engleski

Swift heavy ions for nanopatterning surfaces and defects engineering

Interaction of the swift heavy ion with the material is a violent one, leading to the formation of permanent damage in the material usually called an ion track. While it is still unclear which physical mechanisms should be considered as possible routes to ion track formation and what their relative contributions are, ion tracks have already found numerous applications like hadron therapy, nuclear waste immobilization and track etch membrane production, to name just a few. Therefore, topics in the field of ion track research are still of importance for both theoretical investigations as well as possible novel applications. Historically, ion track research has been conducted at large accelerator facilities because density of deposited energy due to ion impact must surpass certain threshold value in order to trigger phase transformation (most often melting) that ultimately results in nanoscale damage along ion trajectory. Therefore, “swift heavy ion” has traditionally been considered a projectile with mass of at least of 20 amu, and with kinetic ion energy of at least 1 MeV/amu. However, recently it has been recognized that one or even both of these two criteria can be relaxed because ion tracks can be formed by ions that are either lighter or slower. For example, in the recent review [1] criteria for swift heavy ions have been relaxed down to mass of 15 amu, and/or kinetic energy of 0.1 MeV/amu. These criteria should be considered more as a guidance, keeping in mind that swift heavy ions used for ion track production should have electronic stopping power above the ion track threshold, and that nuclear stopping should be negligible. In the present contribution, by showing examples of recent research done at the Zagreb accelerator facility within the ion track field, opportunities for this kind of research will be highlighted, and hopefully a more general strategy for conducting this kind of research at small and medium size accelerator laboratories will emerge. The central point revolves around ion track formation threshold. Since this quantity is of crucial importance in any kind of ion track studies, understanding what exactly contributes to its value is very important. This, in turn, could broaden the scope of the ion track research at smaller accelerator facilities if ways to lower its value can be found. Clearly, the most simple approach is to focus on the materials that are the most sensitive to the swift heavy ion irradiation, like polymers. However, such approach in the end restricts this line of research to relatively narrow range of materials, and consequently impact of this research would be low. Therefore, different ways to lower the threshold for ion track formation and consequently impact of this approach to the scope of our research will be presented.

ion track ; swift heavy ion

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