Dielectric properties of certain biological materials at microwave frequencies.

In the medical field, microwaves play a larger role for treatment than diagnosis. For the detection of diseases by microwave methods, it is essential to know the dielectric properties of biological materials. For the present study, a cavity perturbation technique was employed to determine the dielectric properties of these materials. Rectangular cavity resonators were used to measure the complex permittivity of human bile, bile stones, gastric juice and saliva. The measurements were carried out in the S and J bands. It is observed that normal and infected bile have different dielectric constant and loss tangent. Dielectric constant of infected bile and gastric juice varies from patient to patient. Detection and extraction of bile stone with possible method of treatment is also discussed.

Design and Synthesis of Conjugated Polymers for Photovoltaic and Chemosensor Applications

Department of Applied Chemistry, Cochin University of Science and Technology

Preparation and Characterization ofHigh-k Aluminum Oxide Thin Films by Atomic Layer Deposition for Gate Dielectric Applications

Present work deals with the Preparation and characterization of high-k aluminum oxide thin films by atomic layer deposition for gate dielectric applications.The ever-increasing demand for functionality and speed for semiconductor applications requires enhanced performance, which is achieved by the continuous miniaturization of CMOS dimensions. Because of this miniaturization, several parameters, such as the dielectric thickness, come within reach of their physical limit. As the required oxide thickness approaches the sub- l nm range, SiO 2 become unsuitable as a gate dielectric because its limited physical thickness results in excessive leakage current through the gate stack, affecting the long-term reliability of the device. This leakage issue is solved in the 45 mn technology node by the integration of high-k based gate dielectrics, as their higher k-value allows a physically thicker layer while targeting the same capacitance and Equivalent Oxide Thickness (EOT). Moreover, Intel announced that Atomic Layer Deposition (ALD) would be applied to grow these materials on the Si substrate. ALD is based on the sequential use of self-limiting surface reactions of a metallic and oxidizing precursor. This self-limiting feature allows control of material growth and properties at the atomic level, which makes ALD well-suited for the deposition of highly uniform and conformal layers in CMOS devices, even if these have challenging 3D topologies with high aspect-ratios. ALD has currently acquired the status of state-of-the-art and most preferred deposition technique, for producing nano layers of various materials of technological importance. This technique can be adapted to different situations where precision in thickness and perfection in structures are required, especially in the microelectronic scenario.

Far-infrared spectroscopy of nanoscopic InAs rings

We have employed time-dependent local-spin-density theory to analyze the far-infrared transmission spectrum of InAs self-assembled nanoscopic rings recently reported [A. Lorke et al., Phys. Rev. Lett. (to be published)]. The overall agreement between theory and experiment is fairly good, which on the one hand confirms that the experimental peaks indeed reflect the ringlike structure of the sample, and on the other hand, asseses the suitability of the theoretical method to describe such nanostructures. The addition energies of one- and two-electron rings are also reported and compared with the corresponding capacitance spectra

Synthesis and Characterization of Novel Ionomers based on Styrene Butadiene Copolymer

Novel thermo-reversible zinc sulphonated ionomers based on styrene butadiene rubber (SBR), and high styrene rubber (HSH) were synthesized by sulphonation followed by neutralization with zinc. The sulphonate content of the ionomer was estimated by using x-ray fluorescence spectroscopy. Presence of sulphonate groups has been confirmed by FTIR and FTNMR spectra. The TGA results show improvement in the thermo~oxidative stability of the modified rubber. Both DSC and DMTA studies show that the incorporation of the ionic groups affect the glass rubber transition of the base polymer. lntroduction ol ionic functionality in to the base material improved the physical properties. Retention of the improved physical properties of the novel ionomers even after three repeated cycles of mixing and molding may be considered as the evidence for the reprocessability of the ionomer. Effect of particulate fillers (HAF black, silica and zinc stearate) on the properties of the zinc sulphonated styrene butadiene rubber ionomer has been evaluated. Incorporation of tillers results in improvement in mechanical properties. Zinc stearate plays the dual role of reinforcement and plasticization. The evaluation of dielectric properties of zinc sulphonated styrene butadiene rubber iorpmers at microwave frequencies reveal that the materials show conductivity at semiconductor level. The real and imaginary parts of the complex permittivity increases with increase in ionic functionality. Use of the 38.5 ZnS-SBR ionomer as a compatibiliser for obtaining the technologically compatible blends from the immiscible SBR/NBR system has been discussed.

Elecrical conduction and dielectric behaviour of thin films of vacuum evaporated amorphous silicon, hydrogenated amorphous silicon and chemically deposited cadmium sulphide

A brief account of the several methods used for the production of thin films is presented in this Chapter. The discussions stress on the important methods used for the fabrication of a-si:H thin films. This review' also reveals ‘that almost all the general methods, like vacuum evaporation, sputtering, glow discharge and even chemical methods are currently employed for the production of a-Si:H thin films. Each method has its own advantages and disadvantages. However, certain methods are generally preferred. Subsequently a detailed account of the method used here for the preparation of amorphous silicon thin films and their hydrogenation is presented. The metal chamber used for the electrical and dielectric measurements is also described. A brief mention is made-on the electrode structure, film area and film geometry.

Effective mass and dielectric constant mismatch effects in spherical multishell quantum dots

The role of effective mass and dielectric mismatches on chemical potentials and addition energies of many-electron multishell quantum dots (QDs) is explored within the framework of a recent extension of the spin density functional theory. It is shown that although the gross electronic density is located in the wells of these multishell QDs, taking position-dependent effective mass and dielectric constant into account can lead to the appearance of relevant differences in chemical potential and addition energies as compared to standard calculations in which the effective mass and the dielectric constant of the well is assumed for the whole multishell structure.

Studies on the structural, electrical and magnetic properties of composites based on spinel ferrites

This thesis mainly deals with the preparation and studies on magnetic composites based on spinel ferrites prepared both chemically and mechanically. Rubber ferrite composites (RFC) are chosen because of their mouldability and flexibility and the ease with which the dielectric and magnetic properties can be manipulated to make them as useful devices. Natural rubber is chosen as the Matrix because of its local availability and possible value addition. Moreover, NR represents a typical unsaturated nonpolar matrix. The work can be thought of as two parts. Part l concentrates on the preparation and characterization of nanocomposites based on y-Fe203. Part 2 deals with the preparation and characterization of RFCs containing Nickel zinc ferrit In the present study magnetic nanocomposites have been prepared by ionexchange method and the preparation conditions have been optimized. The insitu incorporation of the magnetic component is carried out chemically. This method is selected as it is the easiest and simplest method for preparation of nanocomposite. Nanocomposite samples thus prepared were studied using VSM, Mossbauer spectroscopy, Iron content estimation, and ESR spectroscopy. For the preparation of RFCs, the filler material namely nickel zinc ferrite having the general formula Ni)_xZnxFez04, where x varies from 0 to 1 in steps of 0.2 have been prepared by the conventional ceramic techniques. The system of Nil_xZn"Fe204 is chosen because of their excellent high frequency characteristics. After characterization they are incorporated into the polymer matrix of natural rubber by mechanical method. The incorporation is done according to a specific recipe and for various Loadings of magnetic fillers and also for all compositions. The cure characteristics, magnetic properties and dielectric properties of these composites are evaluated. The ac electrical conductivity of both ceramic nickel zinc ferrites and rubber ferrite composites are also calculated using a simple relation. The results are correlated.

Investigations on polyaniline based systems for technologically important applications and some novel polymers as prospective candidates for fabricating polymer light emitting diodes

Light emitting polymers (LEP) have drawn considerable attention because of their numerous potential applications in the field of optoelectronic devices. Till date, a large number of organic molecules and polymers have been designed and devices fabricated based on these materials. Optoelectronic devices like polymer light emitting diodes (PLED) have attracted wide-spread research attention owing to their superior properties like flexibility, lower operational power, colour tunability and possibility of obtaining large area coatings. PLEDs can be utilized for the fabrication of flat panel displays and as replacements for incandescent lamps. The internal efficiency of the LEDs mainly depends on the electroluminescent efficiency of the emissive polymer such as quantum efficiency, luminance-voltage profile of LED and the balanced injection of electrons and holes. Poly (p-phenylenevinylene) (PPV) and regio-regular polythiophenes are interesting electro-active polymers which exhibit good electrical conductivity, electroluminescent activity and high film-forming properties. A combination of Red, Green and Blue emitting polymers is necessary for the generation of white light which can replace the high energy consuming incandescent lamps. Most of these polymers show very low solubility, stability and poor mechanical properties. Many of these light emitting polymers are based on conjugated extended chains of alternating phenyl and vinyl units. The intra-chain or inter-chain interactions within these polymer chains can change the emitted colour. Therefore an effective way of synthesizing polymers with reduced π-stacking, high solubility, high thermal stability and high light-emitting efficiency is still a challenge for chemists. New copolymers have to be effectively designed so as to solve these issues. Hence, in the present work, the suitability of a few novel copolymers with very high thermal stability, excellent solubility, intense light emission (blue, cyan and green) and high glass transition temperatures have been investigated to be used as emissive layers for polymer light emitting diodes.

Studies in molecular spectroscopy

This thesis is divided into two parts. The first part deals with some studies in molecular mechanics Using spectroscopic data and has four chapters in it. Certain approximation methods for the evaluation of molecular force fields are herein developed The second part, which consists of the last two chaptcrs, deals with infrared spectral studies of ternary liquid systems and a polymer film prepared by glow discharge method.

Competing tunneling and capacitive paths in Co-ZrO2 granular thin films

The ac electrical response is studied in thin films composed of well-defined nanometric Co particles embedded in an insulating ZrO2 matrix which tends to coat them, preventing the formation of aggregates. In the dielectric regime, ac transport originates from the competition between interparticle capacitive Cp and tunneling Rt channels, the latter being thermally assisted. This competition yields an absorption phenomenon at a characteristic frequency 1/(RtCp), which is observed in the range 1010 000 Hz. In this way, the effective ac properties mimic the universal response of disordered dielectric materials. Temperature and frequency determine the complexity and nature of the ac electrical paths, which have been successfully modeled by an Rt-Cp network.

Spin-Peierls vs Peierls distortions in a family of conjugated polymers

Distortions in a family of conjugated polymers are studied using two complementary approaches: within a many-body valence bond approach using a transfer-matrix technique to treat the Heisenberg model of the systems, and also in terms of the tight-binding band-theoretic model with interactions limited to nearest neighbors. The computations indicate that both methods predict the presence or absence of the same distortions in most of the polymers studied.

Energetic Polymers

High energy materials are essential ingredients in both rocket and explosive formulations. These can be vulnerable due to maltreatment. During gulf war, several catastrophic accidents have been reported from their own payload munitions. The role of energetic binders here was to wrap the explosive formulations to convert it into insensitive munitions. With the aid of energetic binders, the explosive charges are not only protected from tragic accidents due to fire, bullet impact, adjacent detonation, unplanned transportation, but also form total energy output presumption. The use of energetic binders in rocket propellants and explosive charges has been increased after the Second World War. Inert binders in combination with energetic materials, performed well as binders but they diluted the final formulation. Obviously the total energy output was reduced. Currently, the research in the field of energetic polymers is an emerging area, since it plays crucial role in insensitive munitions. The present work emphasises on the synthesis and characterization of oxetanes, oxiranes and polyphosphazene based energetic polymers. The thesis is structured into six chapters. First part of chapter 1 deals with brief history of energetic polymers. The second part describes a brief literature survey of energetic polymers based on oxetanes and oxiranes. Third and fourth parts deal with energetic plasticizers and energetic polyphosphazenes. Finally, the fifth part deals with the various characterization techniques adopted for the current study and sixth part includes objectives of the present work.

Investigation of dielectric and elastic properties of selected dielectric ceramics and oxide glasses

The dielectric and elastic properties are of considerable significance to the science and technology of matter in the solid state. The study of these properties give information about the magnitude of the forces and nature of the bonding between the atoms. Our aim has been to investigate systematically the effect of doping of an appropriate element on the elastic and dielectric properties of selected dielectric ceramics and oxide glasses. These materials have got wide technological applications due to their interesting electrical, optical, thermal and elastic behaviour. Ultrasound propagation and capacitance measurement techniques have been employed for the systematic investigation of the elastic and dielectric properties of selected number of these materials. Details of the work done and results obtained are presented in this thesis.

Synthesis, characterization and properties of Conductive elastomeric composites based on Polypyrrole and short Nylon-6 fiber

The search for new materials especially those possessing special properties continues at a great pace because of ever growing demands of the modern life. The focus on the use of intrinsically conductive polymers in organic electronic devices has led to the development of a totally new class of smart materials. Polypyrrole (PPy) is one of the most stable known conducting polymers and also one of the easiest to synthesize. In addition, its high conductivity, good redox reversibility and excellent microwave absorbing characteristics have led to the existence of wide and diversified applications for PPy. However, as any conjugated conducting polymer, PPy lacks processability, flexibility and strength which are essential for industrial requirements. Among various approaches to making tractable materials based on PPy, incorporating PPy within an electrically insulating polymer appears to be a promising method, and this has triggered the development of blends or composites. Conductive elastomeric composites of polypyrrole are important in that they are composite materials suitable for devices where flexibility is an important parameter. Moreover these composites can be moulded into complex shapes. In this work an attempt has been made to prepare conducting elastomeric composites by the incorporation of PPy and PPy coated short Nylon-6 fiber with insulating elastomer matrices- natural rubber and acrylonitrile butadiene rubber. It is well established that mechanical properties of rubber composites can be greatly improved by adding short fibers. Generally short fiber reinforced rubber composites are popular in industrial fields because of their processing advantages, low cost, and their greatly improved technical properties such as strength, stiffness, modulus and damping. In the present work, PPy coated fiber is expected to improve the mechanical properties of the elastomer-PPy composites, at the same time increasing the conductivity. In addition to determination of DC conductivity and evaluation of mechanical properties, the work aims to study the thermal stability, dielectric properties and electromagnetic interference shielding effectiveness of the composites. The thesis consists of ten chapters.