Low temperature synthesis and properties of MgxZn1?x O:Al UV transparent conducting films by ultrasonic spray pyrolysis

Mg _x Zn_1?x O:Al UV transparent conducting films were synthesized by ultrasonic spray pyrolysis at low temperature. Effects of Mg doping content and substrate temperature on microstructure, electrical and optical properties of Mg_xZn_1?x O:Al films were investigated. With increasing Mg content x from 0.1 to 0.4, the preferred orientation of (002) in Mg_xZn_1?x O:Al films became weak and the grains became to lenticular-like. The electric resistivities of Mg _x Zn_1?x O:Al films with x?<?0.2 are lower than those of ZnO:Al films, but it obviously increases with the increase of Mg doping contents when x?>?0.2. Highly preferred orientation of (002) in Mg_xZn_1?x O:Al films has been observed when the substrate temperature is over 450?°C. Though the Mg doping content and substrate temperature have no significant influence on the optical transmission of Mg _x Zn_1?x O:Al films, the band gap increases and the absorption edge systematically shifts towards the shorter wavelength with the increasing Mg doping contents, which indicate that the transparent spectrum range of Mg _x Zn_1?x O:Al thin films extend to the ultraviolet band.     

Role of Mg doping on morphology and photoluminescence features of MgxZn1?xO films prepared by ultrasonic spray pyrolysis

The Mg_xZn_1?xO thin films with thickness about several μm were fabricated for different Mg doping concentrations on p-type Si substrates by using an ultrasonic spray pyrolysis method. The morphologies, crystal structures and optical properties were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL), respectively. The SEM results indicated that the surface of Mg_xZn_1?xO films with low Mg concentrations was flat and compact, and the roughness of films increased with Mg concentration. The XRD patterns demonstrated that the low Mg concentration Mg_xZn_1?xO (x?<?0.21) film had a wurtzite structure and the MgO phase was absent. The PL spectra revealed that UV emission has an obvious blue shift with the increase of Mg composition.     

Anisotropy of electrical properties in α-Fe2O3 ceramics

Electrical conductivity and thermoelectric power measurements carried out in a heamatite ceramic showed a strong anisotropy in directions normal and parallel to the uniaxial pressing direction. This behaviour is similar to that verified in -Fe₂O₃ single crystal. The results suggest that the extended structural defects, generated during sintering, disturb the magnetic order on the (001) planes of -Fe₂O₃ and limit the mobility of n type carriers.     

Dependence of structural, optical and electrical properties on substrate temperature for hexagonal MgxZn1−xO films

Single hexagonal-phase Mg_xZn_1?xO films were deposited on glass substrates by pulsed laser deposition from a ZnO target mixed with MgO. The effect of substrate temperature on the structural, electrical and optical properties was investigated by X-ray diffraction and the transmittance measurements. It was observed that Mg incorporation lead to a clear shift of the (002) peak position to lower angle with reference to pure ZnO films due to the residual stress change with deposition temperature. It was also found that Mg doping increased the resistivity by 2 orders of magnitude and the maximum resistivity was 0.072 Ω·cm at 550 °C with the carrier concentration of 1.1 × 10¹⁹ cm^?3. The visible transmittance of above 80 % was obtain in the alloy films, which optical band gap was observed to increase with the substrate temperature, attaining 3.85 eV at 600 °C. The possible mechanism was discussed.     

Structural,optical, and electrical properties of NixZn1−xFe2O4 thin film prepared by spray pyrolysis route

Journal of Materials Science: Materials in Electronics - Nanocrystalline spinel NixZn1?xFe2O4 (x?=?0.0, 0.3, 0.5, 0.7) thin films have been deposited on glass substrate at...     

Characterization of β-In2−xAlxS3 thin films prepared by chemical spray pyrolysis technique

Indium sulfide (In₂S₃) is a good window or buffer layer for photovoltaic application. In this work, β-In_2?xAl_xS₃ thin films with different thicknesses (400, 442, 646 and 714 nm) are successfully synthesized on heated glass substrates using a chemical spray pyrolysis technique. The thin film thickness effect on the structural, optical and photoluminescence (PL) properties of β-In_2?xAl_xS₃ material is studied. The X-ray diffraction patterns suggest the formation of β-In₂S₃ cubic phase preferentially oriented towards (400) direction. The level of the residual dislocation seems to be reduced to 3.12 × 10⁹ lines mm^?2 for the optimum thickness (646 nm) for which the β-In_2?xAl_xS₃ film crystallinity is the best one. In order to enhance the electrical properties, β-In_2?xAl_xS₃ layers are annealed in air at 400 °C for different annealing times (15, 30 and 45 min). The minimum resistivity, maximum Hall mobility and carrier concentration are found for β-In_2?xAl_xS₃ films annealed for 30 min. All samples have high transmittance of about 75 % but the wide band gap (E_g = 3.32 eV) is obtained for this optimum thickness. This result indicates good optical quality of β-In_2?xAl_xS₃ layers. Defects-related PL properties are also discussed.     

Influence of annealing temperature and oxygen atmosphere on the optical and photoluminescence properties of BaTiO3 amorphous thin films prepared by sol–gel method

Homogeneous and transparent BaTiO₃ thin films were prepared by sol–gel dip coating method. The prepared BaTiO₃ thin films were annealed in air and O₂ atmosphere at different temperatures. The annealed BaTiO₃ thin films were amorphous in nature. Scanning electron microscopy (SEM) revealed the nucleation and particle growth on the films. Energy-dispersive X-ray (EDX) analysis data revealed the adsorption of oxygen atoms in the BaTiO₃ film. The direct energy band gap was found to vary (3.84–3.58 eV) as functions of annealing atmosphere and temperature. Photoluminescence (PL) revealed intense emission peaks at 393 and 675 nm. Quenching of PL intensity was observed in films annealed at high temperature and in O₂ atmosphere. This is due to reduction in the oxygen vacancy by the adsorption of oxygen in the film. Luminescence spectra also have been related to the results obtained by SEM and EDX analysis. The change in luminescence intensity of BaTiO₃ thin films makes it suitable for optoelectronic temperature sensor applications.     

Nano-sized α and β-TCP powders prepared by high temperature flame spray pyrolysis

Nano-sized α-TCP powders with spherical shape and non-aggregation characteristics were directly prepared by high temperature flame spray pyrolysis from the mixed spray solution of water and ethyl alcohol. The α-TCP powders prepared from the aqueous spray solution without ethyl alcohol had a bimodal size distribution with nanometer and micron sizes. Nano-sized and monodisperse α-TCP powders were prepared when the volume ratio (ethyl alcohol/distilled water, V/V) in the mixed solvent was of 40/60. The mean size of the nano-sized α-TCP powders was 32 nm. The composition ratio of calcium and phosphorous components of the nano-sized α-TCP powders was 1.49. The mean size of the spherical-like powders post-treated at a temperature of 600 °C was 57 nm. The mean size of the powders increased with increasing the post-treatment temperatures. The phase of α-TCP powders prepared by flame spray pyrolysis did not change at post-treatment temperatures below 700 °C. On the other hand, the powders post-treated at temperatures of 800 and 900 °C had single β phase of TCP.     

Influence of different materials on the microstructure and optical band gap of α-Fe2O3 nanoparticles

Composites of hematite (α-Fe₂O₃) nanoparticles with different materials (NiO, TiO₂, MnO₂ and Bi₂O₃) were synthesized. Effects of different materials on the microstructure and optical band gap of α-Fe₂O₃ nanoparticles were studied. Crystallite size and strain analysis indicated that the pure α-Fe₂O₃ nanoparticles were influenced by the presence of different materials in the composite sample. Crystallite size and strain estimated for all the samples followed opposite trends. However, the value of direct band gap decreased from ～2.67 eV for the pure α-Fe₂O₃ nanoparticles to ～2.5 eV for α-Fe₂O₃ composites with different materials. The value of indirect band gap, on the other hand, increased for all composite samples except for α-Fe₂O₃/Bi₂O₃.     

Influence of Fe dopant concentration and annealing temperature on the structural and optical properties of ZnO thin films deposited by sol–gel method

Nanostructured Fe doped ZnO thin films were deposited onto glass substrates by sol–gel spin coating method. Influence of Fe doping concentration and annealing temperature on the structural, compositional, morphological and optical properties were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–Vis spectroscopy and photoluminescence (PL) measurements. XRD analysis showed that all the films prepared in this work possessed a hexagonal wurtzite structure and were preferentially oriented along the c-axis. Pure ZnO thin films possessed extensive strain, whereas Fe doped films possessed compressive strain. In the doped films, least value of stress and strain was observed in the 0.5 at.% Fe doped thin film, annealed at 873 K. Average crystallite size was not significantly affected by Fe doping, but it increased from 15.57 to 17.79 nm with increase in annealing temperature from 673 to 873 K. Fe ions are present in +3 oxidation state as revealed by XPS analysis of the 0.5 at.% Fe doped film. Surface morphology is greatly affected by changes in Fe doping concentration and annealing temperature which is evident in the SEM images. The increase in optical band gap from 3.21 to 3.25 eV, with increase in dopant concentration was attributed to Moss–Burstein shift. But increase in annealing temperature from 673 to 873 K caused a decrease in band gap from 3.22 to 3.20 eV. PL spectra showed emissions due to excitonic combinations in the UV region and defect related emissions in the visible region in all the investigated films.     

Influence of annealing temperature on the structural,topographical and optical properties of sol–gel derived ZnO thin films

This investigation deals with the effect of annealing temperature on the structural, topographical and optical properties of Zinc Oxide thin films prepared by sol–gel method. The structural properties were studied using X-ray diffraction and the recorded patterns indicated that all the films had a preferred orientation along (002) plane and the crystallinity along with the grain size were augmented with annealing temperature. The topographical modification of the films due to heat treatment was probed by atomic force microscopy which revealed that annealing roughened the surface of the film. The optical properties were examined by a UV–visible spectrophotometer which exhibited that maximum transmittance reached nearly 90% and it diminished with increasing annealing temperature.     

Sonochemical fabrication and catalytic properties of α-Fe2O3 nanoparticles

In this study, α-Fe₂O₃ (hematite) nanoparticles were synthesised by a sonochemical method. The influence of different factors such as chemical composition of the precursors, atmosphere of the reactions and type of the sonicator on the chemical formula, crystallinity, morphology and size of the obtained products were investigated. Powder X-ray diffraction, scanning electron microscopy and IR spectroscopy, were used to characterise the nanostructures. The catalytic tests were performed in the reaction of methyl phenyl sulphide oxidation. The results exhibit the good catalytic performance of the as-prepared α-Fe₂O₃ nanoparticles.     

Effect of stabilizer on optical and structural properties of MgO thin films prepared by sol–gel method

The effects of monoethanolamine (MEA) and acetylacetone (ACAC) addition as stabilizer on the crystallization behaviour, morphology and optical properties of magnesium oxide were investigated using thermogravimetry (TG/DTG), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Visible, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. Stabilizer addition reduces transparency of the films. MgO films prepared at 500 °C showed weak orientation of (200). However, the films prepared by addition of stabilizer are amorphous. MgO powders were prepared for exhibiting the structural properties. The patterns of MgO powders showed a preferred orientation of (200). The addition of stabilizer causes a reduction in grain size. SEM micrographs show that a homogenous and crack-free film can be prepared at 500 °C and addition of stabilizer causes an increase in packing density.     

Effect of annealing temperature on optical and electrical properties of ZrO2–SnO2 nanocomposite thin films

ZrO₂–SnO₂ nanocomposite thin films were deposited onto quartz substrate by sol–gel dip-coating technique. Films were annealed at 500, 800 and 1,200 °C respectively. X-ray diffraction pattern showed a mixture of three phases: tetragonal ZrO₂ and SnO₂ and orthorhombic ZrSnO₄. ZrSnO₄ phase and grain size increased with annealing temperature. Fourier transform infra-red spectroscopy spectra indicated the reduction of –OH groups and increase in ZrO₂–SnO₂, by increasing the treatment temperature. Scanning electron microscopy observations showed nucleation and particle growth on the films. The electrical conductivity decreased with increase in annealing temperature. An average transmittance greater than 80 % (in UV–visible region) was observed for all the films. The optical constants of the films were calculated. A decrease in optical band gap from 4.79 to 4.59 eV was observed with increase in annealing temperature. Photoluminescence (PL) spectra revealed an emission peak at 424 nm which indicates the presence of oxygen vacancy in ZrSnO₄. PL spectra of the films exhibited an increase in the emission intensity with increase in temperature which substantiates enhancement of ZrSnO₄ phase and reduction in the non-radiative defects in the films. The nanocomposite modifies the structure of the individual metal oxides, accompanied by the crystallite size change and makes it ideal for gas sensor and optical applications.     

Spray pyrolysis deposition of α-Fe2O3 thin films using iron (III) citric complexes

Thin films of α-Fe₂O₃ have been deposited on fused silica substrates (heated at 500 °C) by an in situ spray pyrolysis method using ethylene glycol solution of Fe(III)-citric complexes and O₂ as a carrier gas. The monophase composition of the films was confirmed by the X-ray diffractometry. Their morphology and roughness have been estimated by means of atomic force microscopy (AFM).     

Preparation of Ni particles by ultrasonic spray pyrolysis of NiCl2·6H2O precursor containing ammonia

The preparation of nickel particles from nickel ammine complex was studied by ultrasonic spray pyrolysis in the presence and the absence of hydrogen. In the presence of H₂ (about 9 vol.%), nickel particles were formed at 500 °C, which is much lower than that reported. Metallic nickel, together with NiO, was obtained as a major phase at 400 °C. In the absence of H₂, metallic Ni was also obtained, but higher temperature (e.g. 900 °C) was needed. It is suggested that the addition of NH₃·H₂O and NH₄HCO₃ to NiCl₂·6H₂O precursor changes the reaction pathway of Ni formation. By careful control, spherical, solid and well-distributed Ni particles of about 0.5 m were obtained at a residence time of 7–9 s in the aerosol reactor.     

Anisotropy in the electrical properties of zirconium doped α -Fe2O3 single crystals

The electrical properties of zirconium doped α -Fe₂O₃ single crystals have been investigated from 470 up to 1300 K.As for the pure crystal, an anisotropy appears for the conductivity between the [001] direction and the (001) plane, although lowered by the dopant.Combining the results of electrical conductivity, thermoelectric power and complex impedance measurements, it was established that there was no significant kinetic contribution of the electrons and that their mobility was lower than a few tenths of cm²V⁻¹s⁻¹.     

The effect of repeated annealing temperature on the structural,optical, and electrical properties of TiO<Subscript>2</Subscript> thin films prepared by dip-coating sol–gel method

In this study, we have studied the effect of repeated annealing temperatures on TiO₂ thin films prepared by dip-coating sol–gel method onto the glasses and silicon substrates. The TiO₂ thin films coated samples were repeatedly annealed in the air at temperatures 100, 200, and 300 °C for 5 min period. The dipping processes were repeated 5 to 10 times in order to increase the thickness of the films and then the TiO₂ thin films were annealed at a fixed temperature of 500 °C for 1 h period. The effect of repeated annealing temperature on the TiO₂ thin films prepared on glass substrate were investigated by means of UV–VIS spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM). It was observed that the thickness, average crystallite size, and average grain size of TiO₂ samples decreased with increasing pre-heating temperature. On the other hand, thickness, average crystallite size, and average grain size of TiO₂ films were increased with increasing number of the layer. Al/TiO₂/p-Si metal–insulator–semiconductor (MIS) structures were obtained from the films prepared on p-type single silicon wafer substrate. Capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements of the prepared MIS structures were conducted at room temperature. Series resistance (R _s) and oxide capacitance (C _ox) of each structures were determined by means of the C–V curves.