Abstract
There is an ongoing debate regarding the mechanism of swift heavy ion (SHI) track formation in CaF2. The objective of this study is to shed light on this important topic using a range of complementary experimental techniques. Evidence of the threshold for ion track formation being below 3 keV nm−1 is provided by both transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy in the channelling mode, which has direct consequences for the validity of models describing the response of CaF2 to SHI irradiation. Furthermore, information about the elemental composition within the ion tracks is obtained using scanning TEM, electron energy loss spectroscopy, and with respect to the stoichiometry of the materials surface by in situ time of flight elastic recoil detection analysis. Advances in the analyses of the experimental data presented here pave the way for a better understanding of the ion track formation.
Highlights
Material modification using swift heavy ions (SHIs) having a mass above 15 atomic mass units, and a specific kinetic energy above 0.1 MeV/amu [FAL16] is an important contemporary research topic [CT09], [EA07], [PK08], [MCR13], [MCR11], [FA11], [NI09] with diverse applications like hadrontherapy [MT09], radiation waste storage [WJW98] and track etched membrane production [CT09]
Interactions of individual SHIs with crystalline materials can result in the formation of ion tracks in the bulk [PK08], [MCR13], [MT04], [MT12], [MB12], accompanied by surface features that can be found at the SHI impact site by means of atomic force microscopy (AFM) [EA07], [MK10], [FA11], [SA11], [OO15]
This suggests melting as requirement for ion track formation since a similar threshold was found for nanohillock formation on the CaF2 surface [YYW14]
Summary
Material modification using swift heavy ions (SHIs) having a mass above 15 atomic mass units (amu), and a specific kinetic energy above 0.1 MeV/amu [FAL16] is an important contemporary research topic [CT09], [EA07], [PK08], [MCR13], [MCR11], [FA11], [NI09] with diverse applications like hadrontherapy [MT09], radiation waste storage [WJW98] and track etched membrane production [CT09]. Interactions of individual SHIs with crystalline materials can result in the formation of ion tracks in the bulk [PK08], [MCR13], [MT04], [MT12], [MB12], accompanied by surface features (nano-hillocks, nano-craters and similar) that can be found at the SHI impact site by means of atomic force microscopy (AFM) [EA07], [MK10], [FA11], [SA11], [OO15]. Despite their nanometric sizes, ion tracks in the bulk can be observed with several techniques. The agreement in measured ion track radii between these two techniques is very good [MT06]
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