| Zinc oxide is a material with great potential for a varietyof practical applications, such as piezoelectric transducers,surface acoustic wave devices, optical waveguides varistors,transparent conductive oxides,spin functional devices and UV-light emitters.Its wide bandgap (3.37 eV at room temperature) makes ZnO a promising material for photonic applications in the UV or blue spectral range, while the high exciton-bindingenergy (60 meV)allows efficient excitonic emission evenat room temperature. It is foud that the properties of ZnO can be varified by doping different elements, which have been successfully reported in many experiments. For example, by doping the proper amount of Mg or Cd to ZnO, the band-gap of ZnO can be modulated, by doping the transition metal (Fe,Co,Ni and so on) the room temperature ferromagnetism obtained, by dopingâ…¢A group n-type conductor obtained and by dopingâ… A andâ…¤A group p-type conductor obtained.In this paper,we prepared (Mg, Co) codoped and Co (or Mg) doped ZnO thin films via hydrothermal method, which were studied for their microstructures, morphologies, optical properties and magnetic properties. The main contents and results of the research are summarized as follows:1. Zn0.95-xCo0.05MgxO single-crystal nanorods have been successfully grown by the hydrothermal technique. The influenece of Mg doping content on the micro-structures, morphologies, optical properties and magnetic properties of the Zn0.95-xCo0.05MgxO have also been studied. SEM and XRD indicate that higher doped Mg concentration is helpful for the nucleation and growth of ZnO nanorods. From the Reflection and Transmission spectra measurements, we can see that varying Mg doping contents can modulate the bandgap of ZnO thin films. Moreover, PL spectra only present a broad emisstion band in visible light region. It can be found that the all samples show the room temperature ferromagnetism.2. The influence of the citrate on Zn0.85Co0.05Mg0.10O thin films for the micro-structures, morphologies, optical properties and magnetic properties have been studied systematically. SEM indicates that citrate can modulate the morphologies of the thin films from slanting nanorods to upright nanorods then to slanting nanosheet, upright nanocrystals. XRD shows that changing citrate concentration in the reaction solution can change the preferential growth orientation of thin films, from [001] to [100] via [101]. Moreover, the Transmittance measurement shows that the bandgap of thin films is increasing with the increase of citrate in the reaction solution, which indicates that citrate can promote the dopants incorporated into ZnO cryatal lattice.VSMmeasurement shows that all thin films present room temperature ferromagnetism.3. The comparative analysis of the micro-structures, optical properties and magnetic properties between (Mg,Co) and Co (or Mg) doped ZnO nanocrystal thin films. The influencce of different dopants on thin films for microstructures, optical properties and magnetism have been studied systematically. XRD indicates that dopant elements affect the function of sodium citrate in modulationg ZnO thin film growth orientation. Mg doping inhibits the preferential growth of ZnO cystal particles along [100] orientation while Co doping promotes the preferential growth of ZnO particles along [100] orientation. However, (Mg,Co) codoping have better effects in promting the preferential growth of ZnO particles along [100] orientation than signal doping of Co or Mg. PL spectra show that doping reduces the emission related to defects and improving the cystalline quality and the Transmittance measurement indicates that the Co or Mg dopant can increase the bandgap of thin film. Magetical measurement also found that Co (or Mg) doping and (Mg, Co) coding can increase the saturation magnetization of ZnO films and all films present room temperature ferromagnetism. |
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