科學家於1967年發現基本上是絕緣體的鈦酸鍶，在高電子載子濃度下，可變為具有超導或半導體特性的氧化物材料，但轉變溫度相當低，而2015年，單層硒化鐵薄膜在鈦酸鍶基板上所引發的超導相變溫度被量到可高達109 K，使鈦酸鍶再度成為熱門研究課題。

由於分子束磊晶法生長此類化合物薄膜對基板表面的平坦度要求極為嚴苛，為了研究高品質硒化鐵薄膜系統的生長過程，故本論文從基板製備之研究開始，探討三種製備方法後的SrTiO3(001)表面結構，目的是為了得到原子級平坦的表面，並儘可能地減少缺陷，再以分子束磊晶法製備硒化鐵薄膜，控制其結構及成長模式。三種基板製備方法包括退火、氬離子濺射以及硒分子束蝕刻，藉由室溫(RT)與低溫(LT)掃描穿隧式顯微鏡(STM)，搭配低能電子繞射儀(LEED)觀察三種製備後的表面形貌；而蒸鍍方法採共鍍模式，將鐵和硒同時沈積於基板上，再利用RT-STM觀察薄膜結構及其成長模式。

基板製備研究結果簡述如下：(1)於單純退火結果得到台階結構的形態變化取決於退火溫度，經950 ℃以上退火可得原子級平坦的波浪狀台階，其高度與STO晶格常數接近，並無混合高度差為0.2 nm的台階或島嶼於表面，故只有一種終端表面，而從LEED顯示我們的製備溫度存有穩定P(1×1)結構，並於800 ℃至950 ℃間出現(2×1)重構。(2)當基板經氬離子濺射後，台階邊緣呈扭折狀，方向符合基板[100]及[010]此兩晶向，經多次氬離子濺射及退火後，表面出現長型條紋——奈米線，經由LT-STM分析，成長出的奈米線結構為(6×2)。(3)利用硒分子束蝕刻950 ℃退火後的STO(001)基板，表面尚殘留硒分子或其化合物，導致表面極不穩定影響STM的掃圖，而此方法適用於經過氬離子濺射後的表面，可使出現在表面上的條紋更加明顯。

上述三種製備方式所得的STO(001)表面，皆只有一種終端表面，由於氬離子濺射及硒分子束蝕刻後的表面，分別會隨退火時間出現凹洞、奈米結構和殘留硒分子或其化合物於表面，而單純950 ℃退火即可重複製備出原子級平坦、規律台階高度差的表面，為了避免影響第二部分實驗上薄膜的判別及品質，因此只採用退火作為第二部分實驗之製備基板的方式。

硒化鐵同時沈積在鈦酸鍶基板上之結果：從RT-STM取得鐵硒薄膜的四方晶格常數原子解析及層與層之間的高度差。此外，於一係列不同參數製備下，發現降低鐵鍍率及提高共鍍時之基板溫度，並搭配事後退火此步驟，可以有效改變薄膜的大小 、品質及去除殘留的硒，且施以不同偏壓下掃圖，薄膜表面具明顯差異的電子狀態密度，以致於產生不同表面形貌的影像，而當薄膜隨蒸鍍時間加長而變厚時，在三層以上，其成長方式不再以完整1TL (Se-Fe-Se)高度差為0.57 nm之倍數成長。

In 1967, scientists discovered that strontium titanate, which is essentially an oxide material and an insulator, could become superconducting at high electron carrier concentrations. However, the transition temperature was quite low. In 2015, the superconducting phase transition temperature for a single-layer FeSe film on STO substrate was found to be as high as 109 K, making it a hot research topic again.

Since the growth of high quality FeSe films by molecular beam epitaxy on an oxide surface requires flatness on the surface of the substrate, in order to study the growth process of the high quality FeSe thin film system, we started from the research to improve the substrate preparation. The surface morphology and atomic ordering of STO(001) after three preparation methods was investigated. The aim is to to obtain an atomically flat terraces with fewer steps and to reduce defects on the terrace as much as possible. Three substrate preparation methods include annealing, argon ion sputtering, and selenium molecular beam etching. The surface morphology of the three preparations was observed by using scanning tunneling microscopy (STM) at both 77K and RT, together with a low energy electron diffractometer (LEED). The FeSe film was prepared by molecular beam epitaxy to control its structure and growth mode. The evaporation method adopts a co-deposition mode, and simultaneously deposits Fe and Se on STO, and then observes the structure of the film and its growth mode by using RT-STM.

The results of the substrate preparation are as follows: (1) The morphology change of the step structure obtained by annealing results depends on the annealing temperature. Annealing above 950 °C leads to a flat wave-like step with a height equal to the STO lattice constant. There is no step or islands on the surface with a height difference other than 0.2 nm, so there is only one terminal surface. LEED shows that our preparation temperature has a stable P(1×1) structure and (2×1) reconstructure upon annealing between 800 °C and 950 °C. (2) When the substrate is sputtered by argon ions, the edge of the steps is kinked, and the direction conforms to the two crystal directions of the substrate, [100] and [010]. After repeated sputtering and annealing, long stripes with (6×2) ordering, termed nanolines, appear on the surface. (3) The STO(001) substrate annealed at 950 °C is etched by selenium molecular beam, and selenium molecules or its compounds remain on the surface, which causes the surface instability to affect the STM scan. This method is suitable for sputtering makes the stripes appearing on the surface more visible. In order to avoid affecting the discrimination and quality of the film in the second part of the experiment, we only use annealing as the method of preparing the substrate.

The result of co-deposition of FeSe on STO substrate: The tetragonal lattice constant atomic analysis of the FeSe thin film and the height difference between the layers were obtained from RT-STM. In addition, under a series of different parameters, it was found that reducing the iron evaporation rate and increasing the substrate temperature during the co-deposition, and matching the post-annealing step, can effectively change the size and quality of the film and remove residual Se. And at different bias voltages, the surface of the film has a distinct electronic state density such that images of different surface topography are produced. When the film becomes thicker as the evaporation time is lengthened, the growth mode of the step of three or more layers is no longer grown by a multiple of the complete 1TL (Se-Fe-Se) height difference of 0.57 nm.

摘 要 I
Abstract III
致 謝 V
目 錄 VI
圖 目 錄 VIII
表 目 錄 XIV
第一章 簡介 1
1.1. 研究動機 1
1.2. 鈦酸鍶結構與特性 3
1.3. 鈦酸鍶的重構種類 5
1.4. 鈦酸鍶的奈米結構 7
1.5. 硒化鐵薄膜結構及超導 10
第二章 實驗儀器工作原理及介紹 12
2.1. 真空系統 12
2.1.1. 真空概念 12
2.1.2. 真空幫浦 15
2.1.3. 真空計 19
2.2. 掃描穿隧顯微鏡 21
2.2.1. 量子穿隧效應 21
2.2.2. 細部構造 24
2.2.3. 取像模式 26
2.3. 蒸鍍槍原理 27
2.3.1. EFM3 27
2.3.2. 克勞森容器 28
2.4. 實驗儀器介紹 29
2.4.1. 實驗儀器裝置 29
2.4.2. 抽真空概略程序 31
2.5. 實驗方法 33
2.5.1. 鈦酸鍶基板製備 33
2.5.2. 硒化鐵蒸鍍製備 36
2.5.3. 探針製備 38
第三章 實驗結果與討論 40
3.1. 鈦酸鍶(001)基板製備實驗 40
3.1.1. 退火的製備結果 41
3.1.2. 氬離子濺射的製備結果 51
3.1.3. 硒分子束蝕刻的製備結果 61
3.2. 共鍍硒化鐵於鈦酸鍶(001)基板之RT-STM實驗 64
3.2.1. 硒化鐵/鈦酸鍶(001)結構之STM數據 65
3.2.2. 硒化鐵/鈦酸鍶(001)不同參數製備之STM數據 67
第四章 結論 74
參考文獻 76

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