二維拓樸絕緣體，包含量子自旋霍爾效應與量子反常霍爾效應，因其能帶結構特殊的拓樸性質，被期許可應用於低功率、低失真的電訊號傳輸，以及自旋電子學。根據理論的預測，量子反常霍爾效應可藉由破壞拓樸絕緣體本身的時間反演對稱性的方式被實現。於近年的實驗中，量子反常霍爾效應於參雜了磁性雜質的三維拓樸絕緣體被觀察到，而到目前為止並沒有關於磁性二維拓樸絕緣體的實驗。

本實驗將具有鐵磁性、兩層原子層的奈米鈷島嶼製備於Cu(111)基板上，並嘗試於鈷島嶼上成長有較大拓樸能隙(0.3eV)的二維拓樸絕緣體stanene。以期透過將二維拓樸絕緣體成長於鐵磁性的奈米島嶼之上的方式，製備具有磁性的二維拓樸絕緣體，嘗試實現量子反常霍爾效應。實驗中我們會以掃描穿隧顯微鏡與掃描穿隧能譜量測樣品原子尺度的形貌、電性與磁性結構。

我們透過分子束磊晶法成功地將stanene製備於鐵磁性的鈷奈米島嶼上。在77 K與4 K的量測中，我們發現在成長於鈷島嶼上的stanene之掃描穿隧能譜於約0.1 V處存在一個峰值，並且於費米能階附近(-0.2 V~0.6 V)的電導圖中觀察到表面電子的散射波紋。這些特徵都不會於單純stanene/Cu(111)系統中被觀察到，很可能是stanene本身的時間反演對稱性受到磁性島嶼的破壞而導致，這為實現磁性二維拓樸絕緣體提供一條明確的提示。

Two-dimensional topological insulators (TIs), where the quantum spin Hall effect and the quantum anomalous Hall effect emerge, are promising to be applied to the low power and the low distortion electrical signal transmission in the spintronics due to the extraordinary topological properties of the band structures. According to the theoretical prediction, the quantum anomalous Hall effect can be realized by breaking the time reversal symmetry in TIs. In recent studies, the quantum anomalous Hall effect has been measured in 3D-TIs doped magnetic impurities at low temperature. But, the experiment of magnetic 2D-TIs has not been reported yet.

We attempt to fabricate magnetic 2D-TI by growing 2D-TI stanene, which has large topological band gap (~0.3 eV) on ferromagnetic 2 ML Cobalt nanoislands on the Cu(111) substrate to realize a system where the quantum anomalous Hall effect could be present. In our experiments, we utilize scanning tunneling microscope and scanning tunneling spectroscopy to measure the atomic and electronic properties of the sample.

We have successfully fabricated the stanene on the ferromagnetic Cobalt nanoislands by molecular beam epitaxy. At 77 K and 4 K measurements, the peak at approximately 0.1 eV in STS spectrum of stanene/Co/Cu(111) can be observed. We also found scatterings of surface electron on the stanene/Co/Cu(111) from the dl/dU mapping near the Fermi level (-0.2V~0.6V). These features do not exist in the stanene/Cu(111) system. It implies that the time reversal symmetry on stanene might be broken by the magnetism of Cobalt nanoisland and offers a hint for realizing magnetic 2D-TIs.

摘要 I
致謝 III
目錄 IV
圖目錄 VI
1. 簡介(Introduction) 1
1.1 動機(Motivation) 1
1.2 二維拓樸絕緣體(2D-Topological Insulator) 3
1.3 文獻回顧(Literature Review) 7
1.3.1 Stanene/Cu(111)相關文獻與簡介 7
1.3.2 Co/Cu(111)相關文獻與簡介 9
2. 實驗儀器與原理(Principle of the Experimental Instrument) 14
2.1 真空系統(Vacuum System) 14
2.1.1 真空條件(Vacuum Condition) 14
2.1.2 真空幫浦(Vacuum Pump) 16
2.1.3 真空計(Vacuum Gauge) 18
2.1.4 殘留氣體分析儀(Residual Gas Analyzer) 20
2.2 電子束蒸鍍槍(E-Beam Evaporator) 22
2.3 自旋極化掃描穿隧顯微鏡(Spin Polarized Scanning Tunneling Microscopy) 23
2.3.1 量子穿隧效應(Quantum Tunneling Effect) 23
2.3.2 巴丁穿隧理論(Bardeen’s Tunneling Theory) 25
2.3.3 取像模式(STM Scanning Mode) 28
2.3.4 掃描穿隧能譜(Scanning Tunneling Spectroscopy) 29
2.3.5 自旋極化掃描穿隧能譜(Spin-Polarized Scanning Tunneling Spectroscopy) 30
3. 實驗結果與討論(Experimental Result and Discussion) 32
3.1 樣品的製備(Sample Fabrication) 32
3.1.1 前置作業 32
3.1.2 鍍膜過程 34
3.2 Co/Cu(111)系統 36
3.2.1 Co/Cu(111)之製備參數 36
3.2.2 Co/Cu(111)系統之磁性量測 39
3.3 Sn/Co/Cu(111)系統 45
4. 結論(Conclusion) 53
5. 參考資料 54

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