Temperature Stable Low Loss Ceramic Dielectrics in (1-x)ZnAI2O4-xTiO2 System for Microwave Substrate Applications

The microwave dielectric properties of ZnAl2O4 spinels were investigated and their properties were tailored by adding different mole fractions of Ti02. The samples were synthesized using the mixed oxide rout.e. The phase purity and crystal structure were identified using X-ray diffraction technique. The sintered specimens were characterized in the microwave frequency range (3-13 GHz). The ZnA12O4 ceramics exhibited interesting dielectric properties (dielectric constant (e,.) = 8.5, unloaded quality factor (Q.) = 4590 at 12.27 GHz and temperature coefficient of resonant frequency (Tf) = -79 ppm/°C). Addition of Ti02 into the spinel improved its properties and the Tf approached zero for 0.83ZnAl2O4- 0.17TiO2• This temperature compensated composition has excellent microwave dielectric properties (Cr _ 12.67, Q, = 9950 at 10.075 GHz) which can be exploited for microwave substrate applications

Photothermal deflection studies of GaAs epitaxial layers

Photothermal beam deflection studies were carried out with GaAs epitaxial double layers grown on semi-insulating GaAs substrates. The impurity densities in thin epitaxial layers were found to influence the effective thermal diffusivity of the entire structure.

HRTEM assessment of Wurtzite and Zinc-Blende phases in GaAs nanowires for optoelectronic devices

Màster en Nanociència i Nanotecnologia. Curs 2007-2008. Directors: Francesca Peiró i Martínez and Jordi Arbiol i Cobos

Spin-orbit effects in GaAs quantum wells: Interplay between Rashba, Dresselhaus, and Zeeman interactions

The interplay between Rashba, Dresselhaus, and Zeeman interactions in a quantum well submitted to an external magnetic field is studied by means of an accurate analytical solution of the Hamiltonian, including electron-electron interactions in a sum-rule approach. This solution allows us to discuss the influence of the spin-orbit coupling on some relevant quantities that have been measured in inelastic light scattering and electron-spin resonance experiments on quantum wells. In particular, we have evaluated the spin-orbit contribution to the spin splitting of the Landau levels and to the splitting of charge- and spin-density excitations. We also discuss how the spin-orbit effects change if the applied magnetic field is tilted with respect to the direction perpendicular to the quantum well.

Spin-orbit effects in GaAs quantum wells: Interplay between Rashba, Dresselhaus, and Zeeman interactions

The interplay between Rashba, Dresselhaus, and Zeeman interactions in a quantum well submitted to an external magnetic field is studied by means of an accurate analytical solution of the Hamiltonian, including electron-electron interactions in a sum-rule approach. This solution allows us to discuss the influence of the spin-orbit coupling on some relevant quantities that have been measured in inelastic light scattering and electron-spin resonance experiments on quantum wells. In particular, we have evaluated the spin-orbit contribution to the spin splitting of the Landau levels and to the splitting of charge- and spin-density excitations. We also discuss how the spin-orbit effects change if the applied magnetic field is tilted with respect to the direction perpendicular to the quantum well.

Giant step bunching from self-organized coalescence of SrRuO3 islands

Step bunching develops in the epitaxy of SrRuO3 on vicinal SrTiO3(001) substrates. We have investigated the formation mechanisms and we show here that step bunching forms by lateral coalescence of wedgelike three-dimensional islands that are nucleated at substrate steps. After coalescence, wedgelike islands become wider and straighter with growth, forming a self-organized network of parallel step bunches with altitudes exceeding 30 unit cells, separated by atomically flat terraces. The formation mechanism of step bunching in SrRuO3, from nucleated islands, radically differs from one-dimensional models used to describe bunching in semiconducting materials. These results illustrate that growth phenomena of complex oxides can be dramatically different to those in semiconducting or metallic systems.

“Studies on extracellular enzyme production during growth of Pleurotus sp. on lignocellulosic agriwaste and the utilization of spent mushroom substrate”

Commercially, Pleurotus spp. of mushroom are cultivated in bags. After mushroom cultivation, spent substrate remains as residual material. Proper recycling of spent substrate is beneficial for our economy. Spent substrate can be utilized for various other value added purposes through the proper knowledge of its components. Composition of various components depends on the activity of extracellular enzymes in the spent substrate. The present study was conducted to know the enzyme profile of some major extracellular enzymes - cellulase, hemicellulase (xylanase), pectinase and ligninase (lignin peroxidase and laccase) and to estimate cellulose, hemicellulose, pectin and lignin in the substrate. The use of spent substrate as a source of fibre and ethanol, and in the biodegradation of phenol by Pleurotus spp. was also investigated

Banana waste as substrate for a-amylase production by Bacillus subtilis (CBTK 106) under solid-state fermentation

Bacillus subtilis CBTK 106, isolated from banana wastes, produced high titres of a-amylase when banana fruit stalk was used as substrate in a solid-state fermentation system. The e¤ects of initial moisture content, particle size, cooking time and temperature, pH, incubation temperature, additional nutrients, inoculum size and incubation period on the production of a- amylase were characterised. A maximum yield of 5 345 000 U mg~1 min~1 was recorded when pretreated banana fruit stalk (autoclaved at 121 ¡C for 60 min) was used as substrate with 70% initial moisture content, 400 lm particle size, an initial pH of 7.0, a temperature of 35 ¡C, and additional nutrients (ammonium sulphate/sodium nitrate at 1.0%, beef extract/peptone at 0.5%, glucose/sucrose/starch/maltose at 0.1% and potassium chloride/sodium chloride at 1.0%) in the medium, with an inoculum-to-substrate ratio of 10% (v/w) for 24 h. The enzyme yield was 2.65-fold higher with banana fruit stalk medium compared to wheat bran

Influence of substrate topography on the growth and magnetic properties of obliquely deposited amorphous nanocolumns of Fe–Ni

We investigated the influence of substrate surface roughness on the structural and magnetic properties of obliquely deposited amorphous nanocolumns of Fe–Ni. Experiments showed that the surface roughness of the substrate greatly determines the morphology of the columnar structures and this in turn has a profound influence on the magnetic properties. Nucleation of Fe–Ni nanocolumns on a smooth silicon substrate was at random, while that on a rough glass substrate was defined by the irregularities on the substrate surface. It has been found that magnetic interaction between the nanocolumns prepared on a silicon substrate was due to their small inter-column separation. Well separated nanocolumns on a glass substrate resulted in exchange isolated magnetic domains. The size, shape and the distribution of nanocolumns can be tailored by appropriately choosing the surface roughness of the substrate. This will find potential applications in thin film magnetism.

Ethanol Production From Spent Substrate Of Pleurotus Eous

Spent substrate, the residual material of mushroom cultivation, causes disposal problems for cultivators. Currently the spent substrate of different mushrooms is used mainly for composting. Edible mushrooms of Pleurotus sp. can grow on a wide range of lignocellulosic substrates. In the present study, Pleurotus eous was grown on paddy straw and the spent substrate was used for the production of ethanol. Lignocellulosic biomass cannot be saccharified by enzymes to high yield of ethanol without pretreatment. The root cause for the recalcitrance of lignocellulosic biomass such as paddy straw is the presence of lignin and hemicelluloses on the surface of cellulose. They form a barrier and prevent cellulase from accessing the cellulose in the substrate. In the untreated paddy straw, the amount of hemicelluloses and lignin (in % dry weight) were 20.30 and 20.34 respectively and the total reducing sugar was estimated to be 5.40 mg/g. Extracellular xylanase and ligninases of P. eous could reduce the amount of hemicelluloses and lignin to 16 and 11(% dry weight) respectively, by 21st day of cultivation. Growth of mushroom brought a seven fold increase in the total reducing sugar yield (39.20 mg/g) and six fold increase in the production of ethanol (6.48 g/L) after 48hrs of fermentation, when compared to untreated paddy straw

Biodegradation Of Phenol Using Spent Substrate Of Pleurotus Sp.

Phenol is an aromatic hydrocarbon which exists as a colorless or white solid in its pure state. Over the past several decades, there is growing concern about wide spread contamination of surface and ground water by phenol, due to rapid development of chemical and petrochemical industries. Phenol affects aquatic life even at relatively low concentration (5-25mg/L). Treatment for removal of phenol includes chemical as well as biological processes. Studies show that ligninases such as Lignin Peroxidase and Laccase, produced by Pleurotus sp., can degrade phenol. Spent substrate of Pleurotus mushrooms consists of ligninases. Present work was to investigate the potential of spent substrate of edible mushroom P. ostreatus for biodegradation of phenol. P. ostreatus was cultivated on paddy straw. After harvest, spent substrate was utilized for phenol degradation. According to the enzyme profile of two ligninases present in the spent substrate of P. ostreatus, maximum specific activity for Laccase was observed in 35 day old spent substrate and LiP activity was maximum in 56 day old spent substrate, which together contributed significantly for removal of phenol. Spent substrate of 35th and 56th day were each incubated with phenol sample (1:1w/v) for one day, which resulted in degradation of phenol by 48% and 45% respectively. From these results it appears that, spent substrate of P. ostreatus can be used effectively to remove phenol from industrial effluents