Investigations On The Preparation And Properties Of Reactively Evaporated Lead Sulphide And Tin Telluride Thin Films

The work reported in this thesis is the preparation, and the structural, electrical and optical properties of reactively evaporated lead sulphide and tin telluride thin films. The three temperature method had been used for the preparation of these semiconductor thin films. In this preparation technique constituent elements are evaporated from separate sources with the substrate kept at a particular temperature. when one of the constituent element is a gas near room temperature, the method is often called reactive evaporation. It has been found for many materials that a stoichiometric interval exists with a limited range of flux and substrate temperature. Usually this technique is used for the preparation of thin films of high melting point compounds or of materials which decompose during evaporation. Tin telluride and lead sulphide are neither high melting point materials nor do they decompose on melting. But even than reactive evaporation offers the possibility of changing the ratios of the flux of the constituent elements within a wide range and studying its effect on the properties of the films

Studies on the optical band gap and cluster size of the polyaniline thin films irradiated with swift heavy Si ions

Polyaniline thin films prepared by RF plasma polymerisation were irradiated with 92MeV Si ions for various fluences of 1 1011, 1 1012 and 1 1013 ions/cm2. FTIR and UV–vis–NIR measurements were carried out on the pristine and Si ion irradiated polyaniline thin films for structural evaluation and optical band gap determination. The effect of swift heavy ions on the structural and optical properties of plasma-polymerised aniline thin film is investigated. Their properties are compared with that of the pristine sample. The FTIR spectrum indicates that the structure of the irradiated sample is altered. The optical studies show that the band gap of irradiated thin film has been considerably modified. This has been attributed to the rearrangement in the ring structure and the formation of CRC terminals. This results in extended conjugated structure causing reduction in optical band gap

Processability And Magnetic Properties Of Rubber Ferrite Composites Containing Barium Ferrite

Rubber ferrite composites (RFC) are magnetic polymer composites and have a variety of applications as flexible magnets, pressure=photo sensors, and microwave absorbers. The mouldability into complex shapes is one of the advantages of these magnetic elastomers. They have the potential of replacing the conventional ceramic materials, due to theire flexible nature. In the present study, the incorporation of pre-characterized hexagonal ferrites, namely barium ferrite (BaFe12O19), into natural rubber matrix is carried out according to a suitable recipe for various loadings of the filler. The processability of these compounds was determined by evaluating the cure characteristics: scorch time, cure time, and minimum and maximum torque. It has been found that the addition of magnetic fillers does not affect the processability of the composites, whereas the physical properties are modified. The magnetic properties of these composites containing various loadings of the magnetic filler were also investigated. The magnetic properties of RFC can be controlled by the addition of appropriate amount of the ferrite filler.

Theory for the optical properties of small Hg_n clusters

The static and dynamical polarizabilities of the Hg-dimer are calculated by using a Hubbard Hamiltonian to describe the electronic structure. The Hamiltonian is diagonalized exactly within a subspace of second-quantized electronic states from which only multiply ionized atomic configurations have been excluded. With this approximation we can describe the most important electronic transitions including the effect of charge fluctuations. We analyze the polarizability as a function of the intraatomic Coulomb interaction which represents the repulsion between electrons. We obtain that this interaction results in strong electronic correlations in the excited states and increases the first excitation energy of the dimer by 0.8 eV in comparison to a calculation which neglects correlations, resulting in a better agreement with the experiment.

Diversity and nutritional properties of Pakistani dates: implications for sustainable value chain and decent living perspectives of rural households

Date palm (Phoenix dactylifera L.) occupies almost three percent of the total worldwide cultivated area, with an annual production of seven million tonnes (t). Pakistan is an ideal place for the cultivation of date palm due to its sandy loam soil and semi-arid climate. In 2012, Pakistan produced 600,000 t of dates, on an area of 95,000 ha. Baluchistan province is the country’s top date producer, followed by Sindh, Punjab and Khyber Pakhtunkhwa (KPK) provinces. More than 300 date varieties are known to exist in Pakistan and some commercially important cultivars are: Karbalaen, Aseel, Muzawati, Fasli, Begum Jhangi, Hillawi, Dashtiari, Sabzo, Koharaba, Jaan Swore, Rabai and Dhakki. Six districts from the four provinces of Pakistan (Jhang, Muzaffargarh and Bahawalpur (Punjab), Dera Ismail Khan (KPK), Khairpur (Sindh) and Panjgur (Baluchistan)) with largest area under date palm cultivation were selected to conduct socio-economic surveys including the income sources of date palm growers. A structured questionnaire with open-ended and closed questions was used for face-to-face interviews of 170 date palm growers. At each location after selection of a first farmer through a local guide, the former was requested to provide names and addresses of three other date growers in his area. From these three names, one was randomly selected for the next sampling. Additionally, date palm fronds and fruits of all available cultivars were collected for morphological and nutritional analyses. Soil samples were collected from the groves for subsequent chemical and physical analyses. Almost all farmers used dates as a food item for their families and some were using low quality dates as a feed for their livestock. Apart from dates, other date palm components (trunk, spadix, frond, inflorescence and seed) were used by date palm growers as a raw material for making many by-products for their families. Date palm had a major contribution in the income of households, 24% received 91-100% of their income from date palms. More than half of the surveyed farmers had date palm groves, but scattered plantations, home gardens and intercropping systems with cereal and other fruits were also present. Dhakki, Muzawati, Aseel, and Karbalaen were the most important commercial cultivars grown in the provinces of KPK, Baluchistan, and Sindh. Aseel, Karoch, Haleni, Karbalaen, and Muzawati cultivars had the most firm fruit and good total soluble sugar, calcium and magnesium contents. The amount of magnesium found in dates of studied cultivars ranged from 0.143 to 0.876 mg g-1. A great variation in frond morphology was recorded among the cultivars. Fruit length and fruit weight was highest in Dhakki date, making it visually more attractive for customers in addition to its good nutritional properties. The seed weight of the studied cultivars ranged from 0.7-2.0 g, while Desi dates had largest seed, making them less attractive for marketing. However, in terms of nutritional value and fruit size, most of the investigated varieties can compete with globally important commercial dates.

Independent evaluation of the ability of spaceborne radar and lidar to retrieve the microphysical and radiative properties of ice clouds

The combination of radar and lidar in space offers the unique potential to retrieve vertical profiles of ice water content and particle size globally, and two algorithms developed recently claim to have overcome the principal difficulty with this approach-that of correcting the lidar signal for extinction. In this paper "blind tests" of these algorithms are carried out, using realistic 94-GHz radar and 355-nm lidar backscatter profiles simulated from aircraft-measured size spectra, and including the effects of molecular scattering, multiple scattering, and instrument noise. Radiation calculations are performed on the true and retrieved microphysical profiles to estimate the accuracy with which radiative flux profiles could be inferred remotely. It is found that the visible extinction profile can be retrieved independent of assumptions on the nature of the size distribution, the habit of the particles, the mean extinction-to-backscatter ratio, or errors in instrument calibration. Local errors in retrieved extinction can occur in proportion to local fluctuations in the extinction-to-backscatter ratio, but down to 400 m above the height of the lowest lidar return, optical depth is typically retrieved to better than 0.2. Retrieval uncertainties are greater at the far end of the profile, and errors in total optical depth can exceed 1, which changes the shortwave radiative effect of the cloud by around 20%. Longwave fluxes are much less sensitive to errors in total optical depth, and may generally be calculated to better than 2 W m(-2) throughout the profile. It is important for retrieval algorithms to account for the effects of lidar multiple scattering, because if this is neglected, then optical depth is underestimated by approximately 35%, resulting in cloud radiative effects being underestimated by around 30% in the shortwave and 15% in the longwave. Unlike the extinction coefficient, the inferred ice water content and particle size can vary by 30%, depending on the assumed mass-size relationship (a problem common to all remote retrieval algorithms). However, radiative fluxes are almost completely determined by the extinction profile, and if this is correct, then errors in these other parameters have only a small effect in the shortwave (around 6%, compared to that of clear sky) and a negligible effect in the longwave.

Determination of the optical properties of plastic films used as cladding materials in novel energy efficient greenhouses

Greenhouse cladding materials are a major component in the design of energy efficient greenhouses. The optical properties of cladding materials determine a major part of the overall performance of a greenhouse both in terms of the energy balance of the greenhouse and on crop behavior. Various film plastic greenhouse-cladding materials were measured under laboratory conditions using a spectroradiometer equipped with an integrating sphere. Films were measured over a range of angles of incidence and the effect of increasing distance between double films was also measured. PAR transmission remained nearly constant for angles of incidence increased up to 30 degrees but fell rapidly thereafter as the angles of incidence increased up to 90 degrees. Increasing distance between double films did not significantly affect PAR transmission in all films examined. These results are discussed in relation to the design criteria for an energy efficient greenhouse.

Structure, and thermal, magnetic and chemical properties of copper(II)iodoacetate monohydrate

Reaction of iodoacetic acid with cupric carbonate in water in dimmed light yields green Cu(ICH2COO)(2 center dot)H2O (1). From X-ray crystallography, it is found to be a tetra-acetato bridged copper(II) dimer with the water molecules occupying the apical positions. In thermogravimetry, the coordinated water molecules are lost in the temperature range 50-100 degrees C. From magnetic susceptibility measurements in the temperature range 300-1.8 K, the exchange coupling constant J is found to be -142(1) cm(-1) and g = 2.18(2) with the spin Hamiltonian H = -2J{S-Cu1 center dot S-Cu2}. It reacts with 2,2'-bipyridine (bpy) to yield [Cu(bpy)(2)I]I. It oxidises thiophenol to Ph-S-S-Ph under dry N-2 atmosphere.

Exposure to space radiation of high performance infrared multilayer filters and materials technology experiment

Infrared optical-multilayer filters and materials were exposed to the space environment of low Earth orbit on LDEF. This paper summarizes the effects of that environment on the physical and optical properties of the filters and materials flown.

Space exposure of infrared filters and materials on the NASA Long Duration Exposure Facility (LDEF)

Infrared optical-multilayer filters and materials were exposed to the space environment of low Earth for a period of nearly six years on the NASA Long Duration Exposure Facility (LDEF) mission. This report describes the effects of that environment on the physical and optical properties of filters and materials used in an experiment designed by the University of reading Infrared multilayer Laboratory. Results of the experiment comprise IR processed spectra both before (1983), and after (1990) exposure, in conjunction with unexposed control samples.

Enhanced second order non-linear optical properties of silica sol-gel thin films through photo-induced poling

Sol-gel derived inorganic materials are of interest as hosts for non-linear optically active guest molecules and they offer particular advantages in the field of non-linear optics. Orientationally ordered glasses have been prepared using a sol-gel system based on tetramethoxysilane, methyltrimethoxysilane and a non-linear optical chromophore Disperse Red 1. The novel technique of photo-induced poling was used to generate enhanced levels of polar order. The level of enhancement is strongly dependent on the extent of gelation and an optimum preparation time of ∼100 h led to an enhancement factor of ∼5. Films prepared in this manner exhibited a high stability of the polar order.

Study of the nonlinear optical properties of a crosslinkable chromophore for use in guest host polymer films

A guest/host material system in which the guest molecule is a functionalized, optically nonlinear, chromophore is described. A verification of the crosslinking process, an assessment of the nonlinear properties of the chromophore, using Solvatochromic methods, and an investigation of the electric field induced molecular orientation using second-harmonic generation are included.

Biaxial optical properties of thermotropic random copolyesters

The optical microstructures of thin sections of two liquid crystalline polymers are examined in the polarizing microscope. The polymers are random copolyesters based on hydroxybenzoic and hydroxynaphthoic acids (B-N), and hydroxybenzoic acid and ethylene terephthalate (B-ET). Sections cut from oriented samples, so as to include the extrusion direction, show microstructures in which there is no apparent preferred orientation of the axes describing the local optical anisotropy. The absence of preferred orientation in the microstructure, despite marked axial alignment of molecular chain segments as demonstrated by X-Ray diffraction, is interpreted in terms of the polymer having biaxial optical properties. The implication of optical biaxiality is that, although the mesophases are nematic, the orientation of the molecules is correlated about three (orthogonal) axes over distances greater than a micron. The structure is classified as a multiaxial nematic.

Structure and magnetic properties of polydisperse ferrofluids: a molecular dynamics study

We study by Langevin molecular dynamics simulations systematically the influence of polydispersity in the particle size, and subsequently in the dipole moment, on the physical properties of ferrofluids. The polydispersity is in a first approximation modeled by a bidisperse system that consists of small and large particles at different ratios of their volume fractions. In the first part of our investigations the total volume fraction of the system is fixed, and the volume fraction phi(L) of the large particles is varied. The initial susceptibility chi and magnetization curve of the systems show a strong dependence on the value of phi(L). With the increase of phi(L), the magnetization M of the system has a much faster increment at weak fields, and thus leads to a larger chi. We performed a cluster analysis that indicates that this is due to the aggregation of the large particles in the systems. The average size of these clusters increases with increasing phi(L). In the second part of our investigations, we fixed the volume fraction of the large particles, and increased the volume fraction phi(S) of the small particles in order to study their influence on the chain formation of the large ones. We found that the average aggregate size formed by large particles decreases when phi(S) is increased, demonstrating a significant effect of the small particles on the structural properties of the system. A topological analysis of the structure reveals that the majority of the small particles remain nonaggregated. Only a small number of them are attracted to the ends of the chains formed by large particles.