Synthesis and Applications of Semiconductor Nanocrystallites
Date Issued
2005
Date
2005
Author(s)
Cheng, Chiu-Ting
DOI
en-US
Abstract
In this thesis, we focus on the syntheses and characterization of various II-VI compound semiconductor nanocrystallites, and type-II quantum dots (QDs) in chief. Our long-term goal is to exploit QDs with chemical modifications in fundamental approaches such as relaxation dynamics and energy/charge transfer processes, or practical applications such as bio labeling. Prior to my work at present, a general review in terms of lasting progress, basis and application of nanoscience is elaborated in Chapter 1.
In Chapter 2, syntheses of CdTe/CdSe type-II quantum dots (QDs) using CdO and CdCl2 as precursors for core and shell, respectively, are reported. Characterization was made via near-IR interband emission, TEM, EDX, and XRD. Femtosecond fluorescence upconversion measurements on the relaxation dynamics of the CdTe core (in CdTe/CdSe) emission and CdTe/CdSe interband emission reveal that as the size of the core increases from 5.3, 6.1 to 6.9 nm, the rate of photoinduced electron separation decreases from 1.96, 1.44 to 1.07 ×1012 s-1. The finite rates of the initial charge separation are tentatively rationalized by the low electron-phonon coupling, causing small coupling between the initial and charge-separated states.
In Chapter 3, syntheses of CdSe/ZnTe/ZnS (core/shell/shell) type-II quantum dots (QDs) are reported. Structural characterization was made via TEM, EDX, XPS and XRD. Photophysical properties were investigated via the interband emission (CdSe ZnTe) and its associated quantum efficiency as well as relaxation dynamics. In comparison to the weak emission (f ~ 4 x 10-3 in toluene) of CdSe/ZnTe (3.9/0.5 nm), capping ZnS (0.4 nm in thickness) enhances the CdSe ZnTe interband emission by ~30 folds (f ~ 0.12), whereas the peak wavelength shifts only slightly to the red. By encapsulating dihydrolipoic acid (DHLA), water soluble CdSe/ZnTe/ZnS was also prepared, and it exhibited an interband emission at ~930 nm with an emission yield of ~0.1. Femtosecond pulse excitation (ex ~ 1200 nm) measurement estimated a two-photon absorption cross section, , of ~70 1050 cm4 s photon1 for DHLA capped CdSe/ZnTe/ZnS in water, supporting its suitability for the use as near infrared (NIR) dyes in biomedical imaging.
Subjects
半導體
奈米粒子
量子點
semiconductors
nano paeticles
quantum dots
Type
thesis
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