Studies of structural evolution and sensing properties of ZnO nanocrystalline films

ZnO nanocrystalline films have been prepared on Si(1 0 0) substrate using direct current (D.C) magnetron sputtering technique at room temperature. The thickness of nanocrystalline films almost linearly increased with deposition duration and the sizes of crystalline grains almost kept unchanged. After deposition, thermal annealing was performed at 800 °C in atmosphere for 2 h in order to improve the qualities of ZnO thin films. Scanning electron microscope (SEM) images showed the surface roughness of the films less than 45 nm. X-ray diffraction (XRD) patterns revealed the slight evolution of the crystal structures. Raman scattering spectra confirmed the data obtained from X-ray diffraction measurements.With these ZnO nanocrystalline films, prototypic gas sensors were fabricated. Both sensitivity and response of the sensors to different gases (H₂ and CH₄) were investigated. A quick response of time, less than 1 second to CH₄ gas sensor has been achieved.     

Synthesis, characterization, growth mechanism, photoluminescence and field emission properties of novel dandelion-like gallium nitride

Dandelion-like gallium nitride (GaN) microstructures were successfully synthesized via Ni catalyst assisted chemical vapor deposition method at 1200 °C under NH₃ atmosphere by pre-treating precursors with aqueous ammonia. The as-synthesized product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). X-ray diffraction analysis revealed that as-synthesized dandelion-like GaN was pure and has hexagonal wurtzite structure. SEM results showed that the size of the dandelion-like GaN structure was in the range of 30-60 μm. Dandelion-like GaN microstructures exhibited reasonable field emission properties with the turn-on field of 9.65 V μm⁻¹ (0.01 mA cm⁻²) and threshold field of 11.35 V μm⁻¹ (1 mA cm⁻²) which is sufficient for applications of electron emission devices, field emission displays and vacuum micro electronic devices. Optical properties were studied at room temperature by using fluorescence spectrophotometer. Photoluminescence (PL) measurements of dandelion-like GaN showed a strong near-band-edge emission at 370.2 nm (3.35 eV) with blue band emission at 450.4 nm (2.75 eV) and 465.2 nm (2.66 eV) but with out yellow band emission. The room-temperature photoluminescence properties showed that it has also potential application in light-emitting devices. The tentative growth mechanism for the growth of dandelion-like GaN was also described.     

Structure elucidation of two new unusual monoterpene glycosides from Euphorbia decipiens, by 1D and 2D NMR experiments

Two new unusual monoterpene glycosides, (Z)-3,6-dimethyl-3-(β-D-O-glucosylmethylene)cyclohept-4-ene-1-one (1) and 3,6-dimethyl-3-(β-D-O-glucosylmethylene)cycloheptanone (2) have been isolated along with five known compounds, 3-hydroxy-4-methoxybenzoic acid, 6,7-dihydroxycoumarin, luteolin, apigenin 5-O-αl-L-rhamnoside, and pinocembrin-7-O-rutinoside from ethyl acetate extract of Euphorbia decipiens. The structures of the isolated compounds were elucidated by extensive 1D- and 2D-NMR, and mass spectroscopic analyses.     

Validated RP-HPLC method for determination of permethrin in bulk and topical preparations using UV-vis detector

An isocratic reversed-phase high-performance liquid chromatographic method for the estimation of permethrin in raw materials and pharmaceutical topical preparations has been devised and validated. The chromatographic analysis was performed on a 5 μm particle C-18 Nucleosil (Macherey-Nagel, Germany) column (250 × 4.6 mm). Mobile phase consisted of methanol and 0.025 mM Phosphoric acid (85:15 v/v) at a flow rate of 1.5 mL/min. UV detection was performed at 272 nm and peaks were identified with retention times as compared with standards. The limit of detection was 1.782 μg/mL, while limit of quantitation was 48.0 μg/mL. The calibration was linear in a concentration range of 48.0-5000 μg/mL with correlation coefficient of 0.999978. Regression equation was absorbance =2833.23 × concentration(μg/mL) + 19.1045 with variance of the response variable, S(yx)(2), calculated to be 1.75328 (six degrees of freedom). The method was validated as per ICH guidelines and USP requirements and found advantageous for the routine analysis of the drug in pharmaceutical formulations and in pharmaceutical investigations involving permethrin.     

Synthesis and Optoelectronic Properties of Symmetrical Thiophene Based 2,5-disubstiuted 1,3,4-oxadiazoles: Highly Fluorescent Materials for OLED Applications

Symmetrical 2,5-disubstituted thiophene derivatives containing 1,3,4-oxadiazole moiety bearing different aromatic substitutions were synthesized by employing convenient and simple synthetic protocols using thiophene-2,5,dicarboxylic acid as a starting material. The structures of these target molecules were established by their analytical and spectral data. The photophysical and electrochemical studies were carried out on these compounds and found that they exhibit good fluorescent properties with high quantum yield.     

Gamma irradiation of sun-dried apricots (Prunus armeniaca L.) for quality maintenance and quarantine purposes

The study is aimed at the optimization of gamma irradiation treatment of sun-dried apricots for quality maintenance and quarantine purposes. Sun-dried apricots pre-treated with potassium meta-bisulphite (KMS) at 2.5% w/v were procured from progressive apricot grower of district Kargil, Ladakh region of Jammu and Kashmir state. The sun-dried apricots were packed in 250 gauge polyethylene packs and gamma irradiated in the dose range 1.0–3.0 kGy. The gamma irradiated fruit including control was stored under ambient (15±2–25±2 °C, RH 70–80%) conditions and periodically evaluated for physico-chemical, sensory and microbial quality parameters. Radiation treatment at dose levels of 2.5 and 3.0 kGy proved significantly (p≤0.05) beneficial in retention of higher levels of β-carotene, ascorbic acid, total sugars and color values without impairing the taste as perceived by the sensory panel analysists. The above optimized doses retained the β-carotene content of sun-dried apricots to the extent of 71.2% and 72.6% compared to 63.9% in control samples after 18 months of storage. Irradiation treatment facilitated the release of residual sulfur dioxide in KMS pre-treated sun-dried apricots significantly (p≤0.05) below the prescribed limit for dried products. During storage, two-fold decrease in sulfur dioxide content was recorded in irradiated samples (3.0 kGy) as compared to 16.9% in control. The above optimized doses besides maintaining the higher overall acceptability of sun-dried apricots resulted in 5 log reductions in microbial load just after irradiation and 1.0 and 1.3 log reductions in yeast and mold and bacterial count after 18 months of ambient storage.     

Highly diastereoselective 1,2-dichlorination of glycals using NCS/PPh3: study of substituent and solvent effects

Highly diastereoselective 1,2-dichlorination of glycals has been achieved at room temperature conditions in good to excellent yields using a milder, more convenient, less hazardous reagent combination NCS/PPh₃ giving only one major product out of four possible diastereomers [either α-gluco (2) or α-manno (4)] depending upon the substituents. The diastereoselectivity is maximum (100% α/β-selectivity as well as cis/trans selectivity) for d-galactal and l-rhamnal derivatives. Detailed studies showed that solvent and substituent effects play a significant role in determining the product distribution.     

Nitriding molybdenum: Effects of duration and fill gas pressure when using 100-Hz pulse DC discharge technique

Molybdenum is nitrided by a 100-Hz pulsed DC glow discharge technique for various time durations and fill gas pressures to study the effects on the surface properties of molybdenum. X-ray diffractometry(XRD), scanning electron microscopy(SEM), and atomic force microscopy(AFM) are used for the structural and morphological analysis of the nitrided layers. Vickers’ microhardness tester is utilized to investigate surface microhardness. Phase analysis shows the formation of more molybdenum nitride molecules for longer nitriding durations at fill gas pressures of 2 mbar and 3 mbar(1 bar = 105Pa). A considerable increase in surface microhardness(approximately by a factor of 2) is observed for longer duration(10 h) and 2-mbar pressure. Longer duration(10 h) and 2-mbar fill gas pressure favors the formation of homogeneous, smooth, hard layers by the incorporation of more nitrogen.