近幾年來，奈米級鹵化鈣鈦礦的開發取得了巨大的進步，因為其具有寬範圍的帶隙和可調控的光學及電子特性等卓越的特性。然而，鹵化鈣鈦礦奈米晶體的低穩定性尚未得到改善，所以為了獲得穩定性較佳的鈣鈦礦奈米晶體，科學家們開發出具有量子阱結構的Ruddlesden-Popper（RP）相鹵化鈣鈦礦。然而到目前為止，Ruddlesden-Popper相的鹵化物鈣鈦礦報導主要都是具有長碳有機鏈的混合有機-無機化合物，有關Ruddlesden-Popper相的全無機鹵化物鈣鈦礦報導目前也僅有層數為一的混鹵素鈣鈦礦(Cs2PbI2Cl2)的報導。並且基於密度泛函理論 (DFT)的計算，低層數Ruddlesden-Popper相的單一鹵化物鈣鈦礦(Cs2PbX4)晶體結構是不穩定的。因此，為了合成相穩定的鈣鈦礦奈米晶體我們使用了更強的表面鍵結配體。所以在我的實驗中使用熱注射法並藉由引入強的表面鍵結配體十八烷二酸(Octadecanedioic acid)成功合成出不同層數(n = 3、4)且相穩定的Csn+1PbnBr3n+1奈米片並且未混雜不同的層數。不同層數的樣品光譜圖呈現不同的放光位置，從2.43 eV到2.70 eV，表現出可調控的能隙特性。而由X-光粉末繞射圖的等間距現象可以證實材料確實為層狀結構，且放置在一般環境下的觀測結果，展現出比三維鈣鈦礦更佳的穩定性，並將結果和X-光粉末繞射圖的密度泛函理論計算做比對，可以發現兩者的繞射峰位置是一致。更進一步使用掃描穿透式電子顯微鏡直接觀察晶體結構的排列，證實確實為Ruddlesden-Popper相的晶格結構排列。最後我們進行了光響應的測量並將其應用於光感測器上，在7V偏壓下測量得到的開關比約為35。

In recent years, great progress has been developed in halide perovskite with nanoscale due to their outstanding properties, such as wide range of band gaps and tunable optoelectronic properties. However, the poor stability of halide perovskite nanocrystals has not been improved. To obtain long-term stability perovskite nanocrystals, the scientists are developed the Ruddlesden-Popper (RP) phase halide perovskite with quantum well structure. So far, most of reports are organic-inorganic hybrid RP phase involving long carbon chains in this class. The all-inorganic RP phase halide perovskite report is currently only reported with n = 1 mixed halide (Cs2PbI2Cl2). Based on DFT calculation, the crystal structure of single halide Cs2PbX4 are unstable. Therefore, to synthesize phase stabilized perovskite nanocrystals, we use stronger bonding surface ligands. In this study, we used hot injection method and successfully synthesized the phase stable Csn+1PbnBr3n+1 nanosheets (n = 3, 4) by introducing stronger bounding surface ligand, octadecanedioic acid. From PL spectra, they exhibit tunable band gap from 2.43 eV to 2.70 eV. The repeating unit of the powder X-ray diffraction pattern confirms that the material is a layered structure, and show better stability than CsPbBr3 in ambient condition. Our results are matched with simulate powder X-ray diffraction by density functional theory (DFT). Furthermore, the images from scanning transmission electron microscope show directly the arrangement of the crystal structure, indicated that the crystal structure is indeed RP phase. Finally, we obtain the photoresponse in visible light, the on-off switching measurements is about 35 under 7V bias voltage.

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