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Electronic excitation, luminescence and particle emission: Studying ion-induced phenomena in ToF-MEIS
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. (Ion physics)
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Medium energy ion scattering (MEIS) is an experimental technique for the high-resolution depth profiling of thin films. Commonly, ions with energies between several ten to a few hundred keV are employed as probes, and backscattered particles are detected. Apart from scattering, keV ions can upon their interaction with matter induce luminescence, electron emission and the sputtering of neutrals and ions. However, research on this secondary particle emission in the medium energy regime is scarce. Thus, this thesis aims to perform a systematic analysis of 1) ion-induced photon emission and 2) the sputtering of positive ions in a time-of-flight (ToF) MEIS set-up. A significant fraction of photons exhibits energies of only a few eV, which is on the order of typical valence transitions in solids. The dependence of the photon yield on several experimental parameters is studied. By analysing the dependence on the employed geometry, it is concluded that photons are produced along the whole trajectory of the incident ion. Furthermore, the photon yield shows a strong material dependence, which seems to be subject to matrix effects. To study the sputtering process, mass spectrometry was integrated into an existing ToF-MEIS set-up. The secondary ions exhibit very low initial kinetic energies and, therefore, need to be accelerated by a sufficiently high voltage. Then, atomic and molecular ions originating both from the employed target material and surface contaminations can be detected. Whereas experimental evidence suggests a predominantly electronic sputtering process for species adsorbed to the surface, target bulk constituents seem to be sputtered by nuclear collision cascades. 

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2018. , p. 42
Keywords [en]
TOF-MEIS, ion beam analysis, deep UV, desorption, electronic sputtering, TiN
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-351261OAI: oai:DiVA.org:uu-351261DiVA, id: diva2:1209285
Presentation
2018-05-24, Å4006, Ångströmlaboratoriet, Uppsala, 14:00 (English)
Opponent
Supervisors
Available from: 2018-05-22 Created: 2018-05-22 Last updated: 2018-05-22Bibliographically approved
List of papers
1. Analysis of photon emission induced by light and heavy ions in time-of-flight medium energy ion scattering
Open this publication in new window or tab >>Analysis of photon emission induced by light and heavy ions in time-of-flight medium energy ion scattering
2018 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 417, p. 75-80Article in journal (Refereed) Published
Abstract [en]

We present a systematic analysis of the photon emission observed due to impact of pulsed keV ion beams in time-of-flight medium energy ion scattering (ToF-MEIS) experiments. Hereby, hydrogen, helium and neon ions served as projectiles and thin gold and titanium nitride films on different substrates were employed as target materials. The present experimental evidence indicates that a significant fraction of the photons has energies of around 10 eV, i.e. on the order of typical valence and conduction band transitions in solids. Furthermore, the scaling properties of the photon emission with respect to several experimental parameters were studied. A dependence of the photon yield on the projectile velocity was observed in all experiments. The photon yield exhibits a dependence on the film thickness and the scattering angle, which can be explained by photon production along the path of the incident ion through the material. Additionally, a strong dependence on the projectile type was found with the photon emission being higher for heavier projectiles. This difference is larger than the respective difference in electronic stopping cross section. The photon yield shows a strong material dependence, and according to a comparison of SiO2 and Si seems to be subject to matrix effects. (C) 2017 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Photons, Deep UV, TOF-MEIS, Au
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-348917 (URN)10.1016/j.nimb.2017.08.005 (DOI)000426030500014 ()
Conference
15th International Conference on Particle Induced X-ray Emission (PIXE), APR 02-07, 2017, Split, CROATIA
Funder
Swedish Foundation for Strategic Research , RIF14-0053Swedish Research Council, 821-2012-5144
Available from: 2018-04-25 Created: 2018-04-25 Last updated: 2018-05-22Bibliographically approved
2. Ion-induced particle desorption in time-of-flight medium energy ion scattering
Open this publication in new window or tab >>Ion-induced particle desorption in time-of-flight medium energy ion scattering
2018 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 423, p. 22-26Article in journal (Refereed) Published
Abstract [en]

Secondary ions emitted from solids upon ion impact are studied in a time-of-flight medium energy ion scattering (ToF-MEIS) set-up. In order to investigate characteristics of the emission processes and to evaluate the potential for surface and thin film analysis, experiments employing TiN and Al samples were conducted. The ejected ions exhibit a low initial kinetic energy of a few eV, thus, requiring a sufficiently high acceleration voltage for detection. Molecular and atomic ions of different charge states originating both from surface contaminations and the sample material are found, and relative yields of several species were determined. Experimental evidence that points towards a predominantly electronic sputtering process is presented. For emitted Ti target atoms an additional nuclear sputtering component is suggested.

Keywords
Desorption, Electronic sputtering, TOF-MEIS, TiN
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-351227 (URN)10.1016/j.nimb.2018.02.016 (DOI)000430901400004 ()
Funder
Swedish Research Council, 821-2012-5144Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2018-07-31Bibliographically approved

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