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Combined effect of energy loss process in ion/matter interaction

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Involved people : Abdenacer Benyagoub, Emmanuel Balanzat, Brigitte Ban d’Etat, Serge Bouffard, Clara Grygiel, Henning Lebius, Florent Moisy, Isabelle Monnet, Marcel Toulemonde

Contract : PICS IiN France-China (2014-2016)

At GANIL and CIRIL plateform the large offer of ion beam allow to vary the ENSP (electronic to nuclear stoping power) and the ratio between kinetic energy and potential energy with multicharged low energy ions. In the past five year, a lot of results concerning combined effect of the different way to deposite energy in ion/matter interaction are obtained.

For semiconductors, in SiC, we have evidenced an athermal recrystallisation by swift heavy ion after amorphisation by low energy ion implantation. On the contrary, in AlN, which is also a resistant material toward ion track formation, we have shown that electronic excitations play a very important role in the formation of color defects. We revealed an unprecedented real synergy between electronic excitations and nuclear collisions in the creation of defects, which induces an absorption band .

(a) Evolution of the area of the absorption band at 4.7 eV versus the number of displacements per atom (dpa) in the AlN layer. (b) Evolution of the synergy parameter beta as function of Se.
Sall M , Monnet I, Grygiel C, Ban D’Etat B, Lebius H, Leclerc S, Balanzat E Europhysics Letters 102 : 26002 (2013)

In a collaboration within a French-Chinese PICS project with the Institute of Modern Physics of Lanzhou and with the Institute of Applied Physics of Vienna, we showed that nano-hillocks on CaF2 crystal surfaces can be formed by individual impact of highly charged xenon ions at medium energy as well as swift xenon ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy (Ep) while for swift heavy ions a minimum electronic energy loss per unit length (Se) is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via Se the Ep-threshold for hillock production can be substantially lowered. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, which can be visualized in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to the case where both kinetic and potential energies are deposited into the surface. See reference : Scientific Reports 4- 5742 (2014).