Browsing by Author "Muslima Zahan, Mst."

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Synthesis and characterization of Zn1-xMnxS thin films deposited by spray pyrolysis technique
(Department of Physics (PHY), 2012-05) Muslima Zahan, Mst.; Podder, Dr. Jiban
Diluted magnetic semiconductor (DMS) thin films (A1-xMxB) are prepared by doping a particular amount of magnetic element (M) into II (A)-VI (B) semiconductor. Zn1-xMnxS with varying Manganese (Mn) concentrations or x = 0.00, 0.10, 0.30, 0.50 and 0.70 mole were synthesized on glass substrates using Spray Pyrolysis Deposition (SPD) technique. An aqueous solution containing Zinc acetated, Manganese acetated and thiourea for Zinc ions (Zn+2), Manganese ions (Mn+2) and sulfide ions (S-2) respectively were used to deposit Zn1-xMnxS thin films at 3500C substrate temperature. The ratio of Zinc acetated, Manganese acetate and thiourea were 1:1:2. The films were characterized by Scanning Electron Microscopy (SEM), energy dispersive X-ray spectrometer (EDX), X-ray diffractometer (XRD), ultraviolet visible light (UV-vis) spectroscopy and Van-der Paw method for electrical property. The results showed that deposition time, temperature, and Mn doping concentration can affect the composition, surface morphology, crystallinity, grain size, and transmission spectra of the films. All the films were annealed at 4500C and 5500C for 1h. All as deposited films showed amorphous in nature and annealed films showed crystalline nature. SEM micrographs showed that the surface morphology of as-deposited Zn1-x MnxS films was inhomogeneous and after annealing the films became homogeneous. Some fibrous like structure was found into the annealed ZnS and Zn1-x MnxS films showed some crystallographic shape which confirmed the presence of Mn into ZnS. EDX spectra revealed the presence of Zn, Mn and S peaks in the films. All XRD patterns showed that crystallinity of the films increased with increasing Mn concentration. The size of the particles increased as the annealing temperature was increased. XRD patterns of the 5500 C annealed samples with different Mn concentrations (0.00, 0.10, 0.30, and 0.50 mole) showed polycrystalline nature. UV-vis transmission spectroscopy showed that the films were highly transparent (>80%) in the visible region. The optical direct band gap of as-deposited films was decreased from 3.51 eV to 3.01eV and indirect band gap from 3.02eV to 1.85eV with increasing Mn concentrations. This indicated that the presence of Mn in the system greatly affected the optical bad gap. The electrical conductivity and activation energy increased with increasing Mn concentrations. The dc conductivity was 10-3 order and activation energy changed from 0.14 eV to 0.45 eV. Also the increase of electrical conductivity with the increase of temperature indicated semi conducting behavior of as-deposited films.
Synthesis of spray pyrolysed transition and rare earth metal oxides (Co3O4, MnO2, WO3, CeO2) thin films and their characterization
(Department of Physics, BUET, 2021-03-31) Muslima Zahan, Mst.; Podder, Dr. Jiban
Semiconducting metal oxide based nano-materials play a very important role in the various fields of sensing materials for gas sensor and bio sensors due to rich physical and chemical stability. In this thesis, Iron (Fe) and Copper (Cu) doped cobalt oxide (Co3O4), manganese dioxide (MnO2), tungsten oxide (WO3) and cerium dioxide (CeO2) nanostructured thin films have been synthesized via spray pyrolysis deposition technique to explore their suitable morphological, structural, optical and electrical properties, pre-requisite for glucose sensing abilities. The presence of low concentration of Fe and Cu (about 4 to 6 at.%) strongly influenced the crystallite size of Co3O4, MnO2, WO3 and CeO2, as analyzed by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). Elemental analysis by energy dispersive X-ray spectroscopy (EDX) confirmed the stoichiometry and homogeneity of the films. XRD patterns of the deposited films showed spinel cubic, body centered tetragonal, monoclinic and face centered cubic crystal structure of Co3O4, MnO2, WO3 and CeO2, respectively, which well agrees with the JCPDS data. Crystallite sizes of Co3O4, MnO2, WO3 and CeO2 were obtained 29 nm, 24nm, 13 nm and 15 nm respectively, measured by Scherer relation. Optical band gaps calculated using Tauc relation were found 2.02 eV, 3.81eV, 2.72 eV and 3.44 eV for Co3O4, MnO2, WO3 and CeO2 films respectively and were tuned by Fe and Cu concentration. The dc electrical resistivity was obtained in the order of 104 -cm and confirmed the semiconducting behavior of the films. p-type carrier of Co3O4, MnO2, and n-type carrier of WO3, CeO2 were obtained by Hall Effect measurements. Glucose (C6H12O6) sensing performance of MnO2 and Fe doped MnO2 were carried out using electrical four point probe method. The highest glucose-sensing response was recorded about 29% at 5 minutes for 4 at% Fe: MnO2. The sensing performance of 4 at% Fe: MnO2 was found higher than undoped MnO2 sample under the same glucose concentration. Thus, Fe and Cu dopant is expected to improve the sensing properties of Co3O4, MnO2, WO3 and CeO2, and could be suitable candidate for biosensor developments.