M. V. Ramana Reddy

Enhancement of the isopropanol gas sensing performance of SnO2/ZnO core/shell nanocomposites

Pure SnO2, ZnO nanoparticles, and a SnO2/ZnO core/shell nanocomposite (NC) were prepared via a sol–gel technique. The structure and morphology of the obtained materials were characterized by X-ray diffraction (XRD), micro-Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). The results showed that highly crystalline materials were formed, and the resulting composites exhibited core/shell structure with a size of 30 nm, whereas the fabricated films exhibited porous morphology. The gas sensing performance of the SnO2, ZnO nanoparticles, and the SnO2/ZnO NC films was investigated for different volatile organic compound (VOC) vapors in the temperature range from 150 to 350 °C. The gas sensing results confirmed that the SnO2/ZnO NC film shows a high selectivity, sensitivity, good stability, and fast response time towards isopropanol at the optimum operating temperature of 300 °C.

Grain size dependent magnetoelectric coupling of BaTiO3 nanoparticles

We report the magnetoelectric (ME) coupling properties of BaTiO3 nanoparticles of different grain sizes ranging from 16–26 nm synthesized using a modified Pechini method. Nanostructured multiferroic BaTiO3 shows good ferroelectric and magnetic properties at room temperature, which is confirmed using temperature dependent dielectric spectroscopy and a magnetometer. A quantitative magnetoelectric coefficient measurement of BaTiO3 samples at room temperature was performed using the dynamic lock-in amplifier technique. The obtained magnetoelectric coefficient values of all the samples indicate the occurrence of strong magnetoelectric coupling and the maximum recorded at an AC magnetic field of 77 Oe is 32 mV cm−1 Oe−1 and exhibits size-dependent magnetoelectric coupling. This enhanced room temperature ME voltage coefficient with perfect ME anisotropy provides the possibility for using such a material in low energy consumption or miniaturized device applications in the area of sensors and memory devices.

Structural and Optical properties of ZnO thin films grown on various substrates by RF magnetron sputtering

ZnO thin films were deposited on glass, quartz and silicon substrates under the same growth condition by r.f. magnetron sputtering technique using a high purity (99.99%) ZnO target of 2-in. diameter and 3 mm thickness in an Argon atmosphere with sputtering power of 50W and sputtering pressure of 2×10−2 Torr. A systematic study has been made of the influence of substrate on the film structural properties. Crystalline properties of ZnO films as a function of deposited substrate were investigated using X-ray diffraction. XRD analysis revealed that the deposited films were polycrystalline in nature with strong preferential orientation of grains along the c-axis. The micro structural parameters, such as the lattice constant, crystallite size, stress and strain are calculated. The effect of substrate on the deposited films was discussed. All the films present a high transmittance of above 90% in the wavelength range of the visible spectrum and sharp absorption edge near 380 nm.

Thermoluminescence characteristics of Sm3+ doped NaYF4 crystals

Thermoluminescence (TL) characteristics of NaYF4 crystals doped with Sm3+ have been studied after γ-ray irradiation. Dependence of luminescence efficiency on Sm3+ concentration and radiation dose has been measured and possible applications of NaYF4: Sm3+ as a novel phosphor for TL dosimetry have been investigated. The efficiency of 0·3 mole% Sm3+ doped NaYF4 crystal has been found to be maximum and comparable with commercial thermoluminescence dosimetric (TLD) materials.

Effect of annealing on ZnO thin films grown on quartz substrate by RF magnetron sputtering

Zinc oxide thin films were grown on quartz substrates by RF magnetron sputtering technique in an Argon atmosphere with sputtering power of 50W and sputtering pressure of 2x10-2 Torr and studied the effect of annealing on the structural and optical properties. Crystalline properties of ZnO films as a function of annealing temperature were investigated using X-ray diffraction. XRD analysis revealed that the deposited films were polycrystalline in nature with strong preferential orientation of grains along the c-axis. The micro structural parameters, such as the lattice constant, crystallite size, stress and strain are calculated. The effect of annealing on the deposited films was discussed. All the films present a high transmittance of above 90% in the wavelength range of the visible spectrum and sharp absorption edge near 380 nm.

Preparation and Characterization of Cobalt Magnesium Nano Ferrites Using Auto-Combustion Method

Co0.6Mg0.4 Fe2O4 samples are prepared by auto-combustion method at various pH values of the solutions (sols). The precursors for the solids are different gels obtained from metal nitrates and citric acid by sol-gel process. The pH is varied by adding ammonia. The gels thus obtained are heated at 2000C and they exhibited self propagating combustion behavior. The residues are heated for one and half hours at 6000C. XRD analysis of the final solids revealed that after combustion the gel is directly transformed into nano sized cobalt magnesium ferrite particles. The samples are sintered at 6000C and higher temperatures. However, the samples sintered at 6000C have shown single phase nano particles. The ferrites formed have shown variation in particle size for varying pH values. FTIR of the samples supported the Octahedral and Tetrahedral site absorption values. The DC conductivity of the above samples has been studied and the results are discussed.

Structural and optical characterization of Indium oxide thin films by vacuum thermal evaporation

Indium oxide of purity 99.99% powder was used as starting material for the preparation of Indium oxide thin films using vacuum thermal evaporation technique. Ultrasonically cleaned and dried glass substrates were used for deposition of In2O3 thin films. Films were grown in vacuum of 3×10-5mbar pressure followed by annealing in air in the temperature range 573K - 873K. The crystallinity of the films were investigated using XRD. The films were found to be polycrystalline in nature and crystallizes in a cubic structure with preferred (222) orientation. The surface morphology was investigated for these films using Scanning Electron Microscope (SEM) and chemical composition of the films was estimated using EDS. The Optical transparency of these films was found to be varying with annealing temperature and at 673K the transmittance was found to be maximum. Thickness of the films was found to be 918nm. The optical band gap was also varying with annealing temperature. The PL emission spectra were taken at excitation wave length of 350nm. In2O3 thin films shown PL emission in the UV region at room temperature, which encourages development of nano scale devices in future.

Structural and optical properties of AgO thin films grown by RF reactive magnetron sputtering technique

Ag and AgO thin films were grown on glass substrates at room temperature by RF reactive magnetron sputtering technique using silver metal target at high oxygen flow rates 10 to 30 sccm. The crystal structure, surface morphology, composition and optical properties of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and UV-VIS spectrometer, respectively. X-ray diffraction data on these films showed a systematic change from metallic silver to silver oxide (AgO). Optical measurements indicate the existence of a direct-band gap-allowed optical transition with a corresponding energy gap in the range of 1.69 - 1.71 eV.

Effect of substrate temperature on structural and optical properties of nanostructured ZnO thin films grown by RF magnetron sputtering

Nanocrystalline Zinc oxide (ZnO) thin films were prepared by using physical vapor deposition under a vacuum of 5 × 10−5 Torr by using rf magnetron sputtering technique at different substrate temperatures ranging from 373K to 573K. X-ray diffraction analysis (XRD) indicates that the films are polycrystalline, with strong preferential orientation of grains along the c-axis irrespective of their substrate temperature. The microstructural parameters, such as the lattice constant, crystallite size, stress, strain and dislocation density are calculated. The effect of substrate temperature on the deposited films was discussed. The grain size of the deposited ZnO films is observed to be small and is within the range of 11 to 48 nm. The grain size is observed to be increase from 11.72 to 48.52 nm with increasing substrate temperature. Optical measurements indicate the existence of a direct-band gap-allowed optical transition with a corresponding energy gap in the range of 3.26 – 3.32 eV. The films posses high transmittance over 90 % in the visible region and sharp absorption edge near 380 nm.

Effect of oxygen partial pressure on the microstructural, optical and gas sensing characterization of nanostructured Gd doped ceria thin films deposited by pulsed laser deposition

Abstract Microstructural properties of 10 mol% gadolinium doped ceria (CeO2) thin films that were deposited on quartz substrate at substrate temperature of 1023 K by using pulsed laser deposition with different oxygen partial pressures in the range of 50–200 mTorr. The influence of oxygen partial pressure on microstructural, morphological, optical and gas sensing characterization of the thin films was systematically studied. The microstructure of the thin films was investigated using X-ray diffraction, atomic force microscopy and Raman spectroscopy. Morphological studies have been carried out using scanning electron microscope. The experimental results confirmed that the films were polycrystalline in nature with cubic fluorite structure. Optical properties of the thin films were examined using UV–vis spectrophotometer. The optical band gap calculated from Tauc’s relation. Gas sensing characterization has been carried at different operating temperatures (room temperature to 523 K) for acetone gas. Response and recovery times of the sensor were calculated using transient response plot.