Understanding the formation of latent track by energetic heavy ions is important for the fields of nuclear waste disposal, nuclear fuel and modification of materials.However, the details of the mechanism for the track formation in non-amorphizable materials are still being debated. Here, we report on the fine structure formation of latent tracks, which changes from cylinder to sandglass as a function of the ion-penetrating length, in a typical non-amorphizable material, rutile TiO 2 . Based on inelastic thermal spike model, we show that the outflow of molten phase produces the hillocks on surface and the void-rich zone near surface, while at a deep depth, the lack of outflow and the rapid recrystallization result in the absence of tracks. Moreover, the morphology of tracks depends on the velocity of molten phase outflow and recrystallization. Our perspective provides a new interpretation in the radiation damage for both amorphizable and non-amorphizable materials.
Graphene is an ideal candidate for the development of solid state nanopores due to its thickness at the atomic scale and its high chemical and mechanical stabilities. A facile method was adopted to prepare single graphene nanopore supported by PET membrane (G/PET nanopore) within the three steps assisted by the swift heavy ion irradiation and asymmetric etching technology. The inversion of the ion rectification effect was confirmed in G/PET nanopore while comparing with bare PET nanopore in KCl electrolyte solution. By modifying the wall charge state of PET conical nanopore with hydrochloric acid from negative to positive, the ion rectification effect of G/PET nanopore was found to be greatly enhanced and the large rectification ratio up to 190 was obtained during this work. Moreover, the high ionic flux and high ion separation efficiency was also observed in the G/PET nanopore system. By comparing the "on" and "off" state conductance of G/PET nanopore while immersed in the solution with pH value lower than the isoelectric point of the etched PET (IEP, pH = 3.8), the voltage dependence of the off conductance was established and it was confirmed that the large rectification effect was strongly dependent on the particularly low off conductance at higher applied voltage.
Highly oriented pyrolytic graphite (HOPG) and monolayer graphene were irradiated by swift heavy ions (SHI, 479 MeV 86 Kr and 250 MeV 112 Sn) and highly charged ions (HCI, 4 MeV 86 Kr 19+). The irradiation effects caused by different types of irradiation were investigated by Raman spectroscopy. It was found that the intensity ratio of D peak to G peak (I D /I G) in the case of HCI was higher than that of SHI for the same ion fluence in HOPG. The larger I D /I G indicates that synergistic effects of kinetic and potential energies of medium energy HCI has to be considered during the energy deposition process. A turning point was detected during the evolution process of I D /I G with fluence obtained from SHI and HCI impacted graphene, while such turning point was absent in the case of HOPG. The Lucchese's phenomenological model was modified and the experimental data of I D /I G vs. fluence for HOPG and graphene was completely following the modified model. According to this model, energetic ions induced both structurally disordered and activated regions in graphene. The competing mechanism of these two regions resulted in three different trends of the I D /I G variation in the case of graphene whereas in HOPG, such mechanism was not observed.
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