強關聯錳氧化物薄膜及釓基金屬團簇富勒烯之電子及原子結構研究

The electronic and atomic structure of strongly correlated manganite thin film and Gadolinium-based metallofullerene

邵禹成(Yu-Cheng Shao)

指導教授 ： 彭維鋒

淡江大學/理學院/物理學系博士班/博士(2017年)

https://doi.org/10.6846/TKU.2017.00984

摘要

由第三代同步輻射光所衍生出來的能譜術，包含針對晶格結構的X射線繞射分析(XRD)，電子或軌域結構的X光吸收近邊結構能譜術(XANES)和X光線偏振二向性能譜術(XLD)，磁結構的X光磁圓偏振二向性能譜術(XMCD)，佔據態及其交互作用的X光發射能譜術(XES)和共振非彈性X光散射能譜術(RIXS)等各項技術被視為探究複雜耦合機制的有力工具。藉由其優異的對稱性及元素選擇性，在眾多錳系陶瓷薄膜及釓系化合物等強關聯系統研究中發揮關鍵的分析功能。
本文第一部分對釓基團簇富勒烯(metallofullerene)化合物
Gd3-xScxN@C80進行XAS及RIXS相關研究。釓基團簇富勒烯作為核磁共振(MRI)高效顯影劑(CAs)的潛能被深入探討，然而其中關鍵的金屬釓離子在電子結構及交互作用上卻尚未被研究透徹。我們利用釓N4,5-edges RIXS對 Gd3-xScxN@C80進行釓4f電子結構以及帶自旋翻轉特性的激發。相較於標準樣品氧化釓以及商用顯影劑釓基螯合物，富勒烯包覆的釓離子在特徵峰能量上位移，且峰形表現出與激發能量無關的寬化現象。並結合理論與實驗，討論釓離子內部軌域各種能量參數如交換場(Jex)、4f-4f庫侖作用、自旋-軌道耦合(SOC)等在富勒烯碳離子環境下所產生的響應。
第二部份利用變溫XRD量測不同膜厚的C-type反鐵磁錳系陶瓷薄膜-釹鍶錳氧(NSMO)/鈦酸鍶(STO)其基板應力對釹鍶錳氧薄膜晶格結構的影響，並配合錳L3,2-edge XLD和理論計算判定此隨溫度變化之應力對於錳離子在室溫及低溫情況下3d eg軌域的有序度，佔據狀態以及分裂程度。並進一步討論由XMCD以及磁化強度對溫度(M-T)曲線所觀察到可隨膜厚調制的尼爾溫度(TN)及低溫鐵磁性與軌域狀態的關聯。
最後則介紹由淡江大學(TKU)，台灣同步輻射(NSRRC)以及美國勞倫茲國家實驗室-先進光源(ALS, LBNL)共同合作建造台灣光子源(TPS)-45A軟X光發射譜(SXE)實驗站XES/RIXS光譜儀的功能、光學設計以及直射X光測試。

關鍵字

X光吸收近邊結構能譜術 ； X光線偏振二向性能譜術 ； X光磁圓偏振二向性 ； X光發射能譜術 ； 共振非彈性X光散射

並列摘要

The third-generation synchrotron radiation based spectroscopies such as X-ray diffraction (XRD) for lattice structure, X-ray absorption near edge structure (XANES) and X-ray linear dichroism (XLD) for electronic and orbital structures, X-ray magnetic circular dichroism (XMCD) for magnetic structure, X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) for information of the occupied states and inherent elementary excitations, are considerable and powerful techniques for the study of various complex couplings in complex systems. Their excellent symmetry and element specific capabilities are certainly exhibited in many strongly correlated systems like manganite thin films and gadolinium (Gd)-based compounds.
In the first part of this thesis, XAS and RIXS study of
Gd-based metallofullerene, Gd3-xScxN@C80, have been carried out. Because of the potentially efficient contrast agents (CAs) in magnetic resonance imaging (MRI), the Gd-based metallofullerene have particularly been well focused. However, the electronic structure and interaction of the key Gd ion remains unclear. Here, we have carried out RIXS experiments on GdxSc3-xN@C80 at Gd N4,5-edges to directly study the electronic structure and spin flip excitations of Gd 4f electrons. Compared with the reference Gd2O3 and contrast agent Gadodiamide, the features in the RIXS spectra of all metallofullerenes exhibit broader spectral lineshape and noticeable energy shift. Using atomic multiplet calculations, we have estimated the key energy scales such as the inter-site spin exchange field, intra-atom 4f-4f Coulomb interactions, and spin-orbit coupling. The implications of these parameters to the 4f states of encapsulated Gd atoms are discussed.
In the second part, temperature-dependent XRD has been used on the C-type antiferromagnetic Nd0.35Sr0.65MnO3 (NSMO)/SrTiO3 (STO) thin films of various thickness to study the response of the lattice structure under the strain of STO substrate. The combination of XRD, experimental and theoretical Mn L3,2-edges XLD is helpful to determine the degree of 3d eg orbital ordering, occupation and splitting with the strain in lattice structure as a function of temperature. Subsequently, the results of XMCD and magnetization vs temperature (M-T) curves, which show the thickness dependent Néel temperature (TN) and ferromagnetism at low temperature, have been discussed.
The final part is associated with the performance, design and straight beam test of XES/RIXS spectrometer at Soft X-ray Emission (SXE) endstation in Taiwan Photon Source (TPS)-BL45A. This spectrometer was jointly built by groups in Tamkang University (TKU), National Synchrotron Radiation Research Center (NSRRC) and Advanced Light Source-Lawrence Berkeley National Laboratory (ALS, LBNL).

並列關鍵字

XANES ； XLD ； XMCD ； XES ； RIXS

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