MPhil Thesis

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Magnetic characteristics of zinc substituted cobalt ferrites
(University of Dhaka, 2019-10-07) Mariam, Tamanna
A series of Co1-xZnxFe2O4 ferrite(x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) compositions were synthesized using the standard double sintering ceramic technique, sintered at 1050°C for 2 hours. Substituting Zn in place of Co influenced the structural, dielectric and magnetic properties of CoFe2O4samples. Structural analyses were carried out using X-ray diffraction (XRD). The XRay diffraction pattern confirmed the single-phase cubic spinel structure and the sharp peak revealed that the samples are in good crystalline form. The lattice parameters were calculated for each composition and found to increase with Zn substitution. A significant increase in density and subsequent decrease in porosity were observed with increasing Zn content. The grain size of the samples was reduced by enhancing the Zn concentration. The dielectric constant (ε′) of the sample is found to decrease with increase in frequency exhibiting normal dielectric behavior. Dielectric relaxation peaks were observed for the frequency dependence of dielectric loss tangent curves. The observed dielectric properties were explained on the basis of electron conduction mechanism. The variation of the resistivity versus temperature was also studied and the dielectric constant of the system has a variation quite similar to that of the resistivity. Vibrating Sample Magnetometer measurement confirmed that the magnetizations of all the samples were saturated. Saturation magnetization and coercivity were estimated with variation of Zn content. These effects are due to facilitation of demagnetization by substitution of the non-magnetic Zn ions. Permeability was found to decrease with increase in Zn content. Cobalt Ferrites have the characteristics of electromagnetism, excellent chemical stability, mechanical hardness, low coercivity, moderate saturation magnetization and high anisotropy constant. Hence, Zinc substituted Cobalt Ferrite is a good candidate for synthesizing as dielectric, magnetic, multiferroic material and also for using in storage devices in advancement of science and technology.
Synthesis and Magnetic Properties of Folate Chitosan Coated Cobalt Ferrite Nanoparticles for Biomedical Applications
(©University of Dhaka, 2022-01-24) Nahar, Arijun
Cobalt ferrite (CoFe2O4) nanoparticles were synthesized by co-precipitation method and were coated with biocompatible, biodegradable folate chitosan. The XRD studies confirmed the formation of single phase with inverse spinel structure. The lattice parameter calculated from XRD was founded to be 8.335 Å and average crystallite size was ~12 nm. Similar particle size (5-15 nm) was determined from the TEM analysis. A good crytallinity and single phase formation of the synthesized nanoparticles were confirmed using the HRTEM lattice fringes and SAED patterns diffraction rings, respectively. The value of saturation magnetization for uncoated CoFe2O4 nanoparticle was 44 emu/g and it was reduced to 40 emu/g for folate chitosan coating. The Mössbauer spectra demonstrated superparamagnetic phases embedded in the ferromagnetic matrix which had the good agreement with the M-H curve. The FTIR and Raman spectroscopy studies confirmed the spinel structure of the CoFe2O4 nanoparticle and coated CoFe2O4 nanoparticles. The DSC-TG curves show that the exothermal reaction and mass loss were occurred in the CoFe2O4 nanoparticle. The hydrodynamic size and polydispersity index of all the samples were varied from 143-361 nm and 0.185-0.331, respectively at different temperature which are promising results for biomedical applications. The positive zeta potential value of all the samples confirmed that the folate chitosan was stably coated on the surface of the nanoparticles. Induction heating of folate chitosan coated CoFe2O4 was investigated to reveal the self-heating temperature rising properties. The heating capability was found in the hyperthermia range (42-45 ºC) for all the samples. To demonstrate CoFe2O4 as a good contrast agent, the MRI images obtained from the phantoms and in-vivo experiments using Albino Wister rats.
Investigation of the electrical and magnetic properties of conductor-insulator (wcco) Composites
(© University of Dhaka, 2025-03-19) akter bally, Most. Asma
Study of photo electromagnetic effect in bulk and thin films of semiconducting materials
(© University of Dhaka, 2025-03-19) islam, Md. Shahidul
Characterization of chemically deposited copper selenide thin films for solar cell application
(© University of Dhaka, 2025-03-19) ...., Al-mamun
Electronic structure, band energy, fermi energy and density of states of metals and disordered alloys
(© University of Dhaka, 2025-03-19)
Preparation and characterization of some relatively unknown III-V semiconducting compounds
(© University of Dhaka, 2025-03-19) sultana, Ms jesmin
A study of atmospheric turbidity coefficients from measurements of the direct solar radiation
(© University of Dhaka, 2025-03-19) alam khan, Md.feroz
Development of a simple 'DLTS’ system for characterization of impurities and defects in semiconductors
(© University of Dhaka, 2025-03-19) Begum, Ms Tahmina
DESIGN AND CONSTRUCTION OF A COMPUTER AIDED CAPACITANCE TRANSIENT SPECTROMETER FOR THE STUDY OF DEEP DEFECT CENTRES IN SEMICONDUCTORS
(© University of Dhaka, 2025-09-03) BEGUM, MS ZERINA
The object of the present work has been to design and construct a computer aided transient capacitance spectrometric system for detection and characterisation of deep defect centres in Semiconductor. It is hoped that the spectrometer would be able to detect, identify and characterise the deep defect centres present in semiconductor devices. It is known that the presence of impurities or lattice defects in a semiconductor crystal creates deep defect centres. The defect states are located deep inside the forbidden zone, which may act either as <■_ «electron/hole traps or recombination centres. So these centres influence the electrical and optical properties of a semiconductor. The identification and study of their characteristics and kinetics would facilitate the understanding of physics of the semiconductor and its devices. The basic idea of a DLTS spectrometer is to implement a “rate window”. There are two methods of implementing the rate window: by the use of (i) a double box car averager or (ii) a Lock-in-amplifier. In the present work we have implemented the rate window with the computer aided electronic circuitry based on the basic principle of box car averager. DLTS spectrometer system is a complicated experimental setup and needs sophisticated instrumentation. To develop our spectrometric system we have used a 710 ACER computer. The main component i.e. the heart of our system is a rapid data acquisition system peculiar to our need and purpose which would collect and store data, for subsequent manipulation, record temperature of the system, and capacitance from a capacitance meter. For the system we need various electronics circuitry including S/H circuit^unity gain amplifier, base line restorer, and pulse amplifier. All these units have been developed and constructed in the laboratory. Other experimental devices and setups such as cryostatic set up, sample assembly etc. have been constructed in the laboratory. Interfacing between the analog world and the computer has been made via interfacing unit, the Keithley made 570 system. The variable width pulse generator and the capacitance meter formp other two major component^ our system. The capacitance meter operates at 1MHz. The necessary softwares needed to run the constructed spectrometer based on BASIC High Level language together with a special software Soft500 have been developed to suit our environment and need. In order to test the performance of our spectrometer system we have used hardware based laboratoiy made artificial and software based computer simulated DLTS signals. A few real samples i.e. Si p-n junctions have been examined and DLTS signals could be detected
STUDY OF SOME COMMERCIALLY FABRICATED SEMICONDUCTOR P-N JUNCTION CHARACTERISTICS AND CHARACTERIZATION OF IMPURITY LEVELS PRESENT THEREIN
(© University of Dhaka, 2025-09-07) Selima Begum, MS Khondaker
The object of present work has been to study junction properties of some commercially available diodes and transistors. We studied over fifty samples out of which twenty were analyzed in details and are reported here. To study the property of depletion layer of p-n junction we carried out a detail C-V measurement. From this study junction capacitance, depletion width, contact potential etc. have been evaluated. From I-V studies (for forward bias and reverse bias conditions) efficiency factor r? has been estimated for large numbers of diodes. These studies indicate the presence of deep impurity centers in most of the samples. To confirm this we carried out detail investigation to detect defect states, if any, and characterized the defect states whenever found. We have observed the presence many and varied deep states both in Si and Ge. The methods used the states are TSCAP and TSC. for characterizing Ip carrying out the investigation we have to construct fixed and variable temperature system, a constant temperature bath and many electronic circuitry needed for our experiments