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International audience; This study compares the charging mechanisms, thermodynamics, lithium ion transport, and operando isothermal calorimetry in lithium-ion battery electrodes made of Ti2Nb2O9 microparticles or nanoparticles synthesized by solid-state or sol-gel methods, respectively. First, electrochemical testing showed that electrodes made of Ti2Nb2O9 nanoparticles exhibited larger specific capacity, smaller polarization, and better capacity retention at large currents than those made of Ti2Nb2O9 microparticles. Furthermore, potentiometric entropy measurements revealed that electrodes made of either Ti2Nb2O9 microparticles or nanoparticles showed similar thermodynamics behavior governed by lithium intercalation in solid solution, as confirmed by in situ XRD measurements. However, electrodes made of Ti2Nb2O9 nanoparticles featured smaller overpotential and faster lithium ion transport than those made of Ti2Nb2O9 microparticles. In fact, operando isothermal calorimetry revealed smaller instantaneous and time-averaged irreversible heat generation rates at electrodes made of Ti2Nb2O9 nanoparticles, highlighting their smaller resistive losses and larger electrical conductivity. Finally, the measured total heat generation over a charging/discharging cycle matched the measured net electrical energy loss. Overall, Ti2Nb2O9 nanoparticles synthesized by the novel sol-gel method displayed excellent cycling performance and reduced heat generation as a fast-charging lithium-ion battery anode material. These features present major advantages for actual battery systems including larger energy and power densities, simpler thermal management, and enhanced safety.

International audience; In this study, the epitaxial growth of co-evaporated Cu(In,Ga)Se2 films (CIGSe) onto GaP/Si(001) pseudo-substrates, where the GaP thin layer is epitaxially grown by Molecular Beam Epitaxy (MBE), is investigated. Extensive structural characterisation of epi-CIGSe is carried out via X-ray diffraction as well as transmission electron microscopy. Sturdy evidence of an epitaxial growth of CIGSe on (GaP/Si)(001) is observed, with the propagation of twins originating from the GaP/Si interface, through the CIGSe/GaP interface. This work aims at paving the way for future CIGSe/GaP/Si structures for the development of tandem solar cells with a c-Si bottom cell, and a GaP interfacial buffer layer for band edge engineering, allowing for the monolithic epitaxial growth of high quality CIGSe as a thin film top cell absorber.

International audience; Two new cubic perovskite oxides Ba3CoSb2O9 and Ba2SrCoSb2O9 were prepared and characterized. Ba3CoSb2O9 was prepared in polycrystalline form by high-pressure (HP) high-temperature treatment of the hexagonal 6H polytype of Ba3CoSb2O9. Polycrystalline samples of Ba2SrCoSb2O9 were obtained at ambient pressure by a solidstate reaction method. Combined Rietveld refinements of X-ray and neutron diffraction patterns indicated that HP Ba3CoSb2O9 and Ba2SrCoSb2O9 both crystallize in a Fm (3) over barm cubic double perovskite A(2)BB'O-6 structure with formulae Ba-2(Sb0.83Co0.17)(Co0.5Sb0.5)O-6 and (Ba1.33Sr0.67)Sb(Co0.7Sb0.3)O-6, respectively. Electron diffraction results obtained for Ba2SrCoSb2O9 showed no sign of additional periodicity. Weiss temperatures extracted from high-temperature magnetic susceptibility data were. theta approximate to -113 K and -118 K for HP Ba3CoSb2O9 and Ba2SrCoSb2O9, respectively. HP Ba3CoSb2O9 displays a weak ZFC-FC magnetic irreversibilty below 8 K. Ba2SrCoSb2O9 exhibits a spin freezing at T-f approximate to 6 K, and mu SR and Sb-121 NMR data revealed a magnetic transition towards a disordered ground state.

International audience; We propose to explore tandem junctions associating single crystalline silicon bottom cell (Eg = 1.12 eV) and wide bandgap (1.7 eV) CIGS top cell, using GaP intermediate layer. Our purpose is to grow CIGS films under epitaxial conditions on GaP to improve the top cell efficiency, thanks to a reduction of the structural defects density detrimental for the cell performance, so that CIGS-Si tandem cells can emerge as cost competitive for the next generation of PV modules. Epitaxy of CIGS (CIGSe or CIGSu) on GaP/Si platform is demonstrated and preliminary results on AZO/ZnMgO/CdS/CIGS cells on Mo/Glass and GaP/Si are reported.

The K

Designing and synthesising new metastable compounds is a major challenge of today’s material science. While exploration of metastable oxides has seen decades-long advancement thanks to the topochemical deintercalation of oxygen as recently spotlighted with the discovery of nickelate superconductor, such unique synthetic pathway has not yet been found for chalcogenide compounds. Here we combine an original soft chemistry approach, structure prediction calculations and advanced electron microscopy techniques to demonstrate the topochemical deintercalation/reintercalation of sulfur in a layered oxychalcogenide leading to the design of novel metastable phases. We demonstrate that La2O2S2 may react with monovalent metals to produce sulfur-deintercalated metastable phases La2O2S1.5 and oA-La2O2S whose lamellar structures were predicted thanks to an evolutionary structure-prediction algorithm. This study paves the way to unexplored topochemistry of mobile chalcogen anions., Great progress has been made in topochemistry of mobile oxygen anions, but metastable compounds have not yet been achieved by deintercalation of sulfur anions. Here, the authors prepare metastable oxychalcogenide phases by taking advantage of redox-reactive sulfur dimers embedded in a layered oxysulfide.

Several new materials with four structure-types (e.g., Cu

Cu2O@CuO core-shell nanoparticles were synthesized via a facile precipitation-thermal oxidation method consisting in the preparation of Cu2O nanoparticles in solution followed by a post-treatment at 300 °C, 350 °C or 400 °C in air. From HRTEM micrographs, it was evidenced that Cu2O particles were uniformly covered by a 5 nm thick CuO layer to form a core-shell structure. This shell may be viewed as a passivating layer that overcomes the natural chemical instability of Cu2O towards electrolytes for instance. The as-obtained Cu2O@CuO nanoparticles were characterized by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. Both techniques concluded to the p-type conductivity of the Cu2O@CuO hetero-structures. These nanoparticles were then deposited as a film on a FTO glass by screen printing and used after sintering as photocathodes for p-DSSCs. Photovoltaic activity was confirmed with DPP-NDI dye as sensitizer and tris(4,4′-ditert-butyl-2,2′-bipyridine)cobalt(III/II) as redox mediator.

The control of the surface area enhancement and the ordering of the mesoporous photoanode is one of the key parameters to overcome the current limits of performance of dye sensitized solar cells (DSSCs). These parameters are expected to improve both the concentration of adsorbed dye molecules on the photoanode and the charge collection. In this paper, reactive magnetron sputtering at glancing angle is employed to synthesize nanostructured TiO2 thin films. A post-annealing treatment under an ambient atmosphere at 773 K allows recrystallization of the films to form individual single crystal-like anatase nanocolumns, as shown on a reference structure constituted by well-separated slanted nanocolumns. Even if the best cells provide an open circuit voltage of 0.8 V, a fill factor of 77%, and a short circuit current density of 4.6 mA/cm2 (JSC) and permit to reach an overall efficiency up to 2.6%, it does not yet reach the performances of the reference TiO2 nanoparticle (NP)-based cell. This is explained by a po...

International audience; Titanium dioxide is a metal oxide used as a white pigment in many food categories, including confectionery. Due to differences in the mass fraction of nanoparticles contained in TiO2, the estimated intakes of TiO2 nanoparticles differ by a factor of 10 in the literature. To resolve this problem, a better estimation of the mass of nanoparticles present in food products is needed. In this study, we focused our efforts on chewing gum, which is one of the food products contributing most to the intake of TiO2. The coatings of four kinds of chewing gum, where the presence of TiO2 was confirmed by Raman spectroscopy, were extracted in aqueous phases. The extracts were analysed by transmission electron microscopy (TEM), X-ray diffraction, Fourier Transform Raman spectroscopy, and inductively coupled plasma atomic emission spectroscopy (ICP-AES) to establish their chemical composition, crystallinity and size distribution. The coatings of the four chewing gums differ chemically from each other, and more specifically the amount of TiO2 varies from one coating to another. TiO2 particles constitute the entire coating of some chewing gums, whereas for others, TiO2 particles are embedded in an organic matrix and/or mixed with minerals like calcium carbonate, talc, or magnesium silicate. We found 1.1 +/- 0.3 to 17.3 +/- 0.9 mg TiO2 particles per piece of chewing gum, with a mean diameter of 135 +/- 42 nm. TiO2 nanoparticles account for 19 +/- 4% of all particles, which represents a mass fraction of 4.2 +/- 0.1% on average. The intake of nanoparticles is thus highly dependent on the kind of chewing gum, with an estimated range extending from 0.04 +/- 0.01 to 0.81 +/- 0.04 mg of nano-TiO2 per piece of chewing gum. These data should serve to refine the exposure scenario.

The corrosion of silver upon exposure to atomic oxygen is a unique effect reported in the 1980s and was highly studied to overcome the fast degradation of space shuttles in low earth orbit. In this work, we explored the conversion mechanisms of nanostructures from solid silver to nanoporous silver oxide upon exposure to radiofrequency air plasma. A broad panel of silver nanostructures with various shapes, sizes, and morphologies were considered to carefully examine the different stages of the oxidation process which evolve according to the considered model-system (e.g., nanosphere, nanowire, nanocube, or nanotriangle). Through a set of time-lapse studies and very specific experiments, we explained the generation of nanoporosity according to a mechanism based on two effects: (i) the high strain in the oxide shell generated as a consequence to the oxidation process and amplified by the bombardment of the material with the energetic species present in the radio frequency air plasma and (ii) the Kirkendall ef...

Recent papers have demonstrated that the growth of carbon nanotubes (CNTs) by plasma enhanced chemical vapor deposition (PECVD) was possible using nanocomposite nickel/carbon (nc-Ni/C) thin films as catalysts. In this study, the growth of CNTs by PECVD in H 2 /C 2 H 4 atmosphere was achieved using nc-Ni/C thin films deposited by a hybrid plasma process combining the sputtering of a nickel target and the deposition of hydrocarbon by PECVD using Ar/CH 4 atmosphere. In order to identify the most favorable conditions to obtain dense CNTs arrays using nc-Ni/C thin films, the Ni content in the catalyst as well as the growth conditions of the CNTs were varied. Films containing 40, 55 and 65 at.% of Ni were selected for this study. The growth temperature of the CNTs was varied between 500 and 700 °C whereas the electrical power applied to the PECVD source was tuned from 30 to 50 W. Scanning electron microscopy and Raman spectroscopy were employed to probe the morphology and the structure of the CNT's. Depending on the chemical composition of the nc-Ni/C thin films, different trends were observed. No CNTs were obtained neither for the highest nickel content (i.e. %Ni = 65 at.%) nor for the lowest growth temperature (i.e. 500 °C). On the other hand, for temperatures exceeding 500 °C, while a high power on the PECVD source (i.e. 50 W) was found to be necessary to obtain CNTs in the case of films with a moderate Ni content (i.e. %Ni = 55 at.%), a lower power (i.e. 30 W) was sufficient for the film with the lowest Ni content (i.e. %Ni = 40 at.%). This difference in behavior was attributed to the differences in microstructure of nc-Ni/C thin films which is directly related to their chemical composition.

Hollow bimetallic nanostructures are of great importance for various applications. Understanding the fundamental mechanisms occurring during the synthesis of such nanomaterials by wet chemistry remains very challenging. This Article reports a mechanistic study on the galvanic replacement reaction between planar arrays of silver nanowires grown site-specifically on tall silicon nanogratings and HAuCl4 in lack of any stabilizing or capping agent, which might complicate and alter the conversion process of silver nanowires into silver–gold nanotubes. The direct contact of the silver nanowires with the substrate is found to modify the reaction as compared to nanowires in suspension. We show that when using diluted HAuCl4, AgCl nanoclusters precipitate on the surface during the process resulting in an increased surface roughness of the nanotubes. Overcoming this drawback requires saturating the HAuCl4 solution with NaCl; this allows distributing the anodic and cathodic sites over the surface of the nano-objects...

Optical and electrical characteristics of solid materials are well-known to be intimately related to the presence of intrinsic or extrinsic defects. Hence, the control of defects in semiconductors is of great importance to achieve specific properties, for example, transparency and conductivity. Herein, a facile and controllable reduction method for modulating the defects is proposed and used for the case of p-type delafossite CuCrO2 nanoparticles. The optical absorption in the infrared region of the CuCrO2 material can then be fine-tuned via the continuous reduction of nonstoichiometric Cu(II), naturally stabilized in small amounts. This reduction modifies the concentration of positive charge carriers in the material, and thus the conductive and reflective properties, as well as the flat band potential. Indeed, this controllable reduction methodology provides a novel strategy to modulate the (opto-) electronic characteristics of semiconductors.

Titanium and silver atoms were magnetron-sputtered either onto pentaerythritol ethoxylate (PEEL) or 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIMTFSI) ionic liquid (IL), and the formation of nanoparticles (NPs) is discussed based on the chemical interaction between the metal atoms and the host liquid. In the case of PEEL, our data reveal that titanium atoms sputtered in low-pressure argon plasma first form a film over the liquid surface. However, the latter dissolves as the film gets oxidized when vented to the air; asymmetric and faceted titanium dioxide NPs are finally obtained as if they were originating from a dismantled polycrystalline thin film. In the case of silver sputtered on PEEL, a film forms and solvation never occurs even after exposing the sample to air because the oxidation of silver is thermodynamically much less favorable than titanium. Quantum-chemical calculations confirm that the chemical interaction of TiO2 with PEEL molecules is favored as compared to metallic...

The cubic phase of pure zirconia (ZrO2) is stabilized in dense thin films through a controlled introduction of oxygen vacancies (O defects) by cold-plasma-based sputtering deposition. Here, we show that the cubic crystals present at the film/substrate interface near-region exhibit fast ionic transport, which is superior to what is obtained with similar yttrium-stabilized cubic zirconia thin films.

Carbon spheres of nanometric dimension are known since the first studies on the synthesis of fullerenes. Their shape originates from the curvature of a carbon sheet similar to fullerenes, but with numerous graphitic rings that regulate the inside structure and the formation of open edges at the surface. This paper focuses on the structural and electronic characterization of carbon spheres obtained from a chemical vapor deposition synthesis process. Two different sets of samples are analyzed in detail, in particular, electron microscopies and Raman spectroscopy help understanding the morphology and the graphitic-sp2 arrangement of the carbon atoms in the architectures. In addition, the iron catalyst used during the reaction process confers the carbon spheres a ferromagnetic response at room temperature. Therefore, both the structural properties of the samples and the active contribution of iron mark the difference in the measured photoresponse as well as in the electrochemical behavior. The X-ray photoelectron spectroscopy study addresses these points by giving information on the composition and the iron chemical state in the assembly. The collected results underline the advantages offered by this nanomaterial for sustainable applications.

Carbon spheres of nanometric dimension are known since the first studies on the synthesis of fullerenes. Their shape originates from the curvature of a carbon sheet similar to fullerenes, but with numerous graphitic rings that regulate the inside structure and the formation of open edges at the surface. This paper focuses on the structural and electronic characterization of carbon spheres obtained from a targeted chemical vapor deposition synthesis process. Two different set of samples are analyzed in detail, in particular, the electron microscopies and Raman spectroscopy help understanding the morphology and the graphitic-sp2 arrangement of the carbon atoms in the architectures. In addition, the iron catalyst used during the reaction process confers the carbon spheres a ferromagnetic response at room temperature. Therefore, both the structural properties of the samples and the active contribution of iron mark the difference in the measured photoresponse as well as in the electrochemical behavior. The X-ray photoelectron spectroscopy study addresses these points by giving information on the composition and the iron chemical state in the assembly. The collected results underline the advantages offered by this synthesis route and the properties of the carbon spheres as active nanomaterial for sustainable applications.

In this work, we report on the development of a novel approach based on three different plasma-based processes (i.e., plasma polymerization, magnetron sputtering, and plasma etching) to fabricate nanostructured polymer thin films. Our strategy involves at first the formation of nitrogen containing plasma polymer film subsequently covered by silver nanoparticles, serving as a hard etching mask, using magnetron sputtering. Then, the exposition of the material to a complex mixture of highly reactive radicals, ions, and photons results in the structuring at the nanoscale of the functionalized plasma polymer films. It has been demonstrated that the dimension, the shape (e.g,. nano-dome, nano-cone, nano-valley, inter-connected porous network, …) and the chemical composition of the nano-objects can be tailored by adjusting the plasma parameters in each step of our overall procedure.

Titanium dioxide is a metal oxide used as a white pigment in many food categories, including confectionery. Due to differences in the mass fraction of nanoparticles contained in TiO

International audience; The original goal of our study is to synthesize by co-evaporation the phase that could be formed at the interface between polycrystalline p-Cu(In,Ga)Se2 treated with KF and n-CdS. Hence, a new buffer layer, CdIn2S4 (C24), deposited by co-evaporation is presented for the use in thin film solar cells, exhibiting device efficiencies as high as 16.2%, comparable to that obtained on a reference standard CdS-buffered device. The physico-chemical and optical properties of close to stoichiometry 400 nm-thick films of C24 show similar properties to what has been reported in the literature for single crystals. The layer stack used for solar cells is investigated by transmission electron microscopy, showing the formation of an ultrathin Cd-deficient C24 layer at the CIGSe/C24 interface, while a clear lattice match is observed at the C24/ZnO interface. Advanced electrical characterizations of the devices suggest that the output voltage and fill factor of the solar cells based on Cu(In,Ga)Se2/(PVD)C24 are limited by tunneling-enhanced recombination through extended band tail states. These results open new routes to explain the superiority of wet processes used for the junction formation compared to vacuum-based approaches.

International audience; Drug delivery systems are proposed for the in situ controlled delivery of therapeutic molecules in the scope of tissue engineering. We propose herein silica nanofibers as carriers for the loading and release of bioactive proteins. The influence of pH, time and concentration on the amount of adsorbed proteins was studied. The interactions allowing loading were then studied by means of electron microscopy, zeta potential measurements, electron energy loss spectroscopy and attenuated total reflectance Fourier transform infrared analysis. Release profiles were determined and biological activities were enzymatically assessed. The first part of the work was carried out with lysozyme as a model protein, and then bioactive growth factors TGF-b1 and GDF-5 were used because their significance in human adipose stromal cell differentiation towards intervertebral disc nucleopulpocytes was previously assessed. It is demonstrated that protein–silica nanofiber interactions are mainly driven by hydrogen bonds and local electrostatic interactions. The present data thus provide a better understanding of the adsorption phenomenon involved, as well as a method to control protein adsorption and release. It is worth pointing out that the kinetic release of growth factors, up to 28 days, and their biological activity maintenance seem to be compatible with intervertebral disc regenerative medicine.

Recent results have revealed that the low deposition time issue of chemical bath deposited (CBD) Zn(S,O,OH) buffer layer used in Cu(In,Ga)Se 2 (CIGSe) solar cells could be resolved using H 2 O 2 as an additive in the chemical bath solution. Although the use of this additive does not hinder the electrical properties of the resulting Zn(S,O,OH)-buffered CIGSe solar cells, the impact of H 2 O 2 on the Zn(S,O,OH) properties remains unclear. The present contribution aims at determining the chemical composition and the microstructure of Zn(S,O,OH) film deposited by CBD using the alternative deposition bath containing the standard zinc sulfate, thiourea, ammonia but also H 2 O 2 additive. Both X-ray photoemission spectroscopy and energy dispersive X-ray spectroscopy analyses reveal higher sulfur content in alternatively deposited Zn(S,O,OH), since the first step growth of the layer. According to transmission electron microscopy analyses, another consequence of the higher deposition rate achieved when adding H 2 O 2 in the bath is the modification of the absorber/buffer interface. This could be explained by the enhancement of the cluster growth mechanism of the layer.

Titanium dioxide (TiO2) is a transition metal oxide widely used as a white pigment in various applications, including food. Due to the classification of TiO2 nanoparticles by the International Agency for Research on Cancer as potentially harmful for humans by inhalation, the presence of nanoparticles in food products needed to be confirmed by a set of independent studies. Seven samples of food-grade TiO2 (E171) were extensively characterised for their size distribution, crystallinity and surface properties by the currently recommended methods. All investigated E171 samples contained a fraction of nanoparticles, however, below the threshold defining the labelling of nanomaterial. On the basis of these results and a statistical analysis, E171 food-grade TiO2 totally differs from the reference material P25, confirming the few published data on this kind of particle. Therefore, the reference material P25 does not appear to be the most suitable model to study the fate of food-grade TiO2 in the gastrointestinal tract. The criteria currently to obtain a representative food-grade sample of TiO2 are the following: (1) crystalline-phase anatase, (2) a powder with an isoelectric point very close to 4.1, (3) a fraction of nanoparticles comprised between 15% and 45%, and (4) a low specific surface area around 10m(2)g(-1).

International audience; Over the last few years, a broad panel of carbon materials was proposed for sensing applications. Among these materials, nanoporous carbon (np-C) is of particular interest due to its high specific surface area and low fabrication cost. In this contribution, the synthesis of np-C thin films using an approach combining the growth of copper/carbon nanocomposite thin films by co-sputtering followed by a selective wet etching of copper in nitric acid is studied. By adjusting the deposition conditions (e.g., powers applied to the sputtering targets, deposition temperature) of the nanocomposite thin films, it is shown that the pore size and the structure of the carbon skeleton can be modified. Furthermore, the possibility of integrating such nanoporous materials in field effect transistors for sensing application is also demonstrated.

International audience

Controlling the porosity, the shape, and the morphology of Kirkendall hollow nanostructures is the key factor to tune the properties of these tailor-made nanomaterials which allow in turn broadening their applications. It is shown that by applying a continuous oxidation to copper nanowires following a temperature ramp protocol, one can synthesize cuprous oxide nanotubes containing periodic copper nanoparticles. A further oxidation of such nanoobjects allows obtaining cupric oxide nanotubes with a bamboo-like structure. On the other hand, by applying a sequential oxidation and reduction reactions to copper nanowires, one can synthesize hollow nanoobjects with complex shapes and morphologies that cannot be obtained using the Kirkendall effect alone, such as necklace-like cuprous oxide nanotubes, periodic solid copper nanoparticles or hollow cuprous oxide nanospheres interconnected with single crystal cuprous oxide nanorods, and aligned and periodic hollow nanospheres embedded in a cuprous oxide nanotube. The strategy demonstrated in this study opens new avenues for the engineering of hollow nanostructures with potential applications in gas sensing, catalysis, and energy storage.

International audience; Sputtered molybdenum (Mo) thin film is commonly used as back contact in CuIn1 − xGaxSe2 (CIGSe)-based solar cell. However, when grown directly on soda-lime glass (SLG) substrate, such Mo layer does not only act as electrical contact but also as tuner for the Na availability during CIGSe growth. Control of the diffusion of sodium from SLG to CIGSe is possible by adjusting the Mo intergrain properties. Samples were prepared by direct current magnetron sputtering with argon pressure of 0.3, 1.2 and 2.0 Pa. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) have been used to characterize intergrain areas; it is observed that they are amorphous and their width increases from few tenths to several nanometers with the Ar sputtering pressure. Low loss region EELS spectra acquired within these intergrain zones have been compared to reference spectra acquired in the same experimental conditions on well known compounds. The presence of sodium within the intergrain areas, most probably in sodium molybdate form and intercalated in molybdenum trioxide, has been confirmed.

In this work, vertically oriented multiwalled carbon nanotubes (MWCNTs) were synthesized at 600 °C by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) on a silicon substrate from Ni catalyst nanoparticles prepared by electrodeposition. Then CNTs were coated with aluminum nitride (AlN) by Metal Organic PECVD (MO-PECVD). The objective of this work is to obtain new nano-composite film based on AlN thin film containing oriented CNTs expected to enhance the thermal transfer compared to a single AlN layer. The final issue is the realization of thermal evacuators for microelectronic devices. Cauliflower-like structures of hexagonal AlN forming a compact thin film well coating vertically aligned CNTs were obtained and structurally characterized.

We have taken advantage of the native surface roughness and the iron content of AISI-316 stainless steel to grow multiwalled carbon nanotubes (MWCNTs) by chemical vapour deposition without the addition of an external catalyst. The structural and electronic properties of the synthesized carbon nanostructures have been investigated by a range of electron microscopy and spectroscopy techniques. The results show the good quality and the high graphitization degree of the synthesized MWCNTs. Through energy-loss spectroscopy we found that the electronic properties of these nanostructures are markedly different from those of highly oriented pyrolytic graphite (HOPG). Notably, a broadening of the π-plasmon peak in the case of MWCNTs is evident. In addition, a photocurrent was measured when MWCNTs were airbrushed onto a silicon substrate. External quantum efficiency (EQE) and photocurrent values were reported both in planar and in top-down geometry of the device. Marked differences in the line shapes and intensities were found for the two configurations, suggesting that two different mechanisms of photocurrent generation and charge collection are in operation. From this comparison, we are able to conclude that the silicon substrate plays an important role in the production of electron–hole pairs.

The deposition of nickel/amorphous carbon (Ni/a-C) films by a hybrid plasma process combining magnetron sputtering of a Ni target and plasma enhanced chemical vapor deposition using methane gas has been investigated. The formation of nickel nanowires encapsulated by a-C matrix has been demonstrated by transmission electron microscopy (TEM). The obtained nanowires array can be easily dispersed or can be simply converted to a Ni-filled CNT array by annealing at 350 °C as confirmed by TEM analysis. The developed fabrication method of Ni-filled CNT array is a low temperature technique compatible with substrates of low melting point.

The present study aims at investigating the influence of Ar sputtering gas pressure on the properties of molybdenum back contact (deposited on soda-lime glass) and consequences on co-evaporated Cu(In,Ga)Se2 (CIGSe) absorber layer and related solar cell. Films 300 nm thick have been grown with argon pressure between 0·75 and 11·25 mTorr; these films have been characterized by several techniques showing that the increase of the sputtering pressure yields wider amorphous areas, containing oxygen and sodium, between the molybdenum grains, thus higher sheet resistance. The volume ratio of these amorphous areas is referenced to as “porosity”. The structural and morphological properties of co-evaporated CIGSe have not been reliably observed influenced by the molybdenum porosity; the only noticeable change is the sodium content of the absorber, which increases with the porosity of the back contact. The impact of the amount of sodium on the device performance has been observed to be very important. On the one hand, as already reported, sodium is beneficial for the open-circuit voltage. On the other hand, a too high amount of sodium is detrimental for the fill factor (hindered shunt resistance), thus the cell efficiency; this latter observation is interpreted as a change in the grain boundary electrical properties. Copyright © 2011 John Wiley & Sons, Ltd.

International audience; Multi wall carbon nanotubes (MWCNTs) were grown on a stainless steel (SS) sheet by chemical vapor deposition without the addition of external metal catalyst. We found that the key for highly efficient growth includes the nanoscale roughness of the SS surface, as shown by scanning tunneling microscopy, that acts as catalyst/template in the nanotube formation. Raman spectroscopy and electron microscopy were used to check the nature and quality of the synthesized nanotubes. We conclude that stainless steel favors a base-growth mechanism. Transmission electron energy loss spectroscopy performed on single metallic particles found inside the nanotubes clarified the atomic nature of the catalytic particles supplied by the steel. Only unoxidized iron was found and no traces of nickel and chromium were detected. In addition, the SS substrate has been used for a second growth process after carefully removing the synthesized CNTs, proving that a continuous production of CNTs from the same substrate is achievable.

Technetium is a long-lived product of nuclear fission which commonly exhibits two oxidation states (IV and VII). Siderite (FeCO3), suspected to be formed as a container corrosion product in geological radioactive waste repositories, may concentrate by coprecipitation more than 90% of technetium-99, present as Tc(IV) in surrounding aqueous fluids. X-ray diffraction and transmission electron microscopy measurements indicate that technetium can be incorporated within the siderite structure, even if we note that technetium-bearing green rust phase may also be observed. These results suggest that siderite might play a beneficial role in limiting Tc diffusion to the next environment of nuclear waste repositories.

Nanoporous materials are of great importance for a broad range of applications including catalysis, optical sensors and water filtration. Although several approaches already exist for the creation of nanoporous materials, the race for the development of versatile methods, more suitable for the nanoelectronics industry, is still ongoing. In this communication we report for the first time on the possibility of generating nanoporosity in silver nanocolumns using a dry approach based on the oxidation of silver by direct exposure to a commercially available radio-frequency air plasma. The silver nanocolumns are created by glancing angle deposition using magnetron sputtering of a silver target in pure argon plasma. We show that upon exposure to the rf air plasma, the nanocolumns transform from solid silver into nanoporous silver oxide. We further show that by tuning the plasma pressure and the exposure duration, the oxidation process can be finely adjusted allowing for precisely controlling the morphology and the nanoporosity of the silver oxide nanocolumns. The generation of porosity within the silver nanocolumns is explained according to a cracking-induced oxidation mechanism based on two repeated events occurring alternately during the oxidation process: (i) oxidation of silver upon exposure to the air plasma and (ii) generation of nanocracks and blisters within the oxide layer due to the high internal stress generated within the material during oxidation.

In p-type dye-sensitized solar cells (p-DSSCs), NiO is the most commonly used p-type semiconductor. Nevertheless, because of the drawbacks of NiO, much effort has been made to search for suitable substitutes. Herein, three different morphologies of CuO nanomaterials were used to prepare photocathodes for p-DSSCs, which have a deeper valence band and a higher dielectric constant compared to that of NiO. We observe that CuO is unstable in the presence of iodide/triiodide electrolyte, while cobalt complexes with bipyridine ligands are more suitable redox shuttles. We also note that the average transport time in CuO is shorter than that in NiO. Finally, the deep absorbance of CuO in the visible range indicates that suitable sensitizers for the CuO p-DSSC must exhibit high extinction coefficient and absorption bands located in the lower energy part of the solar spectrum (>600 nm) to be exploitable. In this case such CuO based photocathodes represent valuable systems to exploit the near-infrared (NIR) region.

p-Type dye-sensitized solar cells (p-DSSCs) have recently become a major research focus because coupling with n-type DSSCs yields highly efficient tandem DSSCs. Indeed many delafossite-like compounds appear as promising candidates for p-DSSCs due to their deep valence band position and high hole mobility. In this paper, the synthesis of CuBO2 was attempted by a facile sol–gel methodology. Then, the as-obtained particles were used to prepare photocathodes for p-DSSCs with DPP-NDI dye as sensitizer and tris(4,4′-di-tert-butyl-2,2′-bipyridine)cobalt(III/II) as redox mediator. Due to the deeper valence band position compared with classical NiO photocathode, the “CuBO2” based p-DSSC presents an open-circuit photovoltage (Voc) of 453 mV, which is 150 mV higher than that of NiO in the same conditions. The results show that “CuBO2” is a potential alternative for NiO in p-DSSCs.

Owing to its high technological importance for optoelectronics, zinc oxide received much attention. In particular, the role of defects on its physical properties has been extensively studied as well as their thermodynamical stability. In particular, a large concentration of Zn vacancies in ZnO bulk materials is so far considered highly unstable. Here we report that the thermal decomposition of zinc peroxide produces wurtzite-type ZnO nanoparticles with an extraordinary large amount of zinc vacancies (>15%). These Zn vacancies segregate at the surface of the nanoparticles, as confirmed by ab initio calculations, to form a pseudo core-shell structure made of a dense ZnO sphere coated by a Zn free oxo-hydroxide mono layer. In others terms, oxygen terminated surfaces are privileged over zinc-terminated surfaces for passivation reasons what accounts for the Zn off-stoichiometry observed in ultra-fine powdered samples. Such Zn-deficient Zn1-xO nanoparticles exhibit an unprecedented photoluminescence signature suggesting that the core-shell-like edifice drastically influences the electronic structure of ZnO. This nanostructuration could be at the origin of the recent stabilisation of p-type charge carriers in nitrogen-doped ZnO nanoparticles.

In this work, we report on the Kirkendall-induced hollowing process occurring upon thermal oxidation of gold–copper (Au–Cu) alloy nanowires and nanodots. Contrary to elemental metals, the oxidation reaction results in the formation of gold nanostructures trapped inside hollow copper oxide nanoshells. We particularly focus on the thermally activated reshaping mechanism of the gold phase forming the core. Using scanning transmission electron microscopy coupled to energy dispersive X-ray spectroscopy mapping, we show that such a reshaping is a consequence to the reorganization of gold at the atomic level. The gold nanostructures forming the core were found to be strongly dependent on the chemical composition of the alloy and the oxidation temperature. By selecting the appropriate annealing conditions (i.e., duration, temperature), one can easily synthesize various heteronanostructures: wire-in-tube, yolk–shell, oxide nanotubes embedding or decorated by Au nanospheres. The advanced understanding of the Kirken...

Polypyrrole, a conductive polymer, was used as support of noble metals, namely, copper and palladium, for application in heterogeneous catalysis. Catalysts were characterized by TEM coupled with EDS and XRD. Their activity and selectivity were determined in the reduction of nitrate and intermediate nitrite in water under 1 bar of hydrogen and at room temperature. In nitrite reduction, these novel catalysts demonstrated a better activity and a higher selectivity towards nitrogen formation than their Pd/Al2O3 counterpart. On the other hand, the bimetallic catalyst tested for nitrate reduction showed an activity similar to the one of a classical Pd–Cu/Al2O3 catalyst, but no intermediate nitrite was observed.

Understanding the dealloying mechanisms of gold-based alloy thin films resulting in the formation of nanoporous gold with a sponge-like structure is essential for the future design and integration of this novel class of material in practical devices. Here we report on the synthesis of nanoporous gold thin films using a free-corrosion approach in nitric acid applied to cosputtered Au-Cu thin films. A relationship is established between the as-grown Au-Cu film characteristics (i.e., composition, morphology, and structure) and the porosity of the sponge-like gold thin films. We further demonstrate that the dealloying approach can be applied to nonhomogenous Au-Cu alloy thin films consisting of periodic and alternate Au-rich/Au-poor nanolayers. In such a case, however, the dealloying process is found to be altered and unusual etching stages arise. Thanks to defects and column boundaries playing the role of channels, the nitric acid is found to quickly penetrate within the films and then laterally (i.e., parallel to the film surface) attacks the nanolayers rather than perpendicularly. As a consequence to this anisotropic etching, the Au-poor layers are etched preferentially and transform into Au pillars holding the Au-rich layers and preventing them against collapsing. A further exposure to nitric acid results in the collapsing of the Au-rich layers accompanied by a transition from a multilayered to a sponge-like structure. A scenario, supported by experimental observations, is further proposed to provide a detailed explanation of the fundamental mechanisms occurring during the dealloying process of films with a multilayered structure.