparticle distance by adjusting the nanocrystal volume fraction in the composite. The findings demonstrate that LSPR coupling effects significantly influence the LSPR intensity of nanocrystals in the composite when the nanocrystal‐to‐nanocrystal distance matches their size. Beyond elucidating the LSPR coupling effect, this study provides insights into the potential use of Cs‐HTB nanocrystals for solar control applications. Through the optimization of morphology and film structure, remarkable selectivity is obtained in terms of maintaining good transparency in the visible range while achieving high absorption in the NIR. (10.1002/adfm.202212845)
  DOI : 10.1002/adfm.202212845
• Assessment of the Impact of Nanowarming on Microstructure of Cryopreserved Fibroblast-Containing 3D Tissue Models Using Mueller Polarimetry
  
  • Ivanov Deyan
  • Hoeppel Anika
  • Weigel Tobias
  • Ossikovski Razvigor
  • Dembski Sofia
  • Novikova Tatiana
  Photonics, MDPI, 2023, 10 (10), pp.1129. We studied the impact of two different thawing mechanisms on the microstructure of defrosted cryopreserved 3D tissue models using transmission Mueller microscopy and a statistical analysis of polarimetric images of thin histological sections of defrosted tissue models. The cryopreserved 3D tissue models were thawed by using either a 37 °C water bath or radio-frequency inductive heating with the magnetic nanoparticles embedded into the 3D tissue model during the preparation process. Polarimetric measurements were conducted at 700 nm and the acquired Mueller matrices of the samples were post-processed using the differential decomposition and the statistical analysis of the maps of the azimuth of the optic axis. Our results indicate the sensitivity of polarimetry to the changes in thawed tissue morphology compared to that of reference non-frozen tissue. Thus, Mueller microscopy can be used as a fast complementary technique to the currently accepted gold standard methods for the assessment of the cryopreserved tissue microstructure after thawing. (10.3390/photonics10101129)
  DOI : 10.3390/photonics10101129
• Tuning Photophysical Properties of Acceptor-Donor-Acceptor Di-2-(2-oxindolin-3-ylidene) Malononitrile Materials via Extended π-Conjugation: A Joint Experimental and Theoretical Study
  
  • Ren Shiwei
  • Habibi Amirhossein
  • Ni Pingping
  • Zhang Yuexing
  • Yassar Abderrahim
  Materials, MDPI, 2023, 16 (19), pp.6410. Organic semiconductor (OSC) materials with a high electron affinity are required for many optoelectronic applications. In this work a series of twelve novel acceptor-donor-acceptor (A-D-A) materials with low-lying LUMO energy levels are designed, synthesized, and characterized. In this strategy, two acceptor dyes, isatin and its dicyanovinyl derivatives are connected by various π-bridges. We have varied the π-conjugation length of the central core and altered the linkage position of the acceptor core (4-position vs. 6-position of the phenyl ring of the isatin moiety) to study the effect of extended π-conjugation and point of linkage of the acceptor on optical and electrochemical properties of the new dyes. Density functional theory (DFT) and time-dependent DFT (TD-DFT) studies have been performed to gain an insight into their electronic properties by determining the energy levels and maps of the HOMO, LUMO as well as HOMO-LUMO gap (energy differences between the highest occupied and lowest unoccupied molecular orbitals). Our findings demonstrate that with increasing the acceptor strength and π-conjugation length of the 2 core, the wavelength of the longest absorption maximum as well as their respective extinction coefficients are enhanced, which resulted in band-gap reduction either by lowering the LUMO and or raising the HOMO energy level of the molecules. Space-charge-limited current measurements (SCLC) were investigated to probe the electron mobility of these molecules. Electron only devices were fabricated by the spin-coating and the trap-limited electron mobility was calculated using Mott-Gurney law. 10a exhibited an intrinsic moderate electron mobility of 8.94×10-4 cm 2 V-1 s-1. The potential practical utility of these materials as an electron-transport material for perovskite solar cells (PSCs) has been demonstrated. (10.3390/ma16196410)
  DOI : 10.3390/ma16196410
• Photocatalytic active ZnO_1−xS_x@CNTs heteronanostructures
  
  • Bjelajac Andjelika
  • Florea Ileana
  • Zamfir Mihai
  • Nenez Sandrine Tusseau
  • Cojocaru Costel Sorin
  Nanotechnology, Institute of Physics, 2023, 34 (49), pp.495704. Herein, we report on the use of vertically aligned multiwall carbon nanotubes (CNTs) films as support for ZnO/ZnS photocatalytic active nanostructures. The CNTs were synthetized via a hot-filament chemical vapor deposition (HfCVD), using Fe catalyst on top of Al2O3 buffer layer. Controlled point defects in the CNTs outer walls were created by exposure to a low pressure nonthermal water vapors diffusive plasma and acted as seeds for subsequent pulsed-electrodeposition of Zn nanoparticles. This was to achieve a direct and improved contact between the nanoparticles and CNTs. To obtain ZnO, ZnS and mix phase of ZnO/ZnS spread on CNTs, the oxidation, sulfurization and 2 steps subsequent annealing in oxygen and sulfur rich atmospheres were applied. High resolution transmission electron microscopy (HRTEM) with energy dispersive X-rays spectroscopy (EDS) in scanning mode, provided the chemical mapping of the structures. X-ray diffraction (XRD) analyses proved the hexagonal phase of ZnO and ZnS, obtained after oxidation in H2O and S vapors, respectively. In the case of the samples obtained by the 2 steps subsequent annealing, XRD showed mainly the presence of ZnO and a small amount of ZnS. The benefit of the secondary annealing in S vapor was seen as absorption enhancement of the ZnO1-xSx@CNTs sample having the absorption edge at 417 nm, whereas the absorption edge of ZnO@CNTs was 408 nm and of ZnS@CNTs 360 nm. For all the samples, compared to the bare ZnO and ZnS, the absorption red shift was observed which is attributed to the CNTs involvement. Therefore, this study showed the double sides benefit to induce the absorption of ZnO of the visible light, one from S doping and second of CNTs involvement. The absorption enhancement had a positive impact on photocatalytic degradation of methyl blue dye, showing that ZnO1-xSx@CNTs heteronanostructure was the best photocatalyst among the studied samples. (10.1088/1361-6528/acf6c8)
  DOI : 10.1088/1361-6528/acf6c8
• A New Design : Three Terminal Band Offset Barrier Organic/Si Tandem Solar Cells
  
  • Connolly James P.
  • Alvarez J
  • Kleider Jean-Paul
  • Roca I Cabarrocas Pere
  • Chambon Sylvain
  • Hirsch Lionel
  • Vignau L.
  • Wantz Guillaume
  • Gueunier-Farret Marie
  , 2023. Organic solar cells are particularly attractive for their very low fabrication cost, and lack of use of critical raw materials. While this has to date been hobbled by low efficiency, recent achievements demonstrate organic single junction technology at 20% efficiency approaching economically viable performance. We survey the reasons for these recent high efficiency organic solar cell achievements. They include bulk heterojunction (BHJ) concepts, composed of electron donor materials, most often a semiconductor polymer and electron accepting materials, most often a small molecule, and the novel non-fullerene acceptor materials. The range of commercially available donor and acceptor materials available offers a large design flexibility for low or high band gap devices. A natural development for this emerging thin film technology reaching competitive efficiencies is its integration in tandem solar cells. In the context of the breakthroughs in organic solar cell efficiency, this work presents first results of the ORGANIST project (2023-2027) supported by the French Research National Agency. The presentation of organic materials for top cells and their efficient integration on a high efficiency silicon IBC cell is discussed with a critical focus on the interface between top organic solar cell and bottom silicon IBC cell. We present preliminary theoretical results evaluating the performance of 3T devices being developed in ORGANIST and based on identified prototype materials for the organic cell, strategies for efficient optical and electrical connection between the two subcells, aiming for low cost three terminal organic / silicon tandems with high efficiencies above the Shockley-Queisser single bandgap limit for Silicon. (10.4229/EUPVSEC2023/2CV.2.25)
  DOI : 10.4229/EUPVSEC2023/2CV.2.25
• Low-pressure, radicals assisted CVD synthesis of SWCNTs for thepotential implementation in-situ and real-time analysis technique (ETEM)
  
  • Truong Thi Thanh Loan
  , 2023. In my thesis, the hot-filament chemical vapor deposition (HFCVD) was used to synthesize the single-walled carbon nanotubes (SWCNTs). The initial step was centered on setting up a HFCVD system with the purpose to identify the optimal growth conditions for producing SWCNTs on silicon substrates. To this goal, the studies of the influence of various growth parameters, including the quantity of catalyst employed, the synthesis temperature, growth pressure in the CVD reactor, were carried out. In particular, the variation of pressure was shown to be effective in controlling the growth of SWCNTs. The obtained SWCNTs were systematically characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy.Thanks to this innovative approach, the growth conditions of promising samples have been used as a prototype for the in-situ investigation in the environment transmission electron microscopy (ETEM) implemented with CVD gas source (NanoMAX). The NanoMAX is a powerful technique, which allows us to study real-time and in-situ the dynamic changes of catalysts during the nucleation and the formation of SWCNTs, followed by the optimization and controlling the growth of SWCNTs.
• Outdoor Performance Monitoring and Characterization of Novel Perovskite Solar Cells
  
  • Chakar Joseph
  • Oswald Frédéric
  • Medjoubi Karim
  • Migan-Dubois Anne
  • Parra Johan
  • Jean-Baptiste Puel
  • Bonnassieux Yvan
  , 2023.
• EPITAXIALLY GROWN CRYSTALLINE SILICON AS ELECTRON SELECTIVE CONTACT LAYER FOR CRYSTALLINE GERMANIUM TPV CELLS
  
  • Gamel M
  • López G
  • Jawhari T
  • Olivares A J
  • Roca I Cabarrocas P
  • Garín M
  • Martín I
  , 2023. Crystalline germanium has been proposed as a cost-effective absorber for the fabrication of thermophotovoltaic (TPV) cells which require, among other technologies, the development of electron-selective contacts. In this work, we explore the deposition process of n-type high-quality crystalline silicon (c-Si(n)) on p-type crystalline germanium (c-Ge) substrates using Plasma-Enhanced Chemical Vapor Deposition (PECVD) to create c-Si(n)/c-Ge(p) heterojunctions that function as electron-selective contacts. Our analysis includes material characterization using Raman spectroscopy, X-ray diffraction, and Spectroscopic Ellipsometry measurements, confirming the crystalline nature of the epitaxially grown silicon layers. The interface quality of the heterojunction is studied by measuring the effective lifetime. The results demonstrate that the addition of a thin intrinsic amorphous silicon layer at the interface improves its passivation. Additional improvement is obtained after depositing a thin n-type amorphous layer on top of the c-Si(n), achieving a surface recombination velocity of 334 cm/s. This better passivation positively impacts both the open circuit voltage and the fill factor of 1x1 cm 2 finished devices, leading to an efficiency of 3.38%. The results suggest the potential of c-Si/c-Ge heterojunction for cost-effective c-Ge cells, with room for efficiency improvements through further optimization. (10.4229/EUPVSEC2023/1CV.3.29)
  DOI : 10.4229/EUPVSEC2023/1CV.3.29
• Mueller polarimetry for the assessment of tissue microstructure in digital histology and cryopreservation
  
  • Ivanov Deyan
  , 2023. Aim and Significance: Polarization of light can be used as an optical modality sensitive to tissue structures and biomedical samples in general. Thus, this vectorial property of light can be applied to diagnose non-invasively healthy, benign and malignant formations. Likewise, when biomedical samples are frozen and then defrosted, the internal damages occurring in the tissue structures due to defrosting can be also detected with polarized light.Approach: An imaging Mueller polarimeter operating in the visible range was used to measure the full polarimetric response of the tissue specimens under study. The optical system was configured as a Mueller microscope in transmission geometry. Thus, medical doctors could be assisted in their diagnosis by performing polarization-sensitive digital histology. For thick tissue specimens, reflection rather than transmission, geometry and scanning were chosen. In that case, the backscattered photons convey diagnosis information by experiencing more scattering events and, thus, being more depolarized, however at the price of lower light intensity and reduced signal-to-noise ratio. Regardless of the experimental geometry, precise calibration (the eigen-value calibration method), as well as a decomposition algorithm to filter data noise and/or experimental errors (physical realizability filtering), are required. Depending on the experimental configuration, transmission or reflection, the differential and Lu-Chipman decompositions or the symmetric decomposition were respectively used. All of these algorithms make it possible to interpret phenomenologically an experimental Mueller matrix, without the need for an explicit physical model of the given tissue sample. Nevertheless, efforts were also spent on relating the decomposition results to the available structural and biomedical information.Results: In transmission, corpus callosum ex vivo brain slides with different spatial orientations were used to study the behavior of the polarimetric parameters provided by the differential and the Lu-Chipman decomposition algorithms at 532 nm and to decide on the most suitable decomposition. In this this study, the Mueller microscope was used to visualize the orientation of brain fiber tracts as well, which can be helpful to guide neurosurgeons during operations. Next, non-frozen (initially frosted at -80°C and then defrosted either with conventional heating or with magnetic-nanoparticle-assisted thawing) tissue models were measured with the Mueller microscope at 700 nm. The experimental results were processed with the differential decomposition algorithm, with the help of which small differences in the tissue structures were detected and confirmed by statistical analysis. This approach has the potential to be used in the field of regenerative medicine to assess any tissue alterations due to cryopreservation and defrosting. In another study, skin samples with degenerative and malignant lesions were measured with the same instrument, geometry and wavelength (700 nm), and a deep learning model was elaborated for image classification. In this way, a step closer to digital histology assessment was made to assist medical doctors. Finally, a non-imaging polarimetric set-up in reflection was used to scan and discriminate the polarization responses of ex vivo colon samples with healthy and tumorous sections at 635 nm. With the increasing amount of experimental data, the problem of the inter-patient variability had to be handled inevitably. Additionally, when classifying the polarization measurements in relation to the medical doctors’ ground truth histological analysis, false positive and false negative data points had to be taken into account. By using statistical analysis, together with supervised and unsupervised machine-learning algorithms, it became possible to find adequate solutions to the aforementioned issues.
• Parallel Aluminum‐Cobalt Oxide Nanosheet Arrays with High‐Temperature Ferromagnetism
  
  • Chen Leilei
  • Huang Rong
  • Ke Xiaoxing
  • Yu Jin
  • Zhang Tiantian
  • Maurice Jean-Luc
  • Li Jiheng
  • Li Kai
  • Ni Lifeng
  • Huang Shuzhao
  • Ren Tiezhen
  • He Zhanbing
  Small, Wiley-VCH Verlag, 2023, 19 (38). Abstract Parallel nanomaterials possess unique properties and show potential applications in industry. Whereas, vertically aligned 2D nanomaterials have plane orientations that are generally chaotic. Simultaneous control of their growth direction and spatial orientation for parallel nanosheets remains a big challenge. Here, a facile preparation of vertically aligned parallel nanosheet arrays of aluminum‐cobalt oxide is reported via a collaborative dealloying and hydrothermal method. The parallel growth of nanosheets is attributed to the lattice‐matching among the nanosheets, the buffer layer, and the substrate, which is verified by a careful transmission electron microscopy study. Furthermore, the aluminum‐cobalt oxide nanosheets exhibit high‐temperature ferromagnetism with a 919 K Curie temperature and a 5.22 emu g −1 saturation magnetization at 300 K, implying the potential applications in high‐temperature ferromagnetic fields. (10.1002/smll.202301513)
  DOI : 10.1002/smll.202301513
• Reactive plasma sputtering deposition of polycrystalline GaN thin films on silicon substrates at room temperature
  
  • Srinivasan Lakshman
  • Jadaud Cyril
  • Silva François
  • Vanel Jean-Charles
  • Maurice Jean-Luc
  • Johnson Erik
  • Roca i Cabarrocas Pere
  • Ouaras Karim
  Journal of Vacuum Science & Technology A, American Vacuum Society, 2023, 41 (5). We report on the successful growth of polycrystalline GaN thin films on Si (100) substrates at room temperature (without intentional heating) using radiofrequency reactive magnetron sputtering. We use Ar and N2 as the main sputtering and N-atom precursor gas sources, respectively, and a gallium cathode as the Ga-atom source. We focus here on studying the effect of working pressure, as it is found to be the parameter that plays the most influential role on the crystalline quality of the thin films in the investigated range (20–95 mTorr). The morphology, microstructure, and composition profile of the GaN thin films are analyzed using a set of ex situ solid-state characterization techniques. This study reveals that for process pressures below 50 mTorr, the resulting films possess an amorphous nature, while for process pressures above that they become polycrystalline. Most of the crystalline films are found to be nanostructured with grain sizes typically ranging from 10 to 30 nm in size. The highest growth rate of ∼ 2.9 Å/s is obtained for the deposition carried out at 50 mTorr. At this pressure, the films exhibit the best crystallinity with a dominant wurtzite hexagonal structure. The elemental distribution of Ga and N throughout the growth profile is uniform with a sharp interface at the substrate, demonstrating one of the interests in working at low temperatures to avoid melt-back etching, a destructive reaction between gallium and silicon, that usually takes place at high temperatures. (10.1116/6.0002718)
  DOI : 10.1116/6.0002718