Optical, electrical and morphological properties of p-type Mn-doped SnO2 nanostructured thin films prepared by sol–gel process

SnO₂ thin films doped with various manganese concentrations were prepared on glass substrates by sol–gel dip coating method. The decomposition procedure of compounds produced by alcoholysis reactions of tin and manganese chlorides was studied by thermogravimetric analysis (TGA). The effects of Mn doping on structural, morphological, electrical and optical properties of prepared films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Hall effect measurement, Fourier Transform Infrared (FTIR) spectral analysis, UV–Vis spectrophotometry, and photoluminescence (PL) spectroscopy. The results of the X-ray diffraction show that the samples are crystalline with a tetragonal rutile structure and the grain size decreases with increasing the doping concentration. The SEM and AFM images demonstrate that the surface morphology of the films was affected from the manganese incorporation. The Sn_1?x Mn _x O₂ thin films exhibited electrically p-type behavior in doping level above x=0.035 and electrical resistivity increases with increase in Mn doping. The optical transmission spectra show a shift in the position of absorption edge towards higher wavelength (lower energy). The optical constants (refractive index and extinction coefficient) and the film thickness were determined by spectral transmittance and using a numerical approximation method. The oscillator and dispersion energies were calculated using the Wemple–DiDomenico dispersion model. The estimated optical band gap is found to decrease with higher manganese doping. The room-temperature PL measurements illustrate the decrease in intensity of the emission lines when content of Mn is increased in Mn-doped SnO₂ thin films.     

DTA study of the dehydration of synthetic goethite αFeOOH

The shape of DTA endothermic peak, associated with the dehydration of goethite FeOOH into hematite, depends strongly on the size of the goethite particles. With samples of low specific surface, two distinct peaks were observed. The dehydration process of a low-specific surface goethite was followed by X-ray diffraction and lowtemperature nitrogen adsorption. The results are in good agreement with the hypothesis of the formation of an impermeable hematite layer on each grain which temporarily stops the dehydration process of the internal part of the grain.

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Zusammenfassung Die Form des mit der Entwässerung von Goethit FeOOH zu Hämatit verbundenen endothermen DTA-Peaks hängt stark von der Grösse der Goethit-Partikel ab. Bei Proben von kleiner spezifischer Oberfläche wurden zwei scharfe Peaks beobachtet. Der Entwässerungsprozess eines Goethits von kleiner spezifischer Oberfläche wurde durch Röntgendiffraktion und Stickstoff-Adsorption bei niedrigen Temperaturen verfolgt. Die Ergebnisse sind in guter Übereinstimmung mit der Hypothese nach welcher eine undurchdringliche Hämatitschicht auf jedem Körnchen gebildet wird, die den Entwässerungs vorgang im inneren des Körnchens vorübergehend stoppt.

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Résumé La déshydratation de la goethite de synthèse se marque en ATD par un phénomène endothermique plus ou moins dédoublé, ce dédoublement étant fonction de la dimension des particules de l'échantillon. La déshydratation d'une goethite de faible surface spécifique a été suivie par diffraction de rayons X et par adsorption d'azote à basse température sur des échantillons refroidis brutalement en cours d'ATD. C'est l'hypothèse de la formation sur chaque grain d'une couche externe d'hématite, bloquant temporairement la diffusion de la vapeur d'eau vers l'extérieur, qui se trouve le plus en accord avec les résultats expérimentaux.

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, FeOOH , . . . , .

     

Reduction Dehydration of Iron Oxide Hydroxide by iron metal in aqueous medium

The reductive dehydration of iron hydroxide (FeOOH) by iron metal in aqueous solutions of ferrous sulphate was found to occur. These reactions of α, β, γ FeOOH and Fe(OH)₃ · nH₂O respectively were carried out in 0.01–1 mol iron(II) sulphate solutions and over the temperature range of 80–100°C to produce Fe₃O₄ in all cases. The reaction rate decreases with increasing Fe²⁺ concentration and depends on the total concentration of sulphate anion. The presence of iron(II) chloride has an inhibiting effect.     

Parametrization of Barrier Characteristics for Spherical-Oblate Systems in any Configuration of Colliding Nuclei

The behaviors of barrier characteristics are analyzed for spherical-oblate systems over different configurations of colliding nuclei. For this purpose, we have extended our previous study [Phys. Rev. C 89(2014) 054607], it is devoted to optimum "cold" and "hot" configuration] to analyze the same reaction systems in various configurations.The investigation on some chosen systems reveals that the barrier height and its position can be parameterized in times of the different orientations.     

Derivation of the optical constants of spin coated CeO2-TiO2-ZrO2 thin films prepared by sol-gel route

Ternary thin films of cerium titanium zirconium mixed oxide were prepared by the sol-gel process and deposited by a spin coating technique at different spin speeds (1000-4000 rpm). Ceric ammonium nitrate, Ce(NO₃)₆(NH₄)₂, titanium butoxide, Ti[O(CH₂)₃CH₃]₄, and zirconium propoxide, Zr(OCH₂CH₂CH₃)₄, were used as starting materials. Differential calorimetric analysis (DSC) and thermogravimetric analysis (TGA) were carried out on the CeO₂-TiO₂-ZrO₂ gel to study the decomposition and phase transition of the gel. For molecular, structural, elemental, and morphological characterization of the films, Fourier Transform Infrared (FTIR) spectral analysis, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), cross-sectional scanning electron microscopy (SEM), and atomic force microscopy (AFM) were carried out. All the ternary oxide thin films were amorphous. The optical constants (refractive index, extinction coefficient, band gap) and thickness of the films were determined in the 350-1000 nm wavelength range by using an nkd spectrophotometer. The refractive index, extinction coefficient, and thickness of the films were changed by varying the spin speed. The oscillator and dispersion energies were obtained using the Wemple-DiDomenico dispersion relationship. The optical band gap is independent of the spin speed and has a value of about E_g≈2.82±0.04 eV for indirect transition.