Morphology of ion irradiation induced nano-porous structures in Ge and Si1-xGex alloys

Crystalline Ge and Si1−xGex alloys (x = 0.83, 0.77) of (100) orientation were implanted with 140 keV Ge− ions at fluences between 5 × 1015 to 3 × 1017 ions/cm2, and at temperatures between 23 °C and 200 °C. The energy deposition of the ions leads to the formation of porous structures consisting of columnar pores separated by narrow sidewalls. Their sizes were characterized with transmission electron microscopy, scanning electron microscopy, and small angle x-ray scattering. We show that the pore radius does not depend significantly on the ion fluence above 5 × 1015 ions/cm2, i.e., when the pores have already developed, yet the pore depth increases from 31 to 516 nm with increasing fluence. The sidewall thickness increases slightly with increasing Si content, while both the pore radius and the sidewall thickness increase at elevated implantation temperaturesWe acknowledge access to NCRIS facilities (ANFF and the Heavy Ion Accelerator Capability) and the Center for Advanced Microscopy, both at the Australian National University. P.K. and M.C.R. thank the Australian Research Council, and Imam Abdulrahman Bin Faisal University for financial support. This research was undertaken on the SAXS/WAXS beamline at the Australian Synchrotron

SAXS investigation of un-etched and etched ion tracks in polycarbonate

Investigation of the ion track morphologies and track etching behaviour in polycarbonate (PC) films was carried out using synchrotron based small-angle X-ray scattering (SAXS) measurements. The tracks were induced by Au ions with kinetic energies of 1.7 and 2.2GeV with applied fluences between 1×1010 and 1×1012 ions/cm2. The average radii of the un-etched tracks were studied as a function of the irradiation fluence, indicating a general ion induced degradation of the polymer, with a simultaneous increase in ion track radius from 2.6±0.002nm to 3.4±0.03nm. Chemical etching of the ion tracks in PC leads to the formation of cylindrical pores. The pore radius increases linearly with etching time. In 3M NaOH at 55°C, a radial etching rate of 9.2nm/min is observedThe research was undertaken on the SAXS/WAXS beamline at the Australian Synchrotron. We acknowledge the DFG (HO 5722/1-1 and SCHL 384-17/1) and the Australian Research Council for financial support

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

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

Ion Tracks in Apatite and Quartz and Their Behaviour with Temperature and Pressure

Interaction between high energetic particles and matter typically leads to structural damage of the irradiated material. Swift heavy ions predominantly interact with a solid by exciting its electrons. The energy transfer from the electrons to the atoms can lead to the formation of so-called ion tracks. These represent damage regions of cylindrical shape, which surround the entire length of the ion trajectory with a radial size of several nanometres. In materials science, ion tracks are utilised for a wide range of applications, from the detection of radiation to the fabrication of nano-pore filters or nano-electronic devices. In geology, similar tracks occur naturally in minerals from the spontaneous fission of radioactive impurities. These fission tracks can partially anneal and shrink in length when exposed to elevated temperatures. In this way, the thermal history of a rock can be determined. The length distributions are routinely studied in the mineral apatite with optical microscopy after the tracks have been dissolved and enlarged by chemical etching. Fission tracks within rocks from thousands of metres below the Earth’s surface have inevitably experienced high pressures of several thousand atmospheres. However, pressure is generally not taken into account when studying formation or annealing rates of fission tracks. The present work shows a detailed investigation of ion tracks in apatite and quartz, specifically a characterisation of their structure, formation, and thermal stability under ambient and high pressure conditions. All tracks were created under controlled conditions by irradiation with ions of energies between 100 MeV to 37.2 GeV in Canberra, Australia, and Darmstadt, Germany. The tracks were subsequently characterised at the Australian Synchrotron in Melbourne through small angle x-ray scattering (SAXS). This allows assessing the track diameter with sub-nanometre precision and without altering their structure. Combining the ability to create tracks under well-controlled conditions with SAXS characterisation, track formation in high-pressure and high-temperature environments was studied. This includes a temperature range between -250 and 640 deg C and elevated pressure conditions up to 4.4 GPa. The size of the track radii showed a positive correlation with temperature as well as pressure. This work further presents an anisotropy for the track radii along different crystallographic axes and a characterisation of the track’s cross-section and longitudinal shape. In situ SAXS was used to monitor the size of the ion tracks, while these were undergoing thermal annealing. For tracks in quartz, an anisotropic annealing behaviour was found, depending on the direction of the tracks within the crystal lattice. To study thermal track annealing at high pressures, apatite samples were annealed in heatable diamond anvil cells. An increase in annealing rate was demonstrated and attributed to the high-pressure environment. The effects of pressure on track annealing were demonstrated to be negligible when extrapolated to geological values. Thus, the present results confirm the validity of current fission track annealing models. Moreover, the present findings contribute to the field of radiation materials under extreme conditions and the theoretical modelling of such effects

Characterization of ion track morphology formed by swift heavy ion irradiation in silicon oxynitride films

Amorphous silicon oxynitride (SiOxNy) possess interesting optical and mechanical properties. Here, we present direct evidence for the formation of ion tracks in 1 μm thick silicon oxynitride of different stoichiometries. The tracks were created by irradiation with 185 MeV Au13+ ions. The samples were studied using spectral reflectometry and Rutherford backscattering spectrometry (RBS), with the track morphology characterised by means of small angle X-ray scattering (SAXS). The radial density of the ion tracks resembles a core-shell structure with a typical radius of ∼ 1.8 + 2.4 nm in the case of Si3N4 and 2.3 + 3.2 nm for SiO2

Structure, morphology and annealing behavior of ion tracks in polycarbonate

Ion tracks created in polycarbonate foils by irradiation with 2.2 GeV Au ions were characterized using a combination of small-angle x-ray and neutron scattering (SAXS/SANS) and Fourier transform infrared spectroscopy (FTIR). The ion tracks were found to consist of a cylindrical damage core with a radius of ∼2.5 ± 0.2 nm and a relative density approximately 5% below that of the pristine polycarbonate. Upon exposure to thermal annealing between 100 and 200 °C, the tracks were observed to double in size. Simultaneously, this led to a recovery in the density of the ion track, reaching a value just below that of the pristine polymer. A mechanism is proposed that explains this behavior by diffusion of radiolysis products/material flow into the under-dense track core from the surrounding region. Treatment of the tracks with UV radiation has shown no significant change in the track structure and size

Composition and orientation dependent annealing of ion tracks in apatite - Implications for fission track thermochronology

The annealing behaviour of swift heavy-ion tracks in apatite from different origins is studied as a function of their crystallographic orientation and the mineral composition. The tracks were generated by irradiating the apatite samples with 2.3 GeV Bi ions, which have a comparable rate of energy loss to fission tracks in this mineral. The track radius was investigated using synchrotron-based small-angle x-ray scattering (SAXS) combined with ex situ annealing. Results indicate that tracks parallel to the c-axis are initially larger and anneal slower than those perpendicular to the c-axis. Natural variation in the mineral composition shows stronger annealing resistance of ion tracks with higher chlorine content. The SAXS results are consistent with previous studies on etched tracks and provide evidence that the orientation and composition effects are directly linked to the property of the un-etched track and not to preferential etchability. The study helps to connect the empirical studies on etched fission tracks to more fundamental solid-state processes.P.K. acknowledges the Australian Research Council for financial support from the Future Fellowship scheme (FT120100289) and Discovery Project scheme (DP120101312). A.N. would like to acknowledge the Universiti Teknologi Mara (Malaysia) and Ministry of Higher Education (MOHE), Malaysia for financial support

Size characterization of ion tracks in PET and PTFE using SAXS

Ion tracks in polyethylene terephthalate (PET) and polytetrafluoroethylene (PTFE) were created by swift heavy ion irradiation and subsequently characterized using small angle X-ray scattering (SAXS). Due to their reduced density compared to the surrounding matrix, cylindrical geometry, and parallel orientation, ion tracks produce a characteristic scattering pattern which allows quantitative analysis of their radius with high precision. For ion tracks in PET thermal annealing led to a gradual fading with a decrease in density difference yet a simultaneous increase in ion track radius. Such an increase in radius is the direct opposite compared to temperature induced ion track shrinking in inorganic materials, and suggests a very different thermal response of the polymer

The shape of ion tracks in natural apatite

Small angle X-ray scattering measurements were performed on natural apatite of different thickness irradiated with 2.2 GeV Au swift heavy ions. The evolution of the track radius along the full ion track length was estimated by considering the electronic energy loss and the velocity of the ions. The shape of the track is nearly cylindrical, slightly widening with a maximum diameter approximately 30 μm before the ions come to rest, followed by a rapid narrowing towards the end within a cigar-like contour. Measurements of average ion track radii in samples of different thicknesses, i.e. containing different sections of the tracks are in good agreement with the shape estimate