| The ability to control the optical and electronic properties of semiconductor nanocrystals via size manipulation has important implications for the development of new materials that can improve existing technologies, as well as provides a basis for the development of new applications. This dissertation focuses on the development of shape control of nanocrystals using surfactant-based syntheses that maintain the high yields and chemical processability required for practical applications that have previously only been successful with spherical nanocrystals. The development of new synthetic methods to grow nanorods, and other three-dimensional nanostructures, while maintaining all the advantages of colloidal syntheses, will be detailed. Through experimentation and characterization, a surfactant-based growth mechanism for both these novel structures and spherical nanocrystals has been developed and tested. The kinetic parameters that control anisotropic growth were isolated, tested, and explained. Structural control of nanocrystals was developed to create even more complex nanocrystal shapes, such as self-orienting tetrapods. To improve the electronic and optical properties of these materials, new techniques such as graded core/shell nanorods and spheres, were synthesized and characterized. The development of indirect control of nanocrystal shape and structure offers new ways to overcome fundamental barriers to the use of nanocrystals in applications, such as Auger recombination. Several of these applications include the use of nanocrystals in photovoltaics, LEDs, lasers, and labels, and are described herein. In addition, the development of these materials enables the study of some fundamental properties of semiconductors, including the transition of optical properties from semiconductors confined in all dimensions to those confined in all but one dimension, the effect of strain as a function of shape, and the influence of the nanocrystal surface on its properties. |
