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In this study, iron oxide cocatalysts were deposited on the surface of ZnO nanostructures by a simple “drop, evaporation, calcination” method. Different deposition concentrations were studied, allowing to extend the photocatalyst absorption spectral range from UV to visible light, improving the photocatalytic efficiency under natural sunlight. An optimal deposition concentration of 0.06% molar percentage of iron against zinc led to improve by 11% the Methyl Orange (MO) photocatalytic degradation after 5 h under natural sunlight. No iron leaching was detected by ICP-MS analysis after the water purification by photocatalysis. By studying the lifetime stability of the optimal sample under a powerful UV light source, no losses of photocatalytic efficiency were recorded after several degradation cycles. Nevertheless, under this powerful light source, photocorrosion damages were observed with two antagonistic effects: (1) no photocorrosion effect for the ZnO regions covered by iron oxide and (2) ZnO photocorrosion and an acceleration of the dissolution of the ZnO nanostructures in uncovered regions. Thus, we assume the electron/hole delocalisation, which is responsible of the photocatalytic activity improvement, is also the reason justifying the ZnO photocorrosion acceleration of uncovered part. The photocorrosion phenomena was observed only under the powerful UV light source, not under natural sunlight.

ZnO nanowire (NW) arrays were successfully grown on pre-seeded indium Tin oxide (ITO)-coated glass substrate using hydrothermal synthesis. Herein, the effects of ZnO seed layer density on the performance of ZnO NWs were investigated in details. The orientation and the dimension of ZnO NWs were found to depend on seeded substrate density as shown by scanning electron microscopy (SEM) micrographs which revealed that the typical morphology with the most uniform size can be obtained. From the X-ray diffraction (XRD) measurement, it can be seen that hexagonal c -axis oriented NWs were grown. The resonant Raman scattering was also investigated in details. It confirmed the wurtzite structure of the NW arrays and expected for good optical properties. The optical band gaps of synthesized ZnO NWs were found to decrease comparing to bulk ZnO and as function of seed layer. The photoluminescence (PL) spectra at room temperature have shown strong UV excitonic emission and weak deep-level emissions which reveal that the as-grown NW arrays have good optical properties with limited deep-level defects.

Structures of the two-dimensional atomic nuclei on ZnO (0001)-Zn and ( 000 1 ¯ )-O polar surfaces were studied by first principles density functional theory. The polarity-dependent nucleation dynamics was investigated by simulating two-dimensional (2D) nuclei consisting of 1-8 ZnO monomers on both polar surfaces. According to total energy calculations, average binding energy per ZnO monomer of the surface nuclei was analyzed to investigate if the nucleation and growth will proceed reasonably in physics. We found nucleation on (0001)-Zn surface was easier than that on ( 000 1 ¯ )-O surface. By using atomistic thermodynamics analysis, we calculated the Gibbs free energy of formation of these nuclei and made a comparison between the two polar surfaces. On (0001)-Zn surface, the critical Gibbs free energy of formation is much lower than that on ( 000 1 ¯ )-O surface under the same supersaturation, which leads to a much larger ZnO growth rate and rougher morphology, in accordance with experimental results. In addition, energetic analysis of nucleation at real thermodynamic conditions was achieved by introducing the temperature- and pressure-dependent chemical potentials of ZnO precursors.

Developing and designing smart civil engineering materials for environmental depollution in our daily life is a major issue. ZnO nanostructures implemented onto civil engineering material surfaces by low cost hydrothermal growth could be one of the most promising solutions, and already showed a good water purification efficiency by photocatalysis under UV light. Nevertheless, there are two main factors to work out in order to simplify and intensify the photocatalyst production on engineering materials. The first one is the reduction of the growth time. The second one is the use of sunlight, which is the most abundant, clean, and renewable light source available. However, reducing the growth time might have an impact on the photocatalytic efficiency due to the surface/volume ratio modification. In this work, a short and efficient hydrothermal synthesis (2 h or 1 h 30 min vs 4 h) was used to grow ZnO nanostructures directly on non-conventional substrates such as tiling and concrete, demonstrating an excellent photocatalytic activity for organic pollutant degradation in water under natural sunlight, even during cloudy days. Decreasing the growth time showed no significant influence on tiling samples and even increased their photocatalytic efficiency until the optimal value obtained with a growth time of 2 h. A strong impact of the shorter growth time was observed on concrete samples, as reducing the growth time leads to complex ZnO nanosheet structures with a lower gap value (3.11 eV for 1 h 30 min against 3.17 eV for 4 h) due to a possible influence of the surface pH value and the complex chemical composition of concrete.

This paper presents a biophysical method to characterize single bacterium in water by using an on-chip optofluidic immersion refractometer. Water safety is a major factor in the well-being of people, but the presence of bacteria such as Escherichia coli (E. coli), bacillus subtilis, Shigella flexneri and vibrio cholera in drinking water can lead to infectious diseases such as typhoid fever. Hence, it is crucial to detect and identify bacteria to prevent bacterial outbreaks. In this paper, an optofluidic immersion refractometer is developed to measure three biophysical parameters, i.e. size, shape and refractive index. The refractive index of a single bacterium is measured in high sensitivity of 0.005 RIU. This system is an innovative method to allow on-site real-time detection of single bacterium in water. It significantly reduces the amount of detection time and do not require trained personnel or additional chemical and biological reagents. © 2014 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of Eurosensors 2014.

International audience; Wereport in this work the fabrication of ZnO nanowires and nano-pillars by electrodeposition using three types of micro- and nano-structured templates. First, ZnO nanowires were synthesized in a nanoporous polycarbonate template and their morphology and monocrystalline structure were checked by conventional transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) techniques. The optical properties of the monocrystalline ZnO nanowires were also studied by measuring the photo-fluorescence spectra of the sample. Then, the micro-structured template was made by optical lithography and the electrodeposited ZnO micro-rods were analysed by scanning electron microscopy (SEM) imaging and X-ray diffraction (XRD). Finally, UV-nanoimprint templates were used for the fabrication of regular ZnO nano-pillar array. SEM images showed quite homogenous ZnO nano-pillar array on which the collective I–V characteristic has been carried out in order to determine the nature of the Au/ZnO contact. SEM images also revealed an effect of size increase of the ZnO microrods and nano-pillars with respect to that of the PMMA template. XRD patterns showed the hexagonal Wurtzite crystalline structure with cell parameters slightly larger than the literature ones.

International audience; Zinc oxide thin films were electrodeposited on different substrates. Electrodeposition was performed with hydrogen peroxide, as hydroxide ions source, at −1.5 V versus mercurial sulfate electrode during one hour, and a temperature maintained at 70 °C. The resulting thin films have a good crystallinity and a high c-axis orientation, and the unit cell parameters determined by X-ray diffraction experiment are a=0.326 nm and c=0.523 nm, respectively. Microstructure studies using scanning electron microscopy and atomic force microscopy show a good homogeneity of the film and a roughness around 22 nm. Optical properties were studied with Raman spectroscopy and photoluminescence spectroscopy. Optical properties of the films revealed a low defect emission in photoluminescence spectra. The E2 vibration mode for ZnO was observed near 439 cm−1, indicating that the as-deposited films were under compressive stress. Oscillations were observed in the photoluminescence spectra, from which the refractive index of ZnO thin films was extracted, that is ~1.90.

Bismuth oxide in its δ-phase (high-temperature fluorite structure) is a well-known solid electrolyte owing to its high oxygen ion conductivity. In this work, δ-Bi 2 O 3 thin film was stabilized at room temperature by electrodeposition on different conductor substrates. Electrodeposited thin films have a good quality with an excellent adhesion to the substrate. The crystalline structure and the stability of the deposit were studied by X-ray diffraction (XRD). Both XRD measurements and transmission electron microscopy (TEM) investigation revealed the nanocrystallinity of the films. XRD measurements showed a decrease of nanocrystallites size after thin film annealing. The resistivity measurements showed an excellent conductivity of electrodeposited δ-Bi 2 O 3 thin films with an ionic conductive behaviour and an electrical conductivity value close to the theoretical value: the thin film deposited on a gilded silver substrate exhibit a conductivity of 0.39 S/cm at 440 °C.

International audience; In this work, we report on the structure study of electrodeposited ZnO nanowires. The samples were mounted as a working electrode and the deposition was per-formed in a classical three electrodes electrochemical cell. For obtaining ZnO nanowires, the working electrode was a polycarbonate membrane with a random distribution of nanometric pores, gilded one side to ensure electric contact. The morphology and structure characterizations of the different diameters ZnO nanowires were carried out by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The electrons pattern diffraction confirmed the same crystal structure of electrodeposited ZnO nanowires indexed by X-ray diffraction (XRD) on electrodeposited ZnO thin films: hexagonal ZnO phase with cell parameters a = 0.32584 nm and c = 0.52289 nm. Both TEM investigations and HRTEM images reveal a monocrystalline structure for electrodeposited ZnO nanowires. A roughness of few nanometers on the wire surface was observed. Meanwhile, no preferential growth direction hash been obviously detected. (c) 2005 Elsevier Ltd. All rights reserved.

High oxide-ion conducting material δ-Bi 2 O 3 was electrodeposited on stainless steel and polycrystalline Au substrates at low temperature. Both X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) images revealed nanocrystallites about 100 nm in size inside the electrodeposited δ-Bi 2 O 3 thin films. High-resolution TEM images showed the existence of smaller nanocrystallites 10–20 nm in diameter. The long-term stability of the electrodeposited δ-Bi 2 O 3 was checked by XRD measurements on 1-year-old samples. Its thermal stability was studied through a series of annealing at different temperatures. At an annealing temperature of 340 °C, the δ-Bi 2 O 3 fcc structure begins to change towards that of Sillenite ( bcc ).

Two types of Cu–Nb microcomposites were studied by transmission electron microscopy. The in-situ composites were prepared by casting, followed by deformation, packing and deformation. The composites were formed by self-assembling and show strong textures and orientation relationship between Cu and Nb. The artificial composites were made by cladding Nb with Cu, packing and deformation, and they developed less pronounced texture than in-situ composites. In spite of the differences in the original orientation relationship and microstructure, the final products of both composite show the {1 1 1}Cu//{1 1 0}Nb orientation relationship and fiber textures. Moreover, both types of composites are composed of Nb ribbons or plates embedded in the copper matrix. A variation in the spacing between the Nb ribbons is observed, particularly in the in-situ composites. In Cu regions, very fine twins have been revealed. Various strain contrasts were observed in the interface regions and the lattice distortion occurred in both components. The high strength of the microcomposite is attributed to large interface areas in the unit volume, lattice distortions and the nanostructures. Those strength contributors are related to each other.

The cathodoluminescence (CL) upon electron excitation of the Ga 2 O 3 nanoribbons and nanowires was characterized using a hybrid set-up based on combination of a scanning probe microscope (SPM) and a field emission scanning electron microscope (FE-SEM). An optical fiber was mounted in the system in such a way that it can be controlled to approach closely a selected nanostructure of interest so as to collect the local CL signal directly arising from it. The thicker nanoribbons (thickness >170 nm) show an emission peak around 410 nm, while the thinner ribbons/nanowires, smaller than 40 nm in thickness/diameter, have a shifted emission around 490 nm. The observed shift in the CL peaks is attributed to the difference of the oxygen vacancies in the nanostructures. Our results demonstrate that the localized CL spectroscopy is a powerful means of selective addressing the optical properties of the semiconductor nanostructures.

Composite nanocables with peculiar structure were synthesized using a solid–liquid–solid mechanism. Each of the nanocables consists of a crystalline core sheathed with an amorphous layer ( 40 nm in average diameter). The crystalline core of the nanocables is so fine (1– 6 nm in diameter), that it is nearly impossible to characterize them using other methods. Fortunately, the powerful high resolution electron energy loss spectroscopy (EELS) technique (with minimum beam size nm ) allowed us to analyze this peculiar nanomaterial. The fine crystalline core was proved to be a hexagonal silicon carbide, while the sheathing layer was silicon oxide. High angle dark field technique was employed to map the nanocable structures. Our results show that the EELS is powerful in nanometric regime characterization, while the SiC nanocables reported here may be useful in future nanotechnology.

International audience; Very thin TiO2 films have been deposited by electron-beam evaporation on Si wafers. X-Ray photoelectron spectroscopy (XPS) was used to investigate the initial stages of TiO2 growth. Chemical composition and stoichiometry of the reaction products were analyzed, based on the Ti2p, O1s, Si2p core levels, with an energy resolution of 0.8 eV. A homogeneous layer model was established for the quantitative analysis. The result of calculation was found in agreement with the result of measurement. (C) 2002 Elsevier Science B.V. All rights reserved.

International audience; A new metal-organic chemical vapour deposition (MOCVD) technique was used for fabrication of epitaxial La-manganite thin films La1-xMnO3-delta with both lanthanum and oxygen deficiencies. Three kinds of substrates, i.e. SrTiO3 (001), LaAlO3 (012) and MgO (001), were chosen for comparison. Electrical and magnetic property measurements revealed that the amplitude of the colossal magnetoresistance (CMR) is dependent on the nature of the substrate whereas the electrical and magnetic transition temperatures are not sensitive to the substrate type. In order to correlate the physical properties of the films to their crystallization quality and their growth morphology, scanning electron microscopy (SEM), transmission electron microscopy (TEM), as well as high-resolution transmission elect:ron microscopy (HRTEM), were employed. Cross-sectional TEM investigations showed that the La1-xMnO3-delta is generally in good epitaxy with all three kinds of substrate. The orientation relationships between the film and substrate are rather well defined at the vicinity of the interface but not at the surface of the film. Deposition of La1-xMnO3-delta on SrTiO3 produces the best interfacial match since these two have the least lattice misfit. This is consistent with the best magnetoresistive property measured for the investigated systems. (C) 2001 Elsevier Science B.V. All rights reserved.

High refractive index TiO 2 thin films have been deposited by electron-beam evaporation on Si (111) wafers. The substrate temperature during deposition was maintained at 250°C and the deposition rate was approximately 0.05 nm/s. Qualitative film analysis was performed with atomic force microscopy (AFM) and transmission electron microscopy (TEM). It was noted that surface roughness of the film increases with layer thickness and that the growth morphology is different for the films evaporated under the same conditions. A correlation was established between the optical properties, surface roughness and growth morphology of the evaporated TiO 2 thin films.

Oxygen ion-assisted TiO 2 thin films have been studied by in situ visible spectroscopic ellipsometry (SE) and transmission electron microscopy (TEM). Influence of the substrate nature and the substrate temperature, the ion kinetic energy E c and the ion/molecule ratio Φ i / Φ at was investigated on the microstructure and the optical properties of the films. It is revealed that the refractive index n varies as a function of the average energy per TiO 2 molecule, E d = E c ( Φ i / Φ at ). Conditions for obtaining dense films with a high refractive index (n ~ 2.60 at λ =0.45 μm) and a low extinction coefficient k have been found for E d > E dth ( E dth ~50 eV). These dense films are insensitive to moisture adsorption with a low surface roughness. Cross-sectional TEM has been mainly used for microstructure observation and phase identification of the films prepared under different evaporation conditions. Comparison is done in relationship with the optical property measurements.

Non-epitaxial CaF 2 thin films were evaporated on Si wafer covered with its 2 nm native oxide SiO 2 . The samples were prepared with different thicknesses and were investigated at two deposition temperatures. Microstructure observations of the deposited films were carried out using transmission electron microscopy (TEM) on both planar and cross-sectional views. It was shown that the evaporated CaF 2 layers have a strong columnar growth and the mean size of the columnar grains increases with the layer thickness. A close examination of the interfaces CaF 2 /SiO 2 /Si, using the high resolution TEM technique, revealed an interaction between them, leading to the inhomogeneous properties of interface.

High refractive index TiO2 thin films have been deposited by electron-beam evaporation on different substrates: Si (111) wafers, thermal SiO2, fused silica and float glass. Optical properties and growth morphology of the evaporated layers have been characterized by in situ spectroscopic ellipsometry and by transmission electron microscopy. Trajectories cos Δ = f(tanω) and spectroscopic ellipsometry measurements give a coherent description of film growth. The necessity of taking into account the presence of a surface layer less dense than the main part of the film is established. For thicker samples (optical thickness higher than half of the wavelength) index gradients are revealed and evaluated. The columnar structure is found in all samples, but differences in column size and fibre packing are observed on TEM images. The influence of the nature of the substrate on the morphology and then the optical properties of the films is not well established.