臺灣博碩士論文加值系統

電場誘發嵌於鹵化鈣鈦礦結構中的有機分子電偶極旋轉已被視為控制鈣鈦礦基本性質與穩定性的要素之一。
然而，截至今日，電場是如何誘發嵌於鹵化鈣鈦礦結構中的有機分子電偶極旋轉仍然是未知的。
我們利用介面-掃描式穿隧顯微鏡與能譜量測紀錄甲基胺溴化鉛實空間的原子級影像，同時測量對應的電流-電壓圖觀察並探討因有機分子電偶極旋轉所造成的電滯現象。
在本實驗中，在順向施加偏壓後立即再逆轉向施加偏壓的掃描模式下，實驗發現在特定電壓區間，分別出現的形貌發生改變與、四個電性似能隙表現(亦即在外加施加偏壓之下，電流沒有變化)，和反曲點異常的電流-電壓電滯現象(分別發生在由施加負至正偏壓時，掃描條件在1.68伏特；以及由施加、正至負電偏壓時，掃描的條件在-0.87伏特)。
我們認為電壓引致分子電偶極翻轉可以造成兩種相反的表面極性。這兩種相異的表面極性，會使表面電性在表面似N型與似P型行為之間發生轉換;。再者，於電流-電壓圖中，兩個反曲點則是對應分子電偶極翻轉的臨界點;。表面極性電性的表現轉換的現象，是主要造成甲基胺溴化鉛異常的電流-電壓電滯現象的原因。

Electric-field-induced dipole rotation of the intercalated organic molecules in halide perovskites has been suggested to be one controllable factor for fundamental properties and stabilities in perovskites. However, up to now, how the electric field triggers the dipole rotation of the intercalated organic molecules is still unknown. Here, we record the real-space atomic image and simultaneously probe the corresponding current-voltage (I-V) hysteresis in the methylammonium lead bromide (MAPbBr3) system using cross-sectional scanning tunneling microscopy and spectroscopy. In this work, we addressed the change of topography at specific bias intervals and anomalous I-V hysteresis with four gap-like regions as well as two unusual inflection points at forward 1.68 V and backward -0.87 V under ramp reversal scanning mode. We suppose that the dipole rotation, initiated by an electric field, concludes to two opposite surface dipole moments, creating an electronic transformation between the n-type-like and p-type-like feature. The two inflection points correspond to the critical voltage of dipole rotation. The transformation thus forms an abnormal I-V hysteresis behavior in MAPbBr3.

口試委員會審定書...........................................................................................................1
致謝...................................................................................................................................2
中文摘要...........................................................................................................................3
Abstract..............................................................................................................................4
List of Figures Captions................................................................................................ - 7 -
Chapter 1. Introduction..................................................................................................- 9 -
Chapter 2. Experimental instrument and methods .....................................................- 12 -
2.1 Cross-sectional scanning tunneling microscopy (XSTM).....................................- 12 -
2.2 Ultra-High Vacuum System...................................................................................- 13 -
2.3 Principles of scanning tunneling microscopy (STM) ...........................................- 22 -
2.4 Scanning mode.......................................................................................................- 24 -
2.5 Scanning Tunneling spectroscopy (STS) ..............................................................- 27 -
2.6 Background of STM FFT image............................................................................- 28 -
2.7 Sample preparation of MAPbBr3..........................................................................- 30 -
Chapter 3. Experimental data analysis.........................................................................- 31 -
3.1 Topography image of MAPbBr3...........................................................................- 31 -
3.2 STS data.................................................................................................................- 33 -
3.3 CITS data and FFT image at specific bias intervals .............................................- 35 -
Chapter 4. Result and discussion.................................................................................- 41 -
4.1 MA dipole rotation.................................................................................................- 41 -
4.2 MAPbBr3 surface image.......................................................................................- 43 -
4.3 Effect of dipole rotation on surface DOS..............................................................- 43 -
4.4 Model of the physical mechanism of the MAPbBr3 surface….............................- 44 -
Chapter 5. Conclusion..................................................................................................- 51 -
Reference list...............................................................................................................- 52 -

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