Publications

2024

• Optical properties of fs laser-created sphere inside CYTOP fiber by Mueller polarimetry
  
  • Que Ruyue
  • Garcia-Caurel Enrique
  • Kalli Kyriacos
  • Pansu Robert
  • Audibert Jean-Frédérique
  • Lancry Matthieu
  • Poumellec Bertrand
  Optics Letters, Optical Society of America - OSA Publishing, 2024, 49 (12), pp.3284. Optical elements embedded in an optical fiber can be used to shape and modulate the light transmitted within. We consistently observe, via Mueller polarimetry, that the optical properties of a femtosecond (fs) laser-created spherical cavity within a perfluorinated fiber exhibit predictable patterns. Specifically, linear birefringence is always induced at the periphery of the cavity, with its value showing a bell-shape distribution. The peak value of LB showed an increase correlating with the laser fluence and power, but its FWHM remains unchanged. Furthermore, it is important to highlight that when the cavity is disrupted, forming a channel to the fiber's surface, a negative LB is observed at the cavity's periphery, with a value reaching up to -0.4 radians. These optical phenomena may pique interest of engineering and technical fields, potentially inspiring innovative approaches in optical fiber technology and its associated applications. (10.1364/OL.519955)
  DOI : 10.1364/OL.519955
• Carbon Dot Synthesis in CYTOP Optical Fiber Using IR Femtosecond Laser Direct Writing and Its Luminescence Properties
  
  • Que Ruyue
  • Audibert Jean-Frédéric
  • Garcia-Caurel Enrique
  • Plantevin Olivier
  • Kalli Kyriacos
  • Lancry Matthieu
  • Poumellec Bertrand
  • Pansu Robert Bernard
  Nanomaterials, MDPI, 2024, 14 (11), pp.941. Luminescent carbon dots (CDs) were locally synthesized in the core of CYTOP fibers using IR femtosecond laser direct writing (FLDW), a one-step simple method serving as a post-treatment of the pristine fiber. This approach enables the creation of several types of modifications such as ellipsoid voids. The CDs and photoluminescence (PL) distribute at the periphery of the voids. The PL spectral properties were studied through the excitation/emission matrix in the visible range and excitation/emission spectra in the UV/visible range. Our findings reveal the presence of at least three distinct luminescent species, facilitating a broad excitation range extending from UV to green, and light emission spanning from blue to red. The average laser power and dose influence the quantity and ratio of these luminescent CD species. Additionally, we measured the spatially resolved lifetime of the luminescence during and after the irradiation. We found longer lifetimes at the periphery of the laser-induced modified regions and shorter ones closer to the center, with a dominant lifetime ~2 ns. Notably, unlike many other luminophores, these laser-induced CDs are insensitive to oxygen, enhancing their potential for display or data storage applications. (10.3390/nano14110941)
  DOI : 10.3390/nano14110941
• Carbon Dot Synthesis in CYTOP Optical Fiber Using IR Femtosecond Laser Direct Writing and Its Luminescence Properties
  
  • Que Ruyue
  • Audibert Jean-Frédéric
  • Garcia-Caurel Enrique
  • Plantevin Olivier
  • Kalli Kyriacos
  • Lancry Matthieu
  • Poumellec Bertrand
  • Pansu Robert B
  Nanomaterials, MDPI, 2024, 14 (12), pp.3284. Luminescent carbon dots (CDs) were locally synthesized in the core of CYTOP fibers using IR femtosecond laser direct writing (FLDW), a one-step simple method serving as a post-treatment of the pristine fiber. This approach enables the creation of several types of modifications such as ellipsoid voids. The CDs and photoluminescence (PL) distribute at the periphery of the voids. The PL spectral properties were studied through the excitation/emission matrix in the visible range and excitation/emission spectra in the UV/visible range. Our findings reveal the presence of at least three distinct luminescent species, facilitating a broad excitation range extending from UV to green, and light emission spanning from blue to red. The average laser power and dose influence the quantity and ratio of these luminescent CD species. Additionally, we measured the spatially resolved lifetime of the luminescence during and after the irradiation. We found longer lifetimes at the periphery of the laser-induced modified regions and shorter ones closer to the center, with a dominant lifetime ~2 ns. Notably, unlike many other luminophores, these laser-induced CDs are insensitive to oxygen, enhancing their potential for display or data storage applications. (10.3390/nano14110941)
  DOI : 10.3390/nano14110941
• Steps Towards the Development of Organic/Silicon Tandem Solar Cells in a 3-Terminal Design
  
  • Gueunier-Farret Marie-Estelle
  • Chambon Sylvain
  • Hirsch Lionel
  • Vignau Laurence
  • Wantz Guillaume
  • Capdevila Joan
  • Alvarez José
  • Connolly J.P.
  • Kleider Jean-Paul
  • Roca i Cabarrocas Pere
  • Pattanasattayavong Pichaya
  • Waiprasoet S.
  , 2024. The laboratory record power conversion efficiencies (PCE) of single junction solar cells are getting closer and closer to the theoretical Shockley-Queisser limit, specifically the Auger limit of 29.4% for crystalline silicon (c-Si) . Strong research efforts are currently devoted to the development of tandem solar cells combining a high bandgap semiconductor for the top cell with a c-Si bottom cell. The recent high PCE, higher than 19%, obtained with single junction organic solar cells makes this technology credible to be associated with c-Si in a tandem configuration. We present here the first steps in the development of organic/silicon tandem solar cells in a 3-terminal architecture . This design consists in combining an interdigitated back contact (IBC) n-type silicon bottom cell with an n-i-p organic top cell. It offers the advantages of suppressing the constraints of photocurrent matching and of the tunnel junction between both subcells, both required in a 2- terminal tandem cell. Early studies were devoted to optimize an organic single junction cell with an active layer made of the wide bandgap non-fullerene acceptor GS-ISO and PBDB-T-2F as donor polymer.. In order to optimize the organic cell, we developed a ternary blend using F8T2 as additive. This strategy led to the increase of the fill factor (FF) by decreasing the recombination in the active layer and PCE up to 10% was achieved with 1.15 V as Voc. We performed the characterization (optical, electrical, morphology) of the active layer and correlated them to the device performance. These experimental results were also used as inputs to develop a realistic numerical model of the organic cells. One of the main objectives of numerical modelling is to simulate the full 3-terminal tandem device for a better understanding of band engineering, optical transmission and transport dynamics at the interface between both subcells. Indeed, the interface between the silicon and the organic subcells is one of the key points of the tandem cell integration. We compare the results obtained experimentally and from simulation for the single organic cells. These results give first insights for the interface optimization between organic cells deposited on n-doped c-Si substrates passivated with different interface layers.
• A Bayesian Inference Approach to Extract Circuit Model Parameters and Analyze Photovoltaic Degradation from Power Production Data
  
  • Chakar Joseph
  • Calin Jean-Paul
  • Pavlov Marko
  • Badosa Jordi
  • Puel Jean-Baptiste
  • Bonnassieux Yvan
  , 2023, pp.112595. (10.1016/j.solener.2024.112595)
  DOI : 10.1016/j.solener.2024.112595
• Nanostructured S@VACNTs Cathode with Lithium Sulfate Barrier Layer for Exceptionally Stable Cycling in Lithium-Sulfur Batteries
  
  • Ezzedine Mariam
  • Jardali Fatme
  • Florea Ileana
  • Cojocaru Costel-Sorin
  Journal of The Electrochemical Society, Electrochemical Society / IOPscience, 2024, 171 (5), pp.050531. Lithium-sulfur technology garners significant interest due to sulfur’s higher specific capacity, cost-effectiveness, and environmentally friendly aspects. However, sulfur’s insulating nature and poor cycle life hinder practical application. To address this, a simple modification to the traditional sulfur electrode configuration is implemented, aiming to achieve high capacity, long cycle life, and rapid charge rates. Binder-free sulfur cathode materials are developed using vertically aligned carbon nanotubes (CNTs) decorated with sulfur and a lithium sulfate barrier layer. The aligned CNT framework provides high conductivity for electron transportation and short lithium-ion pathways. Simultaneously, the sulfate barrier layer significantly suppresses the shuttle of polysulfides. The S@VACNTs with Li 2 SO 4 coating exhibit an extremely stable reversible areal capacity of 0.9 mAh cm −2 after 1600 cycles at 1 C with a capacity retention of 80% after 1200 cycles, over three times higher than lithium iron phosphate cathodes cycled at the same rate. Considering safety concerns related to the formation of lithium dendrite, a full cell Si-Li-S is assembled, displaying good electrochemical performances for up to 100 cycles. The combination of advanced electrode architecture using 1D conductive scaffold with high-specific-capacity active material and the implementation of a novel strategy to suppress polysulfides drastically improves the stability and the performance of Li-S batteries. (10.1149/1945-7111/ad47d5)
  DOI : 10.1149/1945-7111/ad47d5
• Pulsed Electro Decoration of Carbon Nanotubes with FexZn1−xS
  
  • Bjelajac Andjelika
  • Florea Ileana
  • Zamfir Mihai
  • Tusseau-Nenez Sandrine
  • Cojocaru Costel Sorin
  Coatings, MDPI, 2024, 14 (5), pp.619. A wide ranging scientific interest in developing new and simple preparation methods for highly catalytic bimetallic sulfides provided our motivation to explore the possibility of using the pulsed electrodeposition technique for the decoration of a carbon nanotubes forest. The carbon nanotubes were obtained using the hot-filament chemical vapor deposition technique. A non-thermal plasma treatment enabled the controlled creation of defects on the carbon nanotubes’ surface. These defects served as anchoring sites for the subsequent deposition of Fe and Zn nanoparticles using the pulsed electrodeposition technique. Our findings showed that only in the case of Fe deposition prior to Zn provided the formation of FeZn bimetallic-based nanoparticles, with Zn present mainly on the outer surface of the Fe core. To induce sulfurization, a thermal treatment in sulfur vapor was conducted at 500 °C, and the obtained heterostructure consisted of Fe0.3Zn0.7S as the main phase, with the minor presence of ZnS and S residues, which was deduced from the XRD results. This study provides thorough imaging of the process, presenting for each preparation step SEM/HR-TEM findings, coupled with EDS chemical analyses. The samples were tested for photocatalytic degradation of methyl blue dye to demonstrate the photoactive behavior of the heterostructure. (10.3390/coatings14050619)
  DOI : 10.3390/coatings14050619
• Design and synthesis of organic luminescent materials with a 2,2′-bipyrimidine scaffold for hybrid LED lighting.
  
  • Wang Shenming
  , 2024. Organic luminescent materials possess a lot advantages over the inorganic analogues. By carefully designing, they can exhibit efficiency fluorescence in visible area with tunable emission color and strong absorption in near-UV and blue region. Due to this, they can be made in thin films for light-weight optoelectronic devices. They can be highly soluble in organic solvent which provide the possibility for the solution-processing techniques, such as spin-coating and slot-die coating. They are metal-free, which is desired for the sustainable development. In this case, the organic luminescent compound could be a promising alternative to the inorganic phosphor utilized in commercial white LEDs for the improvements of the light quality.In this work, we are aiming at designing and synthesizing greatly efficient organic luminescent materials for down-converting the near-UV or blue light from the light-emitting diodes (LEDs) based on inorganic semiconductors into visible light, ideally white light. Therefore, the target application is called hybrid LEDs. The frequently employed molecular design strategies include: (1) the donor-acceptor (D-A) approach, which can adjust the bandgap in order to tune the absorption wavelength and emission color; (2) aggregation-induced emission (AIE) is introduced for avoiding the significant quenching of the emission in solid state which is owing to the aggregates.Herein, we designed and synthesized a series of D-A molecules M1-M7 implementing new acceptors, 2,2′-bipyrimidine derivatives, as building block. They were purified and taken to the photophysical investigations in both diluted solutions and solid state. They showed tunable emission color, strong fluorescence and absorption, more importantly, high conversion rate from near -UV external source to visible light. We also inspected their photostabilities to estimate their lifespans. In the end, the blenders of different emitters are made for generating white light.
• Low temperature plasma deposition of III-V semiconductors (GaN) on Si
  
  • Srinivasan Lakshman
  , 2024. The importance of the deposition of Gallium Nitride (GaN) thin films on Silicon substrates at reduced temperatures (< 500°C) stems from the increasing demand of the semiconductor industry in mitigating inherent drawbacks associated with high-temperature processing arising from the thermal mismatch between the film and the substrate. This doctoral thesis, done in collaboration with LPICM & IPVF, undertakes a comprehensive exploration of a low-temperature processing methodology, focusing on Plasma based Physical Vapor Deposition (PVD) as a promising avenue for circumventing the constraints of conventional growth techniques such as MOCVD and MBE. The newly custom-built plasma PVD reactor paves way to explore low-cost III-V deposition by plasma, which is a novel topic at the lab. The work delineates a systematic approach encompassing deposition processes, plasma diagnostics, material characterization, and growth optimization strategies for GaN films deposited at room temperature (RT). Plasma diagnostics play a pivotal role when investigating the intricate nuances of Ar-N2 plasmas used in the deposition process. The plasma discharge is characterized via optical emission spectroscopy (OES), two-photon absorption laser-induced fluorescence (TALIF), and microwave interferometry (MWI) to obtain parameters related to plasma temperatures and density. From the plasma diagnostics, two important parameters were estimated - the flux of the sputtered Ga atoms and their average energy at the substrate ((E_Ga^sub ) ̅), which allowed us to address the interplay between plasma characteristics and GaN film properties such as their growth rate and crystalline fraction. The assessment of GaN thin films deposited at room temperature was done using characterization techniques such as SEM, AFM & GIXRD, XPS and Cathodoluminescence (CL). Noteworthy findings include the successful growth of hexagonal wurtzite polycrystalline GaN exhibiting growth rates of ~ 2 Å/s and crystalline fractions of ~ 60% at an optimized sputtering condition (6.6 Pa, 40% N2 and 100 W), elucidating the profound influence of process parameters such as the working pressure, RF power and the N2 flow rate on the morphological, structural & optical properties. It was found that the growth rate estimated through calculations (~ 2.4 Å/s) was in good agreement with experiments, highlighting the validity of our method. Similarly, (E_Ga^sub ) ̅ of Ga correlated well with the crystalline fraction of the GaN films. Further investigation into the influence of substrate temperature from RT to 500°C emphasized the role of thermal energy in enhancing adatom mobility and crystalline quality with the best crystalline fraction of almost ~ 95% obtained at a substrate temperature of 400°C. Overall, this doctoral thesis provides an extensive understanding of the challenges, methodologies, and advancements underpinning the low-temperature processing of GaN thin films via Plasma PVD, by offering tangible insights into its optimization and control.
• Deep-reactive ion etching of silicon nanowire arrays at cryogenic temperatures
  
  • Xu Jiushuai
  • Refino Andam Deatama
  • Delvallée Alexandra
  • Seibert Sebastian
  • Schwalb Christian
  • Hansen Poul Erik
  • Foldyna Martin
  • Siaudinyte Lauryna
  • Hamdana Gerry
  • Wasisto Hutomo Suryo
  • Kottmeier Jonathan
  • Dietzel Andreas
  • Weimann Thomas
  • Prüssing Jan Kristen
  • Bracht Hartmut
  • Peiner Erwin
  Applied Physics Reviews, AIP Publishing, 2024, 11 (2), pp.021411. The pursuit of sculpting materials at increasingly smaller and deeper scales remains a persistent subject in the field of micro- and nanofabrication. Anisotropic deep-reactive ion etching of silicon at cryogenic temperatures (cryo-DRIE) was investigated for fabricating arrays of vertically aligned Si nanowires (NWs) of a large range of dimensions from micrometers down to 30 nm in diameter, combined with commonly used wafer-scale lithography techniques based on optical, electron-beam, nanoimprint, and nanosphere/colloidal masking. Large selectivity of ∼100 to 120 and almost 700 was found with resists and chromium hard masks, respectively. This remarkable selectivity enables the successful transfer of patterned geometries while preserving spatial resolution to a significant extent. Depending on the requirements by applications, various shapes, profiles, and aspect ratios were achieved by varying process parameters synchronously or asynchronously. High aspect ratios of up to 100 comparable to the best result by metal-assisted wet-chemical etching and sub-μm trenches by DRIE were obtained with NW diameter of 200 nm, at an etch rate of ∼4 μm/min without being collapsed. At the same time, low surface roughness values were maintained on the NW top, sidewall, and bottom surface of ∼0.3, ∼13, and ∼2 nm, respectively, as well as high pattern fidelity and integrity, which were measured using angle-resolved Fourier microscopy, combined atomic force, and scanning electron microscopy on selected NWs. This work establishes the foundation in the controllable development of Si nanoarchitectures, especially at sub-100 nm structures, for energy-harvesting and storage, damage-free optoelectronics, quantum, photovoltaics, and biomedical devices. (10.1063/5.0166284)
  DOI : 10.1063/5.0166284
• Bio-inspired Carboxylate-polymer/metal Oxides Material for Electrocatalytic Water Oxidation
  
  • Ahlberg Adrian
  • Collomb Marie-Noëlle
  • Dautreppe Baptiste
  • Pouget Stéphanie
  • Aldakov Dmitry
  • Reiss Peter
  • Lassalle Benedikt
  • Fortage Jérôme
  , 2024.
• Thermodynamics of Oiling-Out in Antisolvent Crystallization. II. Diffusion toward Spinodal Decomposition
  
  • Zhang Zhengyu
  • Audibert Jean-Frédéric
  • Wang Weixi
  • Génot Valérie
  • Park Soo Young
  • Spasojević-de Biré Anne
  • Pansu Robert
  Crystal Growth & Design, American Chemical Society, 2024, 24 (8), pp.3501-3516. The extensive use of antisolvent crystallization for poorly soluble chemicals is hindered by oiling-out. This study delves into solute diffusion kinetics upon antisolvent addition. We conducted time-dependent simulations on a hypothetical micrometric diffusion couple, utilizing chemical potential gradients as driving forces within the Maxwell–Stefan model. Our computations compared two types of interflux coupling: drags and thermodynamics. The thermodynamic force dominates solute diffusion behavior. Antisolvent influx elevates solute chemical potential. This energy wave drives the solute to focus toward the good solvent and leads to the competition between crystallization and oiling-out. Through microfluidics and simulations, characteristic times of oiling-out and two sites of antisolvent-induced spinodal decomposition were identified. Diffusion trajectories on the phase diagram unveiled local thermodynamic conditions and impacts of mixing parameters. Initial antisolvent gradient dominates the strength of the focusing effect. Initial solute concentration acts as an offset in diffusion trajectories. Faster agitation in antisolvent and smaller droplets of solution both effectively enhance solute focusing. These findings are general, allowing mixing processes to be designed into metastable phase regions, with local compositions staying above the designed concentrations for prolonged durations. Elevated supersaturations and extended diffusion times offer favorable conditions for nucleation of metastable phases. (10.1021/acs.cgd.4c00231)
  DOI : 10.1021/acs.cgd.4c00231
• Gallium nitride deposition via magnetron sputtering: Linking plasma-surface interactions and thin film crystalline features
  
  • Srinivasan Lakshman
  • Gazeli Kristaq
  • Prasanna Swaminathan
  • Invernizzi Laurent
  • Roca i Cabarrocas Pere
  • Lombardi Guillaume
  • Ouaras Karim
  Vacuum, Elsevier, 2024, 224, pp.113185. Ga-atoms dynamic in an Ar/N2 magnetron sputtering discharge for GaN deposition is explored employing plasma diagnostic techniques such as optical emission spectroscopy and microwave interferometry. Through the assessment of gas temperature, electron temperature and density measured from the abovementioned diagnostics, we estimated both the flux and average energy of Ga-atoms impinging on the substrate. Emphasizing the working pressure as a pivotal factor, this study uncovers a correlation between the Ga-atoms flux, their average energy, and the growth rate and crystallinity of the GaN films extracted from ex-situ characterizations. Notably, the pressure value (6.6 Pa) at which both the growth rate and crystalline fraction are the greatest is also the condition at which both the flux and energy of Ga-atoms impinging on the target are maximal. The findings pave the way for improving the understanding and control of the complex interplay between plasma conditions and resulting film properties in the sputtering process. (10.1016/j.vacuum.2024.113185)
  DOI : 10.1016/j.vacuum.2024.113185
• A multimodal nanopipette-based imaging and analytical platform for exploring brain communication
  
  • Papa Martina
  , 2024. The brain, composed of billions of neurons and trillions of synapses, communicates through neurotransmitters transferred from sender neurons to effector neurons or cells. N-methyl-D-aspartate (NMDA) glutamate receptors are crucial for brain physiology and their malfunction is consistently linked with pathological conditions. NMDARs require a co-agonist, such as glycine or D-serine, for activation. Despite the two-decades-old discovery of D-serine’s role, the conditions governing the relative synaptic availability and function of glycine and D-serine at synapses remain elusive. This PhD work addresses questions about D-serine by developing an analytical technique for high-resolution, real-time information on local D-serine concentration at synaptic and extrasynaptic nanodomains. Micro- and nano- electrochemical biosensors based on the enzyme D-amino acids oxidase (DAAO) are developed. The first part of the work focuses on fabricating and characterizing micrometric electrochemical sensors. Moreover, we describe their use to monitor local D-serine levels in acute living hippocampal slices in physiological experiments, reporting that D-serine release increases under chemo-induced proconvulsive conditions mimicking epilepsy. The second part introduces electrochemical DAAO-based nano-sensors embedded in Scanning Ion Conductance Microscopy (SICM) glass nanoprobes. This probe features a nanopipette divided into two channels: one housing a nano-version of the DAAO-based sensor and the other serving for SICM topographical mapping. The resulting double-functionality platform will ultimately serve as a powerful analytical tool, combining local D-serine sensing with the acquisition of local topographical information.
• Nitrogen atoms absolute density measurement using two-photon absorption laser induced fluorescence in reactive magnetron discharge for gallium nitride deposition
  
  • Srinivasan Lakshman
  • Invernizzi Laurent
  • Prasanna Swaminathan
  • Gazeli Kristaq
  • Fagnon Nicolas
  • Roca i Cabarrocas Pere
  • Lombardi Guillaume
  • Ouaras Karim
  Applied Physics Letters, American Institute of Physics, 2024, 124 (10). Low-pressure plasmas, in particular magnetron sputtering discharges, are increasingly used for the deposition of wideband gap semiconductor nitrides films (e.g., GaN or AlN) considering many benefits they exhibit with respect to conventional chemical vapor deposition techniques. Plasma-based solutions enable the dissociation of N2 molecules into N-atoms under conditions that would not be possible with the thermal process. However, as the dissociation rate remains quite small due to the strong nitrogen triple bond, it is somewhat complicated to determine and correlate the N-atoms density in the gas phase with that of the grown film in low-pressure discharges. Therefore, ns-two-photon absorption laser induced fluorescence (TALIF) has been carried out to determine the absolute density of N-atoms as a function of the pressure (tens of Pa range) in a radio-frequency sputtering plasma reactor used for GaN deposition. The TALIF set-up has been optimized using a monochromator and adequate signal processing to enhance the detection limit, enabling the measurement of N-atoms density as low as 1011 cm−3 at 15 Pa. These measurements have been completed with electron density measurements performed in the same pressure range using microwave interferometry, thus providing quantitative data on both electron and N-atom densities that can be used for fundamental understanding, process optimization, and modeling of magnetron discharge intended for nitride semiconductor deposition. (10.1063/5.0192748)
  DOI : 10.1063/5.0192748
• Highly conductive p-type nc-SiOX:H thin films deposited at 130°C via efficient incorporation of plasma synthesized silicon nanocrystals and their application in SHJ solar cells
  
  • Olivares Antonio
  • Seif Johannes
  • Repecaud Pierre-Alexis
  • Longeaud Christophe
  • Morales-Masis Monica
  • Bivour Martin
  • Roca I Cabarrocas Pere
  Solar Energy Materials and Solar Cells, Elsevier, 2024, 266, pp.112675. We present highly conductive and transparent p-type hydrogenated nanocrystalline silicon oxide (p-type nc-SiOX:H) layers produced by Plasma Enhanced Chemical Vapor Deposition (PECVD) at 130°C and 150°C. We report on the crystalline volume fraction (XC), spectral broadening parameter C, and dark conductivity (σ) as functions of the growth temperature and RF power, and how these properties evolve with post-deposition annealing at 250°C and 300°C. Interestingly, we observe that the best layers in terms of crystalline volume fraction and conductivity are obtained at the lowest temperature and RF power, which we attribute to the soft landing of silicon nanocrystals synthesized in the plasma. The p-type nc-SiOX:H layers with the best properties on glass substrates are implemented as carrier-selective contacts in silicon heterojunction (SHJ) solar cells with the structure: (n) a-Si:H / (i) a-Si:H / n-type c-Si / (i) a-Si:H / (i) a-SiOX:H / (p) nc-SiOX:H / (p) nc-Si:H where all films are deposited by PECVD. The cells were completed with sputtered ITO on the front and rear sides plus Ag on the rear side, and Ag grid on the front, with the best devices showing conversion efficiencies of 21.8%, which, contrary to a-Si:H contact layers, are preserved or even slightly improved upon annealing at 240°C. © 2023 Elsevier B.V (10.1016/j.solmat.2023.112675)
  DOI : 10.1016/j.solmat.2023.112675
• Rapid and Facile Synthesis of Gold Trisoctahedrons for Surface-Enhanced Raman Spectroscopy and Refractive Index Sensing
  
  • Zhao Guili
  • Lochon Florian
  • Dembélé Kassiogé
  • Florea Ileana
  • Baron Alexandre
  • Ossikovski Razvigor
  • Güell Aleix G
  ACS Applied Nano Materials, American Chemical Society, 2024, 7 (5), pp.5598-5609. Au trisoctahedrons (TOHs) with sharp tips and high-index facets have exceptional properties for diverse applications, such as plasmon-enhanced spectroscopies, catalysis, sensing, and biomedicine. However, the synthesis of Au TOHs remains challenging, and most reported synthetic methods are time-consuming or involve complex steps, hindering the exploration of their potential applications. Herein, we present a facile and fast approach to prepare Au TOHs with high uniformity and good control over the final size and shape, all within less than 10 min of synthesis, for surface-enhanced Raman spectroscopy (SERS) and refractive index sensing. The size of the Au TOHs can be easily tailored over a wide range, from 39 to 268 nm, allowing a tuning of the plasmon resonance at wavelengths from visible to near-infrared regions. The exposed facets of the Au TOHs can also be varied by controlling the growth temperatures. The wide tunability of size and exposed facets of Au TOHs can greatly broaden the range of their applications. We have also encapsulated Au TOHs with zeolite imidazolate framework (ZIF-8), obtaining core–shell hybrid structures. With the ability to tune Au TOH size, we further assessed their SERS performances in function of their size by detecting 2-NaT in solution, exhibiting enhancement factors of the order of 105 with higher values when the LSPR is blue-shifted from the laser excitation wavelength. Au TOHs have been also compared for refractive index sensing applications against Au nanospheres, revealing Au TOHs as better candidates. Overall, this facile and fast method for synthesizing Au TOHs with tunable size and exposed facets simplifies the path toward the exploration of properties and applications of this highly symmetrical and high-index nanostructure (10.1021/acsanm.4c00455)
  DOI : 10.1021/acsanm.4c00455
• Nanoparticles synthesis in microwave plasmas: peculiarities and comprehensive insight
  
  • Ouaras Karim
  • Lombardi Guillaume
  • Hassouni Khaled
  Scientific Reports, Nature Publishing Group, 2024, 14 (1), pp.4653. Abstract Low-pressure plasma processes are routinely used to grow, functionalize or etch materials, and thanks to some of its unique attributes, plasma has become a major player for some applications such as microelectronics. Plasma processes are however still at a research level when it comes to the synthesis and functionalization of nanoparticles. Yet plasma processes can offer a particularly suitable solution to produce nanoparticles having very peculiar features since they enable to: (i) reach particle with a variety of chemical compositions, (ii) tune the size and density of the particle cloud by acting on the transport dynamics of neutral or charged particles through a convenient setting of the thermal gradients or the electric field topology in the reactor chamber and (iii) manipulate nanoparticles and deposit them directly onto a substrate, or codeposit them along with a continuous film to produce nanocomposites or (iv) use them as a template to produce 1D materials. In this article, we present an experimental investigation of nanoparticles synthesis and dynamics in low-pressure microwave plasmas by combining time-resolved and in-situ laser extinction and scattering diagnostics, QCL absorption spectroscopy, mass spectrometry, optical emission spectroscopy and SEM along with a particle transport model. We showed for the first time the thermophoresis-driven dynamic of particle cloud in electrodless microwave plasmas. We showed that this effect is linked to particular fluctuations in the plasma composition and results in the formation of a void region in the bulk of the plasma surrounded by a particle cloud in the peripherical post-discharge. We also reveals and analyze the kinetics of precursor dissociation and molecular growth that result in the observed nanoparticle nucleation. (10.1038/s41598-023-49818-3)
  DOI : 10.1038/s41598-023-49818-3
• Extended eigenvalue calibration method for overdetermined Mueller matrix polarimeters
  
  • Rosales Saúl
  • Garcia Caurel Enrique
  • Ossikovski Razvigor
  Optics Letters, Optical Society of America - OSA Publishing, 2024, 49 (5), pp.1165. The eigenvalue calibration method is a versatile approach that can be applied to any type of the Mueller matrix polarimetic setup because a precise knowledge of the optical response of the setup components is not required. The method has usually been employed in its original form to calibrate non-overdetermined polarimeters dealing with intensity data arranged in 4 × 4 matrices, but it can also be applied to calibrate overdetermined polarimeters with intensity data matrices of higher dimension. The main drawback with the original formulation of the method is its sensitivity to noise in the input data, especially if applied as it is to overdetermined intensity matrices. In the present work, we present a rigorous extension of the conventional eigenvalue calibration method to treat overdetermined data. We experimentally show that the proposed method does not enhance noise propagation, and therefore it does not degrade the quality of Mueller matrices measured with overdetermined polarimeters. (10.1364/OL.513929)
  DOI : 10.1364/OL.513929
• Optical constants of exoplanet haze analogs from 0.3 to 30 µm: Comparative sensitivity between spectrophotometry and ellipsometry
  
  • Drant Thomas
  • Garcia-Caurel E
  • Perrin Zoé
  • Sciamma-O’brien E
  • Carrasco Nathalie
  • Vettier Ludovic
  • Gautier Thomas
  • Brubach J-B
  • Roy P
  • Kitzmann D
  • Heng K
  Astronomy & Astrophysics - A&A, EDP Sciences, 2024, 682, pp.A6. We report new optical constants (refractive index, n, and extinction coefficient, k) for exoplanet haze analogs from 0.3 to 30 µm. The samples were produced in a simulated N 2-dominated atmosphere with two different abundance ratios of CO 2 and CH 4 , using the PAMPRE plasma reactor at LATMOS. We find that our haze analogs present a significantly lower extinction coefficient in the optical and near-infrared (NIR) range compared to the seminal data obtained on Titan haze analogs. We confirm the stronger IR absorption expected for hazes produced in a gas mixture with higher CO 2 abundances. Given the strong impact of the atmospheric composition on the absorbing power of hazes, these new data should be used to characterize early-Earth and CO 2-rich exoplanet atmospheres. The data presented in this paper can be found in the Optical Constants Database. Using ellipsometry or spectrophotometry, the retrieved optical constants are affected by the sensitivity of the measurement and the accuracy of the calculations. A comparative study of both techniques was performed to identify limitations and better understand the discrepancies present in the previous data. For the refractive index n, errors of 1-3% are observed with both optical techniques and the different models, caused by the correlation with the film thickness. We find that UV-visible reflection ellipsometry provides similar n values, regardless of the model used; whereas the Swanepoel method on transmission is more subjected to errors in the UV. In the UV and mid-infrared (MIR), the different calculations lead to rather small errors on k. Larger errors of k arise in the region of weak absorption, where calculations are more sensitive to errors on the refractive index n. (10.1051/0004-6361/202346820)
  DOI : 10.1051/0004-6361/202346820
• Magnetic Signature in Graphene Using Adsorbed Metal–Organic Networks
  
  • Rochefort Alain
  • Anindya Khalid N
  • Bouju Xavier
  • Denawi Adam H
  Journal of Physical Chemistry C, American Chemical Society, 2024, 128 (2), pp.919-926. The interaction of a 2D metal-organic network (MON) stacked on graphene has been studied with the help of first-principles density functional theory (DFT) and DFT+U calculations. By varying the length of a polyphenyl-dicarbonitrile linker, we have evaluated the influence of the metal-metal distance on the electronic and magnetic properties of the MON complexes. Although MON composed of small molecules shows a moderately stable ferromagnetic phase, this magnetic order drops with the size of the complex. After the adsorption of MON on graphene, this last becomes n-doped due to an important charge transfer that improves with the molecular unit size. The MON-graphene interaction contributes to drastically reduce the overall stability of any magnetic order, but the local charge transfer remains strongly spin-polarized-dependent. Hence, the adsorption of magnetic MON on graphene leads to the modification of the electronic and magnetic properties of graphene, mostly in a closed proximity region to the active metal atoms of the MON. Spin-polarized scanning tunneling microscopy simulations reveal a magnetic signature in graphene that originates from its interaction with the MONs and that could be experimentally observed. (10.1021/acs.jpcc.3c06657)
  DOI : 10.1021/acs.jpcc.3c06657
• Thermodynamics of oiling-out in antisolvent crystallization. I. Extrapolation of ternary phase diagram from solubility to instability
  
  • Zhang Zhengyu
  • Bi Ran
  • Audibert Jean-Frédéric
  • Wang Weixi
  • Park Soo Young
  • Spasojevic - de Biré Anne
  • Pansu Robert Bernard
  Crystal Growth & Design, American Chemical Society, 2024, 24 (1), pp.224-237. The competition between crystallization and oiling-out is a major concern in the process design of antisolvent crystallization for poorly water-soluble drugs. Within the CALPHAD framework, this study demonstrates the extrapolation of the ternary phase diagram for antisolvent crystallization from the solubility data, resorting to the Jouyban-Acree model and the Gibbs-Helmholtz type equation. The ternary phase diagram for DBDCS (a fluorophore exhibiting aggregation-induced emission) in water-[1,4-dioxane] is constructed by calculating the polymorph solid-liquid equilibria, the metastable liquid-liquid equilibrium, and the spinodal limit. Our computational results agree with the phase diagram measured through microfluidics. By analyzing the chemical potential, we show that the solute uphill diffusion relies on the antisolvent gradient. The energy of disorder upon nucleation is found to be much smaller compared to the solute energy gain upon antisolvent addition. The characteristics of the parallel solubility curves of the polymorphs are explained with the analysis of the molecular interactions. By evaluating the energy of composition fluctuation, we suggest the optimal conditions for antisolvent crystallization. The insights obtained from this study can be extended to the process design of antisolvent crystallization for similar systems, and form the basis for further kinetic analysis of the competition between oiling-out and crystallization. (10.1021/acs.cgd.3c00916)
  DOI : 10.1021/acs.cgd.3c00916
• Spatial dispersion in silicon
  
  • Bian Subiao
  • Ossikovski Razvigor
  • Canillas Adolf
  • Jellison Gerald
  • Arteaga Oriol
  Physical Review B, American Physical Society, 2024, 109 (3), pp.035201. (10.1103/PhysRevB.109.035201)
  DOI : 10.1103/PhysRevB.109.035201
• Effect of an artificial cavity on the microlayer and contact line dynamics during bubble growth in nucleate boiling
  
  • Tecchio Cassiano
  • Regoli Iacopo
  • Cariteau Benjamin
  • Zalczer Gilbert
  • Roca I Cabarrocas Pere
  • Bulkin Pavel
  • Charliac Jérôme
  • Vassant Simon
  • Nikolayev Vadim
  Journal of Physics: Conference Series, IOP Science, 2024, 2766, pp.012121. We present an experimental study on the near-wall phenomena during the growth of a single bubble in saturated pool boiling of water at atmospheric pressure. Our focus is on the dynamics of triple contact line and liquid microlayer that can form between the heater and the liquid-vapor interface of the bubble. The microlayer thickness, the wall temperature distribution and the bubble shape are measured simultaneously and synchronously at 4000 fps by white light interferometry, infrared thermography and sidewise shadowgraphy, respectively. To study the effect of cavities (artificial nucleation sites) we compare two experiments using different heaters. In the first experiment, the bubble grows on a smooth surface of nanometric roughness whereas in the second, the bubble grows over a cylindrical cavity of 25 µm diameter and 50 µm depth. We found that the cavity reduces three times the required wall superheating to trigger the bubble growth. Moreover, the radii of the bubble, microlayer and dry spot are smaller by half and the macroscale bubble dynamics is also slower. The microlayer is thinner and is measurable in a larger portion of its extent. Based on the absence of interference fringes near the contact line (due to high interface slopes) and on recent numerical simulations, we conclude that the microlayer consists in two regions: a dewetting ridge near the contact line that grows over time and a flatter and wider region that thins over time. The microlayer can be seen as a film deposited by the receding meniscus and its profile is controlled by the viscous and surface tension effects; its thinning over time is due to local evaporation only. The ridge is a result of liquid accumulation due to contact line receding and strong viscous shear in the film. (10.1088/1742-6596/2766/1/012121)
  DOI : 10.1088/1742-6596/2766/1/012121
• Connecting the microscopic depolarizing origin of samples with macroscopic measures of the Indices of Polarimetric Purity
  
  • Canabal-Carbia Mónica
  • Estévez Irene
  • Nabadda Esther
  • Garcia-Caurel Enrique
  • Gil J.J.
  • Ossikovski Razvigor
  • Márquez Andrés
  • Moreno Ignacio
  • Campos Juan
  • Lizana Angel
  Optics and Lasers in Engineering, Elsevier, 2024, 172, pp.107830. (10.1016/j.optlaseng.2023.107830)
  DOI : 10.1016/j.optlaseng.2023.107830