Near-surface modification of defective KTaO3 by ionizing ion irradiation

International audienceThe synergistic effect of nuclear (Sn) and electronic (Se) energy loss observed in some ABO3 perovskites has attracted considerable attention due to the real possibility to modify various near-surface properties, such as the electronic and optical properties, by patterning ion tracks in the defective near-surface regions. In this study, we show that low-energy ion-induced disordering in conjunction with ionizing ion irradiation (18 MeV Si, 21 MeV Ni and 91.6 MeV Xe) is a promising approach for tailoring ion tracks in the near-surface of defective KTaO3. Experimental characterization and computer simulations reveal that the size of these latent ion tracks increases with Se and level of pre-existing damage. These results further reveal that the threshold Se value (Seth) for track creation increases with decreasing pre-damage level. The values of Seth increase from 5.02 keV nm−1, for a pre-existing fractional disorder of 0.53 in KTaO3, to 10.81 keV nm−1 for pristine KTaO3. Above these thresholds, amorphous latent tracks are produced due local melting and rapid quenching. Below a disorder fraction of 0.08 and Se ⩽ 6.68 keV nm−1, the synergistic effect is not active, and damage accumulation is suppressed due to a competing ionization-induced damage annealing process. These results indicate that, depending on Se and the amount of pre-existing damage, highly ionizing ions can either enhance or suppress damage accumulation in KTaO3, thus providing a pathway to tailoring defects states. Comprehending the conflicting roles of highly ionizing ions in defective ABO3 oxides is vital for understanding and predictive modeling of ion-solid interactions in complex oxides, as well as for achieving control over ion track size in the near-surface of defective KTaO3

Delayed damage accumulation by athermal suppression of defect production in concentrated solid solution alloys

<p>A combined experimental and computational evaluation of damage accumulation in ion-irradiated Ni, NiFe, and NiFeCoCr is presented. A suppressed damage accumulation, at early stages (low-fluence irradiations), is revealed in NiFeCoCr, with a linear dependence as a function of ion fluence, in sharp contrast to Ni and NiFe. This effect, observed at 16 K, is attributed to the complex energy landscape in these alloys that limits defect mobility and therefore enhances defect interaction and recombination. These results, together with previous room-temperature and high-temperature investigations, suggest ‘self-healing’ as an intrinsic property of complex alloys that is not a thermally activated process.</p> <p><b>IMPACT STATEMENT</b> A combined experimental and computational evaluation reveals a remarkable delayed damage accumulation due to significant athermal suppression of defect production in ion-irradiated concentrated solid solution alloys at 16 K.</p