Positron Lifetime Study Of Zn

Author : Taojun Zhou
Publisher : Open Dissertation Press
ISBN 13 : 9781374667372
Total Pages : pages
Book Rating : 4.6/5 (673 download)

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Download or read book All-Electron and Full-Potential Positron Annihilation Calculations for Intrinsic and Defective Zinc and Zinc Oxide written by Taojun Zhou and published by Open Dissertation Press. This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "All-electron and Full-potential Positron Annihilation Calculations for Intrinsic and Defective Zinc and Zinc Oxide" by Taojun, Zhou, 周濤俊, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled ALL-ELECTRON AND FULL-POTENTIAL POSITRON ANNIHILATION CALCULATIONS FOR INTRINSIC AND DEFECTIVE ZINC AND ZINC OXIDE submitted by ZHOU Tao Jun for the Degree of Doctor of Philosophy at The University of Hong Kong in January 2008 Positron annihilation spectroscopy (PAS) is a useful experimental method for studying the electronic structure of materials. To achieve its full poten- tial, however, theoretical methods must be used to interpret PAS results. The studies performed in this work have involved the development of a high ac- curacy positron package capable of theoretically predicting positron-electron momentum distributions and positron lifetimes. The package is based on the WIEN2k package, which utilizes a full potential linearized augmented plane wave (FLAPW) formalism to obtain accurate electron densities. The positron packagewasdevelopedusingthetwocomponentdensityformalismandiscapa- ble of dealing not just with positron annihilation from a bulk crystal state, but also for positrons that are localized in crystal defects. This type of defect studyuses a large sized super-cell. The relaxation of a defect under the inuence of a localized positron has been incorporated into the package. It is shown that experimental data such as Coincidence Doppler Broadening Spectroscopy(CDBS), AngularCorrelationofAnnihilationRadiation(ACAR), andPositronAnnihilationLifetimeSpectroscopy(PALS), canbewellsimulated using this package. The ecacy of the positron package has been demonstrated with respect to two material systems; namely zinc (Zn)/copper (Cu) and zinc oxide (ZnO), with vacancy type defects being considered in both cases. For the transition metal Zn, the local density approximation (LDA), gen- eralized gradient approximation (GGA) and the state-dependent scheme are applied. The GGA value for the positron lifetime is found to be 157ps. The positron-electron momentum spectrum of Zn is compared with that of Cu. The simulationsshow, ingoodagreementwithexperiment, thatthesetwotransition metals of similar electronic structure, have markedly di(R)erent shapes for their positron-electronmomentumdistributions. Reasonsforthisarediscussedbased upon the nature of the 3d electron wavefunctions. The positron package gives a GGA positron lifetime of 191ps for the Zn monovacancy which is in reasonable agreement with experiment. When the positron package is applied to ZnO a GGA positron lifetime of 162ps is obtained which is within the present experimental range. In the GGA approximation, the positron lifetime of the oxygen vacancy is 165ps while that of the Zn vacancy is 220ps - values which are both well within the experimental range. Positron-electron momentum distributions were obtained and compared with experiment. These studies clearly demonstrate the positron package is reliable and useful in the analysis of the experimental results. DOI: 10.5353/th_b3963416 Subjects: Positron annihilation Electron spectroscopy Zinc Zinc oxide