Department of Electrical and Electronic Engineering

A Study of Electrical and Optical Properties of Transparent Conducting Sno2 and In203 Thin Films Prepared by Pyrosol Process

Fri, 01 Dec 1989 00:00:00 GMT

A Study of Electrical and Optical Properties of Transparent Conducting Sno2 and In203 Thin Films Prepared by Pyrosol Process Hakim, Md. Obaidul The design and construction of a simple and low-cost device for the deposition of thin films by the pyrosol process has been described. Doped and undoped films of SnO2 and In203 have been pre- pared on glass substrates. These films were highly conducting and at the same time highly transparent. They were non-stoichiometric but homogeneous and polycrystalline in structure. It is found that an activation energy of about 0.2 eV is associated with the growth process of these films. The sheet resistance of these films shows a size effect below a thickness of about 0.3 um. Doping has been performed by adding autimony (Sb) and fluorine (F) in SnO2 film and higher figure of merit in comparison to other earlier reports has been obtained. In In203 film Sn has been used as doping element to obtain films of higher conductivity and all mobility. The electrical transport properties and the optical transmission coefficients in the UV-VIS range of these films in the carrier concon-tration range~ 6 x 1018 to ~ 1.3 x 1021 cm3 for Sno2 and from ~3x1018 to~ X1020 са-3 for In203 films with thickness about 0.2 μm have been studied in detail to establish a tontative energy band picture of these degenerate samples. The thermoelectric power of the films were measured in the temperature range 27° to 160°C for Sno2 and upto 175°C for In20 films. Using the thermopower and optical transmission data the effective masses of electrons and of holes have res- pectively been determined as a function of the carrier coneen- tration. The optical band gap and the position of the Fermi levels were determined. It has been observed that the Formi levels are pinned near the conduction band edge at decreasing carrier concentrations, and the optical band gap shows an appre- ciable loss-Burstein shift in the investigatod range of carrier concentration. The effect of post-deposition heat treatment on some of the SnO2 and In203 films has been studied. It has been obser- ved that heat treatment in different ambients have remarkable effects on the film resistivity. No appreciable change of carrier concentration was noticed in SnO2 film but it was noticed in the In203 films. Hall mobilities in these films are found thermally activated at temperatures ranging from room temperature upto about 250°c. Oxygen diffusion mechanism at the grain boundaries of these films has been discussed critically to explain the observed mobility data. It is inferred from the heat treatment experiments that the role of oxygen diffusion process in the film is only to modulate the inter-grain boundary potential barrier heights. For SnO thin films two distinct scattering processes viz the grain boundary scattering and the ionized impurity scatte- ring are found to play a predominant role in limiting the Hall mobility in the two different ranges of carrier concentrations at room temperature. For the In203 films however the lattice scattering is found to be the dominant process limiting the carrier mobility. Finally, an attempt has been made to determine the electron affinity and work function of these samples on an empiri- cal basis using the electro negativity concept. The crystal bindings of these samples were also determined and were found to be of fairly ionic in nature. This thesis is Submitted to the Department of Electrical and Electronic Engineering (Former Department of Applied Physics and Electronic Engineering), University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD)

Electrical and Optical Properties of Vanadium Dioxide and Vanadium Oxyfluoride Thermochromic Thin Filmsa and Their Applications to Energy Efficient Smart Windows

Fri, 01 Dec 1989 00:00:00 GMT

Electrical and Optical Properties of Vanadium Dioxide and Vanadium Oxyfluoride Thermochromic Thin Filmsa and Their Applications to Energy Efficient Smart Windows Alam Khan, M. Khairul This thesis reports on the rmochromic thin films of Vanadium dioxide and Vanadium oxyfluoride produced by reactive rf magnetron sputtering followed by annealing post-treatment. Such coatings have optical properites that make them interesting for application on energy-efficient Smart Windows. The VO2 coatings were characterized by transmission electron micro- scopy. They were polycrystalline with grains 50 nm to 100 nm in diameter. Thin films of VOXFy were made by rf magnetron sputtering of V in Ar + O2 + CF4. They were analysed by Rutherford Backscattering Spectrometry and transmission electron microscopy. Imaging in bright-field and dark-field modes showed that the crystallites were 50-90 nm in linear size. Electron diffractograms showed ring type patterns, characteristic of microcrystalline samples. Electrical measurements on VO films gave a metal-insulator transition temperature (t) at 68°C. Spectral measurements on these films in the whole solar and thermal wavelength range exhibit thermochromism. Electrical measurements as a function temperature in the range 20 100 nm. At t = 200 nm, VOXFy has Tlum = 25 % while VO2 only has Tlum = 10 %, where Tlum refers to integrated luminous transmittance. Optical properties at the metal-insulator transition in thermochromic VOXFy thin films were measured in detail as a function of temperature. This study verified that the spectral transmittance as well as the reflectance were essentially wavelength independent at a temperature which corre- sponds to 65°C, i.e. at the metal-insulator transition. The complex dielectric function of VO2 and VO Fy coatings in the whole solar range (0.3 2.5 μm) were determined by spectrophotometric measurements. The author's results for VO2 are in overall agreement with earlier published dielectric functions. The optical constants for VOXFy, as far as author knows, have not been measured before. This thesis is Submitted to the Department of Electrical and Electronic Engineering (Former Department of Applied Physics and Electronic Engineering), University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD)

Analysis and Modelling of Seismic Surface Wave for Studying the Crustal Structure of the South-Eastern Region of Bangladesh

Sat, 01 Jan 2011 00:00:00 GMT

Analysis and Modelling of Seismic Surface Wave for Studying the Crustal Structure of the South-Eastern Region of Bangladesh Faruk, Md. Omar Earthquake is one of the catastrophic events of the natural disasters that are prone to cause great damage to life and property. In order to decrease the damages, it is essential to gain knowledge for studying the crustal structure of the earth. In this dissertation crustal structure of the south-eastern region of Bangladesh is estimated by using seismic surface wave data. The parameters of the recorded earthquake data are ideally related to the subsurface geology. Geologic properties beneath a region have a major impact on the ground motion by modifying the amplitude, phase, duration, and shape of seismic waves. The main purpose of our work is to study the crustal structure, particularly major crustal boundaries and thicknesses of the structures. Three earthquake events of the south-eastern region of Bangladesh have been deliberated in this research. The events are respectively of magnitude 5.6 occurred on 26 July 2003 at the south-west of Daluchari, Chittagong, Bangladesh, magnitude 5.1 occurred on 27 July 2003 at Kolabunia, Chittagong, Bangladesh and magnitude 5.6 occurred on 21 September 2003 at the south of Meiktila, Myanmar nearer to the study area…………………………… This Thesis is Submitted to the Department of Electrical and Electronic Engineering, University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD)

Recognition of Human Faces

Wed, 01 Jan 2003 00:00:00 GMT

Recognition of Human Faces Ferdousi, Afroza This dissertation is devoted to the development of some image processing algorithms and implementation of these algorithms in face recognition system. At first face images were scanned and stored as windows bitmap file (bmp), in order to extract features. In features extraction, the original face, edge-detected face and threshold-face were taken to extract three types of features. The face was divided into small grids. Each grid of the face includes 10x10 matrix of gray level values. Thus 100 data were taken from a grid and the averages of these 100 data were taken as a feature. The recognition systems include the template matching by distance measurement (Hamming and Euclidean) between known and unknown features and a neural network. Fifty faces of ten persons were used to test the system. The highest recognition rate was 92%. Using features from threshold face and neural network as recognition tool achieved this result. This thesis is Submitted to Department of Electrical and Electronic Engineering, University of Rajshahi, Rajshahi, Bangladesh for The Degree of Master of Philosophy (MPhil)