Electronic and atomic structures of the nano-material studied by X-ray absorption spectroscopy and scanning photoelectron microscopy

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Title:	Electronic and atomic structures of the nano-material studied by X-ray absorption spectroscopy and scanning photoelectron microscopy
Other Titles:	X光吸收光譜及掃描式光電子顯微能譜術研究奈米材料的電子與原子結構
Authors:	邱昭文;Chiou, Jau-wern
Contributors:	淡江大學物理學系博士班彭維鋒;Pong, Way-faung
Date:	2005
Issue Date:	2010-01-11 02:18:07 (UTC+8)
Abstract:	第三代同步輻射的發展對奈米材料電子結構的探討提供了強而有力的能譜技術，包括X光吸收能譜術(XAS)(主要是X光吸收近緣結構能譜，XANES)、X光光電子能譜術(XPS)、掃描式光電子顯微能譜術(SPEM)、X光磁圓偏振二向性(XMCD)和X光輻射能譜術(XES)已然被廣泛應用在了解奈米碳管(CNTs)、氧化鋅(ZnO)和氧化鈷鋅奈米柱(Zn1-xCoxO nanorods)、氮化鎵奈米線(GaN nanowires)及氮化鋁奈米針(AlN nanotips)等奈米材料電子結構的佔據態和未佔據態。藉由不同入射角度的量測，我們可以比較奈米碳管和氧化鋅奈米柱在尖端和側面的局域電子結構。從結果發現，奈米碳管的尖端具有相當均勻且延伸了大約10 eV的價帶強度;而在氧化鋅方面則發現，奈米柱的尖端主要是由氧原子所佔據，並且沿著[000 ]方向成長。針對不同管徑氧化鋅奈米柱量測鋅和氧的K邊X光吸收近緣結構能譜圖，得知管徑愈小則所受的表面效應愈大。在氧化鋅奈米柱的成長過程中添加鈷元素使其成為帶有鐵磁性的稀磁性半導體的能譜研究中，提出了鐵磁性的產生和深層缺陷的電子轉移至價帶的鈷3d軌道有很強烈的關聯性。比較氮化鎵奈米線和氮化鎵薄膜，因為負(正)電荷效應的增加所以造成奈米線中氮(鎵) 的K邊X光近緣結構能譜圖具有較大(小)的強度。除此外，在p-type和n-type矽基板上成長氮化鋁奈米針的SPEM研究中可以看到，在靠近費米面的地方，AlN/p-Si擁有較大的態密度。 The development of third generation synchrotron radiation sources has provided powerful spectroscopic techniques for probing the electronic structures of nanomaterials. Primarily five techniques namely; X-ray absorption spectroscopy (XAS) (mainly X-ray absorption near edge structure, XANES), X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), X-ray magnetic circular dichroism (XMCD), and X-ray emission spectroscopy (XES), have been extensively employed to understand the unoccupied as well as occupied states of electronic structures of nanomaterials; carbon nanotubes (CNTs), ZnO & Zn1-xCoxO nanorods, GaN nanowires, and AlN nanotips. Angle-dependent measurements were performed to understand the local electronic structures of the tips and sidewalls of highly aligned CNTs and ZnO nanorods. It suggests that increase in tip intensities is quite uniform over an energy range wider than 10 eV and the tip surfaces of the highly aligned ZnO nanorods are terminated by O atoms and the nanorods are oriented in [000 ]. An analysis of XANES spectra at O K- and Zn K-edge of ZnO nanorods at various diameters showed enhancement of surface states with decrease of diameter. Spectroscopic studies on Zn1-xCoxO nanorods showed that the ferromagnetism is strongly associated with the transfer of electrons from deep defect states to valence-band Co 3d orbitals. A comparison of the XANES spectra at N (Ga) K-edge revealed that the GaN nanowires have smaller (larger) intensity than that of GaN thin film, which suggests an increase of the N (Ga) negative (positive) effective charge in the nanowires. Apart from this, a comparison of the electronic structures was carried on AlN nanotips grown on p- and n-type Si substrates and the SPEM study indicates that the former have larger density of states than the latter near Fermi level.
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