Fabrication And Properties Of Doped T-ZnO

ZnO is a wide and direct band gap Ⅱ—Ⅵ semiconductor with many applications, such as a transparent conductive contact, thin-film gas sensor, varistor, solar cell, luminescent material, surface electro-acoustic wave device, heterojunction laser diode, ultraviolet laser, and others.In this dissertation, Al, Fe, Ag and Cu-doped tetra-needle-like zinc oxide whiskers (T-ZnO) were prepared using the high temperature solid solution treatment. Many kinds of instruments were employed to characterize the physical properties of the samples. Several novel and important properties such as adsorption effect, conductivity, gas sensitivity, green luminescence, magnetism, and the related applications of these samples were investigated experimentally. Main procedures and results are listed as blow:The adsorbability of T-ZnO for Al³⁺, Fe³⁺, and Cu²⁺ is studied respectively. The result revealed that the absorption capacity of T-ZnO for Al³⁺, Fe³⁺, and Cu²⁺ was 10.64mg/g, 9.22mg/g and 9.96mg/g, respectively. New complex compound formed on the surface of T-ZnO when etching in the corresponding solution.The Al-doped T-ZnO were prepared by means of dipping followed sintering procedures, the influence of annealing condition and dopants on the morphologies, structure and powder resistsivity of the T-ZnO were analyzed. Composites of T-ZnO/polyvinyl were prepared and their electrical resistivities were also measured. The results showed that it was helpful to decrease the resistivity of T-ZnO annealing in H₂ at 900℃;the resistivity of T-ZnO decreased obviously by doping with Al³⁺, the decrease was up to six orders of magnitude;the suitable addition of Al-doped T-ZnO in T-ZnO/PVC composites was 5vol%.The gas sensors were prepared by T-ZnO doped with Al³⁺, Fe³⁺, Ag⁺ and the gas sensing properties were investigated to different concentration of hydrogen, ammonia, alcohol, and hydrogen sulfide gases. The effect of doping, morphology and structure of the material on the gas sensing properties was discussed. The results showed that the T-ZnO based gassensor had more notable gas sensitivity to the alcohol and hydrogen gas than that to hydrogen and ammonia gases. The Al doped samples, which showed a maximum sensitivity of 127 towards lOOppm of hydrogen sulfide at work temperature of 268.5°C, had a better sensitivity than other samples. The response-recovery characteristics of the sensors for H2S were improved by introducing Al3+ in the lattice of ZnO.The Fe-doped T-ZnO samples have been prepared with different concentrations by the high temperature solid solution treatment. The structural and green luminescent properties have been studied by XRD and PL measurements. The X-ray diffraction patterns show that the wurzite structure of ZnO does not change for the doping concentration below 0.7%. Furthermore, we could not find any Fe cluster or phase separation in the X-ray diffraction patterns. The intensity of the green luminescence varies with the doping concentrations. The results obtain in the present paper supported the point of view that the mechanism of green luminescence was due to the transition between Vo and Vzn.The magnetic property, measuredment on superconducting quantum interference device revealed that some of the Fe-doped T-ZnO exhibited ferromagnetic behaviors with the Curie temperature higher than room temperature. And the correlation of structure and magnetic properties of Fe-doped ZnO were investigated and the room-temperature ferromagnetism in the Fe-doped ZnO system was ascribed to be orginated from the change of the electronic states of ZnO caused by Fe doping.