Near-surface modification of defective KTaO₃ by ionizing ion irradiation

Abstract

The synergistic effect of nuclear (S n) and electronic (S e) 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 S e and level of pre-existing damage. These results further reveal that the threshold S e value (S e th) for track creation increases with decreasing pre-damage level. The values of S e th 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 S e ⩽ 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 S e 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.

Ion velocity effect governs damage annealing process in defective KTaO3

“…In very good accordance with previous experimental studies, irradiation at 300 K with 2.0 MeV Au ions to an ion fluence of 0.11 ions nm −2 has resulted in the creation of a predamaged layer with a maximum initial fractional disorder state (f 0 ) of ∼0.35 on the Ta sublattice. According to previous damage accumulation curves [12], the sample with f 0 ∼ 0.35 corresponds to the intermediate level of disorder, where interstitial point defects, interstitial clusters and some minor nanoscale amorphous domains are expected to be present within the layer irradiated with 2.0 MeV Au ions to an ion fluence of 0.11 ions nm −2 [16]. The occurrence of a competitive two-stage phase transition process in pre-damaged KTaO 3 12 MeV O ions at the indicated ion fluences.…”

“…In crystalline KTaO 3 , ion irradiation with low-energy ion results in amorphization of the implanted layer at a given ion fluence (or dose), through a defect-stimulated mechanism [12], and the corresponding critical ion fluence necessary for amorphization shifts to higher values with increasing irradiation temperature [13,14]. The response of pristine crystalline KTaO 3 to high-energy ion irradiations has also been the subject of several investigations [8,15,16], and these lead to the conclusion that pristine KTaO 3 is relatively sensitive to swift heavy ions irradiations (E > 1 MeV amu −1 ) and undergoes discontinuous to continuous amorphous ion track formation with increasing ion energy or electronic energy loss. Discontinuous amorphous track formation in KTaO 3 occurs for S e > 11 keV nm −1 [15,16], while continuous ion tracks are observed at much higher S e values (S e > 23 keV nm −1 ) [8,16].…”

“…The response of pristine crystalline KTaO 3 to high-energy ion irradiations has also been the subject of several investigations [8,15,16], and these lead to the conclusion that pristine KTaO 3 is relatively sensitive to swift heavy ions irradiations (E > 1 MeV amu −1 ) and undergoes discontinuous to continuous amorphous ion track formation with increasing ion energy or electronic energy loss. Discontinuous amorphous track formation in KTaO 3 occurs for S e > 11 keV nm −1 [15,16], while continuous ion tracks are observed at much higher S e values (S e > 23 keV nm −1 ) [8,16]. Since the electronic conductivity and optical properties of these ion tracks differ significantly from the corresponding bulk material, the utilization of such differences enables the fabrication of durable field emission cathodes [17] and waveguides [18], respectively.…”

“…Introducing a pre-damaged state in KTaO 3 leads to significant reductions in threshold S e values (S e th) for ion track formation and moreover, the corresponding S e th shifts to lower values with increasing pre-existing disorder, i.e. S e th decreases to 4.83 keV nm −1 for pre-existing defects with a maximum initial disorder fraction f 0 of 0.3 in KTaO 3 [19], from 6.68 keV nm −1 for f 0 ∼0.08 [16]. Lower S e th values promote the use of small and medium particle accelerator facilities, which do not have severe limitations in terms of portability and flexibility, such in the case of large accelerator facilities.…”

KTaO3—The New Kid on the Spintronics Block

“…Bae et al reported the preparation of single terminated KTO substrates using buffered hydrofluoric acid (BHF) followed by high temperature annealing. [139,174,175] B-site terminated surfaces were achieved by controlling the concentration of BHF, and the temperature and time of annealing. The major drawback of this technique is the use of the strong etchant which may leave a rough surface that would affect the film growth.…”