Search

Nickel sulfide (NiS) thin film has been deposited on glass substrates by spray-pyrolysis at 325 ± 5 °C. The precursor aqueous solution was synthetized using hexahydrated nickel nitrates and thiourea. The structural, morphological, optical and electrical properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy and four probes electrical measurements. The XRD analysis confirmed the hexagonal structure of NiS thin film, which was found to crystalize along [010] direction with an average crystallites size of 10.5 nm. The lattice parameters are a = b = 3.420 Å and c = 5.300 Å in the space group P63/mmc. The optical properties of the films were investigated through the transmittance and the reflectance measurements. The results revealed that the material exhibits a direct optical band gap of 1.03 eV. The elementary composition analysis confirmed the presence of Ni and S with a stoichiometry ratio (Ni/S) of 1.05. The morphology analysis revealed a homogenous crack-free, compact appearance and a granular surface in all scanned areas. The average roughness of the surface was 6.48 nm. On the other hand, the film exhibits a high electrical conductivity ca. 1.10 × 105 S/cm at room temperature. The above results show that the prepared NiS in this study has a good crystallization, dense morphology, good stoichiometric ratio and high conductivity; therefore, it stands as a potential candidate for application in supercapacitors as an electrode material.

Pure and Cu-doped NiO films were synthesized via a soft chemical process. They were deposited on glass substrates heated to 400 °C. Different atomic percentage ratios (2, 4, 6, 8, and 10%) of Cu-doping were used. The prepared samples were characterized by several techniques such as X-ray diffraction for crystallographic study, SEM and AFM for microstructural and morphological properties, and UV-Visible spectroscopy for optical and photocatalytical analysis. XRD results of pure and Cu-doped NiO films indicated the formation of NiO polycrystalline phases under a cubic structure with a favored orientation along the (200) plane noticed in all sprayed films. SEM images revealed the formation of NiO nanoparticles of spherical forms whose sizes increase and agglomerate with increasing Cu-doping. At 10% Cu-doping, NiO agglomeration was extended to the whole surface. AFM images showed a textured and rough surface composed of NiO nanoparticles of average size varying from 16 to 10 nm depending on Cu-doping concentration. UV-visible spectroscopy confirmed the transparency of NiO films and their semiconducting character with a band gap ranging from 3.4450 eV to 2.8648 eV. The photocatalytical properties of pure and Cu-NiO films were enhanced by Cu-doping particles as revealed by the degradation of methylene blue (MB) solution subjected to irradiation.

ZnO thin films were synthesized on silicon and glass substrates using the plasma-enhanced chemical vapor deposition (PECVD) technique. Three samples were prepared at substrates temperatures of 200, 300, and 400◦C. The surface chemical composition was analyzed by the use of X-Ray Photoelectron spectroscopy (XPS). Structural and morphological properties were studied by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Optical properties were carried out by UV-visible spectroscopy. XPS spectra showed typical peaks of Zn(2p3/2), Zn(2p1/2), and O(1s) of ZnO with a slight shift attributed to the substrate temperature. XRD analysis revealed hexagonal wurtzite phases with a preferred (002) growth orientation that improved with temperature. Calculation of grain size and dislocation density revealed the crystallization improvement of ZnO when the substrate temperature varied from 200 to 400◦C. SEM images of ZnO films showed textured surfaces composed of grains of spherical shape uniformly distributed. The transmittance yields are reaching 80%, and the values of the band-gap energy indicate that the ZnO films prepared by PECVD present transparent and semiconducting properties.

This work highlights some physical properties related to the influence of aluminum, tin and copper incorporation on nanostructured zinc oxide (ZnO:M; M:Al, Sn and Cu) thin films prepared by ultrasonic spray pyrolysis technique (USP) on glass substrate at 350±5 °C. For the as-grown layers, M- to Zn-ratio was fixed at 1.5 %. The effects of metal doping on structural, morphological, optical and electrical properties were investigated. X-ray diffraction pattern revealed that the as-prepared thin films crystallized in hexagonal structure with (0 0 2) preferred orientation. The surface topography of the films was performed by atomic force microscopy. AFM images revealed inhibition of grain growth due to the doping elements incorporation into ZnO matrix, which induced the formation of ZnO nanoparticles. Optical measurements showed a high transparency around 90 % in visible range. Some optical parameters, such as optical band gap, Urbach energy, refractive index, extinction coeffi-cient and dielectric constant were studied in terms of doping element. Particularly, dispersion of refractive index was discussed in terms of both Cauchy and single oscillator model proposed by Wemple and DiDomenico. Cauchy parameters and single oscillator energy E0 as well as dispersion energy Ed were calculated. Finally, electrical properties were investigated by means of electrical conductivity and Hall effect measurements. The measurements confirmed n type conductivity of the prepared thin films and a good agreement between the resistivity values and the oxidation number of doping element. The main aim of this work was the selection of the best candidate for doping ZnO for optoelectronics applications. The comparative study of M doped ZnO (M:Al, Sn and Cu) was performed. High rectifying efficiency of the Al/n-ZnO/p-Si/Al device was achieved and non-ideal behavior was revealed with n > 4.

Lithium-doped zinc oxide thin films (ZnO:Li) at different percentages (0–4%) were deposited on glass substrates at 460 °C using the spray pyrolysis technique. The effect of lithium content on the structural, morphological and optical properties of ZnO:Li thin films was investigated. First, X-ray diffraction study revealed that undoped and Li-doped ZnO thin films crystallize in hexagonal wurtzite structure with a preferred orientation of the crystallites along (002) direction. The scanning electron microscopy (SEM) showed a clear hexagonal-shaped granular onto the surface of such films. Indeed, the averaged grain size, visualized by SEM, varied from 100 nm, for undoped ZnO, to 200 nm for ZnO:Li 4%. Second, the optical analysis by means of the transmittance and the reflectance measurements revealed that in UV–Vis domain, the average transmittance of the ZnO:Li thin films was 75%, while the average reflectance was

International audience

Nanostructured thin films of Nickel oxide NiO were synthesized using spray coating method. The samples were irradiated at different γ-doses by Co-60 radioisotope. The obtained films were studied using X-ray diffraction (XRD), scanning electron microscopy, UV–visible spectrophotometry, Raman spectroscopy, photoluminescence (PL) spectroscopy and FT-IR. The experimental results demonstrated that the irradiation of NiO led to significant changes. XRD and Raman spectroscopy demonstrate that the as-deposited NiO samples show a cubic structure with (111) preferred orientation common at all gamma radiation doses. The optical energy gaps of the samples were found to decrease when increasing the γ ray dose, the Eg value decreases from 3.84 eV for as deposited NiO thin film to 3.60 eV for sample irradiated at 50 kGy. Scanning electron microscope (SEM) image of sprayed NiO films shows the high porosity and the presence of microcavities in surface of films.

In2O3 : Eu thin films were successfully grown by spray pyrolysis. XRD studies showed that the films had In2O3 cubic structure with (004) preferential orientation and best crystal properties at 1.5% Eu doping level. The optical band gap energy decreased with Eu content around 4.1 eV. Urbach energy was of the order of 278 meV, it decreased with Eu content which indicates a decrease in the defects by doping. The dispersion of the refractive index was discussed. Raman spectroscopy showed the band positions corresponding to In2O3 cubic phase with a small shift related to europium incorporation within In2O3 matrix. PL measurements showed a large band which was located at 410 nm and related to the band-to-band transitions and other bands related to impurity levels. Finally, the electric conductivity was investigated depending on the effect of temperature. Activation energy was found to range from 45 to 60 meV for films which were prepared with 1% Eu content.

International audience; In this paper, ZnO nanocrystals were synthesized using a simple micro-droplets technique from a solution prepared by dissolving zinc acetate di-hydrate [Zn(CH 3 COO) 2 , 2H 2 O] in methanol. Microdroplets were deposited on glass substrates heated at 100 °C, the obtained samples of ZnO films were investigated by XRD, AES, AFM, ellipsometry and PL. XRD patterns reveal the wurtzite structure of ZnO where the lattice parameters a and c, calculated from XRD signals, show a nanometric character of ZnO nanoparticles. The chemical composition of ZnO film surfaces was verified by Auger electron spectroscopy (AES). From Auger signals, oxygen (O-KLL) and zinc (Zn-LMM) Auger transitions indicate well the presence of Zn-O bonding. The surface topography of the samples was measured by atomic force microscopy (AFM) where ZnO nanoparticles of average size ranging between 20 and 80 nm were determined. Some optical properties as dielectric constants, refractive index, extinction coefficient as well as the optical band gap were determined from ellipsometry analysis. The dispersion of the refractive index was discussed in terms of both Cauchy parameters and Wemple & Di-Dominico single oscillator model. The photoluminescence (PL) measurements exhibited two emission peaks. The first at 338 nm, corresponding to the band gap of ZnO, is due to excitonic emission while the second around 400 nm, is attributed to the single ionized oxygen vacancies. Ó 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Introduction Zinc oxide (ZnO) is a material which is very familiar to scientists because it is well known for its excellent physical properties as ultra violet absorbance, piezoelectricity and luminescence at high temperatures. We can count thousands of papers dating back as early as 1935 [1]. More recently, ZnO has again entered the scientific spotlight, this time for its semiconducting properties. ZnO is a semiconductor with interesting characteristics such as a wide and direct bandgap (3.37 eV at room temperature) and a larger exciton binding energy (60 meV) [2,3]. It is a very interesting material for its large applications in many technological fields for its useful properties (optical, electrical, mechanical, chemical.. .). A considerable research interest in ZnO was performed due to many potential applications particularly in short wavelength for optoelectronic devices operating in the blue and ultraviolet (UV) region such as light-emitting diodes (LED) [4] and gas-sensing applications [5]. Today, the research is focused on the nanostructured ZnO because there is a high surface-to-volume ratio and show enhanced chemical stability and electrical performances [6,7]. Several chemical and physical methods have been used for the preparation of ZnO thin films nanostructured such as MOCVD [8], chemical vapor transport (CVT) [9], spray pyrolysis [10–12], sputtering [13], laser ablation [14,15]. The purpose of this paper is to provide a simple chemical synthesis route of ZnO nanofilms. This technique called ''micro-droplets technique " is low cost and easy to implement. It is based on the deposit of microdroplets on heated glass substrates. The detail of this technique is described in the following paragraph. Experimental part ZnO nanofilms preparation ZnO nanofilms were obtained by micro-droplets route. The principle of this method is to prepare a solution by dissolving 10 À2 M of zinc acetate di-hydrate [Zn(CH 3 COO) 2 , 2H 2 O] in a beaker containing 150 ml of methanol. Microdroplets of 0.05 ml of volume http://dx.

Recently, metal oxide nanolayered semiconductors revealed their increasing usefulness as UV detectors and transparent conductors in optoelectronic devices. In the present paper, a simple fabrication process has been carried out to prepare layered TCO compounds with different controlled thicknesses. Conjoint physical investigations allowed discussion of the validity of optimality in terms of geometrical parameters. A synthetic function based on pondered physical parameters was a practical guide to reach optimality.

Conducting and transparent optical ZnO thin films were deposited on glass substrates by a simple mini spray technique. Alternatively, some of the obtained films were doped with indium and ytterbium at the molar rates of: 1, 2, and 3% (In) and 100, 200, and 300 ppm (Yb). In addition to the classical structural investigations including XRD, microhardness vickers (Hv), and optothermal techniques, thorough optical measurements have been carried out for comparison purposes. The refractive indices and the extinction coefficients of the differently doped layers have been deduced from their transmission-reflection spectra over an extended wavelength range. Analysis of the refractive index data through Wemple-DiDomenico single oscillator model yielded quantum characteristics along with the values of long-wavelength dielectric constant, average oscillator wavelength, average oscillator strength, average oscillator energy and dispersion energy. Real and imaginary parts of dielectric constant have also been used to calculate free carrier plasma resonance frequency, optical relaxation time, and free carriers concentration-to-effective mass ratio. Finally, analysis of Urbach-Martienssen model parameters allowed proposing nanoscale explanations to the divergence about doping-related evolution of Urbach tails, this intriguing item having been intensively discussed in the literature in the last decades.