Shape-controlled synthesis and application of one-dimensional cadmium chalcogenide nanocrystals

• Main Author: Xi, Lifei
• Other Authors: Lam Yeng Ming
• Format: Theses and Dissertations
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Materials::Photonics and optoelectronics materials
• Online Access: https://hdl.handle.net/10356/19267
• Institution: Nanyang Technological University

In recent years, the synthesis of one-dimensional (1D) nanocrystals has attracted considerable interest. The morphologies of the 1D nanocrystals studied include rods, wires, belts and tubes whose lateral dimensions fall within the 1 to 100 nm range. Their potential applications are related to their size- and shape-dependent physicochemical and optoelectronic properties. 1D cadmium chalcogenide nanocrystals have become important potential building blocks for new electronic and optical nanodevices. As the electronic and optical properties are dependent on the crystal dimensions, the issue of how to control the growth of 1D cadmium chalcogenide nanocrystals is of prime importance and this issue remains one of the most challenging issues to address in both chemistry and materials science. This is one of the motivations behind this study. In this work, three catalyst-free and solution-based methods were used for the synthesis of 1D cadmium chalcogenide nanocrystals. These methods are the reverse micelle method, the hydrothermal method and the hot coordinating solvents method. Using both the reverse micelle method and the hydrothermal method, we have successfully synthesized CdSe nanorods. We found that the reverse micelle method has better morphological control than the hydrothermal method, but the latter has both the higher crystallinity and yield. Using the hot coordinating solvents method, good size distribution, controllable growth and an aspect ratio as high as 170 has been achieved. This is significant because in the past fifteen years, this method has only been able to generate low aspect ratio nanorods (less than 20). Contrary to the existing mechanisms, an oriented attachment mechanism was observed and proposed in this study. We also attempted to synthesiz CdSe nanowires using the same method. Although this method has been successful in producing cadmium selenide (CdSe) nanodots, nanorods and tetrapods, it remains a challenge to obtain nanowires. After systematically varying the parameters, we were able to gain some understanding in the growth of anisotropic nanocrystals. CdSe nanowires with a length of 220 nm and a diameter of 8 nm were successfully synthesized.