The demand for novel optoelectronic and photonic technologies has fueled an intense research effort to synthesize and characterize nanostructured semiconductor materials with unique characteristics that lend themselves to technological innovation. However, the persistence of defects in these materials can have far reaching effects on their overall properties and remains a controversial subject. The controversy is due in part to different synthetic methods and the effect of size and shape between single structures in a population. These differences are well characterized but the effect of changing shape and size within a single structure is not. The question thus arises: Can similar heterogeneous behaviors be observed at spatially distinct locations in a single object? This dissertation is a methodical exploration of this question and our overall results show that changes in an object's shape can give rise to different behaviors within different regions of a single structure.
Zinc Oxide has emerged as an attractive candidate for a variety of applications due in part to a large second order nonlinear susceptibility, its wide band-gap and large exciton binding energy. Several other properties make it amenable to the experiments described herein and it is therefore the focus of our studies. We have used time-resolved nonlinear two-photon emission microscopy to characterize the optical properties and excited state dynamics at different locations within individual ZnO rods. We characterize the trap-emission signatures in these structures and the spatial dependence of band-edge and trap emission within a single structure. Collectively, the results from these experiments further our understanding of how defect states affect semiconducting materials and how they differ, not only between, but within single structures. Eventually, these results will prove to be fundamentally important to many problems in nanoscience and nanotechnology and will prove useful to those wishing to understand and exploit nanoscience.
|Advisor:||Papanikolas, John M.|
|Commitee:||Erie, Dorothy, Fecko, Chris, Superfine, Richard, Thompson, Nancy|
|School:||The University of North Carolina at Chapel Hill|
|School Location:||United States -- North Carolina|
|Source:||DAI-B 72/01, Dissertation Abstracts International|
|Keywords:||Defect emission, Trap states, Two-photon, Ultrafast carrier, Zinc oxide|
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