Study of the phase transition and the thermal nitridation of nanocrystalline sol-gel titania films

Nanocrystalline titania films were prepared by a complexing agent-assisted sol-gel method and converted to titanium nitride by a thermal nitridation process. The effect of acetylacetone (AcAc), diethanolamine (DEA) and acid catalysts (HCl and HNO₃) on the structure and morphology of the heat-treated titania films and on their nitridation products was examined by FTIR spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). The carbothermal reduction of titania during the nitridation process with the formation of carboxynitrides has been considered. The results showed that the oxide to nitride transition strongly depends on the complexing agent used to prepare the titania films. The XRD results indicated the dependence of the lattice parameter of the nitridation product on the complexing agent or acid catalyst: AcAc and DEA lead to TiN_x with a lattice parameter α close to the theoretical value, while with HCl the lattice parameter was found sensibly lower showing the presence of an oxynitride. These results are accounted for by the effect of complexing agents and acid catalysts on the size of both TiO₂ and TiN grains and the different reactivity of the anatase and rutile phases. The possibility of tailoring the composition and morphology of TiN films by using complexing agents is envisaged.     

Structural characterization of light-induced crystal growth in Se98Sb2 chalcogenide glass

The present paper reports the detailed study of crystallization morphology of light-induced crystal growth in Se₉₈Sb₂ chalcogenide glass using DSC, XRD and SEM techniques. Thermally-activated crystallization of the samples in powder form is analyzed by Differential Scanning Calorimetry (DSC) at different heating rates under non-isothermal conditions. The activation energy of crystallization has been calculated by analyzing the data using the classical Johnson–Mehl–Avrami (JMA) model.Amorphous thin films of Se₉₈Sb₂ are used for light-induced crystal growth. The d.c. conductivity of the films is taken as a characteristic quantity to measure the extent of light-induced crystal growth. X-ray diffraction (XRD) analysis has been carried out on Se₉₈Sb₂ samples for different illumination time and their diffractograms are analyzed to obtain information about various crystallographic aspects. Scanning electron microscopy has been used to confirm light-induced crystal growth.     

Structural Properties of CuGaxIn1-xSe2 Thin Films Deposited by Spray Pyrolysis

Thin films of CuGa_xIn_1-xSe₂ (x=0.0-1.0) have been prepared by spray pyrolysis onto soda-lime glass substrates heated to a temperature of 325° C. The structure, crystal orientations, lattice parameters and grain size of the experimental films have been studied using the X-ray diffraction and scanning electron microscopy. All the deposited films were polycrystalline and showed single phase with an intense (112) orientation. The lattice parameters, a and c of the films vary linearly with the change of gallium composition. The grain size of the films decrease with the increase of gallium content.     

Mesoporous materials from SiO2 and NiTiO3

In this work, we synthesized and characterized mesoporous thin films of SiO₂ and NiTiO₃ structured by a surfactant called Brij58. These films were fabricated by the method of dip coating and the best conditions for well-structured thin films were investigated as a function of surfactant concentration and different types of substrates. These films have been characterized by X-ray reflectivity which was calculated using the matrix formalism. We demonstrated that the silicon substrate had a great effect on the structure and porosity of the fabricated films for both SiO₂ and NiTiO₃. Furthermore, we found that mesoporosity has been increased as a function of the surfactant concentration in the solution. This experimental procedure allows also to produce NiTiO₃ powders which have been characterized by X-ray diffraction. The XRD coupled to the crystallographic software “Maud”shows that the samples are constituted by 98, 2% NiTiO₃ powders.     

Structural properties of Zn1–xMgxO nanomaterials prepared by sol‐gel method

The mixed oxides Zn_1‐xMg_xO (ZMO) were prepared as nano‐polycrystalline powders and thin films by a simple sol–gel process and dip coating method. Thermogravimetric (TG) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structural and microstructural analysis was carried out applying x‐ray diffraction (XRD) and Rietveld method. Analysis showed that for x < 0.25, Mg replaces Zn substitutionally yielding ZMO single phase, while for x ≥ 0.25 two phases are identified ZMO and MgO. Replacing Zn²⁺ by Mg²⁺ distorts the cation tetrahedrons and decreases the lattice constants ratio c/a of the wurtzite ZMO which deviate the lattice gradually from the hexagonal structure as Mg⁺² increases. These distortions are attributed to the difference in electronic configuration of the two cations which suppress the paraelectric‐ferroelectric phase transition in the ZMO wurtzite. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical band gap of zinc nitride films prepared by reactive rf magnetron sputtering

Polycrystalline Zn₃N₂ films are prepared on Si and quartz glass substrates by RF magnetron sputtering at room temperature. The structural and optical properties are studied by X‐ray diffraction and double beam spectrophotometer, respectively. X‐ray diffraction indicates that the Zn₃N₂ films deposited on Si and quartz glass substrates both have a preferred orientation in (321) and (442), also are cubic in structure with the lattice constant a=0.9847 and 0.9783 nm, respectively. The absorption coefficients as well as the film thickness are calculated from the transmission spectra, and their dependence on photon energy is examined to determine the optical band gap. Zn₃N₂ is determined to be an indirect‐gap semiconductor with the band gap of 2.11(2) eV. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thickness Dependence of Electrical and Structural Properties of FTO Films

Fluorine (0.8 M) doped tin oxide films of various thicknesses were prepared on heated glass substrates (520 °C) by spray pyrolysis technique. The chemical and thermal stabilities of FTO films were found to be very good. The characterization has been done by XRD and found to agree with the reported results. As thickness of the film increases, intensities of peaks increased. From the X-ray diffraction data, grain size of the crystallites have been calculated. The electrical and structural properties were studied for different thicknesses. Hall measurements showed that thicker films have relatively high Hall mobilities compared to those of thinner films. The high carrier concentration showed that the films are degenerate. The relationship between carrier concentration and Hall mobility revealed that the ionized impurity scattering centres were the dominant cause of scattering.     

Nanocrystalline properties of chemically deposited (Cd0.95‐Pb0.05)S:CdCl2, Gd/Dy films

Results of SEM and XRD studies, optical absorption spectra and photoluminescence emission spectra are presented for the films of (Cd_0.95‐Pb_0.05)S:CdCl₂, Gd/Dy prepared by chemical bath deposition technique and using thiophenol and methanol as capping agents. The deposition of films is based on precipitation followed by condensation on the substrates. SEM studies show existence of irregular distribution of particles alongwith presence of rod/tube type structure. The XRD studies show diffraction lines of CdS, PbS and CdCl₂. Blue shift has been observed in absorption spectra showing quantum confinement. Particle sizes determined from XRD studies and absorption spectral studies are found to lie in the nano range. Photoluminescence emission spectra consist of emissions in blue and green‐yellow regions. The observed emissions are related to the combination of defect levels and levels due to rare earths. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of substrate temperature on structural and materials properties of zirconium nitride films on D9 steel substrates

Thin zirconium nitride (ZrN) films were prepared by using reactive direct current (DC) magnetron sputtering onto D9 steel substrates. XRD technique was employed to study the coatings, observing variations of crystallite size, crystallite texture and lattice constant, as a function of substrate temperature. Chemical states of the ZrN thin films were determined by X‐ray photoelectron microscopy (XPS). AFM picture showed the presence of spherical shaped grains on the top of homogeneous granular surface. The hardness and elastic modulus values were measured by nanoindendation and their values are 18.5 and 343 GPa respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sensitivity of YBa2Cu3O7 thick films to gamma rays

Superconducting YBa₂Cu₃O₇ (YBCO) thick films have been prepared using the screen printing method. Effects of gamma irradiation on their structure and transport properties have been investigated up to a gamma dose of 50 MR. A considerable decrease in the intensities of the major diffraction peaks of the XRD pattern was observed due to gamma irradiation. A gradual increase in the normal state resistance, with a gradual increase in the slope of the resistance‐temperature (R‐T) curves was observed with increasing gamma doses. However, slight decrease in the transition temperature has been observed. The Voltage‐current (V‐I) data were fitted to the power law V ∼ I^β in which the power exponent β was found to increase gradually with gamma dose. The sensitivity of the R‐T and V‐I curves to gamma rays where precisely estimated and from which the regions of linear response were deduced. The possibility of using YBCO thick film as a candidate device for gamma rays sensing was presented. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of thermoannealing on crystallinity and optical properties of Sb2S3 thin films

Sb₂S₃ thin films are obtained by evaporating of Sb₂S₃ powder onto glass substrates maintained at room temperature under pressure of 2×10^‐5 torr. The composition of the thin films was determined by energy dispersive analysis of X‐ray (EDAX). The effect of thermal annealing in vacuum on the structural properties was studied using X‐ray diffraction (XRD) technique and scanning electron microscopy (SEM). The as‐deposition films were amorphous, while the annealed films have an orthorhombic polycrystalline structure. The optical constants of as‐deposited and annealed Sb₂S₃ thin films were obtained from the analysis of the experimental recorded transmission spectral data over the wavelength range 400‐1400 nm. The transmittance analysis allowed the determination of refractive index as function of wavelength. It was found that the refractive dispersion data obeyed the single oscillator model, from which the dispersion parameters (oscillator energy, E₀, dispersion energy, E_d) were determined. The static refractive index n(0), static dielectric constant, ε_∞, and optical band gap energy, E_g, were also calculated using the values of dispersion parameters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and investigation of (CuInSe2)x(2ZnSe)1‐x and (CuInTe2)x(2ZnTe)1‐x solid solution crystals

The (CuInSe₂)_x(2ZnSe)_1‐x and (CuInTe₂)_x(2ZnTe)_1‐x solid solution crystals prepared by Bridgman method and chemical vapor transport have been studied. The nature of the crystalline phases, the local structure homogeneity and composition of these materials have been investigated by X‐ray diffraction (XRD) and Electron Probe Microanalysis (EPMA) methods. The analysis revealed the presence of chalcopyrite‐sphalerite phase transition between 0.6 ≤ X ≤ 0.7. Lattice constants, value of σ position parameter and bond length between atoms were also calculated. It was found that the lattice parameters exhibit a linear dependence versus composition. The transmission spectra of solid solution crystals in the region of the main absorption edge were studied. It was established that the optical band gap of these materials changes non‐linearly with the X composition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure of Polycrystalline Cu Films as Solar Selective Coatings

Copper thin films (5–150 nm) were prepared by vacuum deposition with different rates (0.7, 1.5 and 3 nm/s). The position, intensity and profile of X-ray diffraction lines were analysed to study the phases, the crystallographic preferred orientation as well as the residual strain and crystallite size. The fcc polycrystalline Cu phase was revealed and no oxide phases were identified. The films were highly oriented with 〈111〉 fiber texture. The ratio of P₁₁₁/P₂₀₀ increased with the film thickness. Thus, in case of amorphous substrate, the type of the crystallographic texture of a film depends mainly on the structure of the deposited material. The crystallite size increases while the residual strain decreases, as the film thickness or the deposition rate is increased. The crystallite size was very small compared with the film thickness. The effect of deposition rate was pronounced specially from 0.7 to 1.5 nm/s.     

Effect of substrate temperature on polycrystalline Cd0.9Zn0.1Te thin films studied by Raman scattering spectroscopy

Cd_0.9Zn_0.1Te thin films were prepared by vacuum evaporation onto well‐cleaned glass substrates maintained at 300, 373 and 473 K. X‐ray diffraction studies revealed that the films have zinc blende structure with preferential (111) orientation. Raman peak of the room temperature deposited film appeared at 140.30 cm^‐1 and 159.65 cm^‐1 were for the transverse optic (TO) and longitudinal optic (LO) phonons respectively. The XRD patterns of the higher substrate temperature deposited films exhibited an improvement in the crystallinity of the films. The Raman peak intensity increases and the FWHM decreases for the films deposited at higher substrate temperature. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric properties of bis(2,4 pentanedionato)copper(II) crystalline films grown on Si substrate for low-k applications

Bis(acetylacetonato)copper(II) thin films were prepared by sublimation at about 245 °C in vacuum on p-Si and glass substrates for dielectric and optical investigations. They were characterized by the X-ray diffraction (XRD) and energy-dispersion X-ray fluorescence (EDXRF) methods. The XRD pattern reveals that the prepared films were polycrystalline of monoclinic P2₁/n structure. The optical absorption spectrum of the prepared film was not identical to that of the molecular one, which identified by a strong absorption peak at 635 nm. The onset energy of the optical absorption of the complex was calculated by using Hamberg et al. method, which is usually used for common solid-state semiconductors and insulators. The dielectric properties for the complex as insulator were investigated on samples made in form of a metal-insulator-semiconductor (MIS) structure. The dielectric properties were studied in frequency range 1–1000 kHz and temperature range 298–333 K. The dielectric relaxation was analyzed in-terms of dielectric modulus M¹(ω). Generally, the present study shows that films of the complex grown on Si substrate are a promising candidate for low-k dielectric applications; it displays low-k value around 1.7 ± 0.1 at high frequencies.     

Influence of the substrate temperature on the structural,optical, and electrical properties of tin selenide thin films deposited by thermal evaporation method

Thin films of tin selenide (SnSe) were deposited on sodalime glass substrates, which were held at different temperatures in the range of 350‐550 K, from the pulverized compound material using thermal evaporation method. The effect of substrate temperature (T_s) on the structural, morphological, optical, and electrical properties of the films were investigated using x‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission measurements, and Hall‐effect characterization techniques. The temperature dependence of the resistance of the films was also studied in the temperature range of 80‐330 K. The XRD spectra and the SEM image analyses suggest that the polycrystalline thin films having uniform distribution of grains along the (111) diffraction plane was obtained at all T_s. With the increase of T_s the intensity of the diffraction peaks increased and well‐resolved peaks at 550 K, substrate temperature, were obtained. The analysis of the data of the optical transmission spectra suggests that the films had energy band gap in the range of 1.38‐1.18 eV. Hall‐effect measurements revealed the resistivity of films in the range 112‐20 Ω cm for films deposited at different T_s. The activation energy for films deposited at different T_s was in the range of 0.14 eV‐0.28 eV as derived from the analysis of the data of low‐temperature resistivity measurements. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lanthanum manganite phase diagram

Based on neutron diffraction studies the magnetic moments have been calculated and the magnetic phase relation has been determined in the lanthanum manganite samples (LaMnO₃) with different degree of crystallographic lattice distortions. It is established that with the decrease of the distortions the ferromagnetic phase content increases at the expense of the antiferromagnetic phase. The lanthanum manganite phase diagram has been plotted from the obtained data.     

Microstructural,optical and electrical properties of GeO2 thin films prepared by sol‐gel method

GeO₂ thin films were prepared by sol‐gel method on ITO/Glass substrate. The electrical and optical properties and the microstructures of these films were investigated with special emphasis on the effects of an annealing treatment in ambient air. The films were annealed at various temperatures from 500 °C to 700 °C. Structural analysis through X‐ray diffraction (XRD) and atomic force microscope (AFM) showed that surface structure and morphological characteristics were sensitive to the treatment conditions. The optical transmittance spectra of the GeO₂/ITO/Glass were measured using a UV‐visible spectrophotometer. All films exhibited GeO₂ (101) orientation perpendicular to the substrate surface where the grain size increased with increasing annealing temperature. The optical transmittance spectroscopy further revealed high transparency (over 70 %) in the wave range 400 – 800 nm of the visible region. At an annealing temperature level of 700 °C, the GeO₂ films were found to possess a leakage current density of 1.31×10^‐6A/cm² at an electrical field of 20 kV/cm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation into the growth and structure of thin-film solid solutions of iron-based superconductors in the FeSe0.92-FeSe0.5Te0.5 system

Thin films of FeSe_0.92 and FeSe_0.5Te_0.5 iron chalcogenide superconductors and solid solutions containing these components in different ratios have been grown on the surface of LaAlO₃ (10 $\bar 1$ 2) crystals by pulsed laser deposition. Films of solid solutions have been deposited by simultaneous laser ablation from two targets of the FeSe_0.92 and FeSe_0.5Te_0.5 stoichiometric compositions onto one substrate. An X-ray diffraction study of the film structure shows that the films grown are epitaxial and their lattice parameters regularly vary with the ratio of the deposited components, which was controllably varied by changing the ablation intensities from the targets.     

Effect of annealing temperature on the structural and optical properties of amorphous Sb2Te2Se thin films

Thin films of Sb₂Te₂Se were prepared by conventional thermal evaporation of the presynthesized material on Corning glass substrates. The chemical composition of the samples was determined by means of energy‐dispersive X‐ray spectrometry. X‐ray diffraction studies on the as‐deposited and annealed films revealed an amorphous‐to‐crystalline phase transition. The as‐deposited and annealed films at T _a = 323 and 373 K are amorphous, while those annealed at T _a= 423 and 473 K are crystalline with a single‐phase of a rhombohedral crystalline structure as that of the source material. The unit‐cell lattice parameters were determined and compared with the reported data. The optical constants (n , k ) of the investigated films were determined from the transmittance and reflectance data at normal incidence in the spectral range 400–2500 nm. The analysis of the absorption spectra revealed non‐direct energy gaps, characterizing the amorphous films, while the crystalline films exhibited direct energy gaps. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)