Development Of Low Energy Positron Beams And Their Application To The Study Of The Surface Region In Metals

Author : Chor-Keung Cheung
Publisher : Open Dissertation Press
ISBN 13 : 9781374666696
Total Pages : pages
Book Rating : 4.6/5 (666 download)

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Download or read book The Construction of a Focused Low Energy Positron Beam Facility and Its Application in the Study of Various Optoelectronic Materials written by Chor-Keung Cheung 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, "The Construction of a Focused Low Energy Positron Beam Facility and Its Application in the Study of Various Optoelectronic Materials" by Chor-keung, Cheung, 張初強, 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 THE CONSTRUCTION OF A FOCUSED LOW ENERGY POSITRON BEAM FACILITY AND ITS APPLICATION IN THE STUDY OF VARIOUS OPTOELECTRONIC MATERIALS submitted by CHEUNG Chor Keung for the Degree of Doctor of Philosophy at The University of Hong Kong in August 2006 Lowenergypositronbeamshaveanimportantplaceinmaterialssciencebecause they allow non-destructive observations to be made on the nature of crystal de- fects as a function of depth. The old positron beam facility at the University of Hong Kong that operated between 1996 and 2001 had a relatively large beam 4 + 1 diameter of1/4 6 mm and a low intensity1/4 10 e s . As such it had limited use in depth defect proling of metal-semiconductor systems. The studies per- formed in this work have involved a reconstruction of the HKU positron beam so as to make the focused spot at the target with submillimeter diameter. The 5 + 1 beam intensity has been increased up to 1 10 e s .Thenewdesignofthefacilityrequirespositronstobeemittedfromthemod- erator in a magnetic eld free region so as to minimize the canonical angular momentum carried by the particles. The hybrid lens system employed consists of a standard Soa extraction lens in a magnetic eld free region followed by a gridded Einzel lens that focuses positrons into a 100 G magnetic funnel at an energy of 10 keV. After E B ltering the positrons are transported to the target. The nal focus at the target is adjusted by changing the magnetic eld near the target chamber. The slow positron beam system has been successfully constructedanditsperformancematchescomputersimulations. Theimplemen- tation of the Variable Energy-Doppler Broadening of Annihilation Radiation Spectroscopy (VEDBARS) to the beam allows taking standard defect-depth measurement. Coincidence Doppler Broadening Spectroscopy(CDBS) has also been installed for more detailed defect characterization. The beam is equipped with an S parameter imaging system for diagnosing defect patterns, and loca- tion of surface metalizations. PositronAnnihilationSpectroscopy(PAS)employingtheslowpositronbeam facilityhas been demonstrated in various studies of a number of optoelectronics materials. These include the study of the interfacial properties of several insu- lating oxide layers grown on InP substrate, the study of defect characterization onsmalldimensionITOcontactsgrownon n-GaNunderdi(R)erentgaseousenvi- ronments, the porosity characterization of porous silicon and the study of ZnO nanorodsgrownonSisubstrateunder di(R)erentgaseous ambientsandannealing temperatures. These measurements clearly demonstrate that the reconstructed well focused slow positron beam facility is useful as a non-destructive tool for open volume defect studies in optoelectronics materials. DOI: 10.5353/th_b3743492 Subjects: Positron beams Optoelectronic devises - Defects Optoelectronics - Materials