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Construction of a pulsing system for low-energy positrons

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dc.contributor Aalto-yliopisto fi
dc.contributor Aalto University en
dc.contributor.author Laakso, Antti
dc.date.accessioned 2012-02-17T07:06:03Z
dc.date.available 2012-02-17T07:06:03Z
dc.date.issued 2005-06-29
dc.identifier.isbn 951-22-7746-8
dc.identifier.issn 1455-1802
dc.identifier.uri https://aaltodoc.aalto.fi/handle/123456789/2587
dc.description.abstract Positron lifetime spectroscopy is a powerful tool to identify vacancy type defects in semiconductor materials. Conventionally, applicability of the positron lifetime measurement has been limited to bulk samples. However, many interesting materials are nowadays available only as thin epitaxial samples. In order to measure these samples a positron lifetime beam is needed. This work describes the concept and the design of a pulsed low-energy positron lifetime beam facility. The theoretical background of the beam pulsing is reviewed. The construction of the pulsing system is presented in detail and results from electron and positron tests with this beam facility are introduced. As an application of the pulsed lifetime beam the results of the measurements on InN layers done at Universität der Bundeswehr are also presented. The pulsing system in this work is composed of three different components, two bunchers and a chopper. The bunchers modulate the beam velocity to create a time varying positron beam intensity and to result a very narrow positron bunch at the target. The chopper is used to get rid of the background between the pulses and to improve the peak to background ratio. When this pulsing system is tested with electrons, a full width at half maximum of 160 ps and a peak to background ratio of 5000:1 is obtained. For positrons, the values are 270 ps and 4000:1 respectively. en
dc.format.extent 45, [app]
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher Helsinki University of Technology en
dc.publisher Teknillinen korkeakoulu fi
dc.relation.ispartofseries Dissertations of Laboratory of Physics, Helsinki University of Technology en
dc.relation.ispartofseries 133 en
dc.relation.haspart A. Laakso, K. Saarinen, and P. Hautojärvi. 2001. Positron lifetime beam for defect studies in thin epitaxial semiconductor structures. Physica B, 308-310: 1157-1160. [article1.pdf] © 2001 Elsevier Science. By permission.
dc.relation.haspart A. Laakso, M. Hakala, A. Pelli, K. Rytsölä, K. Saarinen, and P. Hautojärvi. 2004. Scattering effects in a positron lifetime beam line. Materials Science Forum, 445-446: 489-491. [article2.pdf] © 2004 Trans Tech Publications. By permission.
dc.relation.haspart F. Reurings, A. Laakso, K. Rytsölä, A. Pelli, and K. Saarinen. 2005. Compact positron beam for measurement of transmission moderator efficiencies and positron yields of encapsulated sources. Applied Surface Science, accepted for publication. [article3.pdf] © 2005 by authors and © 2005 Elsevier Science. By permission.
dc.relation.haspart A. Pelli, A. Laakso, K. Rytsölä, R. Aavikko, M. Rummukainen, and K. Saarinen. 2004. HV design of a pulsed lifetime beam with a grounded sample. Materials Science Forum, 445-446: 504-506. [article4.pdf] © 2004 Trans Tech Publications. By permission.
dc.relation.haspart A. Laakso, A. Pelli, K. Rytsölä, K. Saarinen, and P. Hautojärvi. 2005. Determination of the timing properties of the pulsed positron lifetime beam by the application of an electron gun and a fast microchannel plate. Applied Surface Science, accepted for publication. [article5.pdf] © 2005 by authors and © 2005 Elsevier Science. By permission.
dc.relation.haspart J. Oila, A. Kemppinen, A. Laakso, K. Saarinen, W. Egger, L. Liszkay, P. Sperr, H. Lu, and W. J. Schaff. 2004. Influence of layer thickness on the formation of In vacancies in InN grown by molecular beam epitaxy. Applied Physics Letters, 84: 1486-1489. [article6.pdf] © 2004 American Institute of Physics. By permission.
dc.relation.haspart A. Laakso, J. Oila, A. Kemppinen, K. Saarinen, W. Egger, L. Liszkay, P. Sperr, H. Lu, and W. J. Schaff. 2004. Vacancy defects in epitaxial InN: identification and electrical properties. Journal of Crystal Growth, 269: 41-49. [article7.pdf] © 2004 Elsevier Science. By permission.
dc.subject.other Physics en
dc.title Construction of a pulsing system for low-energy positrons en
dc.type G5 Artikkeliväitöskirja fi
dc.description.version reviewed en
dc.contributor.department Department of Engineering Physics and Mathematics en
dc.contributor.department Teknillisen fysiikan ja matematiikan osasto fi
dc.subject.keyword pulsed positron beam en
dc.subject.keyword positron spectroscopy en
dc.subject.keyword pulsing systems en
dc.subject.keyword low-energy positrons en
dc.identifier.urn urn:nbn:fi:tkk-005410
dc.type.dcmitype text en
dc.type.ontasot Väitöskirja (artikkeli) fi
dc.type.ontasot Doctoral dissertation (article-based) en
dc.contributor.lab Laboratory of Physics en
dc.contributor.lab Fysiikan laboratorio fi
local.aalto.digifolder Aalto_63968
local.aalto.digiauth ask


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