Dielectric and optical properties of europium oxide films

The dielectric properties of vacuum-deposited europium oxide films have been investigated in the frequency range from 1 kHz to 1 MHz at various temperatures (300-543 K). The dielectric constant is found to depend on film thickness and it attains a constant value beyond 1000 Å. Films deposited at higher substrate temperatures (above 423 K) exhibit improved dielectric properties owing to the recovery of stoichiometry. The frequency variation of the loss factor exhibits a minimum which increases with rise in temperature. The breakdown field strength (about 106V cm-1) is found to be thickness dependent and it varies in accordance with the Forlani-Minnaja relation. The films exhibit ohmic conduction with an activation energy of 0.86 eV at low electric fields but at higher fields the conductivity becomes space charge limited. X-ray studies show that the films are amorphous in nature. The a.c. conductivity is proportional to ω at low frequency, whereas a square law dependence is observed at higher frequencies. The optical constants n, α and k and optical band gap are calculated from the UV-visible-near-IR spectra.

Magnetic, Dielectric and Physicomechanical Properties of Rubber Ferrite Nanocomposites

In the present study the preparation and characterisation of rubber ferrite composites containing nickel ferrite and gamma ferric oxide have been dealt with.Synthetic rubbers viz. ethylene propylene diene rubber and neoprene rubber were used for the incorporation of nickel ferrite and gamma ferric oxide for the synthesis of RFCs. Incorporation of ferrites were carried out according to a specific recipe for various loadings of the magnetic fillers. The ferrites used for the preparation of RFCs were synthesised using sol-gel method and structural characterisation was carried out. Experimental techniques like X-ray diffraction, Transmission electron microscopy and other analytical techniques were used for this. Precharaterised ferrites were then incorporated at different loading into rubber according to conventional mixing methods. The cure characteristics, mechanical, dielectric, magnetic and microwave properties of these composites were evaluated. The effect of carbon black on these properties of RFCs were carried out.

Hexagonal dielectric resonator antenna - A novel DR antenna for wireless communication

In this thesis, the author proposes a new geometry DR antenna-the Hexagonal Dielectric Resonator Antenna(HDRA)-capable of multiple frequency operation on a single feed of excitation.This avoids the conventional use of miniaturizes the structure.The properties of the HDRA on microstrip as well as coaxial feeding have been studied.The analysis of radiation characteristics indicates a gain comparable with other shapes.The antenna is capable of providing efficiency around 98%.The simulation using HFSS also yields results in conformity with the experimental results.Mode analysis is carried out and the modes are identified.The determination of the reflection characteristics through theoretical analysis using FDTD validates the multifrequency operation of the antenna,The antenna finds application in DCT,PCS and WLAN bands.

Scattering Behaviour of fractal based metallo-dielectric structures

The scattering behaviour of fractal based metallodielectric structures loaded over metallic targets of different shapes such as flat plate, cylinder and dihedral corner reflector are investigated for both TE and TM polarizations of the incident wave. Out of the various fractal structures studied,square Sierpinski carpet structure is found to give backscattering reduction for an appreciable range of frequencies. The frequency of minimum backscattering depends on the geometry of the structure as well as on the thickness of the substrate. This structure when loaded over a dihedral corner reflector is showing an enhancement in RCS for corner angles other than 90◦.

Development and Analysis of a Novel Isosceles Trapezoidal Dielectric Resonator Antenna For Wireless Communication

This thesis describes the development and analysis of an Isosceles Trapezoidal Dielectric Resonator Antenna (ITDRA) by realizing different DR orientations with suitable feed configurations enabling it to be used as multiband, dual band dual polarized and wideband applications. The motivation for this work has been inspired by the need for compact, high efficient, low cost antenna suitable for multi band application, dual band dual polarized operation and broadband operation with the possibility of using with MICs, and to ensure less expensive, more efficient and quality wireless communication systems. To satisfy these challenging demands a novel shaped Dielectric Resonator (DR) is fabricated and investigated for the possibility of above required properties by trying out different orientations of the DR on a simple microstrip feed and with slotted ground plane as well. The thesis initially discusses and evaluates recent and past developments taken place within the microwave industry on this topic through a concise review of literature. Then the theoretical aspects of DRA and different feeding techniques are described. Following this, fabrication and characterization of DRA is explained. To achieve the desired requirements as above both simulations and experimental measurements were undertaken. A 3-D finite element method (FEM) electromagnetic simulation tool, HFSSTM by Agilent, is used to determine the optimum geometry of the dielectric resonator. It was found to be useful in producing approximate results although it had some limitations. A numerical analysis technique, finite difference time domain (FDTD) is used for validating the results of wide band design at the end. MATLAB is used for modeling the ITDR and implementing FDTD analysis. In conclusion this work offers a new, efficient and relatively simple alternative for antennas to be used for multiple requirements in the wireless communication system.

Synthesis of nickel–rubber nanocomposites and evaluation of their dielectric properties

Nanocomposites based on natural rubber and nano-sized nickelwere synthesized by incorporating nickel nanoparticles in a natural rubber matrix for various loadings of the filler. Structural, morphological, magnetic and mechanical properties of the compositeswere evaluated along with a detailed study of dielectric properties. Itwas found that nickel particleswere uniformly distributed in the matrix without agglomeration resulting in a magnetic nanocomposite. The elastic properties showed an improvement with increase in filler content but breaking stress and breaking strain were found to decrease. Dielectric permittivity was found to decrease with increase in frequency, and found to increase with increase in nickel loading. The decrease in permittivity with temperature is attributed to the high volume expansivity of rubber at elevated temperatures. Dielectric loss of blank rubber as well as the composites was found to increase with temperature.

Thermal transport properties of selected ferroelectrics, mixed valance perovskites and dielectric ceramics using photopyroelectric technique

Photothermal spectroscopy is a group of high sensitivity methods used to measure optical absorption and thermal characteristics of a sample.The basis of photothermal spectroscopy is a photo-induced change in the thermal state of the sample.Light energy absorbed and not lost by subsequent emission results in sample heating.This heating results in a temperature change as well as changes in thermodynamic parameters of the sample which are related to temperature.Measurements of the temperature,pressure,or density changes that occur due to optical absorption are ultimately the basis for the photothermal spectroscopic methods.This is a more direct measure of optical absorption than optical transmission based spectroscopies.Sample heating is a direct consequence of optical absorption and so photothermal spectroscopy signals are directly dependent on light absorption.Scattering and reflection losses do not produce photothermal signals.Subsequently,photothermal spectroscopy more accurately measures optical absorption in scattering solutions,in solids,and at interfaces.This aspect makes it particularly attractive for application to surface and solid absorption studies,and studies in scattering media.

Development of Free Space Method for Material Characterisation and GPR Study & A Case Study on Biological Samples

The thesis mainly focuses on material characterization in different environments: freely available samples taken in planar fonn, biological samples available in small quantities and buried objects.Free space method, finds many applications in the fields of industry, medicine and communication. As it is a non-contact method, it can be employed for monitoring the electrical properties of materials moving through a conveyor belt in real time. Also, measurement on such systems at high temperature is possible. NID theory can be applied to the characterization of thin films. Dielectric properties of thin films deposited on any dielectric substrate can be determined. ln chemical industry, the stages of a chemical reaction can be monitored online. Online monitoring will be more efficient as it saves time and avoids risk of sample collection.Dielectric contrast is one of the main factors, which decides the detectability of a system. lt could be noted that the two dielectric objects of same dielectric constant 3.2 (s, of plastic mine) placed in a medium of dielectric constant 2.56 (er of sand) could even be detected employing the time domain analysis of the reflected signal. This type of detection finds strategic importance as it provides solution to the problem of clearance of non-metallic mines. The demining of these mines using the conventional techniques had been proved futile. The studies on the detection of voids and leakage in pipes find many applications.The determined electrical properties of tissues can be used for numerical modeling of cells, microwave imaging, SAR test etc. All these techniques need the accurate determination of dielectric constant. ln the modem world, the use of cellular and other wireless communication systems is booming up. At the same time people are concemed about the hazardous effects of microwaves on living cells. The effect is usually studied on human phantom models. The construction of the models requires the knowledge of the dielectric parameters of the various body tissues. lt is in this context that the present study gains significance. The case study on biological samples shows that the properties of normal and infected body tissues are different. Even though the change in the dielectric properties of infected samples from that of normal one may not be a clear evidence of an ailment, it is an indication of some disorder.ln medical field, the free space method may be adapted for imaging the biological samples. This method can also be used in wireless technology. Evaluation of electrical properties and attenuation of obstacles in the path of RF waves can be done using free waves. An intelligent system for controlling the power output or frequency depending on the feed back values of the attenuation may be developed.The simulation employed in GPR can be extended for the exploration of the effects due to the factors such as the different proportion of water content in the soil, the level and roughness of the soil etc on the reflected signal. This may find applications in geological explorations. ln the detection of mines, a state-of-the art technique for scanning and imaging an active mine field can be developed using GPR. The probing antenna can be attached to a robotic arm capable of three degrees of rotation and the whole detecting system can be housed in a military vehicle. In industry, a system based on the GPR principle can be developed for monitoring liquid or gas through a pipe, as pipe with and without the sample gives different reflection responses. lt may also be implemented for the online monitoring of different stages of extraction and purification of crude petroleum in a plant.Since biological samples show fluctuation in the dielectric nature with time and other physiological conditions, more investigation in this direction should be done. The infected cells at various stages of advancement and the normal cells should be analysed. The results from these comparative studies can be utilized for the detection of the onset of such diseases. Studying the properties of infected tissues at different stages, the threshold of detectability of infected cells can be determined.

Strip-loaded hollow dielectric H-plane sectoral horn antennas for square radiation pattern

The radiation characteristics of a new type of hollow dielectric H-plane sectoral horn antenna are presented. Metallic strips of optimum length are loaded on the H-walls of the sectoral horns. The effects of strip loading for producing square patterns in the H plane are discussed.

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.

Investigations on the structural, optical and Magnetic properties of nanostructured cerium oxide in pure and doped forms and its polymer nanocomposiets

This thesis Entitled INVESTIGATIONS ON THE STRUCTURAL, OPTICAL AND MAGNETIC PROPERTIES OF NANOSTRUCTURED CERIUM OXIDE IN PURE AND DOPED FORMS AND ITS POLYMER NANOCOMPOSITES.Synthesis and processing of nanomatelials and nanostmctures are the essential aspects of nanotechnology. Studies on new physical properties and applications of nanomaterials and nanostructures are possible only when nanostructured materials are made available with desired size, morphology,crystal structure and chemical composition.Recently, several methods have been developed to prepare pure and doped CeO2 powder, including wet chemical synthesis, thermal hydrolysis, flux method, hydrothermal synthesis, gas condensation method, microwave technique etc. In all these, some special reaction conditions, such as high temperature, high pressure, capping agents, expensive or toxic solvents etc. have been involved.Another hi gh-li ght of the present work is room temperature ferromagnetism in cerium oxdie thin films deposited by spray pyrolysis technique.The observation of self trapped exciton mediated PL in ceria nanocrystals is another important outcome of the present study. STE mediated mechanism has been proposed for CeO2 nanocrystals based on the dependence of PL intensity on the annealing temperature. It would be interesting to extent these investigations to the doped forms of cerium oxide and cerium oxide thin films to get deeper Insight into STE mechanism.Due to time constraints detailed investigations could not be canied out on the preparation and properties of free standing films of polymer/ceria nanocomposites. It has been observed that good quality free standing films of PVDF/ceria, PS/C61‘l8, PMMA/ceria can be obtained using solution casting technique. These polymer nanocomposite films show high dielectric constant around 20 and offer prospects of applications as gate electrodes in metal-oxide semiconductor devices.

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.