硫化鎘(CdS)奈米粒子之製備與其特性之探討
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2007
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本論文以研究硫化鎘（CdS）半導體奈米粒子之合成、光學性質與粒子在基材上分佈的情形為主。實驗內容包括兩部份，首先對奈米粒子進行光照蝕刻，期望能控制奈米粒子的尺寸單一性；以及藉由電化學方法在基材上(玻璃碳電極、高溫取向熱解石墨)沈積 CdS奈米粒子。經由控制電鍍的條件，合成出均勻度佳、分散性好的奈米粒子。此法的優點包含高產量、低成本以及易操作等特性。
在光照蝕刻部份，我們以非錯合性溶劑反應系統合成出 CdS奈米粒子，利用白光照射粒子進行蝕刻；經由改變光照時間，探討粒子尺寸的變化。從UV-Vis光譜儀，發現蝕刻後的粒子尺寸會隨著光照時間的增加而變小，在吸收光譜上呈現藍位移。此外，藉由公式估算及AFM可獲知粒子尺寸大小與在基材表面的分布情形，發現粒子粒徑經蝕刻後有明顯變小的現象。
在電化學部份，我們利用定電位的方式，電鍍CdS奈米粒子。根據實驗結果，從AFM及SEM的影像中，發現奈米粒子的大小與電鍍時間成正比；並利用XPS確認以定電位的方式能成功合成出CdS奈米粒子。
Abstract In this study, the optical properties and morphology of CdS semiconductor nanoparticles on the substrate are investigated. There are two experimental parts for preparing CdS nanoparticles; “top-down” and “bottom-up”. For the first part, we examined the characterization of CdS semiconductor nanoparticles prepared by the size-selective photoetching technique; in the second part, CdS nanoparticles were deposited on the GC (glassy carbon) or HOPG (highly oriented pyrolytic graphite) by electrochemical/chemical synthesis. The latter has not only higher yield but also lower cost and better control. We also hope to get a uniform and good quantity of nanoparticles by changing the synthesis conditions. In the size-selective photoetching, CdS nanoparticle were prepared by the noncoordinating solvent system and the different sizes were obtained by changing the irradiation time with the monochromatic light. It is a well-known fact that semiconductors exhibit quantum size effects when their size is smaller than the bulk exciton radius as a result of the spatial confinement of the charge carriers. This effect caused the shift of the onset of UV-Vis absorption to higher energy (blue shift). The size-selective properties were characterized by AFM measurements and were compared with Henglein’s empirical equation. We also used the electrochemical/chemical method to prepare the CdS nanoparticles at a constant potential. AFM and SEM images showed that the sizes of the nanoparticles depend on the depositing time. The Cd 3d and S 2p XPS peaks indicate the presence of CdS nanoparticles on the surface.
Abstract In this study, the optical properties and morphology of CdS semiconductor nanoparticles on the substrate are investigated. There are two experimental parts for preparing CdS nanoparticles; “top-down” and “bottom-up”. For the first part, we examined the characterization of CdS semiconductor nanoparticles prepared by the size-selective photoetching technique; in the second part, CdS nanoparticles were deposited on the GC (glassy carbon) or HOPG (highly oriented pyrolytic graphite) by electrochemical/chemical synthesis. The latter has not only higher yield but also lower cost and better control. We also hope to get a uniform and good quantity of nanoparticles by changing the synthesis conditions. In the size-selective photoetching, CdS nanoparticle were prepared by the noncoordinating solvent system and the different sizes were obtained by changing the irradiation time with the monochromatic light. It is a well-known fact that semiconductors exhibit quantum size effects when their size is smaller than the bulk exciton radius as a result of the spatial confinement of the charge carriers. This effect caused the shift of the onset of UV-Vis absorption to higher energy (blue shift). The size-selective properties were characterized by AFM measurements and were compared with Henglein’s empirical equation. We also used the electrochemical/chemical method to prepare the CdS nanoparticles at a constant potential. AFM and SEM images showed that the sizes of the nanoparticles depend on the depositing time. The Cd 3d and S 2p XPS peaks indicate the presence of CdS nanoparticles on the surface.
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硫化格奈米粒子, CdS nanoparticles