Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1945 Beyond scattering – what more can be learned from pulsed keV ion beams? SVENJA LOHMANN ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 ISBN 978-91-513-0964-4 UPPSALA urn:nbn:se:uu:diva-409892 2020 Dissertation presented at Uppsala University to be publicly examined in Polhelmsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, Friday, 12 June 2020 at 09:15 for the degree of Doctor of Philosophy. The examination will be conducted in English. Faculty examiner: Professor Andreas Wucher (University of Duisburg-Essen, Faculty of Physics). Abstract Lohmann, S. 2020. Beyond scattering – what more can be learned from pulsed keV ion beams? Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1945. 90 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-513-0964-4. Interactions of energetic ions with matter govern processes as diverse as the influence of solar wind, hadron therapy for cancer treatment and plasma-wall interactions in fusion devices, and are used for controlled manipulation of materials properties as well as analytical methods. The scattering of ions from target nuclei and electrons does not only lead to energy deposition, but can induce the emission of different secondary particles including electrons, photons, sputtered target ions and neutrals as well as nuclear reaction products. In the medium-energy regime (ion energies between several ten to a few hundred keV), ions are expected to primarily interact with valence electrons. Dynamic electronic excitations are, however, not understood in full detail, and remain an active field of experimental and theoretical research. In addition, whereas scattered ions are employed for high-resolution depth profiling in medium energy ion scattering (MEIS), research on secondary particle emission in this regime is scarce. This thesis explores possibilities to experimentally study ion-solid interactions in the medium- energy regime beyond a backscattering approach. The capability for detection of electrons, photons and sputtered ions was integrated into the time-of-flight (ToF-) MEIS set-up at Uppsala University. Additionally, transmission of ions in combination with crystalline samples was employed to study impact-parameter dependent electronic excitations. In all cases, the use of pulsed ion beams with nanosecond pulse widths proves to be imperative for achieving energy measurements with sufficient resolution as well as low doses for non-destructive interactions even with sensitive samples. Trajectory-dependent energy loss of various ions in Si(100) was studied. For all ions heavier than protons, experimental evidence shows that, if close collisions are not suppressed by channelling, consequent charge-exchange events increase the mean charge state of the ion and heavily influence the experienced energy loss. Furthermore, measurements of electron emission are presented. For medium-energy ions, electrons emitted in forward direction from carbon foils exhibit energies between 10 and 400 eV. Scaling with ion velocity indicates binary collisions as the primary energy transfer mechanism. Detected photons also have energies of a few eV, i.e. on the order of typical valence transitions in solids. For photon emission, pronounced chemical matrix effects are observed. Finally, the sputtering process at medium energies was studied. Target bulk constituents exhibit similar behaviour as known from established methods at lower energies, i.e. sputtering by nuclear collision cascades. In contrast, the desorption of surface species seems to be governed by electronic energy transfer mechanisms. Keywords: Charge exchange, Deep UV photons, Electron emission, Silicon, Sputtering, TOF- MEIS Svenja Lohmann, Department of Physics and Astronomy, Applied Nuclear Physics, Box 516, Uppsala University, SE-751 20 Uppsala, Sweden. © Svenja Lohmann 2020 ISSN 1651-6214 ISBN 978-91-513-0964-4 urn:nbn:se:uu:diva-409892 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-409892) List of Papers This thesis is based on the following papers, which are referred to in the text by their Roman numerals. I. Disparate energy scaling of trajectory-dependent electronic excita- tions for slow protons and He ions S. Lohmann, and D. Primetzhofer. Phys. Rev. Lett., 124: 096601. 2020. II. Trajectory-dependent electronic excitations by light and heavy ions around and below the Bohr velocity S. Lohmann, R. Holenák,ˇ and D. Primetzhofer. In manuscript form. III. Assessing electron emission induced by pulsed ion beams: a time-of- flight approach S. Lohmann, A. Niggas, V. Charnay, R. Holenák,ˇ and D. Primetzhofer. Manuscript submitted for publication. IV. Analysis of photon emission induced by light and heavy ions in time- of-flight medium energy ion scattering S. Lohmann, M. A. Sortica, V. Paneta, and D. Primetzhofer. Nucl. In- strum. Methods Phys. Res., Sect. B, 417: 75–8. 2018. V. Ion-induced particle desorption in time-of-flight medium energy ion scattering S. Lohmann, and D. Primetzhofer. Nucl. Instrum. Methods Phys. Res., Sect. B, 423: 22–26. 2018. Reprints were made with permission from the publishers. iii My contributions to the included papers: Paper I I participated in planning the study, conducted all experiments and analysed the data. I interpreted the results together with my supervisor and wrote the initial manuscript. Paper II I was involved in planning this study. I measured parts of the data and assisted with the remaining experiments. I did the analysis, interpreted the results to- gether with the other authors and wrote the manuscript. Paper III I was involved in planning the study and in making necessary changes to the set-up. I conducted the experiments together with co-authors. I anal- ysed all data and interpreted them together with the other authors. I wrote the manuscript. Paper IV I manufactured the Au samples and conducted the majority of experiments. I analysed the data, interpreted the results in discussion with the other authors and wrote the manuscript. Paper V I was involved in planning the experiments and implemented necessary ad- justments for secondary ion detection. I performed the measurements and analysed the data. I interpreted the results together with my supervisor and wrote the manuscript. iv Related publications with my authorship not included in this thesis: VI. Electronic energy-loss mechanisms for H, He, and Ne in TiN M. A. Sortica, V. Paneta, B. Bruckner, S. Lohmann, M. Hans, T. Nyberg, P. Bauer and D. Primetzhofer. Phys. Rev. A, 96(3): 032703. 2017. VII. On the Z1-dependence of electronic stopping in TiN M. A. Sortica, V. Paneta, B. Bruckner, S. Lohmann, T. Nyberg, P. Bauer, and D. Primetzhofer. Sci. Rep., 9(1): 176. 2019. VIII. A versatile time-of-flight medium-energy ion scattering setup using multiple delay-line detectors M. A. Sortica, M. K. Linnarsson, D. Wessman, S. Lohmann, and D. Primetzhofer. Nucl. Instrum. Methods Phys. Res., Sect. B, 463: 16–20. 2020. IX. Contrast modes in a 3D ion transmission approach at keV energies R. Holenák,ˇ S. Lohmann, and D. Primetzhofer. Manuscript submitted for publication. v My contributions to the non-included papers: Paper VI I conducted some of the experiments, contributed to the analysis and critically revised the manuscript. Paper VII I helped with some of the measurements and contributed to the analysis. I critically revised the manuscript. Paper VIII I was responsible for the development of transmission experiments and for the integration of mass spectrometry and electron detection into the set-up. I was also involved in improving in-situ sample cleaning methods. I revised the manuscript. Paper IX I was involved in planning this study and contributed the experimental data. I helped interpret the results and critically revised the manuscript. vi Contents List of Papers .................................................................................................... iii Abbreviations ..................................................................................................... x 1 Introduction .................................................................................................. 1 2 Ion-solid interactions ................................................................................... 5 2.1 Binary collisions ............................................................................... 5 2.2 Scattering in the solid: channelling and blocking .......................... 7 2.3 The role of electrons ........................................................................ 9 2.3.1 Screening ............................................................................ 9 2.3.2 Stopping models .............................................................. 10 2.3.3 Charge-exchange processes ............................................ 13 2.4 Ion-induced emission phenomena ................................................. 16 2.4.1 General concepts ............................................................. 16 2.4.2 Electron emission ............................................................ 16 2.4.3 Photon emission ............................................................... 19 2.4.4 Sputtering and desorption ............................................... 20 3 Experimental set-up and methods ............................................................ 23 3.1 Medium energy ion scattering ....................................................... 23 3.1.1 General set-up .................................................................