本論文主要以X光吸收光譜實驗研究單晶樣品La5/3Sr1/3NiO4的電子與原子結構。實驗包含室溫時不同極化方向O K- edge、Ni K-edge、La L3-edge與La M5-edge X光吸收近邊緣結構(X-ray absorption near edge structure，XANES)，以及分別在不同溫度下量測O K- edge、La L3-edge、La M5-edge和Ni K-edge延伸X光吸收精細結構(Extended x-ray absorption fine structure，EXAFS)。由不同極化方向O K-edge與Ni K-edge XANES光譜圖中發現樣品有著結構異向性，並且從La L3-edge與La M5-edge XANES光譜圖可印證樣品絕緣層的存在與影響電子的傳輸方向。由不同溫度的O K-edge XANES光譜顯示，在溫度T = 240K時電荷條紋與溫度T = 180K電子自旋條紋形成時由於未佔據態數目改變造成電阻非線性的變化。並且從Ni K-edge EXAFS光譜圖指出，隨著溫度改變，Ni原子周圍的原子結構是相似的，這顯示樣品中CDW的轉變機制與原子結構變化並無明顯直接關聯。

The electronic and atomic structures of the single crystal La5/3Sr1/3NiO4 were investigated by angle-dependent x-ray absorption near-edge structure (XANES) at O and Ni K-, La L3-, and La M5-edges at various temperatures. Apart from this, the extended x-ray absorption fine structure (EXAFS) at Ni K-edge was measured at different temperatures. These studies show the structural and electronic anisotropic nature of La5/3Sr1/3NiO4. From the spectra of different polarization of the La L3-edge and La M5-edge XANES, it is evident that this spacer layer (La-O) affect the electronic structure. According to the O K-edge spectra at different temperatures, when the charge stripes at T = 240K and spin stripesthe at T = 180K was formed, the unchanged number of unoccupied states can caused the non-linear changes of resistance. The spectra of the Ni K-edge EXAFS indicates that the atomic structure around the Ni atom does not change as the temperature is varied. Thus we find that the charge density wave phase and the dynamical properties of La5/3Sr1/3NiO4 have no direct relation to the atomic structure.

第一章	緒論...............................................1
第二章	X光吸收光譜簡介....................................3
1.	X光吸收近邊緣結構(XANES)...........................7
2.	X光延伸吸收精細結構(EXAFS).........................9
3.	實驗方法..........................................11
第三章	樣品特性與相關理論................................15
1.	樣品簡介..........................................15
2.	晶格場效應與Jahn-Teller效應.......................19
3.	電子自旋與電荷有序排列............................22
4.	電荷密度波........................................23
第四章	La5/3Sr1/3NiO4的電子結構與原子結構之研究..........26
1.	電子結構異向性之研究..............................27
2.	La5/3Sr1/3NiO4變溫下電子結構及晶體結構改變之研....39
第五章	結論..............................................54
參考文獻..................................................55

 
圖表目錄
圖2-1 光子能量與典型物質(銅)吸收截面關係。.................6
圖2-2 XANES與EXAFS分界圖。.................................6
圖2-3 光電子平均自由路徑與能量關係圖。.....................8
圖2-4 單一散射與多重散射之圖像(a)單一散射路程示意(b)多重散  
      射路程示意...........................................8
圖2-5 吸收光譜與電子末態關係示意圖。.......................9
圖2-6 吸收原子入射電子波與鄰近原子背向散射波示意圖。......11
圖2-7 X光吸收光譜實驗示意圖。.............................13
圖2-8 三種光譜量測法。....................................14
圖3-1 La2-xSrxNiO4樣品單位晶胞結構示意圖。................16
圖3-2 La2-xSrxNiO4單位晶胞中鈣鈦礦結構示意圖。............16
圖3-3 La2-xSrxNiO4中Ni-O層為主要的電子傳輸層，La-Sr-O為絕緣
      層。..................................17
圖3-4 在二維基本導體中，電荷條紋(charge stripe)的類型(a)水平
      排列(b)垂直排列(c)對角排列。........................18
圖3-5 當溫度由高溫絳至低溫時，La2-xSrxNiO4在ab平面上的相變情
      況。圖(a)為240K以上時電荷呈現一個無序的狀態，圖(b)在  
      240K至180K之間Ni3+呈現一個"45°" 週期性排列(電荷有序)，
      圖(c)在180K以下電荷有序之間出現了電子自旋有序的排列。
      ....................................................18
圖3-6 晶格場分裂所造成的3d軌域分佈示意圖。................20
圖3-7 Jahn-Teller形變示意圖。.............................20
圖3-8 (a) 一維線性金屬系統在忽略電子-聲子、電子-電子作用下，
      原子間等距分布。....................................25
圖3-8 (b) Peirels所預測的一維線性金屬系統中的原子呈現遠近-遠
      近的排列與電子密度呈現週期性的排列。................25
圖4-1 常溫下歸一化後樣品的O K-edge XANES，右上角插圖為吸收峰
      放大疊合比較圖。....................................28
圖4-2 常溫下歸一化後的O K-edge扣除一Gaussian函數之背景值，  
      紅色虛線為Sr電洞掺雜，藍色為Ni 3d 3z2-r2 - O 2p未佔據
      態，橘色為Ni 3d x2-y2– O 2p未佔據態。..............30
圖4-3 樣品的O K-edge扣除背景值後擬合結果分別積分得到面積積
      分值。..............................................31
圖4-4 常溫下歸一化後樣品的Ni K-edge XANES，右上角插圖為Ni K-
      edge對應角度之一次微分最大值。......................32
圖4-5 Ni K-edge XANES一次微分最大值能量對應角度關係圖。...34
圖4-6 常溫下歸一化後樣品的La L3-edge XANES。右上角插圖為經由
      歸一化後的La L3-edge扣除一Gaussian函數之背景值。....35
圖4-7 常溫下歸一化後樣品的La M5-edge XANES。左上角插圖為經由
      歸一化後的La M5-edge扣除一arctangent函數之背景值。..36
圖4-8 樣品的La M5-edge、La L3-edge扣除背景值所得到的面積積分
      值。................................................37
圖4-9在不同溫度和晶軸條件下歸一化後樣品的O K-edge XANES。.40
圖4-10 為不同溫度和晶軸條件下經由歸一化後的O K-edge扣除一
       Gaussian函數之背景值。紅色虛線為Sr電洞掺雜，藍色為Ni 
       Ni 3d 3z2-r2 - O 2p未占據態，橘色為Ni 3d x2-y2– O 2p
       未占據態。.........41
圖4-11 在不同溫度和晶軸條件下，樣品的O K-edge XANES扣除背
       景所得到的A1’ peak(Sr)、B1’* peak(Ni 3d 3z2-r2)與
       B1 peak(Ni 3d x2-y2)面積積分值。...................43
圖4-12 在不同溫度和晶軸條件下歸一化後樣品的La L3-edge 
       XANES。............................................45
圖4-13 為不同溫度和晶軸條件下經由歸一化後的La L3-edge扣除一
       Gaussian函數之背景值。.............................46
圖4-14 在不同溫度和晶軸條件下歸一化後樣品的La M5-edge 
       XANES。............................................47
圖4-15 為不同溫度和晶軸條件下經由歸一化後的La M5-edge扣除一
       arctangent函數之背景值。...........................48
圖4-16 在不同溫度和晶軸條件下，樣品的La L3-edge與La M5-edge 
       XANES扣除背景所得到的面積積分值。..................49
圖4-17 在不同溫度條件底下歸一化後樣品的Ni K-edge XANES，右下
       角插圖為吸收峰放大疊合比較圖。.....................50
圖4-18 在不同溫度條件下 Ni K-edge EXAFS傅利葉轉換圖，右上角
       插圖為k空間圖，其中k空間範圍為3.2Å~13.3Å。.........51
圖4-19 在不同溫度條件底下歸一化後樣品的Ni K-edge XANES，右  
       下角插圖為吸收峰放大疊合比較圖。...................52

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