[en] This work highlights some physical investigations on tin oxide thin films doped with different lanthanum content (ratio La–to-Sn = 0–3%). Such doped thin films have been successfully grown by spray pyrolysis onto glass substrates at 450 °C. X-ray diffraction (XRD) patterns showed that SnO_2:La thin films were polycrystalline with tetragonal crystal structure. The preferred orientation of crystallites for undoped SnO_2 thin film was along (110) plane, whereas La-doped ones have rather preferential orientations along (200) direction. Although the grain size values exhibited a decreasing tendency with increasing doping content confirming the role of La as a grain growth inhibitor, dislocation density and microstrain values showed an increasing tendency. Also, Raman spectroscopy shows the bands corresponding to the tetragonal structure for the entire range of La doping. The same technique confirms the presence of La_2O_3 as secondary phase. Moreover, SEM images showed a porous architecture with presence of big clusters with different sizes and shapes resulting from the agglomeration of small grains round shaped. Photoluminescence spectra of SnO_2:La thin films exhibit a decrease in the emission intensity with La concentration due to the decrease in grain size. Optical transmittance spectra of the films showed high transparency (∼80%) in the visible region. The dispersion of the refractive index is discussed using both Cauchy model and Wemple–Di-Domenico method. The optical band gap values vary slightly with La doping and were found to be around 3.8 eV. It has been found that La doping causes a pronounced decrease in the sheet resistance by up to two orders of magnitude and allows improving the Haacke's figure of merit (Φ) of the sprayed thin films. Moreover, we have introduced for a first time a new figure of merit for qualifying photo-thermal conversion applications. The obtained high conducting and transparent SnO_2:La thin films are promising to be useful in various optoelectronic applications. - Highlights: • La-doped SnO_2 has been synthesized by the facile spray pyrolysis method. • Influences of doping on the electrical and optical properties of the films were investigated. • La doped SnO_2 films exhibit high transparency in the visible range and low sheet resistance. • The calculated values of Haacke's figure of merit show that La doping improves the optoelectronic properties of SnO_2. • A new figure of merit has been introduced to qualify the photo-thermal conversion applications.

[en] Hausmannite Mn₃O₄ thin film have been synthesized using spray pyrolysis method. These films are characterized using X-ray diffraction (XRD), atomic force microscope AFM, UV–vis–NIR spectroscopy and impedance spectroscopy. XRD study confirms the tetragonal structure of the as-deposited films with lattice parameters, a = 5.1822 Å and c = 9.4563 Å and a grain size of about 56 nm. UV–vis–NIR spectroscopy was further used to estimate optical constants such as extinction coefficient, refractive index, band gap and Urbach energy. Moreover, impedance spectroscopy analysis was employed to estimate electrical and dielectrical properties of the sprayed thin films. The activation energy values deduced from DC conductivity and relaxation frequency were almost the same, revealing that the transport phenomena is thermally activated by hopping between localized states. The AC conductivity is found to be proportional to ω^s. The temperature dependence of the AC conductivity and the frequency exponent, s was reasonably well interpreted in terms of the correlated barrier-hopping CBH model. The dielectric properties were sensitive to temperature and frequency. The study of the electrical modulus indicated that the charge carrier was localized. Experimental results concerning optical constants as Urbach energy, dielectric constant, electric modulus and AC and DC conductivity were discussed in terms of the hopping model as suggested by Elliott

[en] Lanthanum-doped Zinc oxide (ZnO:La) thin films were successfully grown on glass substrates by the spray pyrolysis technique at 460 °C. Alternatively, some of the obtained films were doped with lanthanum at the molar rates of: 1, 2, 3 and 4%. The structural properties of the prepared samples were characterized by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). It is shown that ZnO:La thin films crystallize in hexagonal wurtzite structure with a preferred orientation of the crystallites along (002) direction. Also, Raman spectroscopy shows the bands corresponding to ZnO structure and confirms the presence of La_2O_3 secondary phase. Furthermore, it is found that the lattice parameters a and c of La-doped ZnO films decrease with La content. UV–vis measurements show that the average transmittance of the ZnO:La thin films is 75% and the average reflectance is less than 25% in the visible range. In the same line, it is noted that the optical band gap, Urbach energy, and the optical constants are significantly influenced by the lanthanum incorporation. The photoluminescence (PL) measurements exhibit emission in the visible region (a strong band located around 480 nm and a weak band around 420 nm). The intensity of level emission varies with La doping. Moreover, it is observed a significant variation of both electrical resistivity and activation energy with La concentration. The electrical conductivity of films dependence of temperature was measured to reach the dominant conductivity mechanism. - Highlights: • La doped ZnO nanorods have been synthesized by facile spray pyrolysis method. • Influences of doping on the surface and optical properties of the ZnO films were investigated. • The photoluminescence show the effect of La incorporation on optical properties. • La doped ZnO films indicate high transparency in visible range. • Highly c-axis oriented ZnO nanorods were grown on glass substrates

[en] This paper deals with the results on the structural, electrical, vibrational and optical properties of LaMn${}_{1-<!--\; ???\; -->x}$Ni${}_x$O${}_3$ (0 ≤ x ≤ 0.3) thin films prepared by the spray pyrolysis technique on glass substrates at 460 °C using (LaCl${}_3$·7H${}_2$O), (MnCl${}_2$·4H${}_2$O) and (NiCl${}_2$·6H${}_2$O) as precursors. First, XRD analysis shows an orthorhombic structure of all prepared thin films. Second, room temperature Raman spectra showed broad and intense bands characteristic of LaMnO${}_3$ parent compound modes. An important shift to higher frequencies was observed and attributed to disorder induced by Ni composition and Frenkel defects associated to the formation of vacancy and interstitial oxygen sites. The optical measurements show that the optical band gap energy value varies sparsely in terms of Ni content. On the other hand, the electric conductivity measurements were investigated using the impedance spectroscopy technique in the frequency range 5 Hz–10 MHz at various temperatures (410–500 °C). AC conductivity of LaMn${}_{1-<!--\; ???\; -->x}$Ni${}_x$O${}_3$ thin films is found to follow the Jonsher law. The temperature dependence of the AC conductivity is consistent with the correlated barrier-hopping model with activation energy Ea varying in (0.70–1.29) eV domain. Finally, the magnetic hysteresis loops of such films exhibit obvious ferromagnetic behavior with a high dependency with Ni content particularly the coercivity value (H${}_c$) increases with Ni concentration.

[en] Nickel molybdate (NiMoO₄) thin film has been prepared by the spray pyrolysis method, using nickel chloride hexahydrate (NiCl₂.6H₂O) and ammonium molybdate tetrahydrate [(NH₄) 6Mo₇O₂₄.4H₂O] as precursors in the aqueous starting solution. First, the structure and the surface morphology characterizations were carried out by scanning electron spectroscopy (SEM), Raman and X-ray diffraction (XRD) techniques. Structural analysis by using XRD technique shows that the NiMoO₄ thin film crystallizes in the monoclinic phase, mainly orientation along (110), (021), (204), (220), (150) and (152), directions. In addition to these studies, the stoichiometric composition has been reached by the energy dispersion analysis technique. Second, the optical properties have been studied by means of the reflectance and the transmittance spectra, in the wavelength range of 300–1800 nm. This study shows a direct transition of this ternary oxide with an optical bandgap about 3.12 eV and Urbach energy EU in the order of 663 MeV. Finally, the photoluminescence emission spectrum of the NiMoO₄ thin film showed emissions peaks in the violet and blue regions and others emission related to some defects in the prepared film. (author)

[en] This paper deals with synthesis and physical investigation of iron doped Lanthanum oxide thin films (La₂O₃: Fe). These films are grown on glass substrates at 460 °C by spray pyrolysis with different molar ratios of Fe to La, varying from 0 to 5%. X-ray diffraction analysis shows that undoped La₂O₃ thin film crystallizes under a mixture of hexagonal and cubic structures. SEM images reveal porous and fuzzy network of nanocrystalline La₂O₃. AFM images confirm the granular and nanocristalline structure of these films. The principal Raman peak owed to La–O vibration mode at 340 cm⁻¹, confirms the formation of lanthanum oxide La₂O₃. For iron- doped films, FTIR spectroscopy reveals not only the La–O vibration mode at 457 cm⁻¹ but also a peak at 1394 cm⁻¹ which is related to the ternary LaFeO₃. Photoluminescence spectra show that iron doping reduces radiative recombination. Thereby, doped samples can be used for photocatalysis experiment with methylene blue (MB). After 120 min exposure to solar light, a noticeably photodegradation of MB is obtained with 4% Fe doped La₂O₃. This work shows that Fe doped La₂O₃ is a promising material for various sensitive applications such as gas detection and bio-sensors. (paper)

[en] Highlights: • Co:Ni-codoped MoO₃ thin films were synthesized by Spray pyrolysis. • MoO₃ is a large band gap compound. • The deposit thin films crystallized in orthorhombic space group. • These films have interesting optical and magnetic properties. This work covers some physical investigations on (Co, Ni) codoped molybdenum oxide thin films deposited on glass substrates at 460 °C by the spray pyrolysis technique. The effects of Co and Ni contents on the structural, morphological, optical and magnetic properties of these films were studied using several physical investigations. First, X-ray diffraction analysis revealed the formation of an orthorhombic structure related to α-MoO₃ allotropic phase with (020) and (040) preferred orientations. Also, the scanning electron microscopy (SEM) micrographs showed the enhancement of the surface roughness of MoO₃ films by cobalt and nickel concentrations. Second, the optical investigations through reflectance and transmittance measurements indicated a direct transition of all prepared thin films with a remarkable increase of the optical band gap from 3.70 to 3.95 eV with increasing both Co and Ni elements. Finally, the magnetic measurements at room temperature revealed a ferromagnetic behavior of Co and Ni codoped MoO₃ films. A ferro-diamagnetic transition phenomenon was occurred for codoped film at Ni 2%and Co 2%.

[en] Thin films of bismuth sulfide (Bi₂S₃) have been electrochemically deposited on indium–doped tin oxide substrates from aqueous solutions of Bi(NO₃)₃, ethylene diamine tetraacetic acid (EDTA) and Na₂S₂O₃. The structural properties of the films were characterized using X–ray diffraction and high–resolution transmission electron microscopy analyses. The film crystallizes in an orthorhombic structure of Bi₂S₃ along with metallic bismuth. Thermal annealing of the prepared film in sulfur atmosphere improves its crystallinity and cohesion. The band gap values of the deposited film before and after annealing at 400 °C were found to be 1.28 and 1.33 eV, respectively. - Highlights: • Bismuth sulfide (Bi₂S₃) thin films were synthesized by electrodeposition process. • Films crystallize in orthorhombic structure with (021) preferential orientation. • The effect of annealing under sulfur atmosphere has been investigated. • The band gap after annealing is 1.34 eV which hold for solar cell conversion.

[en] In this study, conducting and transparent indium-doped zinc oxide (ZnO) thin films have been deposited on glass substrates by the micro-spray technique. First, zinc oxide layers were obtained by spaying a solution of propanol and zinc acetate in acidified medium. Alternatively, some of the obtained films were doped with indium (In) at the molar rates of: 1%, 2% and 3%. In addition to the classical structural investigated using XRD, AFM and SEM techniques, microhardness Vickers (Hv) measurements have been carried out along with comparative morphological prospecting. The specific gases sensitivity-related surface morphology of the doped ZnO compounds was favorably different from that of the non-doped ones, and showed a thin overlay structure. Results were compared to those recorded for similar ytterbium-doped material.

[en] Highlights: • Highlighting the effect of cobalt doping on structural and morphology properties. • AFM observations show the formation of micro-plates parallel to the surface plane with a roughness ranging from 33 to 54 nm. • Ferromagnetic behavior of MoO₃ nanofilms induced by Co-doping. - Abstract: Pristine and Cobalt (Co)-doped MoO₃ nanofilms were synthesized on glass substrates using the spray pyrolysis method. The nanometric pristine MoO₃ films were prepared from the 10⁻² M.L^-1 solution of ammonium molybdate tetrahydrate [(NH₄)₆Mo₇O₂₄,4H₂O] in distilled water. Co-doping at 0.5, 0.75 and 1% was achieved by adding cobalt (II) chloride hexahydrate (Cl₂CoH₁₂O₆) in the pristine solution. The structure and the morphology of the films were investigated by means of X-ray diffraction and atomic force microscopy: two pronounced (020) and (040) peaks corresponding to the orthorhombic structure phase of α-MoO₃ were detected. The AFM observations revealed the formation of micro-plates, parallel to the surface plane, with a roughness ranging from 33 nm to 54 nm. Optical properties were investigated through reflectance, transmittance and photoluminescence measurements. The optical band gap, the Urbach energy and the refractive index were deduced from these measurements. The presence of oxygen vacancies was revealed from the interband transitions in the blue and green domains. Co-doped MoO₃ nanofilms showed ferromagnetic behavior. The photocatalytic degradation of an aqueous solution of methylene blue (MB) under UV irradiation, in the presence of Co-MoO₃ nanomfilms, has been carried out using UV–vis spectrometery: the intensity of the absorption peak recorded at 660 nm decreased with the increase of the UV-illumination time while the color of the initial MB solution was drastically waned.