Stability of materials in radiation harsh environment is an important issue because damage build-up within a material in such an environment can exhibit complex behavior. Of special interest is the response of materials to fission-fragments that can produce extended damage known as fission tracks. To address this, the response of a wide range of crystalline ceramics to swift heavy ion (i.e. fission fragment-like) irradiation has been systematically investigated for nuclear waste applications [1-3].
Dense electronic excitation in the wake of the swift heavy ion can lead to nanoscale material damage along its trajectory called ion (i.e. fission) track. The thermal spike scenario describes this process as a transfer of the deposited swift heavy ion energy from the electronic subsystem into the phonon subsystem via electron-phonon coupling. If the density of the deposited energy is sufficient to induce melting, then an ion track can be formed during rapid quenching of the melt. Otherwise, the deposited energy simply dissipates away without producing damage. This is the origin of the ion track formation threshold and its high valueis desirable for any material used in nuclear energy applications. Lowering of threshold value can have significant, detrimental effects.
We present results of RBS/c, TEM and AFM investigations of ion track formation thresholds in swift heavy ion irradiation resistant materials MgO, Al2O3, MgAl2O4 and GaN. In case of oxides, we compare thresholds for ion track formation in the bulk ,  and on the surface . Based on the AFM measurements, we present evidence that ion tracks can be easily formed on the oxide surfaces after grazing-incidence swift heavy ion irradiation. Similar to our previous studies on ion tracks on GaN, SrTiO3 and TiO2 surfaces [6-8], we show how the threshold for ion track formation can be significantly reduced by applying grazing incidence irradiation geometry.
Another way how this threshold can be reduced is via introduction of defects, usually by means of low energy ion irradiation. Recently, synergistic effects of nuclear and electronic energy loss came into research focus, for example defects in SrTiO3 can promote ion track formation , . As a follow-up of our previous study on GaN , we investigated the role of defects in this material with respect to the ion track formation and report additive effects similar to the case of SrTiO3.
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