II-VI族化合物半導體奈米粒子合成、鑑定、光物理性質及其應用之研究

Abstract

在整個博士論文的研究工作中，我們致力於II-VI族化合物半導體奈米粒子之合成與鑑定，在此我們採用了新發展的一鍋式(one-pot)合成法以及改良後的兩步(two-step)合成法來製備type-I與type-II之量子點(QDs)。我們的長期目標，是要將經表面修飾後的量子點應用於基本的緩解動力學(relaxation dynamics)與能量/電荷轉移機制(energy/charge transfer processes)抑或是實用的生物標定(bio labeling)之研究。在此論文的首章(Chapter 1)，就讓我們來回顧一下半導體奈米粒子的一些原理及應用。 經過這四年的研究，我們成功的合成出品質優良之type-I量子點。而這些量子點具有高重製性之優點及其平均量子產率可達50~70%左右(Chapter 2)。量子點在經由表面修飾後，可轉而溶在水相裡，於是我們便可以將此放光性強的奈米粒子應用於水中汞離子的檢測(Chapter 3)。 在第四、五及六章裡，我們將興趣移轉到type-II量子點的合成與鑑定。我們的目標之ㄧ，就是利用type-II量子點其電子(electron)與電洞(hole)在被激發分離後，分居在核(core)與層(shell)之特性達到製備太陽能電池的基本原理。截至目前為止，我們已經成功的製備及鑑定出三種不同種類的type-II量子點，分別是CdSe/ZnTe 、CdTe/CdSe 以及CdSe/ZnTe/ZnS 。除此之外，我們也對其相對的光譜、飛杪緩解動力學(femtosecond relaxation dynamics)具有相當的了解。

In this thesis, we focus on the syntheses and characterization of various II-VI compound semiconductor nanocrystallites, including type-I and II quantum dots (QDs), either by a newly developed one-pot synthesis or via the modified methodologies on two-step approaches. Our long-term goal is to exploit this chemically modified QDs in fundamental approaches such as relaxation dynamics and energy/charge transfer processes, or practical application such as bio labeling. Prior to present my work, a general review in terms of chronic progress, fundamental and application of nanoscience is elaborated in Chapter 1. Through the four-year efforts, I have successfully prepared highly luminescent type-I quantum dots (QDs) with narrow emission spectra. The resulting nanoparticles have been characterized by their corresponding optical properties, EDX, XPS, TEM and powder-XRD. These approaches are highly reproducible, and the average quantum efficiency of as high as 0.5~0.7 can be achieved (Chapter 2). Phase transfer of the QDs from organic solvents to aqueous media was also achieved. The mercaptoacid-capped CdSe/ZnS QDs unveiled remarkable metal ion (e.g. Hg2+) recognition, in which the highly luminescent QDs were drastically quenched upon the addition of Hg(ClO4)2. Although an actual mechanism is pending for resolution, a tentative mechanism is proposed on the basis of redox type of reaction. The practical application onto the solid matrix was also elaborated in Chapter 3. In Chapters 4, 5 and 6, we then switched our gear toward the synthesis and characterization of type-II QDs, in which the carriers are no longer confined in the core. One of our goals is to utilize the spatial separation between core and shell so that the electron can be ejected out of the shell for further application such as photovoltaic cells. Three classes of type-II QDs, namely CdSe/ZnTe, CdTe/CdSe and CdSe/ZnTe/ZnS, were prepared and characterized, and their corresponding spectroscopes and femtosecond relaxation dynamics were examined comprehensively. Of particular interest is the observation of the size-dependent relaxation dynamics of the excited core electron as well as the acoustic phonon oscillation (in CdTe/CdSe) for the interband emission, which is believed to spark a broad spectrum of interest in the relevant fields.