A High Sensitivity Isopropanol Vapor Sensor Based on Cr2O3-SnO2 Heterojunction Nanocomposites via Chemical Precipitation Route.

Cr2O3-SnO2 heterojunction nanocomposites were prepared via chemical precipitation method. The prepared samples were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectra and Field Emission Electron Microscopy (FESEM). The XRD spectrum confirms the presence of both tetragonal rutile SnO2 and rhombohedral corundum Cr2O3 structure. Further investigation into the gas sensing performances of the prepared Cr2O3-SnO2 nanocomposites exhibited an enhanced sensitivity towards VOPs such as isopropanol, acetone, ethanol and formaldehyde. Especially, isopropanol vapor sensor shows excellent sensitivity at an operating temperature of 100 °C. The highest sensitivity for Cr2O3-SnO2 heterojunction nanocomposites indicate that these materials can be a good candidate for the production of high-performance isopropanol sensors.

Spectroscopic and fiber optic ethanol sensing properties Gd doped ZnO nanoparticles.

We report the structural, optical and gas sensing properties of prepared pure and Gd doped ZnO nanoparticles through solgel method at moderate temperature. Structural studies are carried out by X-ray diffraction method confirms hexagonal wurtzite structure and doping induced changes in lattice parameters is observed. Optical absorption spectral studies shows red shift in the absorption peak corresponds to band-gap from 3.42 eV to 3.05 eV and broad absorption in the visible range after Gd doping is observed. Scanning electron microscopic studies shows increase in particle size where the particle diameters increase from few nm to micrometers after Gd doping. The clad modified ethanol fiber-optic sensor studies for ethanol sensing exhibits best sensitivity for the 3% Gd doped ZnO nanoparticles and the sensitivity get lowered incase of higher percentage of Gd doped ZnO sample.

Phase transition and thermal expansion studies of alumina thin films prepared by reactive pulsed laser deposition.

Aluminium oxide (Al2O3) thin films were deposited on Si (100) substrates at an optimized oxygen partial pressure of 3 x 10(-3) mbar at room temperature by pulsed laser deposition (PLD). The films were characterized by high temperature X-ray diffraction (HTXRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The HTXRD pattern showed the cubic y-Al2O3 phase in the temperature range 300-973 K. At temperatures ≥ 1073 K, the δ and θ-phases of Al2O3 were observed. The mean linear thermal expansion coefficient and volume thermal expansion coefficient of γ-Al2O3 was found to be 12.66 x 10(-6) K(-1) and 38.87 x 10(-6) K(-1) in the temperature range 300 K-1073 K. The field emission scanning electron microscopy revealed a smooth and structureless morphology of the films deposited on Si (100). The atomic force microscopy study indicated the increased crystallinity and surface roughness of the films after annealing at high temperature.

Synthesis, growth and characterization of 4-bromo-4'chloro benzylidene aniline--a third order non linear optical material.

The organic nonlinear optical material of 4-bromo-4'chloro benzylidene aniline (BCBA) was synthesized and single crystal of BCBA was grown from acetone solution by solvent evaporation method at room temperature. Its three dimensional structure was elucidated from single crystal X-ray diffraction analysis at 173 K. Synthesized compound of BCBA was subjected to FTIR and (1)H and (13)C NMR spectral analyses. The range and percentage of optical transmission of BCBA was determined by UV-vis-NIR spectrum and its fluorescence spectrum was recorded using spectrofluorometer. The mechanical strength of the crystal was estimated using Vickers microhardness test on the (001) plane. Dielectric constant of the grown crystal was measured for various frequencies along (001) plane. The third order nonlinear optical properties of BCBA were investigated by Z-scan technique with He-Ne laser radiation of wavelength at 632.8 nm and the corresponding nonlinear refractive index, absorption coefficient and optical susceptibility were calculated.

Synthesis and properties of ceria thin films prepared by pulsed laser deposition.

Cerium oxide (CeO2) thin films were prepared on (100) Si and glass substrates using pulsed laser ablation at different oxygen partial pressures (2.5 x 10(-5)-3.5 x 10(-1) mbar) and at a substrate temperature of 873 K. XRD studies on the films showed that the films are polycrystalline having fluorite structure. The oxygen partial pressure has a dominant effect on the thickness, crystallite size and preferred orientation of the films. At an oxygen partial pressure of 3.5 x 10(-2) mbar, the intensity of (200) reflection is maximum and film possesses the maximum crystallite size of about 50 nm. Though all the films are highly transparent in the visible region, films prepared at an oxygen partial pressure of 3.5 x 10(-1) mbar, exhibits maximum transmittance (>90% @ 632 nm). The optical band gap is found to decrease from 3.66 to 3.42 eV with the increasing oxygen partial pressure.