Investigations On Evolution Of Morphologies And Properties In ZnO

ZnO is a significant technological material. The absence of a centre of symmetry in its wurtzite structure, along with large electromechanical coupling, results in strong piezoelectric and pyroelectric properties. ZnO is therefore widely used in mechanical actuators and piezoelectric sensors. In addition, ZnO is a wide band-gap (3.37eV) compound semiconductor that is appropriate for short wavelength optoelectronic applications. The high exciton binding energy (60meV) in ZnO crystal allows efficient excitonic emission at room temperature. ZnO is transparent to visible light and its conductivity can be increased through doping. ZnO nanostructures have a wide range of high technology applications like surface acoustic wave filters, photonic crystals, photodetectors, light emitting diodes, photodiodes, gas sensors, optical modulator waveguides, solar cells and varistors. ZnO is also receiving a lot of attention because of its antibacterial property and its bactericidal efficacy has been reported to increase as the particle size decreases.In this paper, ZnO nanostructures are synthesized by hydrothermal synthesis method. The raw materials are Zinc acetate, sodium hydroxide, anhydrous ethanol and deionized water. Different types of surfactants as additives are used under different conditions. Products were characterized to study the formation mechanism of ZnO by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorption spectroscopy (UV-Vis) analysis techniques. The main results obtained are as follows:1.Different surfactants on the ZnO morphology1) Non-ionic surfactant:PEG400 as the surfactant, flower-like structure ZnO are prepared which is made of neddle-like rod.2) Anionic surfactants:DBS as the surfactant, tflower-like ZnO are formed which is made of thin sheets. 3) Cationic surfactants:DTAC as the surfactant, flower-like ZnO are prepared in the alkali solution which is made of rod.2. Particle size factorsZnO grain size varies directly with the molar ratio, temperature, time. Particle size rise proportionately to ionic surfactant concentration While it is inversely proportional with the proportion of non-ionic surfactant. Using anhydrous ethanol as solvent produced a smaller ZnO particle size than the water as the solvent.3. UV absorption of ZnO prepared by three kinds of surfactantsIn the 300 to 400nm wavelength range, absorption rate of ZnO prepared by three kinds of surfactant are 15%-95%.Absorption rate of the order (from high to low):zinc oxide prepared by the DBS as a surfactant, zinc oxide prepared by PEG400 as a surfactant, zinc oxide prepared by DTAC as a surfactant. Nanostructure ZnO possess a strong absorption in the UV region.