一維硒化鎘奈米棒之合成與性質分析

Abstract

本論文之目的在於探討不同合成條件對於硒化鎘奈米棒形狀與長寬比之影響，並研究其光學特性，進而利用具有週期性排列之雙塊式高分子作為基版達到操控之目的。 在合成方面，以高溫裂解製備硒化鎘奈米棒，可增加其均勻度，此外，在固定高溫下，經由前驅物鎘與硒之間的比例、表面活性劑之種類與比例、鎘之單體濃度、反應時間、注入方式與莫耳數之改變，可以控制硒化鎘奈米棒之長寬比，並藉穿透式電子顯微鏡影像觀察其成長情形，進而推測其成長機制。 結構性質方面的鑑定，以粉末X光繞射儀量測可以得知硒化鎘奈米棒為wurtzite結構。另外，經由高解析度穿透式電子顯微鏡觀察其晶格影像並藉由晶格間距之計算驗證晶體之結構。電子能譜為一探討晶體表面結構強而有力之工具，可用以推測晶粒表面與包覆有機分子之間的鍵結。 在光學性質方面，由於有一維的尺度已超過量子侷限之範圍，改變能階軌域的位置，僅有極少部分會藉由發光方式回到基態，故光激發光效率不佳。由紫外光-可見光譜中可知，長短軸之間的差異使訊號峰擁有較大之半高寬。此外，經由大長寬比且不同粗細之CdSe NRs的光譜比較可發現，短軸尺寸將主導決定其光吸收峰位置。 量測電性方面，利用具週期性排列之塊式高分子作為基版及選擇性分散技術，將可得到規則排列之硒化鎘奈米棒陣列，並藉由控制硒化鎘奈米棒之添加量可得到單一獨立之陣列。製備成簡單的元件裝置，量測其電場與電流密度之間的關係，並推導其電子遷移率。

This thesis is focused on the synthesis of CdSe nanords and the optical characterization. Besides, the special distribution of CdSe nanorods has been fabricated by self-assembled block copolymers as template. To improve the uniformity, high temperature decompose method was used to prepare CdSe nanorods. CdSe nanorods with various aspect ratio is tunable by controlling some factors, such as the ratio of the precursor of Cd and Se, the ratio between surfactants, monomer concentration, reaction time, injection method. Among the studies, transmission electron microscopy is powerful to monitor the growth and the shape of CdSe nanorods. To identify the structural feature, the wide angle X-ray diffraction and the higher magnification TEM lattice images were used to determine the wurtzite structure and calculate the d-spacing distance of single crystal CdSe nanorods. Moreover, high-resolution photoemission from synchrotron X-ray source was used to determine the element state of the CdSe sample. In optical properties, the difference between of long axis and short axis makes the FWHM of the peak become broad. In particular, as the aspect ratio larger, the position of the peak only depends on short axis. Then, it blue shifts to shorter wavelength. At last, diblock copolymer with periodic pattern is the template and the technique of selectively dispersion can obtain the array of periodic arrangement of CdSe nanorods. Additionally, controlling the amounts of CdSe nanorods will obtain a single nanorod incorporated in a single nonodomain. Using this manipulative technique, the electron mobility of a single nanorod can be estimated by current-voltage characteristics.