SYNTHESIS AND CHARACTERIZATION OF NANOCRYSTALLINO DOPED ZINC OXIDE

Abstract

Nano-crystalline samples with compositions Zn1-x-yMnxAlyO (x = 0.03 and y=0, 0.01, 0.02) have been synthesized using co-precipitation method. The X-ray diffraction (XRD) data reveal the presence of wurtzite crystal structure in all synthesized samples. Xray diffraction and field emission scanning electron microscopic (FESEM) investigations confirm nanocrystalline nature of the synthesized samples. UV-vis spectroscopy results show that band gap of the samples varies with concentration of the doping and it decreases with increasing doping concentration. Magnetic measurements exhibit paramagnetic behavior in all the samples at room temperature. In chapter 1 we briefly introduced about properties of ZnO. We also provide an overview of diluted magnetic semiconductors (DMS) and ZnO based DMS. We provide applications of our work and motivation about recently work. In chapter 2 we discuss the synthesis and characterization techniques that are used in the dissertation. Synthesis techniques include the co-precipitation method which makes it possible the synthesis of material at lower temperatures. Co-precipitation method also makes it useful to control the particle size by varying the annealing temperature. The single phase nature and crystallinity is determined by X-ray diffraction technique. X-Ray diffraction data was obtained with the help of X – Ray diffractomter (BRUKER AXS D - 8). XRD data can be analyzed to determine the lattice parameters, particle size. Field emission scanning electron microscopy (FESEM) Model FEI Quanta 200F is used to determine the surface morphology of the samples. It uses the electric field effect in order to produce the electrons. These electrons eject the secondary electrons from the object which are used in the image formation of the samples. Energy dispersive X – ray analyzer (EDAX) technique confirms the stoichiometry of the sample. Four probe method because of its advantage of rectifying contact resistance is used for the measurement of electrical resistance. Four probe method uses the procedure in which the current is provided from the outer probes and voltage is measured from the inner two probes. Optical properties measured by UV-vis spectroscopy. By Kubelka-Munk treatment [(αℎ ) 1/2] vs. ℎ (eV) plots, we find band gap of samples. SQUID magnetometer (MPMS XL Quantum) is used for plotting the M – H loop at 300 K. V SQUID comprises superconductors separated by the insulating layer which creates the Josephson junction. In chapter 3 we present our work in dissertation. Material was synthesized by the coprecipitation method in order to make the particle size in nano. XRD pattern characterize the lattice structure and it was determined that samples exhibit hexagonal structure (a = b ≠ c) and particle size of the samples are obtained from the “Debye – Scherrer” formula. Particle sizes varying with the annealing temperature and doping. FESEM technique is used to provide the surface morphology of the samples and grain size and connectivity. EDAX results for all the samples confirms the desired stoichiometry within experimental error. Conductivity was measured from four probe method and we observed that conductivity is increasing with doping. From SQUID we observed relation between magnetization (M) and magnetic field (H). The M-H curve shows linear variation in magnetization with magnetic field, suggesting paramagnetic behavior.