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Assisted self-healing in ripped graphene
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 19, 195434- p.Article in journal (Refereed) Published
Abstract [en]

A monolayer of sp(2)-bonded carbon (graphene) is a material with great technological promise because of, for example, its transport, electrical, optical, and mechanical properties. In this work noble gas diffusion through ripped graphene sheets is explored. The motivation is improved detection systems used worldwide to verify compliance of the Comprehensive Nuclear-Test-Ban Treaty. It is demonstrated that even ripped graphene sheets and/or nonoverlapping graphene flakes inhibit noble gas diffusion. The latter has been shown for He and Xe where an infinitely long rip was constructed to have Stone-Wales edges. It is also shown that the ripped graphene layer self-heal in an alternating pentagon, hexagon, heptagon (5-6-7) and 7-6-5 pattern perpendicular to the rip. Moreover, the noble gas (He and Xe) assists in the healing process of wider rips.

Place, publisher, year, edition, pages
2010. Vol. 82, no 19, 195434- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-139385DOI: 10.1103/PhysRevB.82.195434ISI: 000284306100008OAI: oai:DiVA.org:uu-139385DiVA: diva2:381318
Available from: 2010-12-27 Created: 2010-12-23 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Surface Coatings as Xenon Diffusion Barriers for Improved Detection of Clandestine Nuclear Explosions
Open this publication in new window or tab >>Surface Coatings as Xenon Diffusion Barriers for Improved Detection of Clandestine Nuclear Explosions
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates surface coatings as xenon diffusion barriers on plastic scintillators. The motivation for the work is improved radioxenon detection systems, used within the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT).

One type of radioxenon detection systems used in this context is the Swedish SAUNA system. This system uses a cylindrical plastic scintillator cell to measure the beta decay from radioxenon isotopes. The detector cell also acts as a container for the xenon sample during the measurement.

One problem with this setup is that part of the xenon sample diffuses into the plastic scintillator material during the measurement, resulting in residual activity left in the detector during subsequent measurements. This residual activity is here referred to as the memory effect.

It is here proposed, and demonstrated, that it is possible to coat the plastic scintillator material with a transparent oxide coating, working as a xenon diffusion barrier. It is found that a 425 nm Al2O3 coating, deposited with Atomic Layer Deposition, reduces the memory effect by a factor of 1000, compared an uncoated detector. Furthermore, simulations show that the coating might also improve the light collection in the detector. Finally, the energy resolution of a coated detector is studied, and no degradation is observed.

The focus of the thesis is measurements of the diffusion barrier properties of Al2O3 films of different thicknesses deposited on plastic scintillators, as well as an evaluation of the expected effect of a coating on the energy resolution of the detector. The latter is studied through light transport simulations. As a final step, a complete coated plastic scintillator cell is evaluated in terms of memory effect, efficiency and energy resolution.

In addition, the xenon diffusion process in the plastic material is studied, and molecular dynamics simulations of the Xe-Al2O3 system are performed in order to investigate the reason for the need for a rather thick coating to significantly reduce the memory effect.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 94 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1111
Keyword
Radioxenon, Gas Diffusion Barrier, Plastic Scintillator, Comprehensive Nuclear-Test-Ban Treaty, Atomic Layer Deposition, Al2O3, Molecular Dynamics, Light Transport
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-215562 (URN)978-91-554-8848-2 (ISBN)
Public defence
2014-02-28, 80121, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2014-02-06 Created: 2014-01-14 Last updated: 2014-02-10

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Bläckberg, LisaKlintenberg, Mattias K.

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