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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.

Perovskite solar cells (PSCs) research is an intense field that could benefit from every available research tool. Synchrotron tools have played an important role in fundamental and applied research for decades. Many synchrotron-based hard X-ray tools are already providing effective feedback to the PSC research community. With several fourth-generation light sources up and running or under development, this contribution will continue to impact every aspect of scientific advancement including PSC research. Arguably, the contribution of soft X-rays in PSC research is relatively limited. In view of the developments in the synchrotron world and the fact that a multimethod approach, combining laboratory-based techniques as well as synchrotron-based techniques, is necessary to provide constructive feedback to the PSC community we present here a collection of arguments and procedures with the aim of highlighting the use of soft X-ray scanning transmission X-ray microscopy (STXM). Some aspects of these arguments are elaborated with STXM investigation of perovskite material formamidinium-methylammonium lead iodide (FA1-xMAxPbI3).

Silicon is one of the most promising anode materials for Lithium-ion batteries. Silicon endures volume changes upon cycling, which leads to subsequent pulverization and capacity fading. These drawbacks lead to a poor lifespan and hamper the commercialization of silicon anodes. In this work, a hybrid nanostructured anode based on silicon nanoparticles (SiNPs) anchored on vertically aligned carbon nanotubes (VACNTs) with defined spacing to accommodate volumetric changes is synthesized on commercial macroscopic current collector. Achieving electrodes with good stability and excellent electrochemical properties remain a challenge. Therefore, we herein tune the active silicon areal loading either through the modulation of the SiNPs volume by changing the silicon deposition time at a fixed VACNTs carpet length or through the variation of the VACNT length at a fixed SiNPs volume. The low areal loading of SiNPs improves capacity stability during cycling but triggers large irreversible capacity losses due to the formation of the solid electrolyte interphase (SEI) layer. By contrast, higher areal loading electrode reduces the quantity of the SEI formed, but negatively impacts the capacity stability of the electrode during the subsequent cycles. A higher gravimetric capacity and higher areal loading mass of silicon is achieved via an increase of VACNTs carpet length without compromising cycling stability. This hybrid nanostructured electrode shows an excellent stability with reversible capacity of 1330 mAh g-1 after 2000 cycles., Batteries & Supercaps, 2022

International audience; Silicon-based anode fabrication with nanoscale structuration improves the energy density and life cycle of Li-ion batteries. As-synthesized silicon (Si) nanowires (NWs) or nanoparticles (NPs) directly on the current collector represent a credible alternative to conventional graphite anodes. However, the operating potentials of these electrodes are below the electrochemical stability window of all electrolytes used in commercial Li-ion systems. During the first charging phase of the cell, partial decomposition of the electrolyte takes place, which leads to the formation of a layer at the surface of the electrode, called solid electrolyte interphase (SEI). A stable and continuous SEI layer formation is a critical factor to achieve reliable lifetime stability of the battery. Once formed, the SEI acts as a passivation layer that minimizes further degradation of the electrolyte during cycling, while allowing lithium-ion diffusion with their subsequent insertion into the active material and ensuring reversible operation of the electrode. However, one of the major issues requiring deeper investigation is the assessment of the morphological extension of the SEI layer into the active material, which is one of the main parameters affecting the anode performances. In the present study, we use electron tomography with a low electron dose to retrieve three-dimensional information on the SEI layer formation and its stability around SiNWs and SiNPs. The possible mechanisms of SEI evolution could be inferred from the interpretation and analysis of the reconstructed volumes. Significant volume variations in the SiNW and an inhomogeneous distribution of the SEI layer around the NWs are observed during cycling and provide insights into the potential mechanism leading to the generally reported SiNW anode capacity fading. By contrast, analysis of the reconstructed SiNPs’ volume for a sample undergoing one lithiation–delithiation cycle shows that the SEI remains homogeneously distributed around the NPs that retain their spherical morphology and points to the potential benefit of such nanoscale Si anode materials to improve their cycling lifetime.

Orientation analyses of macromolecules or artificial particles are vital for both fundamental research and practical bio-applications. An accurate approach is monitoring the polarization spectroscopy of lanthanide-doped nanocrystalline materials. However, nanomaterials are often far from ideal for the colloidal and polarization luminescence properties. In the present study, we synthesize well-dispersed LaPO4:Eu3+ nanomaterials in an anisotropic rod shape. Microwave heating with excess addition of phosphate precursor invokes a rapid phase transition of rhabdophane into monazite. The colloidal stability of the nanorod suspension is outstanding, demonstrated by showing liquid crystalline behaviors. The monazite nanorods are also superior in luminescence efficiency with limited defects. The emission spectrum of Eu3+ consists of well-defined lines with prominent polarization dependencies for both the forced electric dipole transitions and the magnetic dipole transitions. All the results demonstrate that the synthesized monazite nanorods can serve as an accurate probe in orientation analyses and potential applications, such as in microfluidics and biological detections.

raphene 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, Hubert Curien─Fundação para a Ciência e a Tecnologia (FCT) Partnership (PHC-PESSOA 2D GAS SENS). Graphene field-effect transistors were provided through ASCENT+ collaboration from European Union’s Horizon 2020 research and innovation programme, grant agreement 871130. In addition, FCT partially supported UMinho’s research in the framework of the Strategic Funding UIDB/04650/2020. This work was carried out with partial support from LABEX MMCD. The authors acknowledge financial support from the French state managed by the National Research Agency under the Investments for the Future program under the references ANR-10-EQPX-50, pole NanoMAX, and pole NanoTEM. Part of the TEM analysis was carried out at Centre Interdisciplinaire de Microscopie électronique de l’X (CIMEX), which is gratefully acknowledged. The authors acknowledge the help and support from Dr. Simons Hallais for AFM analysis

Transparent conducting oxides (TCOs) used in solar cells must be optimized to achieve minimum parasitic absorption losses while providing sufficient lateral conductivity. Low contact resistance with the adjacent device layers and low damage to the substrate during deposition of the TCO are also important requirements to ensure high solar cell efficiencies. Pulsed laser deposition (PLD) has been proposed as an alternative low-damage TCO deposition technique on top of sensitive layers and interfaces in organic and perovskite solar cells but is yet to be studied for the more mature silicon technology. Focusing on the PLD deposition pressure as the key parameter to reduce damage, we developed tin-doped indium oxide (ITO) with a sheet resistance of 60 ω □-1 at different pressures and implemented it in silicon heterojunction (SHJ) solar cells. Buffer-free semi-transparent perovskite cells with the same PLD ITO electrodes were also fabricated for comparison. While in the perovskite cells increased ITO deposition pressure leads to an improved open circuit voltage and fill factor indicative of damage reduction, SHJ cells with PLD ITO at all conditions maintained a high passivation quality, but increased pressures lead to high series resistance. Transmission electron microscopy and time-of-flight secondary ion mass spectrometry confirmed the formation of a parasitic SiOx at the ITO/a-Si:H interface of the SHJ cell causing a transport barrier. The optimized ITO films with the highest carrier density were able to obtain >21% SHJ efficiency with 75 nm-thick PLD ITO. Moreover, reducing the ITO thickness to ∼45 nm and using TiOx for optical compensation enables fabrication of SHJ devices with reduced indium consumption and efficiencies of >22%. This journal is

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Orientation analyses of macromolecules or artificial particles are vital for both fundamental research and practical bio-applications. An accurate approach is monitoring the polarization spectroscopy of lanthanide-doped nanocrystalline materials. However, nanomaterials are often far from ideal for the colloidal and polarization luminescence properties. In the present study, we synthesize well-dispersed LaPO

International audience; The vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) growth mechanisms are widely used to obtain silicon nanowires. In this paper, we report on a hybrid method based on the use of a dual-phase catalyst made of liquid Sn and solid Cu 3 Si, which results in a liquid-assisted VSS (LA-VSS) mechanism. The silicon atoms are brought by atomic hydrogen-assisted dissociation of silane molecules. We observe the growth in situ, in the transmission electron microscope, at

An in situ Modulated Photoluminescence (MPL) measurement setup mounted on a Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor is described. A method for deriving the actual minority carrier lifetime at the specific injection level of 1.1015 cm−3 is presented. This tool was used in a case study to monitor the passivation properties of aluminum oxide (AlOx) thin films upon annealing. Interesting kinetics, such as a drop of lifetime at temperatures higher than 250 °C along with a recovery of the lifetime during the cooling phase, are shown. Moreover, these in situ results combined with ex situ studies allowed us to demonstrate the formation a stable high positive fixed charge density in the AlOx layer (+1.1012 cm−2) as a consequence of the combination of annealing and light exposure.

In this work, we report the same trends for the contact potential difference measured by Kelvin probe force microscopy and the effective carrier lifetime on crystalline silicon (c-Si) wafers passivated by AlOx layers of different thicknesses and submitted to annealing under various conditions. The changes in contact potential difference values and in the effective carrier lifetimes of the wafers are discussed in view of structural changes of the c-Si/SiO2/AlOx interface thanks to high resolution transmission electron microscopy. Indeed, we observed the presence of a crystalline silicon oxide interfacial layer in as-deposited (200 °C) AlOx, and a phase transformation from crystalline to amorphous silicon oxide when they were annealed in vacuum at 300 °C.

This work reports experiments on the oriented growth by electric field of free-standing carbon nanotubes(CNTs) by chemical vapor deposition (CVD) for field emission (FE) applications. The growths were observed in a scanning electron microscope (SEM) and in an environmental transmission electron microscope (ETEM) with the ETEM growths observed in real time. The effects of various applied voltage during growth will be presented. For high voltages, videos show that the maximum length of CNTs are limited either by the mechanical breakdown or FE induced thermal evaporation. Finally, the I(V) curves and current densities obtained will be presented with a focus on the different destruction mechanisms.

This work reports the non-covalent functionalization of SWNTs with Fe-porphyrin, Co-porphyrin and Co-phthalocyanine molecules. The functionalized SWNTs were first characterized using Raman and X-ray photoelectron spectroscopies. Observations down to nanoscale resolution were also performed by atomic force microscopy, as well as scanning and transmission electron microscopies. The spectroscopic methods evidenced an electronic interaction between the metal-centered molecules and the SWNTs, ensuring the robustness of the functionalization. High resolution microscopy characterizations reveal that the porphyrin and phthalocyanine molecules are adsorbed on the surface of SWNTs. The electrical characterizations show a weak charge transfer between those grafted molecules and the SWNTs, confirming the electronic interaction between the molecules and the SWNTs. Density functional theory (DFT) supports experimental data and helps understanding the experimental results of selective interaction of metal complexes with one type of semiconducting SWNTs.

Single-walled carbon nanotubes (SWCNTs) are promising candidates for gas sensing applications, providing an efficient solution to the device miniaturization challenge and allowing low power consumption. SWCNT gas sensors are mainly based on field-effect transistors (SWCNT-FETs) where the modification of the current flowing through the nanotube is used for gas detection. A major limitation of these SWCNT-FETs lies in the difficulty to measure their transfer curves, since the flowing current typically varies between 10(-12) and 10(-3) A. Thus, voluminous and energy consuming systems are necessary, severely limiting the miniaturization and low energy consumption. Here, we propose an inverter device that combines two SWCNT-FETs which brings a concrete solution to these limitations and simplifies data processing. In this innovative sensing configuration, the gas detection is based on the variation of an electric potential in the volt range instead of a current intensity variation in the microampere range. In this study, the proof of concept is performed using NO2 gas but can be easily extended to a wide range of gases.

International audience; Highly symmetrical gold nanocages can be produced with a controllable number of circular windows of either 2, 3, 4, 6 or 12 via an original fabrication route. The synthetic pathway includes three main stages: the synthesis of silica/polystyrene multipod templates, the regioselective seeded growth of a gold shell on the unmasked part of the silica surface and the development of gold nanocages by dissolving/etching the templates. Electron microscopy and tomography provide evidence of the symmetrical features of the as-obtained nanostructures. The optical properties of nanocages with 4 and 12 windows were measured at the single particle level by spatial modulation spectroscopy and correlated with numerical simulations based on finite-element modeling. The new multi-step synthesis approach reported here also allows the synthesis of rattle-like nanostructures through filling of the nanocages with a guest nano-object. With the potential to adjust the chemical composition, size and geometry of both the guest particle and the host cage, it opens new routes towards the fabrication of hollow nanostructures of high interest for a variety of applications including sensing devices, catalytic reactors and biomedicine. New concepts We demonstrate a new concept for making hollow nanoscale structures which are central to the advances in many current and emerging areas of technology. Nanocages are hollow and porous nanostructures. The ones made of metal are needed for optics, catalysis, biomedicine, and sensing. But, they are difficult to make. In particular, it is difficult to yield precise nanoscale control of the porosity as well as the composition. We address this challenge by combining inorganic colloidal synthesis and metal deposition on biphasic sacrificial templates. The single-particle spectroscopy and simulation confirm that our approach affords tight control over the morphology and porosity at the nanoscale. Previous approaches to making metal nanocages rely on galvanic replacement reactions and siteselective deposition. They offer control over morphology, but limited control over composition, porosity and scaleup. Our approach provides a simple and general strategy to circumvent these issues. It can be applied to a wide range of materials, and with further developement to any nanorattle-like nanostructures.

Supplement1 - Demonstration of the developed model on sample from alternative manufacturer.

Modulated Photoluminescence (MPL) is a powerful tool for measuring the minority carrier lifetime of solar cells. An in house in situ MPL equipped Plasma Enhanced Chemical Vapor Deposition reactor enables the monitoring of passivation properties of solar cells during the fabrication steps of devices. In this study, this tool was used to analyze the impact of annealing steps on passivation properties. First, samples passivated by an aluminum oxide layer were annealed and the evolution of the effective lifetime in the wafer was studied. This allowed to optimize the temperature and duration of the heat treatment. A similar study was made on Fired Passivating Contacts with a passivating stack of SiO x /(p) $\mu\mathrm{c}$ -Si:H/SiN x :H. An interesting low-lifetime regime is consistently observed when the samples undergo a high temperature ( $\mathrm{T} > 350^{\circ}\mathrm{C}$ ) annealing step, followed by a lifetime recovery during the subsequent cooling step. Corona charge and TEM images allowed to get a deeper understanding of the passivation mechanisms evidenced during in situ MPL measurements.

Droplet based micro/nanofluidics has been demonstrated as a versatile tool in a wide range of fields. In particular, seeded growth of planar low-dimensional nanomaterials often relies on crawling metal droplets as catalytic media where nucleation and crystal growth proceed. However, direct observations of nanomaterials growth led by self-propelled droplet transport remain rare, which leaves many open questions on droplet behavior during growth. Here, we report in situ observations of in-plane Si nanowire growth in a transmission electron microscope, where an indium droplet migrates on a silicon nitride membrane coated by a layer of hydrogenated amorphous silicon (a-Si:H), dissolves the a-Si:H coating film on the membrane, and results in the production of a crystalline Si nanowire in its trail. This in situ observation, combined with the geometric investigation of the nanowires, presents nice consistency with de Gennes’ theoretical prediction of reactive wetting induced droplet motion. Interestingly, we recorded a nanoflake-to-nanowire transition when the growth rate was increased by heating the membrane from 350 °C to 400 °C. This work directly unveils rich transport mechanism of catalytic droplets, which are expected to be a new platform for producing diverse low-dimensional nanomaterials and promote their potential applications in nanoscience and technologies.

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.

International audience; Achieving stability with highly active Ru nanoparticles for electrocatalysis is a major challenge for the oxygen evolution reaction. As improved stability of Ru catalysts has been shown for bulk surfaces with low‐index facets, there is an opportunity to incorporate these stable facets into Ru nanoparticles. Now, a new solution synthesis is presented in which hexagonal close‐packed structured Ru is grown on Au to form nanoparticles with 3D branches. Exposing low‐index facets on these 3D branches creates stable reaction kinetics to achieve high activity and the highest stability observed for Ru nanoparticle oxygen evolution reaction catalysts. These design principles provide a synthetic strategy to achieve stable and active electrocatalysts.

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The shape and porous configuration of supports are key parameters to design outstanding catalysts. However, the selection of a proper mesoporous support, such as SBA-15, by itself does not guarantee accessibility to catalytic sites. The distribution of the active phase and its stability are strongly related to the procedure used to deposit it on the catalytic substrate. Herein, we have prepared rod-shaped SBA-15 silica supports functionalized with amine groups to facilitate the electrostatic attraction and a good distribution of the resulting Pt-based catalytic nanoparticles along the pore walls. Additionally, the use of tetrakis-(hydroxymethyl)-phosphonium chloride (THPC) as both reductant and stabilizer is presented as a novel alternative for Pt nanoparticle synthesis. The behaviour of this catalyst in the total oxidation of n-hexane demonstrates high activity and excellent stability after 70 h on reaction stream. STEM-HAADF and 3-D tomography were used to confirm the presence of the metallic nanoparticles within the mesochannels and to corroborate their reduced sintering after reaction.

The present work aims to become a standard step for the fabrication of the next generation porous anodic alumina (PAA) templates based devices and to provide new insights on the mechanism involved in the porous anodic alumina formation. The oxide barrier layer at the bottom of the pores has been successfully thinned by applying an exponential voltage decrease process followed by a wet chemical etching. The impact of the potential drop on the PAA structure has been deeply investigated, as well as the electrolyte temperature, the number of potential steps and the exponential decay rate. The presented results underline that a smart adjustment between the anodization conditions and exponential voltage decay parameters can simultaneously give PAA structures with straight pores and remove the dielectric layer in spite of applying the exponential voltage decay step. Additionally, the PAA structure has been tuned to fabricate hierarchically nanoporous templates with secondary pores ranging from 2 up to 10 branches.

Owing to their sensitive chemical-to-electrical transducer capabilities and compatibility with device miniaturization and low operation temperature, single-walled carbon nanotube field-effect transistor (SWCNT-FET) represents an attractive platform to provide solutions in the gas sensing field. In this work, SWCNT-FETs were fabricated and their performances for detecting low NO2 concentrations were evaluated. Outstanding devices response was obtained, which was shown to follow a 2 power law dependence between the response and the NO2 concentration in the range of 100 ppb up to 10 ppm. Such ultra-high response is attributed to an enhancement of the Schottky barrier modulation triggered by the specific device configuration. The device configuration is based on individual semiconducting SWCNTs directly connecting the interdigitated Source-Drain electrodes. To the best of our knowledge, the results reported here correspond to the most sensitive device among the devices based on non-functionalized carbon materials and operational at low temperatures. Furthermore, the obtained results are supported by a deep SWCNT characterization, and the changes in Schottky barrier's height induced by the presence of gas molecules are estimated and discussed. Overall, the present reported results provide useful information for establishing a robust process for the fabrication of the next generation of CNT based gas-sensing devices. (C) 2019 Elsevier Ltd. All rights reserved.

In this work, we study the properties of re-assembled graphene nanoplatelets as an effective anticorrosion coating for aluminum (Al) substrate in 0.5 M Sodium Chloride (NaCl) at room temperature (30°C). Scanning and Transmission Electron Microscopy (TEM) as well as Raman spectroscopy reveal the high quality multilayer graphene nanoplatelets. The modifications of the corrosion resistance characteristic were investigated by Open Circuit Potential (OCP), followed by electrochemical tests such as potentiodynamic polarization (Tafel curves) and Electrochemical Impedance Spectroscopy (EIS). The electrochemical results show that the graphene nanoplatelets provide effective resistance against the corrosive medium during the two weeks of immersion in the saline medium. Scanning Electron Microscopy (SEM), Raman spectroscopy and Energy Dispersive X-ray (EDX) studies carried out after immersion in the corrosive medium confirm that a graphene-coated aluminum surface is well protected compared to an uncoated substrate.

We report on metal assisted chemical etching of Si for the synthesis of mechanically-stable, hybrid crystallographic orientation Si superstructures with high aspect ratio, above 200. This one-pot-type method sustains high etching rates and facilitates reproducible results. The protocol enables the control of the number, angle and location of kinks via successive etch-quench sequences. We analysed relevant Au mask catalyst features to systematically assess their impact on a wide spectrum of etched morphologies that can be easily attained and customized by fine tuning of the critical etching parameters. For instance, the designed kinked Si nanowires can be internalized in biological cells, without affecting their viability. An accessible numerical model is provided to explain the etch profiles and the physico-chemical events at the Si-Au-electrolyte interface and offers guidelines for the development of finite-element modeling of metal assisted Si chemical etching.

International audience; Plasma Enhanced Chemical Vapor Deposition of silicon from SiF4/H2/Ar gas mixture is observed on a SiOxNy surface, while under the same plasma conditions, silicon films do not grow on AlOx nor Al surfaces. Transmission electron microscopy confirms that the silicon deposited on SiOxNy has a microcrystalline structure. After the plasma process, fluorine is detected in abundance on the AlOx surface by X-ray photoelectron spectroscopy and energy dispersive X-ray chemical analyses. This suggests that Al-F bonds are formed on this surface, blocking any deposition of silicon on it. In-situ ellipsometry studies show that deposition can be initiated on AlOx surfaces by increasing the temperature of the electrodes or increasing the RF plasma power, leading to a loss of selectivity.

The matrix-distributed electron cyclotron resonance plasma-enhanced chemical vapor deposition (MDECR-PECVD) technique has been shown to achieve high deposition rates for hydrogenated microcrystalline silicon (μc-Si:H) thin film. Due to the fact that plasma is sustained by a microwave discharge, by biasing the substrate holder with additional power supply, one can achieve independent control over the plasma density and the maximum ion bombardment energy (IBE). In this work, we present studies of the impact of IBE on the microstructural properties of the μc-Si:H film deposited by MDECR-PECVD. Insufficient ion bombardment is found to be responsible for the substantial presence of nano-porous regions within the material, resulting in significant post-deposition oxidation. Good agreement between transmission electron microscopy (TEM) Fresnel contrast analysis and the results of infrared absorption and hydrogen effusion measurements for the deposited films suggest that moderate IBE is of vital importance to achieve high quality μc-Si:H. In doing so, denser films with significantly decreased nano-porous regions and better stability are obtained, which is of great interest to optimize the process parameters for solar cell applications. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Multifunctional Bi- and Fe-modified carbon xerogel composites (CXBiFe), with different Fe concentrations, were obtained by a resorcinol&ndash, formaldehyde sol&ndash, gel method, followed by drying in ambient conditions and pyrolysis treatment. The morphological and structural characterization performed by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption/desorption porosimetry, scanning electron microscopy (SEM) and scanning/transmission electron microscopy (STEM) analyses, indicates the formation of carbon-based nanocomposites with integrated Bi and Fe oxide nanoparticles. At higher Fe concentrations, Bi-Fe-O interactions lead to the formation of hybrid nanostructures and off-stoichiometric Bi2Fe4O9 mullite-like structures together with an excess of iron oxide nanoparticles. To examine the effect of the Fe content on the electrochemical performance of the CXBiFe composites, the obtained powders were initially dispersed in a chitosan solution and applied on the surface of glassy carbon electrodes. Then, the multifunctional character of the CXBiFe systems is assessed by involving the obtained modified electrodes for the detection of different analytes, such as biomarkers (hydrogen peroxide) and heavy metal ions (i.e., Pb2+). The achieved results indicate a drop in the detection limit for H2O2 as Fe content increases. Even though the current results suggest that the surface modifications of the Bi phase with Fe and O impurities lower Pb2+ detection efficiencies, Pb2+ sensing well below the admitted concentrations for drinkable water is also noticed.

Recent advances in structural control during the synthesis of SWCNTs have in common the use of bimetallic nanoparticles as catalysts, despite the fact that their exact role is not fully understood. We therefore analyze the effect of the catalyst' s chemical composition on the structure of the resulting SWCNTs by comparing three bimetallic catalysts (FeRu, CoRu and NiRu). A specific synthesis protocol is designed to impede the catalyst nanoparticle coalescence mechanisms and stabilize their diameter distributions throughout the growth. Owing to the ruthenium component which has a limited carbon solubility, tubes grow in tangential mode and their diameter is close to that of their seeding nanoparticle. By using as-synthesized SWCNTs as a channel material in field effect transistors, we show how the chemical composition of the catalysts and temperature can be used as parameters to tune the diameter distribution and semiconducting-to-metallic ratio of SWCNT samples. Finally, a phenomenological model, based on the dependence of the carbon solubility as a function of catalyst nanoparticle size and nature of the alloying elements, is proposed to interpret the results., 10 pages, 6 figures

Crystal growth often proceeds by atomic step flow. When the surface area available for growth is limited, the nucleation and progression of the steps can be affected. This issue is particularly relevant to the formation of nanocrystals. We examine the case of Au-catalyzed GaAs nanowires, which we grow in a transmission electron microscope. Our in situ observations show that atomic layers nucleate at the periphery of the interface between the nanowire and the catalyst droplet. From this starting location, the atomic step flows within a restricted area of hexagonal shape. At specific partial coverages, the monolayer configuration changes abruptly. A simple model based on the geometry of the system and its edge energies explains these observations. In particular, we observe an inversion of the step curvature which reveals that the effective energy per unit length of monolayer edge is much lower at the interface periphery than inside the catalyst droplet.

International audience; Ordered porous anodic alumina (PAA) templates are of great interest as they facilitate the future development of nanodevices. The present study focuses on the impact of substrates with different crystallographic orientations on the template's pore structure. Characteristics such as pore diameter, interpore distance, pore regularity, porosity, and circularity are calculated as a function of the anodization potential for three different Al crystal orientations. The presented experiments reveal that the different crystallographic orientations mainly impact the pore ordering, while other structural parameters, such as the pore diameter and interpore distance, are not significantly affected.