臺灣博碩士論文加值系統

近年來，Majorana費米子在量子存儲、量子計算等領域的前景極大程度吸引了物理學家對它的廣泛研究。而作為Majorana費米子研究的平台，拓撲超導體也成為許多實驗的研究重點。本論文主要討論在傳統超導材料鈮(Nb)薄膜上濺鍍拓撲材料碲化銻(Sb2Te3)，分析該雙層膜系統之電磁傳輸特性與二維材料特性。
首先，本論文著重於以磁控濺鍍(Magnetron Sputtering)的方式在Si(100)基板上製備超導臨界溫度(T_c)為9.1 K的Nb薄膜樣品。經過多次調整參數後確認最佳基板溫度為540 ℃ ，並且增加薄膜厚度至120 nm以上可得到高T_c的Nb薄膜樣品。另外，發現在製程中淬火(Quenching)對Nb薄膜品質的提升優於退火(Annealing)，有助於提高系統T_c。
進一步，在固定Nb薄膜製程參數後，在其上方濺鍍20 nm和50 nm厚度的Sb2Te3薄膜，以探討其對整個系統的影響。由於鄰近效應的影響，各組樣品的T_c下降了0.03~3.75 K，上臨界磁場(H_c2)增加了284~14958 Oe。除了以上對系統的研究之外，本論文還通過系統釘扎能U對外部磁場H之間的關係以及測量系統BKT相變兩方面來證明其二維材料特性。
最後量測系統在不同溫度下電導性與偏壓之間的關係，但沒有從中觀察到零偏電導峰(ZBCP) ，計算其能隙與超導臨界溫度比△/(k_B T_c )大於傳統BCS的理論計算結果，代表該系統為非傳統超導材料。

In recent years, the prospects of Majorana fermions in fields such as quantum storage and quantum computing have attracted significant attention from physicists, leading to extensive research. As a platform for Majorana fermion studies, topological superconductors have become a focal point of many experimental investigations. This paper primarily discusses the deposition of antimony telluride (Sb2Te3), a topological material, on niobium (Nb) thin films, analyzing the electromagnetic transport properties and two-dimensional characteristics of this bilayer film system.
First, this paper focuses on preparing Nb thin film samples with a superconducting critical temperature (T_c) of 9.1 K on Si(100) substrates using magnetron sputtering. After adjusting various parameters, the optimal substrate temperature was determined to be 540℃, and increasing the film thickness to above 120 nm resulted in high T_c Nb thin film samples. Additionally, it was found that quenching during the process improves the quality of Nb films more effectively than annealing, which helps to enhance the system's T_c.
Furthermore, after fixing the Nb thin film fabrication parameters, Sb2Te3 thin films with thicknesses of 20 nm and 50 nm were sputtered on top of the Nb film to investigate their effects on the entire system. Due to the proximity effect, the T_c of each set of samples decreased by 0.03 to 3.75 K, and the upper critical magnetic field (H_c2) increased by 284 to 14958 Oe. In addition to studying the system, this paper demonstrates the two-dimensional characteristics through the relationship between the pinning potential U and the external magnetic field H, as well as measuring the system's BKT phase transition.
Lastly, by examining the relationship between conductivity and bias voltage at different temperatures, no zero-bias conductance peak (ZBCP) was observed. The calculated energy gap and the ratio △/(k_B T_c ) were found to be greater than the theoretical calculations of traditional BCS theory, indicating that the system belongs to unconventional superconducting materials.

口試委員會審定書 i
致謝 ii
摘要 iii
Abstract iv
目錄 vi
圖目錄 x
表目錄 xv
第一章 緒論 1
1.1 拓撲超導材料 1
1.2 Majorana費米子 1
1.3 鈮(Nb)簡介 2
1.4 碲化銻(Sb2Te3)簡介 3
1.5 研究動機 3
第二章 理論基礎簡介 5
2.1 超導體之發展歷史 5
2.2 超導體性質 6
2.2.1 零電阻(Zero Resistance) 6
2.2.2 完全反磁性(Perfect Resistance) 7
2.2.3 臨界電流(Critical Current)與臨界磁場(Critical Magnetic Field) 7
2.2.4 一類超導體(Type I Superconductor)與二類超導體(Type II Superconductor) 7
2.3 超導體原理 10
2.3.1 二流體模型(Two-fluid Model) 10
2.3.2 倫敦方程(London Equation) 10
2.3.3 相干長度(Coherence Length) 12
2.3.4 釘扎效應(Pinning Effect) 13
2.3.5 安德森-金磁通蠕動模型(Anderson-Kim Flux Creep Model) 15
2.3.6 BKT相變 (Berezinskii–Kosterlitz–Thouless Transition) 15
2.3.7 比恩模型(Bean Model) 16
2.3.8 鄰近效應(Proximity Effect) 17
2.3.9 反鄰近效應(Inverse Proximity Effect) 19
2.3.10 磁冷(Field Cooling，FC)與零磁冷(Zero Field Cooling，ZFC) 20
2.3.11 零偏電導峰(Zero-Bias Conductance Peak，ZBCP) 22
2.3.12 p-wave超導體 22
第三章 實驗方法 23
3.1 實驗過程 23
3.2 樣品製程 24
3.2.1 系統搭建 24
3.2.2 濺鍍原理 25
3.2.3 樣品製程流程 26
3.2.4 樣品蝕刻流程 29
3.3 量測系統 33
3.3.1 X光繞射分析儀(X-ray Diffractometer) 33
3.3.2 場發射掃描式電子顯微鏡(Field Emission Scanning Electron Microscope，SEM) 35
3.3.3 磁性量測系統(Magnetic Property Measurement System，MPMS) 36
3.3.4 原子力顯微鏡(Atomic Force Microscope，AFM) 39
第四章 實驗結果與討論 40
4.1 Nb單層薄膜成長條件最佳化 40
4.1.1 調整基板溫度 40
4.1.2 調整薄膜厚度 46
4.1.3 增加退火(Annealing)過程 51
4.1.4 晶體結構與超導臨界溫度的關係 55
4.2 Nb/Sb2Te3雙層薄膜 56
4.2.1 SEM量測 56
4.2.2 XRD量測 57
4.2.3 R-T量測 58
4.2.4 磁性量測 61
4.2.5 外加磁場垂直於樣品之電性量測 64
4.2.6 外加磁場平行於樣品之電性量測 69
4.2.7 釘扎位能(Activation Energy)與磁場之關係 73
4.2.8 BKT相變量測 82
4.2.9 拓撲特性量測 91
第五章 結論 92
Conclusion 94
參考文獻 97

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