Electrical conductivity of ferroelectric sodium vanadate,rubidium vanadate,cesium vanadate and their solid solutions

The d.c. electrical conductivity of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions sodium-rubidium vanadate and sodium-cesium vanadate were studied by a two-probe method in the temperature range covering their transition points. The electrical conductivity shows sharp change at the phase transition temperature of these materials. In NaVO₃, RbVO₃ and CsVO₃, increase in d.c. conductivity is observed in the ferroelectric region while nonlinearities are observed above transition temperatures. In solid solutions, the activation energy in the paraelectric state is higher than that in the ferroelectric state and depends upon sodium concentration.     

Optical and mechanical properties of diamond like carbon films deposited by microwave ECR plasma CVD

Diamond like carbon (DLC) films were deposited on Si (111) substrates by microwave electron cyclotron resonance (ECR) plasma chemical vapour deposition (CVD) process using plasma of argon and methane gases. During deposition, a d.c. self-bias was applied to the substrates by application of 13·56 MHz rf power. DLC films deposited at three different bias voltages (−60 V, −100 V and −150 V) were characterized by FTIR, Raman spectroscopy and spectroscopic ellipsometry to study the variation in the bonding and optical properties of the deposited coatings with process parameters. The mechanical properties such as hardness and elastic modulus were measured by load depth sensing indentation technique. The DLC film deposited at −100 V bias exhibit high hardness (∼ 19 GPa), high elastic modulus (∼ 160 GPa) and high refractive index (∼ 2·16–2·26) as compared to films deposited at −60 V and −150 V substrate bias. This study clearly shows the significance of substrate bias in controlling the optical and mechanical properties of DLC films.     

Diamond like carbon coatings deposited by microwave plasma CVD: XPS and ellipsometric studies

Diamond-like carbon (DLC) films were deposited by microwave assisted chemical vapour deposition system using d.c. bias voltage ranging from −100 V to −300 V. These films were characterized by X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry techniques for estimating sp ³/sp ² ratio. The sp ³/sp ² ratio obtained by XPS is found to have an opposite trend to that obtained by spectroscopic ellipsometry. These results are explained using sub-plantation picture of DLC growth. Our results clearly indicate that the film is composed of two different layers, having entirely different properties in terms of void percentage and sp ³/sp ² ratio. The upper layer is relatively thinner as compared to the bottom layer.     

Theoretical analysis of effect of temperature on threshold parameters and field intensity in GaN material based heterostructure

Temperature dependent analysis to achieve better performance by reducing threshold current requirements and field intensity has been carried out for GaN/AlGaN heterostructure lasers. The mirror loss in the GaN cavity has been obtained as a function of temperature and cavity length. The quantum efficiency has been deduced for different values of cavity length. Dependence of recombination rate on band gap and temperature has been investigated. Threshold current density has been deduced for GaN lasers and effect of temperature on it has been investigated. The near field intensity analysis has been carried out at different temperatures for 10% aluminum mole fraction in GaN/AlGaN heterostructure lasers. Furthermore, the effective index and FWHM of near field has been investigated as a function of temperature. It has been deduced from our analysis that temperature has a dominant effect on the threshold conditions and near field intensity in the wide band gap GaN based lasers.     

Sensitized monomer fluorescence and excitation energy transfer in perylene-doped phenanthrene in crystalline and in polymer matrix

Sensitized monomer fluorescence and excitation energy transfer in crystalline and spin cast polymer films was investigated at room temperature. The fluorescence spectra of perylene doped phenanthrene reveals the characteristic monomeric emission of perylene and partial quenching of phenanthrene emission. The excimer formation of perylene is not observed in mixed crystalline luminophors and in spin cast films of the phenanthrene luminophors. The observed quenching of phenanthrene emission indicates the excitation energy transfer from phenanthrene to perylene in crystalline as well as in polymer matrix. Energy transfer is not observed in the experiments when phenanthrene and perylene were physically mixed where the components exist separately. The overlap between the excitation spectrum of perylene and emission spectrum of the phenanthrene supports the fact that the perylene molecules accept the excitation energy from phenanthrene. The energy transfer was found to depend upon the perylene concentration.     

Hexamethylenetetramine: A New Fuel for Solution Combustion Synthesis of Complex Metal Oxides

Hexamethylenetetramine, (CH₂)₆N₄ (HMT) has been employed as a fuel for the first time to synthesize several binary, ternary, and quaternary oxides by the solution combustion method. Technologically important oxides, namely, zirconia, ceria, and their solid solutions, -Al₂O₃, Cr³⁺-doped -Al₂O₃, spinels, MAl₂O₄ (M = Ca, Mg, Zn and Ni), perovskites, LaMO₃ (M = Mn, Cr and Al), La_0.67Sr_0.33MnO₃, and La_0.67Ca_0.33MnO₃, have been synthesized. The oxides synthesized are characterized by X-ray powder diffraction, resistivity, fluorescence spectra, particle size, and surface area measurements. Decomposition of nickel nitrate-HMT complex has been investigated by TG, DTA, TPD, and evolved-gas analysis to elucidate the mechanism.     

Sustained release microspheres of diclofenac sodium using PEGylated rosin derivatives

The PEGylated derivatives of rosin-PD-1 and PD-2 synthesized and characterized earlier (Nande et al., 2006) were investigated as potential materials for sustained release microsphere prepared by emulsion solvent evaporation method using diclofenac sodium (DCS) as model drug. All the microspheres exhibited smooth surfaces intercepted by pores; their sizes (d(90)) ranged between 11-24 microm. The entrapment efficiency (< 80%) of the microspheres increased proportionally with derivative concentration. Presence of solvent like isopropyl alcohol or dichloromethane rendered the microspheres with large sizes but with reduced drug entrapment. Microspheres with small size were obtained at an optimum viscosity of liquid paraffin; any change lead to increase in the particle size. Magnesium stearate was found to be most suitable detackifier in the present system. The drug release was directly related to the particle size--small sized microspheres released drug at a faster rate. The dissolution data complied with Higuchi equation while the mechanism of drug release was Fickian diffusion (n approximately 0.5). Controlled inhibition of edema, as tested by hind paw edema method, was observed for 10 h when the microspheres were administered intraperitoneally. The present study found the derivatives as promising materials for preparing microspheres for sustained delivery of DCS.     

Novel method for fabrication of NiO sensor for NO2 monitoring

Nickel oxide (NiO) sensor films were prepared on glass substrate by a sol–gel spin coating technique. These films were characterized for their structural and morphological properties by means of X-ray diffraction, field emission scanning microscopy and atomic force microscopy. The NiO films are oriented along (200) plane with the cubic crystal structure. These films were utilized in nitrogen dioxide gas (NO₂) sensor. The dependence of the NO₂ response on operating temperature, NO₂ concentration was investigated. The NiO film showed selectivity for NO₂ over Cl₂ compared to H₂S $ \left( {{\text{S}}_{{{\text{NO}}_{ 2} }} /{\text{S}}_{{{\text{Cl}}_{ 2} }} = 3 7. 5,{\text{ S}}_{{{\text{NO}}_{ 2} }} /{\text{S}}_{{{\text{H}}_{ 2} {\text{S}}}} = 3. 4} \right) $ . The maximum NO₂ response of 23.3 % with 85 % stability at gas concentration of 200 ppm at 200 °C was achieved. The response time of 20 s and recovery time of 498 s was also recorded with same operating parameters.