The surface of ZnO semiconductor nanosystems is a key performance-defining factor in numerous applications. In this work we present experimental results for the surface defect-related properties of ZnO nanoscale systems. Surface photovoltage spectroscopy was used to determine the defect level energies within the band gap, the conduction vs. valence band nature of the defect-related transitions, and to probe key dynamic parameters of the surface on a number of commercially available ZnO nanopowders. In our experimental setup, surface photovoltage characterization is conducted in high vacuum in tandem with in situ oxygen remote plasma treatments. Surface photovoltage investigations of the as-received and plasma-processed samples revealed a number of common spectral features related to surface states. Furthermore, we observed significant plasma-induced changes in the surface defect properties. Ex situ positron annihilation and photoluminescence measurements were
performed on the studied samples and correlated with surface photovoltage results. The average positron lifetimes were found to be substantially longer than in a bulk single crystalline sample, which is consistent with the model of grains with defect-rich surface
and subsurface layers. Compression of the powders into pellets yielded reduction of the average positron lifetimes. Surface photovoltage, positron annihilation, and photoluminescence spectra
consistently showed sample-to-sample differences due to the variation in the overall quality of the nanopowders, which partially obscures observation of the scaling effects. However, the results demonstrated that our approach is efficient in detecting specific
surface states in nanoscale ZnO specimens and in elucidating their nature.
| Identifer | oai:union.ndltd.org:TCU/oai:etd.tcu.edu:etd-03282011-125929 |
| Date | 28 March 2011 |
| Creators | Peters, Raul M. |
| Contributors | Yuri Strzhemechny |
| Publisher | Texas Christian University |
| Source Sets | Texas Christian University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.tcu.edu/etdfiles/available/etd-03282011-125929/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to TCU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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