Date of Award

8-2013

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor

Robert W. Meulenberg

Second Committee Member

George P. Bernhardt

Third Committee Member

William N. Unertl

Abstract

We seek to study the effects of dopants on the electronic structure of CdSe quantum dots (QDs). QDs are large clusters of atoms typically only a few nanometers in diameter. These materials are thought to be the foundation for the next generation of devices, smaller and more efficient than existing technology. By introducing dopants, we show that the electronic structure of these QDs can be finely tuned. Currently, the existing model for modification of the QD bandgap is a purely size dependent phenomenon known as quantum confinement. Controlling the bandgap through other means, such as dopants, allows for a more refined approach to enhance or create new optical properties or adjust the electronic states to more desireable ones. Towards this, this dissertation discusses the development of a theory supported experimental evidence that not only accurately describes how the effect of a dopant atom modifies the electronic structure of nanomaterials, but also, in a more fundamental manner, the formation of hybrid orbitals between the dopant and the host lattice structure. The hybridization of orbitals is known to have a lowering effect on the band edges as electrons tend to the lowest energy state. Results of the theoretical model can predict the changes in electronic structure for any nanoscale range of particle sizes as well as dopant levels up to 3%. Full testing of the theory results in the more rigorously defined model being more accurate and more generalized allowing for calculations outside of simple hybridization effects to be calculated, thus extending the model to further uses.

Experimental results are performed using an x-ray absorption spectroscopic technique called X-ray absorption near edge spectroscopy (XANES). This technique allows for element specific, angular momentum resolved probing of the conduction band. This technique is performed at multiple synchrotron facilities on a myriad of samples at various sizes and doping concentrations. Measurements obtained via XANES agrees well with theoretical results. Furthermore, the theoretical model can be applied prior to experiments and provides excellent predictability of results. Results are shown to be within 0.02 eV of experiment, a result that is limited by the experimental error of the synchrotron.

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