Condensed Matter

Nanocrystalline zinc sulphide (ZnS) thin films have been successfully deposited on silica glass substrates from acidic chemical baths containing tartaric acid and hydrazine as complexing agents, thioacetamide as a sulphur source and zinc acetate as the source of zinc ions. The influence of temperature on the structural-, optical-, morphological properties and elemental composition of the films were investigated by a variety of techniques. Powder x-ray diffraction patterns of the films exhibited the cubic structure. The deposition temperature had a significant influence on the lattice parameter and crystallite size. Scanning electron microscope and energy dispersive x-ray investigations have shown an improvement in morphology and stoichiometry of the films with increasing deposition temperature. The band gap of the thin films obtained by optical absorption spectroscopy showed a decrease from 3.88 eV to 3.75 eV as the deposition temperature increased. Transmittance of the films increased with decreasing deposition temperature.

Pressure induced exciton binding energy, optical transition energy, second order optical rectification coefficient and the third order harmonic generation of third order susceptibility are computed in Zn0.1Mg0.9Se / Zn0.8Mg0.2Se / Zn0.1Mg0.9Se quantum well. The effects of geometrical confinement and the contribution from the induced strain are included in the Hamiltonian. The effects of internal electric field comprising spontaneous and piezoelectric polarization are considered throughout the calculations. Exciton binding energies, in the presence of hydrostatic pressure, are computed using single band effective mass approximation. Calculations are done employing the variational method and the density matrix method. The second order optical rectification coefficient and the third order susceptibility with the incident photon energy are calculated in the presence of hydrostatic pressure. It is observed that the effect of pressure has influence on the nonlinear optical properties in the Mg based ZnSe quantum well.

Responsivity of silicon photodiodes was measured for different values of temperatures and magnetic field in light and darkens. Group of silicon photodiodes was studied. The surface layer of these diodes was a thin metal silicide surface layer. As the temperature decreases the increase in current is consistent the theoretical relation. These results are particularly important for the measurement of current in extreme cooling. One has studied the effect of cooling on the photodiodes current in the presence of a magnetic field. A recognized change has been observed. The current is observed to increase as the magnetic flux density increase, which is again is conformity with the theoretical relation.

Nanocrystallites of Cadmium oxide (CdO) thin films with different gelation time were deposited by sol-gel spin coating method on a glass substrate. A comparative analysis of the effect of viscosity of sol-gel on the structural, electrical, and optical properties of as deposited films was made. Films were grown with gelation time of one to four days and optimum gelation time of third day of sol-gel viscosity of 3.28 x 10-3 Nsm-2 was determined. From the X-ray diffraction studies the polycrystalline nature of the grown film with a preferential orientation (1 1 1) was analyzed. The resistivity of the material decreases with the increase of gelation time and then increases after the optimum value of gelation time. The films showed resistivity of 2.16 x 10-4 ? m with an optical transmission of 80 % at the wavelength of 625 nm. The observed band gap of the developed film was found to be 2.25 eV. Also optical studies confirm that the optical transmittance was decreased when the viscosity was increased.

Special relativity (SR) in the presence of the gravitational field is obtained from the expression of invariant length and a photon equation of motion. Two expressions explain both mass and energy are obtained; one is generalized special relativity (GSR), the other is of Savickas. The (GSR) model is more realistic than Savickas since it is based on the effect of gravity on time which is not recognized by Savickas expression. Moreover (GSR) model predicts pair production phenomena and its equations of motion which are reduced to Newton's second law. Using the equation of motion of the electron in the electromagnetic (E.M) as a simple expression for the total momentum the sum of photon and electron mechanical momentum was found.

Single-crystalline magnesium borate Mg2B2O5 nanowires in bundle form have been synthesized via a simple route based on heating a precursor powder made of aqueous solutions of magnesium chloride and de-sodium tetraborate with citric acid. The results show that each bundle composed of nanowires of high-purity with diameter of approximately ca. 90 nm and lengths up to a few micrometers. The effect of citric acid, the optimum experimental parameters and possible growth mechanism for the compound nanowires have been presented.

Interband optical absorption coefficients in a strained Zn0.2Cd0.8S/ZnS quantum dot are discussed theoretically taking into account the internal field induced by the spontaneous and piezoelectric polarizations. The effects of geometrical quantum confinement on the exciton binding energies in ZnxCd1-xS/ZnS quantum dot are investigated for various confinement potentials and thereby the interband optical transition energy associated with the photon is brought out. The effects of quantum confinement on the heavy hole exciton are brought out here. We calculate the oscillator strengths for the heavy hole and light hole excitons and the total nonlinear optical absorption coefficients in a Zn0.2Cd0.8S /ZnS quantum dot with the incident photon energy taking into account the effective mass anisotropy of holes. Our results bring out that the oscillator strength depends on the geometrical confinement, electron and hole wave functions and the interaction between them, and the nonlinear optical absorption coefficient shows larger values for smaller dots.

Electric field induced heavy hole excitons in a strained GaxIn1-xAs/GaAs quantum dot are studied by considering geometrical confinement. The exciton binding energy and some nonlinear optical properties in the presence of electric field are discussed. Calculations include the anisotropy, non-parabolicity of the conduction band, strain effects and the spatial confinement. A cylindrical dot of GaxIn1-xAs surrounded by a GaAs barrier material with the constant Ga alloy content, x =0.2 is taken as the model. The exciton binding energy is found within the framework of the variational technique and the nonlinear optical properties are performed using matrix formulism. It is shown that the electronic and optical properties are strongly dependent on the application of electric field.

In this paper, the electronic and the structural (lattice constant) properties of ?-MgH2 are calculated, using density functional theory. The Kohn-Sham equations were solved using the full potential-linearized augmented plane wave (FP-LAPW). Generalized Gradient Approximation (GGA) and GGA+U approximations are the exchange-correlation potential used in this study. It was found that adding Hubbard-U term to GGA improved calculated structural property, energy band structure results and are in better agreement with the experimental data.

Surfactants are basic cleaning agents in soaps and detergents. Most surfactants are less toxic to aquatic organisms due to their surface activity which will react with the biological membranes of the organisms. The study of surfactant materials along with the other additive compounds seeks more attention because of their increasing industrial and domestic applications. Dyes and enzymes which are the important ingredient in detergents have their own cleaning properties. Nowdays, lipases stand amongst the most important biocatalysts carrying out novel reactions in both aqueous and non-aqueous media. They also possess massive applications in various areas of industrial microbiology and biotechnology. This statement is well documented by the enormous number of research investigations undertaken in the last one and a half decades. Lipases show immense versatility regarding their catalytic behaviour. Therefore, there is a lot of scope to search for newer lipases with desired selectivity and substrate tolerance. The present study is an attempt to investigate the thermodynamic properties like internal pressure, free volume, ??i, molar and molal hydration numbers of anionic surfactant SDS with sodium sulphate in the presence of dye (methylene blue) and an enzyme (lipase) at 303K, 313K and 323K temperatures. The determination of the above properties has thrown light into the various types of molecular interactions existing in aqueous ternary solutions.