Investigation of ion-track morphology and annealing behavior using small-angle X-ray scattering

When heavy ions with energies in the range of hundreds of MeV to GeV penetrate a solid, they lose their energy through inelastic interactions with the target electrons and can leave narrow cylindrical trails of permanent damage along their path, known as ion tracks. Ion tracks are typically a few nanometers in diameter and can be up to tens of micrometers long. When these tracks are annealed at elevated temperatures, they shrink in size and eventually the damage inside the material can recover. In this project ion tracks are studied in Durango apatite, San Carlos olive and synthetic quartz. In minerals such as apatite track formation can result from spontaneous fission of naturally occurring uranium inclusions that produces high energetic fragments. These so called “fission tracks” are used for dating and constraining the thermal history of geological samples. The current dating methods, however, utilize chemical etching, which destroys the primary damage such that essential information on the actual scale of the underlying radiation damage is irrevocably lost. A detailed understanding of the un-etched track damage in minerals and its dependence on geologically relevant conditions is of fundamental importance for the application of etched tracks in geo- and thermochronology. Tracks in olivine are used for identification of cosmic rays in meteorites. Many meteorites contain different amounts of olivine which is a crystalline mineral susceptible to ion track formation from high energetic cosmic particles. Studying the annealing behavior of ion tracks in meteorites can lead to estimation of the temperature of the mineral during track formation. In quartz, swift heavy ion irradiation leads to a change in the refractive index of the material inside the narrow tracks and provides new possibilities for fabrication and micromachining of optical devices. Annealing of ion tracks in quartz is of interest as for example device fabrication processes often involve elevated temperatures. In this work synchrotron based small angle x-ray scattering in combination with in situ and ex situ annealing experiments is used to study the morphology and damage recovery of un-etched ion tracks. It is demonstrated that SAXS is a powerful tool for studying ion track damage in a variety of materials as it is sensitive to small density changes at the nanometer scale that often occur in the damaged regions. It is a non-destructive technique and can be used to determine changes in the track radii with sub-nanometer precision. Short acquisition times make it well suited for studying track annealing kinetics in situ. The work presented in this thesis has aided in developing the possibilities that small angle x-ray scattering can provide for studying the morphology and annealing behavior of nano sized damage structures. The high accuracy with which the track radii can be determined using SAXS, the nondestructive, artifact-free measurement methodology, as well as the data analysis models introduced in this work provide an effective means for in-depth studies of ion-track morphology and annealing behavior in a variety of materials

Morphology and annealing kinetics of ion tracks in minerals

We have studied the morphology and annealing kinetics of ion tracks in Durango apatite using synchrotron small angle X-ray scattering. The non-destructive, artefact-free technique enables us to determine the track radii with a resolution of fractions of

SAXS study of ion tracks in San Carlos olivine and Durango apatite

Ion tracks were generated in crystalline San Carlos olivine (Mg,Fe) 2SiO 4 and Durango apatite Ca 10(PO 4) 6F 2 using different heavy ions ( 58Ni, 101Ru, 129Xe, 197Au, and 238U) with energies ranging between 185 MeV and 2.6 GeV. The tracks and their annealing behavior were studied by means of synchrotron based small angle X-ray scattering in combination with in situ annealing. Track radii vary as a function of electronic energy loss but are very similar in both minerals. Furthermore, the annealing behavior of the track radii has been investigated and preliminary results reveal a lower recovery rate of the damaged area in olivine compared with apatite

Modification of Fe-B based metallic glasses using swift heavy ions

We report on small-angle x-ray scattering (SAXS) measurements of amorphous Fe80B20, Fe85B15, Fe 81B135Si35C2, and Fe 40Ni40B20 metallic alloys irradiated with 11.1 MeV/u 132Xe, 152Sm, 197Au, and 8.2 MeV/u 238U ions. SAXS experiments are nondestructive an

Latent ion tracks in amorphous silicon

We present experimental evidence for the formation of ion tracks in amorphous Si induced by swift heavy-ion irradiation. An underlying core-shell structure consistent with remnants of a high-density liquid structure was revealed by small-angle x-ray scattering and molecular dynamics simulations. Ion track dimensions differ for as-implanted and relaxed Si as attributed to differentmicrostructures andmelting temperatures. The identification and characterization of ion tracks in amorphous Si yields new insight into mechanisms of damage formation due to swift heavy-ion irradiation in amorphous semiconductors

Tracks and voids in amorphous Ge induced by swift heavy-ion irradiation

Ion tracks formed in amorphous Ge by swift heavy-ion irradiation have been identified with experiment and modeling to yield unambiguous evidence of tracks in an amorphous semiconductor. Their underdense core and overdense shell result from quenched-in ra

Orientation dependence of swift heavy ion track formation in potassium titanyl phosphate

Potassium titanyl phosphate crystals in both x-cut and z-cut were irradiated with 185 MeV Au ions. The morphology of the resulting ion tracks was investigated using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). SAXS measurements indicate the presence of cylindrical ion tracks with abrupt boundaries and a density contrast of 1 ± 0.5% compared to the surrounding matrix, consistent with amorphous tracks. The track radius depends on the crystalline orientation, with 6.0 ± 0.1 nm measured for ion tracks along the x-axis and 6.3 ± 0.1 nm for those along the z-axis. TEM images in both cross-section and plan-view show amorphous ion tracks with radii comparable to those determined from SAXS analysis. The protruding hillocks covering the sample surface detected by AFM are consistent with a lower density of the amorphous material within the ion tracks compared to the surrounding matrix. Simulations using an inelastic thermal-spike model indicate that differences in the thermal conductivity along the z- and x-axis can partially explain the different track radii along these directions.The authors acknowledge the National Nature Science Foundation of China (Grant No. 51272135) and the Australian Research Council for financial support and thank the staff of the ANU Heavy Ion Accelerator Facility for technical support. Part of this research was undertaken on the SAXS/WAXS beamline at the Australian Synchrotron, Victoria, Australia