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    Please use this identifier to cite or link to this item: http://tkuir.lib.tku.edu.tw:8080/dspace/handle/987654321/114231

    Title: Defect induced magnetism in nano-materials studied by X-ray-based spectroscopic and microscopic techniques
    Other Titles: 利用X光能譜及顯像技術探討缺陷對奈米材料磁性的誘發機制
    Authors: 王玉富;Wang, Yu-Fu
    Contributors: 淡江大學物理學系博士班
    Keywords: 掃描式穿透X光顯像術;X光磁圓偏振二向性;X光吸收近邊結構;衍生X光吸收精細結構;X光光電子能譜術;X光激發螢光;STXM;XMCD;XANES;EXAFS;XPS;XEOL
    Date: 2017
    Issue Date: 2018-08-03 14:45:53 (UTC+8)
    Abstract: X光顯像及相關能譜實驗技術提供了具備高空間解析度及元素針對性的電子、原子結構資訊於基礎科學研究、材料研發及產業應用上,包括X光吸收近邊結構(X-ray Absorption Near Edge Structure, XANES)、X光光電子能譜術(X-ray Photoelectron Spectroscopy, XPS)、X光磁圓偏振二向性(X-ray Magnetic Circular Dichroism, XMCD)、X光激發螢光(X-ray Excited Optical Luminescence, XEOL)、衍生X光吸收精細結構(Extended X-ray Absorption Fine Structure, EXAFS)及掃描式穿透X光顯像術(Scanning Transmission X-ray Microscopy, STXM)等,這些新穎技術提供了研究非磁性材料之室溫鐵磁現象誘發機制更豐富多元的實驗證據及方法。
    X-ray microscopic and spectroscopic techniques provide highly spatial-resolved and element-specific information of electronic and atomic structures for fundamental researches, material studies and industrial applications. Techniques include X-ray absorption near edge structure (XANES), X-ray photoelectron spectroscopy (XPS), X-ray magnetic circular dichroism (XMCD), X-ray excited optical luminescence (XEOL), extended X-ray absorption fine structure (EXAFS) and scanning transmission X-ray microscopy (STXM) provide fruitful experimental evidences which are using to unravel the mechanism of room temperature ferromagnetism in non-magnetic materials.
    The results of C K-edge STXM-XANES provide clear evidence that the higher number of C 2p(σ*)-derived defect/vacancies states, rather than of the C 2p(π*) states that are bound with oxygen-containing and/or hydroxyl groups on the graphene oxide (GO) surface, is related to the change of magnetic behavior from that of ferromagnetic GO to that of paramagnetic photo-thermal reduced GO observed from experimentally. The spin-polarized density functional theory calculations of graphene with monovacancy further support the finding that the magnetism originates in defects/vacancies, and in particular that the J-T distortion of the local defect structure is responsible for magnetic moments in GO.
    Results of O K-edge STXM-XANES and XMCD confirm the argument that the magnetic moments are arising from the O 2p orbitals in the surface of ZnO nanostructures rather than from Zn d orbitals. Local density approximation calculations further support the conclusion that the presence of defects and/or vacancies or dangling/unpaired 2p bonds at O sites around cation vacancy centers is responsible for room temperature ferromagnetism in ZnO. Furthermore, the C-implanted ZnO nanowires shows strongly enhanced in saturation magnetization, results of X-ray-based spectroscopy and microscopy suggest interstitial C is responsible for the enhancement.
    Appears in Collections:[Graduate Institute & Department of Physics] Thesis

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