臺灣博碩士論文加值系統

最近拓樸絕緣體的一個議題是如何改變拓樸的狀態，可以藉由參雜的成分或是場效元件來達成。本實驗先藉由成長〖(〖Bi〗_(1-x) 〖Sb〗_x)〗_2 〖Se〗_3高比例的成分在sapphire(0001)上面，在確認晶格結構沒問題後，我們針對接近拓樸態轉換Sb成分的樣品做電性上和ARPES的分析。我們確認高Sb參雜比例和改變厚度即便是增加樣品的電阻值使樣品更接近絕緣的狀態，其在低溫下的磁導表現仍然保有拓樸的行為，更進一步我們調查和觀察到參雜Sb雖然降低樣品的自旋軌道藕荷行為，卻不會改變樣品的bulk band gap。最後我雖然在材料上我們無法改變樣品的狀態，我們成長薄膜在SrTiO3基板上，最後使用場效的方式使樣品的拓樸金屬態更皆近強局籲的絕緣態。

Ultrathin topological insulator film are promising for use in field effect device. We expect that increasing the Sb doping level and reducing the film thickness cause a crossover of transport phenomena from the quantum diffusive regime to the intermediate insulating regime. The crossover of different quantum transport under an electric field may form the basis for spin transistor in the future.
Magneto-transport measurements have been carried out on (Bi1-xSbx)2Se3 (x=0.26, 0.37, 0.52, 0.63, 0.7) film at 2K temperature in the magnetic field range of 0 to 9T. Weak anti-localization (WAL) were observed in samples with Sb concentration up to x=0.26~0.7. The analyses of observed in magneto-resistance data using HLN equation reveal all sample show WAL phenomenon. All sample show metallic temperature dependent in R-T measurement. We also report thickness-independent magneto-transport properties from 4.6nm to 8nm. We get Kfl≥3 in all sample at 2K temperature, where KF is the 3d Fermi wave vector and l is mean free path. The lowest K_f l we getting is 3.4, this means that all sample locate in quantum diffusive regime.
Sb doping cause decreasing spin orbit coupling (SOC), so that the bulk band gap may decrease when inducing doping level. We then check sample’s band structure by ARPES analysis. The magnitude of bulk band gap are 0.5eV、0.44eV for X=0、0.63, respectively, indicating slight change upon doping. We suggest that the microscopic mechanism of topological phase transition (TPT) could not be simply elucidated by SOC effect.
Finally, the field-effect properties of ultrathin (Bi1-xSbx)2Se3 that is grown on SrTiO3(111) using molecular beam epitaxy (MBE) are investigated. The 15nm (Bi0.68Sb0.32)2Se3 film exhibits the large field effect (FE), as the transport is turn into intermediate disorder regime (Kf l=1.2). The crossover of different quantum transport under electric field may form the basis for topological insulator-base spin transition in the future.

摘要 I
Abstract II
誌謝 X
目錄 XI
圖目錄 XIII
表目錄 XVI
第一章 緒論 1
1-1前言 1
1-2拓樸絕緣體的特性簡介 2
1-3文獻探討 2
1-4實驗動機 11
第二章 基本理論介紹 13
2-1薄膜成長理論 13
2-1-1薄膜沉積原理 13
2-1-2成長模式 15
2-1-3成長相關理論 16
2-2電性相關理論 18
2-2-1霍爾效應 18
2-3磁性相關理論 19
2-3-1弱(反)局域效應-weak (anti-)localization 19
第三章 儀器介紹與實驗流程 24
3-1實驗流程 24
3-1-1成長薄膜實驗流程 24
3-1-2元件製程 24
3-1-3分析方式 26
3-2 成長儀器之介紹 26
3-2-1 分子束磊晶 26
3-3分析樣品之儀器介紹 31
3-3-1 X-ray分析儀 31
3-3-2原子力顯微鏡(Atom force microscope) 32
3-3-3物理性質量測系統儀(Physical Property Measurement System,PPMS) 33
3-3-4角分辨光電子能譜 (ARPES) 33
第四章 實驗與討論 35
4-1 材料結構成分分析 35
4-1-1 合金薄膜磊晶結構(RHEED、AFM、XRD) 35
4-1-2 成分確認(TEM) 39
4-2 電性磁性分析 41
4-2-1 電性分析(常溫) 41
4-2-2 低溫PPMS分析(磁、電性) 44
4-3 ARPES分析 47
4-4 場效元件 52
4-4-1基板處理(退火、未退火) 52
4-4-2 樣品結構和電性(STO有無退火) 53
4-4-3 低溫磁電性量測(3.8K) 56
第五章 結論 59
參考文獻 60

[1] Moore, J. E., ＆ Balents, L. (2007). Topological invariants of time-reversal-invariant band structures. Physical Review B, 75(12), 121306
[2] Hasan, M. Z., ＆ Kane, C. L. (2010). Colloquium: topological insulators. Reviews of Modern Physics, 82(4), 3045.
[3] Liu, X., Smith, D. J., Fan, J., Zhang, Y. H., Cao, H., Chen, Y. P., ... ＆ Furdyna, J. K. (2011). Structural properties of Bi2Te3 and Bi2Se3 topological insulators grown by molecular beam epitaxy on GaAs (001) substrates. Applied Physics Letters, 99(17), 171903.
[4] Liu, Y. H., Chong, C. W., FanChiang, C. M., Huang, J. C. A., Han, H. C., Li, Z., ... ＆ Liu, C. P. (2017). Ultrathin (Bi1–x Sb x) 2Se3 Field Effect Transistor with Large ON/OFF Ratio. ACS Applied Materials ＆ Interfaces, 9(14), 12859-12864.
[5] Liu, J., ＆ Vanderbilt, D. (2013). Topological phase transitions in (Bi 1− x In x) 2 Se 3 and (Bi 1− x Sb x) 2 Se 3. Physical Review B, 88(22), 224202.
[6]Devidas, T. R., Amaladass, E. P., Sharma, S., Mani, A., Rajaraman, R., Sundar, C. S., ＆ Bharathi, A. (2017). Effect of Sb substitution on the Topological Surface States in Bi2Se3 single crystals: a magneto-transport study. Materials Research Express, 4(2), 026101.
[7]Brahlek, M., Bansal, N., Koirala, N., Xu, S. Y., Neupane, M., Liu, C., ... ＆ Oh, S. (2012). Topological-metal to band-insulator transition in (Bi 1− x In x) 2 Se 3 thin films. Physical Review Letters, 109(18), 186403.
[8] Salehi, M., Shapourian, H., Koirala, N., Brahlek, M. J., Moon, J., ＆ Oh, S. (2016). Finite-Size and Composition-Driven Topological Phase Transition in (Bi1–x In x) 2Se3 Thin Films. Nano letters, 16(9), 5528-5532.
[9] Lou, R., Liu, Z., Jin, W., Wang, H., Han, Z., Liu, K., ... ＆ Osgood Jr, R. M. (2015). Sudden gap closure across the topological phase transition in Bi 2− x In x Se 3. Physical Review B, 92(11), 115150.
[10] Kong, D., Chen, Y., Cha, J. J., Zhang, Q., Analytis, J. G., Lai, K., ... ＆ Hussain, Z. (2011). Ambipolar field effect in the ternary topological insulator (BixSb1-x) 2Te3 by composition tuning. Nature nanotechnology, 6(11), 705-709.
[11] Chang, J., Park, Y. S., ＆ Kim, S. K. (2008). Atomically flat single-terminated SrTiO3 (111) surface. Applied Physics Letters, 92(15), 152910.
[12]陳姿謹，成功大學物理系碩士論文(2016)
[13]陳聖文，成功大學物理系碩士論文(2017)