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Synthesis of Mn, Co or Ni Doped ZnO Diluted Magnetic Semiconductors

Author: JiangYingJing
Tutor: JingChengBin
School: Qingdao University of Science and Technology
Course: Materials Physics and Chemistry
Keywords: diluted magnetic semiconductors (DMS) ZnO solvothermal method sol-gel method magnetic properties
CLC: TN304.7
Type: Master's thesis
Year: 2011
Downloads: 55
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Abstract


This work focuses on synthesis of Mn, Co or Ni doped ZnO diluted magnetic semiconductors (DMS) through a solvothermal method and a sol-gel method. Mn, Co or Ni doped ZnO film and powder samples were obtained by optimizing fabrication conditions. The crystalline structures, morphology and magnetic properties of the as-synthesized products were characterized. The magnetic as well as optical properties of the samples are discussed.A great deal of research work has been done to develop an ethylacetoacetate (EAcAc) modified solvothermal process for synthesis of transition metal doped ZnO film and powder samples. XRD, SEM, EDS and XRF analyses disclose that homogeneous and well crystallized ZnO film and powder products could be obtained by solvothermally treated ethanol aqueous solution containing zinc acetate (0.25M), urea (precipitator), and ethylacetoacetate (chelator) at 180℃for 5h. Mn, Co or Ni salt (acetate or sulphate) has been successfully introduced into the above solvothermal reaction system based on chelating reaction between metal ions (Zn2+, Mn2+, Co2+ or Ni2+) and EAcAc in ethanol aqueous solution. Mn, Co or Ni doped ZnO films and powders were obtained by solvothermally treaed the solution containg Zn2+ and Mn2+, Co2+ or Ni2+ under same conditions. Much stable and transparent sol with proper viscosity has been prepared by adding pvppolyvinylpyrrolidone (PVP) into the solution containing Zn2+ and transition metal ions. Mn, Co or Ni doped ZnO compact, uniform thin films were fabricated using a sol-gel spin-coating approach. PVP contributes to adjusting the sol viscosity as well as prolonging the gel time of the sol. Actually, it also plays a key role in preventing the sol-gel film from cracking during subjected to heat treatment.XRD and Raman analyses show that ZnO film samples with a small amount of Mn, Co or Ni dopants have a single phase. These dopants occupy Zn sites in the ZnO latticle, without changing the hexagonal wurtzite crystal structure of ZnO matrix. However, a secondary phase is observed in the ZnO samples with a higher dopant concentration. ZnMnO3 phase is detected in a 10% Mn doped ZnO sample. (Zn0.99Co2.01)O4 impurity phase appears in a 5% Co doped ZnO sample. The ZnO sample with Ni content up to 10% contains a Ni0.7Zn0.3O phase. Mn, Co or Ni doped ZnO products consist of nano-scale particles exhibited by SEM and HRTEM analyses.An ultraviolet (UV) photoluminescence (PL) peak centering at 380 nm(3.26 eV) is observed in the Mn doped ZnO sample. Furhter PL analyses show that the 380 nm peak undergoes a small blue-shift with increase of Mn concentration. It has been found by magnetic meansurements that the ZnO sample doped with different kinds of dopants or diffent amounts of a same dopant differs largely in magnetic performance. Room-temperature ferromagnetisms are observed in the <5% Mn, Co doped ZnO or the doped ZnO with Ni concentration up to 10%. Based on structural and compositional analyses, the as-observed ferromagnetisms are considered to arise from ZnO DMS as well as some unknown nanophases.

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