| This dissertation focuses on the development of synthetic chemistry for complex multi-semiconductor nanocrystals. The interest in these complex nanocrystals stems from their unique characteristics that are not typically available for plain single-composition semiconductor nanocrystals. The optical and structural properties of the resulting complex nanocrystals are also discussed.; The first area of focus details the creation of III-V semiconductor nanocrystals, InP and InAs, which are common semiconductors used in the creation of complex systems on solid substrates. The success of the new methods relies on identifying the sensitive role of the concentration and chain length of the fatty acid ligands used. The high quality InAs nanocrystals were tested as templates for the growth of a relatively simple type of complex nanocrystals, core/shell structures. Through the creation of these core/shell structures, emission intensities and nanocrystal stabilities were greatly improved.; The second type of complex structures developed is one-dimensionally confined semiconductor nanocrystals, a new type of quantumly confined nanostructures. Here, a small band gap semiconductor, CdSe, was controllably layered onto a wide band gap semiconductor, CdS. These CdSe quantum shells/wells exhibit high emission quantum yields, over 40%, as well as emission wavelengths covering most of the visible spectral range, blue-green to red.; The third type of complex structures studied were a 2D quantum shell coupled with a 0D quantum dot, dual quantum systems on a single nanocrystal. This was achieved through the epitaxial growth of a ZnS barrier layer between the two CdSe based systems. By altering the thickness of the barrier layer, the quantum systems were controlled to either electronically couple or decouple. Evidences of optical coupling between the two quantum systems was also observed. The position and relative intensity of the two emissions can be independently tuned through reaction conditions.; Finally, by using known band alignments of semiconductors, complex type-II nanocrystals were synthesized. Here type-II nanocrystals of CdSe/CdTe quantum dots and CdS/CdSe/CdTe quantum wells were created. High quantum yields, near 60%, as well as surprising stabilities were also seen for the type-II nanocrystals. Different from the other complex structures discussed above that were all created through a SILAR (Successive Ionic Layer Adsorption and Reaction) technique reported in literature, the successful synthesis of type-II semiconductor nanocrystals in this thesis required us to further the synthetic chemistry for layer-by-layer epitaxial growth. This new technique, thermal cycling, requires the reaction system to go through a temperature cycle during the growth of each layer. |
