塊狀硒化鐵的超導臨界溫度為 8 K，但利用分子束磊晶方式成長單層硒化鐵薄膜在鈦酸鍶基板，其超導臨界溫度高達 109 K。藉由研究鐵基超導體，可以幫助瞭解更多的高溫超導體機制，而鐵基超導體硒化鐵的薄膜在多種長晶條件下之成長模式沒有被清楚地報告。因此，本研究欲深入瞭解硒化鐵薄膜成長在鈦酸鍶基板的成長模式與表面相關現象，欲找出更穩定成長之方法。希望使用分子束磊晶之方式蒸鍍硒與鐵元素，期望硒化鐵薄膜成長在鈦酸鍶基板上，並且透過掃描穿隧顯微鏡進行研究，尤其掃描穿隧顯微鏡是非常有利於觀測表面變化與原子排列的顯微技術。
本研究之實驗分為兩大部分，第一部分之實驗為同時蒸鍍硒與鐵在鈦酸鍶基板上，此部分再分為兩小節：一為兩者之蒸鍍時間相同，調整蒸鍍通量比以達到所需之蒸鍍量。可得知一次給予樣品足夠的硒與鐵鍍量，接著再利用後續退火使多餘的硒脫附，能夠成功製備出單層到三層以上的硒化鐵薄膜。且可以藉由提高蒸鍍的時間，使硒化鐵薄膜面積越大。另外，所長出的硒化鐵薄膜可以持續存在到 620 到 700 度，即高於塊狀硒化鐵的分解溫度 457 度，代表硒化鐵薄膜和鈦酸鍶基板之間具有強鍵結。二為兩者之蒸鍍時間不同，調整蒸鍍時間長度以達到所需之蒸鍍量。因為硒化鐵薄膜的成長環境須在硒充足的環境用以彌補硒元素易揮發的特性，所以嘗試事後補充足夠的硒鍍量，欲形成硒化鐵薄膜。可得知將硒蒸鍍時間拉成，易使表面有過多的硒元素造成長出過厚的薄膜。
第二部分之實驗為分開蒸鍍硒與鐵在鈦酸鍶基板上，此部分也再分為兩小節：一為蒸鍍硒在鈦酸鍶基板上，成長二硒化鈦薄膜。可得知若鈦酸鍶基板被預退火在 950 度，接著蒸鍍硒在鈦酸鍶基板，樣品表面將形成二硒化鈦薄膜。其中，硒之蒸鍍時間為 75 秒再後續退火於 650 度的樣品，將此樣品之二硒化鈦薄膜當作緩衝層來嘗試成長硒化鐵薄膜最為適當。二為蒸鍍鐵在二硒化鈦薄膜，欲成長硒化鐵薄膜並研究其表面特性。可得知二硒化鈦將在硒化鐵薄膜成長中，扮演雜質相而非緩衝層的角色，因此無法成長硒化鐵薄膜。
本篇論文探討硒化鐵薄膜成長在鈦酸鍶基板的多種成長方法。同時蒸鍍兩元素之蒸鍍通量比與適當的基板成長溫度皆是成功長出薄膜的重要關鍵。而序列處理之成長方式雖能更好地控制蒸鍍之時間，但本研究清楚顯示此方法對於成長硒化鐵薄膜是不利的。若事後補充大量的硒以彌補硒元素易揮發的特性，可能會造成樣品表面具有過多的硒。而先蒸鍍硒再蒸鍍鐵，可能造成二硒化鈦扮演雜質相，而無法成長硒化鐵薄膜。未來，實驗室同學們將在鈦酸鍶基板上嘗試成長其它元素，期望能夠藉由本論文的成長方式，作為後續研究的基礎。

The superconducting transition temperature for bulk FeSe is 8 K. Fortunately, with molecular beam epitaxy, it can be raised to 109 K by growing one unit-cell FeSe film on the SrTiO3 (001) substrate. The studies of iron-based superconductors provide the information of high-temperature superconductive mechanism, but epitaxial growth processes of iron-based superconductor FeSe films under different conditions have not been clearly reported. Thus, in this thesis, we are devoted to further studying the growth processes of FeSe films on the SrTiO3 (001) surface and the relative properties, and also to looking for more stable methods of the growth. For preparing FeSe crystalline thin films on SrTiO3 (001) substrate, we utilized molecular beam epitaxy to evaporate Se and Fe. Besides, we observed the change of surface during growth and the atomic arrangement via scanning tunneling microscope (STM).
There are two main aspects in this study. First aspect is co-evaporating Se and Fe on the SrTiO3 (001) surface. Then, growth conditions of co-evaporation are described in two sections. In growth condition of section 1, we set the evaporation time of Se and Fe equal. Then, we adjusted flux ratio of Se to Fe to get the required deposition amount. One to three or more unit-cell FeSe films could be successfully obtained on SrTiO3 (001) surface, as we provided enough deposition amount and then post-annealed the sample to desorb excess Se atoms. Next, the results show that the coverage of FeSe films became larger with the increment of evaporation time. Furthermore, the FeSe films can exist at the annealing temperature from 620 °C to 700 °C, higher than the decomposition temperature of bulk FeSe (457 °C), which means there were strong bonds between the FeSe layer and the SrTiO3 (001) substrate.
In growth condition of section 2, we set the evaporation time of Se and Fe unequal. Therefore, we adjusted evaporation time of Se and Fe to get the necessary deposition amount. Since the growth of FeSe film was carried out under Se-rich condition to compensates the losses of volatile Se molecules and to grow the stoichiometric FeSe film, we co-evaporated Se and Fe and then supplemented enough Se dosage to grow FeSe films on SrTiO3 (001) substrate. It reveals that elongating evaporation time of Se tends to form excessive thick films.
Second aspect, we evaporated Se and Fe separately on SrTiO3 (001) surface. Growth conditions of evaporation are also described in two sections. In growth condition of section 1, we evaporated Se on SrTiO3 (001) surface to form TiSe2 films. The results indicate that the sample which is deposited by Se for 75 seconds and is annealed at 650 °C, is served as an appropriate buffer layer to form FeSe films on it. In growth condition of section 2, we evaporated Fe on TiSe2 buffer layer to form FeSe films and investigated its surface properties via STM. The results show if we pre-anneal the SrTiO3 (001) substrate at 950 °C, TiSe2 films will form on the surface, which act as an impurity phase for the growth of FeSe instead of a buffer layer.
This study shows the various growth processes of FeSe films on the SrTiO3 (001) surface. The flux ratio of co-evaporation and the substrate temperature on the growth are crucial to form FeSe film. Although serial processing growth has better evaporation time control, this thesis clearly reveals that it is unfeasible to form FeSe film. After co-evaporation, Se supplement to remedy highly volatile properties of Se may bring out excessive Se on the surface. Moreover, after evaporating Se on the SrTiO3 (001) surface, the surface presents TiSe2 films which may act as an impurity phase to obstruct the growth of FeSe, so Fe clusters grow above TiSe2 films without forming FeSe films if we evaporate Fe after evaporating Se. In the future, the colleagues in our laboratory will try to grow other elements on SrTiO3 (001) surface. Hope the growth processes in this thesis can be a foundation for further progress.

目錄
第一章 簡介硒化鐵..............................................................1
1.1 研究硒化鐵之動機..........................................................1
1.2 超導體...........................................................................2
1.3 硒化鐵晶格結構.............................................................4
1.4 硒化鐵相關文獻.............................................................6
1.4.1 介面結構與超導性的關聯.............................................6
1. 介面結構..........................................................................6
2. 改善介面結構..................................................................7
1.4.2 基板超結構與超導性的關聯.........................................9
1.4.3 二硒化鈦成長在二氧化鈦上之異質結構的磊晶成長.......13
第二章 儀器工作原理...........................................................15
2.1 真空系統與實驗儀器......................................................15
2.1.1 真空系統.....................................................................15
2.1.2 真空幫浦及氣壓測量儀介紹.........................................18
1. 真空幫浦原理...................................................................18
2. 氣壓量測儀原理...............................................................21
2.1.3 抽真空概略程序...........................................................22
2.2 掃描穿隧顯微鏡.............................................................24
2.2.1 掃描穿隧顯微鏡原理...................................................24
2.2.2 掃描穿隧式顯微鏡細部構造.........................................27
2.2.3 掃描穿隧式顯微鏡取像模式.........................................29
1.定電流取像法....................................................................29
2.定高度取像法....................................................................29
2.3 蒸鍍槍原理....................................................................30
2.3.1 EFM3..........................................................................30
2.3.2 克勞森容器..................................................................31
2.4 探針製作........................................................................32
2.5 樣品製備資訊.................................................................34
2.5.1 基板鈦酸鍶 (001) 的製備..............................................34
2.5.2 硒化鐵成長於鈦酸鍶(001)的樣品製備...........................35
2.5.3 二硒化鈦成長於鈦酸鍶(001)的樣品製備.......................36
第三章 實驗結果與討論.........................................................37
3.1 同時蒸鍍硒與鐵在鈦酸鍶基板..........................................38
3.1.1 硒與鐵之蒸鍍時間相同..................................................38
1. 蒸鍍通量比與基板成長溫度................................................38
2. 原子解析的硒化鐵薄膜......................................................42
3. 成長大面積的硒化鐵薄膜...................................................45
3.1.2 硒與鐵之蒸鍍時間不同..................................................50
1. 蒸鍍 2 分鐘的鐵與硒在被濺鍍與蝕刻的鈦酸鍶基板.............50
2. 蒸鍍 1 分鐘的鐵與硒在被濺鍍與蝕刻的鈦酸鍶基板.............52
3. 蒸鍍 1 分鐘的鐵與硒在鈦酸鍶基板.....................................54
3.2 分開蒸鍍硒與鐵在鈦酸鍶基板..........................................56
3.2.1 成長二硒化鈦薄膜在鈦酸鍶基板上.................................56
1. 蒸鍍硒...............................................................................56
2. 後續退火於 650 度、750 度..............................................58
3. 後續退火於 950 度............................................................62
3.2.2 蒸鍍鐵在二硒化鈦薄膜上..............................................64
第四章 結論...........................................................................67
參考文獻...............................................................................69
圖目錄...................................................................................72

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