Inelastic Thermal Spike Model Research Articles

Microstructural changes in GaN and AlN under 950 MeV Au swift heavy ion irradiation

The radiation hardness of GaN-based devices is a critical metric for applications in extreme environments. This study investigates the structural changes in GaN and AlN induced by swift heavy ion (SHI) irradiation, characteristic of space radiation environments. A multilayered GaN/AlN structure is exposed to 950 MeV Au ions at fluences of 1×1012 and 8×1012 ions/cm2. Subsequent post-irradiation characterization, including transmission electron microscopy and energy-dispersive x-ray spectroscopy, reveal no apparent amorphization across the entire sample. Notably, significant nanometer-sized cavities are observed in both GaN and AlN. The cavities in GaN exhibit an increase in number density and diameter with increasing SHI irradiation, with the average diameter progressing from 1.80 to 2.10 nm. In contrast, cavities in AlN appear considerably smaller. Molecular dynamics simulations, coupled with the inelastic thermal spike model, reproduce the presence of cavities in GaN and no cavities in the AlN structure. This difference is attributed to the faster heat dissipation and stronger bonding in AlN. Considering the overlapping of ion impacts at high fluences, simulations confirm the enlargement of cavity size in GaN. These findings contribute to a mechanistic understanding of the contrast in ion–matter interactions and induced microstructures between AlN and GaN under extreme ionizing radiation conditions. This disparity could potentially impact electronic performance through the formation of defect traps and interfacial strain fields.

Sputtering and structural modifications induced in silicon dioxide (SiO2) thin films under (10–40 MeV) Auq+heavy ion irradiation

Surface sputtering and structural modifications induced in silicon dioxide thin films (SiO2/Si) deposited on silicon substrates and irradiated by swift (10–40 MeV) heavy Auq+(q = +4, +6, +7, and +9) ions were investigated by grazing‐incidence X‐ray diffraction (GIXRD) spectroscopy, Rutherford backscattering (RBS) spectrometry and time‐of‐flight elastic recoil detection (ToF‐ERDA) technique. The GIXRD analysis of the as‐deposited and irradiated samples revealed increasing structural modifications of the SiO2thin films under Auq+ion impacts with increasing ion‐beam energy. The changes consisted of decreased grain sizes with increased strain accompanied by a phase transformation from crystalline to amorphous films. RBS analysis showed a decrease in the mean stoichiometric (O/Si) ratio from (2.2 ± 0.1) to (1.7 ± 0.1), due to preferential sputtering of oxygen, as the incident ion energy increased. The obtained RBS‐results were then completed by those of ToF‐ERDA analysis technique using a 40 MeV Au9+heavy ion beam. The preferential sputtering yield ratios (YSi/YO) were determined experimentally both versus electronic stopping power and ion fluence. The obtained results were then compared to numerical values derived from the inelastic thermal spike (i‐TS) model, Sigmund's analytical formula and SRIM simulation code. A good agreement was observed between the measured preferential sputtering data and the i‐TS calculated values, when considering both nuclear elastic and electronic inelastic collision mechanisms. Besides, a close correlation is observed between the electronic stopping power dependent measured sputtering yields and the XRD peak intensity degradation per unit fluence. These observations suggest that the same mechanism of MeV heavy ion‐irradiation induced extended atomic disordering, occurs both in the case of structural modifications and surface sputtering. Finally, the obtained experimental results are discussed on the basis of the i‐TS model.

Swift heavy ion irradiation effect on structural, morphological and mechanical properties of Zr70Ni30 metallic glass

Metallic glass films are considered for coating applications in the nuclear field owing to their advantageous performances. However, the response to irradiation remains to be more thoroughly characterized. Zr70Ni30 metallic glass films were irradiated by 0.71MeV/u129Xe23+ ions in the fluence range from 5 × 1012 to 8 × 1013 ions cm−2. The structural, morphological, and mechanical properties were determined using grazing incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and nanoindentation for the as-deposited and irradiated samples. The Xe ion induced surface smoothening, thereby increasing the corrosion resistance. One-dimensional power spectral density of the AFM data of irradiated film demonstrated that the irradiation-induced evolution of the surface morphology could be attributed to a transition between viscous flow and the evaporation-condensation mechanism. The amorphous structure was unaffected after irradiation up to a fluence of 8 × 1013 ions cm−2. Nanoindentation revealed first a softening as the fluence increases up to 4 × 1013 ions cm−2, reflecting the creation of free volume defects. Then the hardness and Young’s modulus slightly increase when reaching 8 × 1013 ions cm−2. Moreover, at a critical dose of 0.008 dpa, the hardness is found to increase. Moreover, the calculation of the inelastic thermal spike model reveals the formation of the track with a radius of 7 nm.

Theoretical Study of Intermixing in Au/Si System under Swift Heavy Ion Irradiation

Abstract: The behavior of the metallic multilayer Au100Å/Si100Å/Si under swift heavy ion irradiation has been studied within the inelastic thermal spike model. Gold has been chosen due to its insensitivity to irradiation. The heat transport in the electronic and lattice subsystem has been simulated using a three-dimensional numerical code that includes the energy transfer between the layers in a direction perpendicular to layer surfaces. The simulations have been done for four kinds of ions Pb, Xe, Kr, and Ar, at a specific energy of 3Mev/amu in order to study the influence of the electronic stopping power on the intermixing process. The results show that for Pb, Xe, and Kr, intermixing at the interface of Au/Si has been obtained. However, no mixing has been observed with Ar. Furthermore, the value of the interdiffusion coefficient for Au has been estimated to be approximately 11x10-4 cm2 s-1, which is characteristic of the liquid phase and, thus, supports the thermal spike model of mixing. For comparison, similar thermal spike simulations have been applied to Ti100Å/Si100Å/Si under the same irradiation conditions. We have found that Ti, which is a sensitive material, exhibits considerable intermixing with Si during Pb, Xe, and Kr irradiation. Whereas, a weak intermixing has been found after Ar irradiation; this is completely different from what has been observed in the Au/Si system. Keywords: Irradiation, Swift heavy ions, Thermal spike model, Ion beam mixing. PACS: 61.80.Az, 61.80.Jh, 61.80.LJ.

Study on structural properties of swift heavy ion induced damage in Al2O3

Polycrystalline α-Al2O3 is irradiated using 100 MeV Au ion, with fluences range extended from 1 × 1012 to 1 × 1014 ions/cm2. The objective of this work is to study the impact of swift heavy ion (SHI) on structural and morphological properties of α-Al2O3 and confirm the predicted results with the help of thermal spike (TS) model. XRD result reveals that there is a decrease in peak intensities with an increase in ion fluence. The reduction of peak intensity indicates the increased disorder or defect formation in α-Al2O3 due to SHI irradiation. Further, PL results also corroborated with the XRD outcome. Information on damage formation and molten track radius is extracted from the XRD data, and the molten track radius is obtained to be ∼2.42 ± 0.13 nm. Morphological changes due to SHI irradiation are studied using FESEM and AFM techniques and reveal the increase of surface roughness with the SHI fluences. Furthermore, the radius of latent track formation and radiation-induced lattice temperature spike are estimated for SHI irradiated Al2O3 using three cases; elastic TS model (only Sn), inelastic TS model (only Se), and unified TS model (Sn + Se). The numerically calculated latent track considering the combined contribution of Sn and Se in the unified TS model is around 2.6 nm, which is in good agreement with the experimental determination. The present study investigates the overall performance of structural properties of Al2O3 for SHI irradiation and explains the radiation tolerance of ceramic for corresponding ion fluence.

Defect evolution under intense electronic energy deposition in uranium dioxide

The coupled effects of nuclear and electronic energy losses were investigated in uranium dioxide (UO2). Single and sequential ion irradiations were carried out with 92 MeV Xe ions and 0.9 MeV I ions. Raman spectroscopy and X-ray diffraction analyses were combined with the inelastic thermal spike (iTS) model to investigate the effect of electronic ionizations on the ballistic damage. It appears that the high-energy ions induce a significant change in the defect distribution with an amplitude that depends on the level of pre-existing disorder. This modification essentially results in an acceleration of the transformation from the dislocation loops to the dislocation lines, a process that is accompanied by a stress relaxation. Surprisingly, with the fluence increase of 92 MeV Xe ions, the stress starts to increase again, highlighting a possible synergetic effect between the pre-existing defects and those generated by the 92 MeV Xe ions irradiation.

Applying the Inelastic Thermal Spike Model to the Investigation of Damage Induced by High‐Energy Ions in Polymers

AbstractThis work reports on damage production in polymers by high‐energy ions within the framework of the inelastic thermal spike model (i‐TS). The model is used to describe the effective size of the damaged region around the ion path (the track size) in amorphous poly(methyl methacrylate) (PMMA) and the semicrystalline poly(p‐phenylene sulphide) (PPS), poly(ethylene terephthalate) (PET), and poly(vinylidene difluoride) (PVDF). Track size calculations are compared to experimental data deduced from measurements of crater size, bond‐breaking cross‐sections, changes in crystallinity and electron density, track etching, and electrical depolarization. The use of data obtained from distinct types of damage provides a broad platform to test the applicability of the model to polymers. This work shows that the i‐TS correctly describes the dependence of the track size on energy loss obtained from most experimental probes, when the activation energy of thermal decomposition of the polymers is used as the criterion of track formation, using an electron–phonon mean free path of ≈3 nm. As damage is not uniform across the ion track radial dimension, there are fine variations in the experimental damage radii that can only be accounted for by using multiple activation processes. Amorphization radii of the semicrystalline polymers are not directly correlated to melting induced by the ions.

Thermal Spike Responses and Structure Evolutions in Lithium Niobate on Insulator (LNOI) under Swift Ion Irradiation

Irradiating solid materials with energetic ions are extensively used to explore the evolution of structural damage and specific properties in structural and functional materials under natural and artificial radiation environments. Lithium niobate on insulator (LNOI) technology is revolutionizing the lithium niobate industry and has been widely applied in various fields of photonics, electronics, optoelectronics, etc. Based on 30 MeV 35Cl and 40Ar ion irradiation, thermal spike responses and microstructure evolution of LNOI under the action of extreme electronic energy loss are discussed in detail. Combining experimental transmission electron microscopy characterizations with numerical calculations of the inelastic thermal spike model, discontinuous and continuous tracks with a lattice disorder structure in the crystalline LiNbO3 layer and recrystallization in the amorphous SiO2 layer are confirmed, and the ionization process via energetic ion irradiation is demonstrated to inherently connect energy exchange and temperature evolution processes in the electron and lattice subsystems of LNOI. According to Rutherford backscattering/channeling spectrometry and the direct impact model, the calculated track damage cross–section is further verified, coinciding with the experimental observations, and the LiNbO3 layer with a thickness of several hundred nanometers presents track damage behavior similar to that of bulk LiNbO3. Systematic research into the damage responses of LNOI is conducive to better understanding and predicting radiation effects in multilayer thin film materials under extreme radiation environments, as well as to designing novel multifunctional devices.

Electronic energy loss and ion velocity correlation effects in track production in swift-ion-irradiated LiNbO3: A quantitative assessment between structural damage morphology and energy deposition

• Essential factors including electronic energy loss and ion velocity co-affect latent track damage. • Damage morphologies from spherical defects to discontinuous and continuous tracks are confirmed. • Atomic energy deposition and temperature evolution are determined by inelastic thermal spike model. • A quantitative relationship between ion irradiation condition and track damage response is proposed. • The work provides a deeper insight for understanding ion-solid interactions and damage behaviors. The primary motivation for studying how irradiation modifies the structures and properties of solid materials involves the understanding of undesirable phenomena, including irradiation-induced degradation of components in nuclear reactors and space exploration, and beneficial applications, including material performance tailoring through ion beam modification and defect engineering. In this work, the formation mechanism of latent tracks with different damage morphologies in LiNbO 3 crystals under 0.09–6.17 MeV/u ion irradiation with an electronic energy loss from 2.6–13.2 keV/nm is analyzed by experimental characterizations and numerical calculations. Irradiation-induced damage is preliminarily evaluated via the prism coupling technique to analyze the correlation between the dark-mode spectra and energy loss profiles of irradiated regions. Under the irradiation conditions of different ion velocities and electronic energy losses, different damage morphologies, from individual spherical defects to discontinuous and continuous tracks, are experimentally characterized. During ion penetration process, the ion velocity determines the spatiotemporal distribution of deposited irradiation energy induced by electronic energy loss, meaning that the two essential factors including electronic energy loss and ion velocity co-affect the track damage. The inelastic thermal spike model is used to numerically calculate the spatiotemporal evolutions of energy deposition and the corresponding atomic temperature under different irradiation conditions, and a quantitative relationship is proposed by comparison with corresponding experimentally observed track damage morphologies. The obtained quantitative relationship between irradiation conditions and track damage provides deep insight and guidance for understanding the damage behavior of crystal materials in extreme radiation environments and selecting irradiation parameters, including ion species and energies, for ion beam technique application in atomic-level defect manipulation, material modification, and micro/nanofabrication.

Mechanistic insights into ion-beam induced reduction of graphene oxide: An experimental and theoretical study

Interest in graphene oxide (GO) due to its controllable and adjustable properties has been increasing, especially in the field of electronic and electrochemical charge storage devices. Hence, the modification of surface chemistry and structure of GO can be outlined as crucial for achieving the preferable properties. In this study, we have investigated the influence of 15 keV proton-beam irradiation on GO structure and surface chemistry. The results obtained by Raman spectroscopy, Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were complemented with theoretical ones, obtained by using density functional theory (DFT), semi-empirical (SE) calculations and inelastic thermal spike (iTS) model. The FTIR and XPS results showed that proton irradiation partially reduces the GO with the preferential removal of the alkoxy and epoxy groups. Also, we identified a clear linear relation between the decresase of oxygen content and the decrease of ID/IG ratio i.e. increasing disorder of GO structure. The SE and DFT calculations highlighted a reduction of GO as a single- or multi-step process depending on the type of basal-plane or edge oxygen group. Dynamic SE calculations revealed that for kinetic energy of hydrogen below 1.5 eV the reduction is chemically driven, while at energies higher than 20 eV, the reduction of GO is a result of physical processes. iTS results showed that increase of temperature might contribute to reduction of GO via desorption of epoxy and alcoxy groups, as the least thermally stable groups (T ∼200 °C). The results of this work emphasize the capabilities ion beam irradiation for gradual modification of surface chemistry and structural properties of GO by providing more information about the mechanisms of hydrogen interaction with individual groups, interplay between defect creation, oxygen content and accompaning effects of ion energy loss processes.

Investigation of radiation damage using thermal spike model for SHI irradiation on Al2O3

The material exposed to energetic radiation may change its properties and performance. Ion beam irradiation is an established method to investigate radiation damage in materials. In the present study, SRIM code is employed as a tool to determine the electronic and nuclear energy losses and displacement per atom (DPA) associated with the damage induced in Al2O3 using 100 MeV Au ion. We have further studied the creation of 100 MeV Au ion induced molten zone along the ion track in Al2O3 in the framework of the thermal spike (TS) model. Using the in-elastic thermal spike model, elastic thermal spike model, and unified thermal spike model, the evolution of lattice temperature and latent track radius as a function of depth of Al2O3 for 100 MeV Au ion irradiation are investigated. The current results demonstrate that the latent track radius shows a U-shaped variation based on the combined effect of electronic stopping power and nuclear stopping power. In order to corroborate these results, an additional irradiation experiment was performed using swift heavy ion (SHI), 100 MeV Au ions with fluence 1×1014 ions/cm2 for Al2O3. To investigate the structural properties, surface morphology and to identify the defects in the samples, pristine and irradiated Al2O3 samples were characterized by Grazing Incident X-Ray Diffraction (GIXRD), Atomic Force Microscopy (AFM) and Photoluminescence Spectroscopy (PL). AFM study shows the increase in roughness after SHI irradiation. A decrease in intensity of PL spectra upon SHI irradiation indicates the formation of new defects and disordered structures in the material, which is quite in agreement with the theoretical results.

A spatial and temporal characterisation of single proton acoustic waves in proton beam cancer therapy.

An in vivo range verification technology for proton beam cancer therapy, preferably in real-time and with submillimeter resolution, is desired to reduce the present uncertainty in dose localization. Acoustical imaging technologies exploiting possible local interactions between protons and microbubbles or nanodroplets might be an interesting option. Unfortunately, a theoretical model capable of characterising the acoustical field generated by an individual proton on nanometer and micrometer scales is still missing. In this work, such a model is presented. The proton acoustic field is generated by the adiabatic expansion of a region that is locally heated by a passing proton. To model the proton heat deposition, secondary electron production due to protons has been quantified using a semi-empirical model based on Rutherford's scattering theory, which reproduces experimentally obtained electronic stopping power values for protons in water within 10% over the full energy range. The electrons transfer energy into heat via electron-phonon coupling to atoms along the proton track. The resulting temperature increase is calculated using an inelastic thermal spike model. Heat deposition can be regarded as instantaneous, thus, stress confinement is ensured and acoustical initial conditions are set. The resulting thermoacoustic field in the nanometer and micrometer range from the single proton track is computed by solving the thermoacoustic wave equation using k-space Green's functions, yielding the characteristic amplitudes and frequencies present in the acoustic signal generated by a single proton in an aqueous medium. Wavefield expansion and asymptotic approximations are used to extend the spatial and temporal ranges of the proton acoustic field.

Electron–phonon coupling factor and electron heat capacity of 6H-SiC

ABSTRACT For high-energy single ion events, the relationship between electronic energy loss mechanism and atomic processes is generally described by the inelastic thermal spike model. However, the parameters required for the model are not accurately known and are often estimated from a free electron gas model. To ensure this model is more reliable and predictive, a more accurate calculation for the parameters should be taken. In this paper, the temperature dependence of the electronic heat capacity and electron–phonon coupling factor (e-ph) has been calculated, using density functional theory (DFT). The calculation results demonstrate that the effect of electron thermal excitation on the thermodynamic parameters is sensitive to the bandgap, and these parameters vary immensely with the electron temperature. Besides, to verify the accuracy of obtained parameters, both the swift heavy ions (SHI) irradiation in crystalline 6H-SiC and amorphous 6H-SiC are simulated, using the inelastic thermal spike model. And the results are more consistent with the experiment conclusion, for the obtained parameters by DFT. Hence, the calculated temperature-dependent parameters are more suitable for the inelastic thermal spike model.

Interface modification of Fe/Cr/Al magnetic multilayer by swift heavy ion irradiation

Interface mixing in [Fe/Cr/Al]x10 multilayer is studied under 120 MeV Ag9+swift heavy ions (SHIs) irradiation. The multilayers with different thicknesses were deposited using electron beam evaporation technique. The SHIs induced modifications in structural and magnetic properties were examined with X-ray reflectivity (XRR), magneto-optic Kerr effect (MOKE), and X-ray absorption fine structure (XAFS) to reveal interface diffusivity, including variation in magnetic coercivity, in-plane anisotropy, and local structure. The height of 1st order Bragg peak of XRR is used to determine the diffusion length as a function of ion fluence, and it is evident that the lower thickness of [Fe/Cr/Al]x10 multilayer possesses higher interface mixing as compared to samples with higher thickness. MOKE results confirm that both multilayers are soft magnetic in nature and show different behavior of in-plane anisotropy. With the SHIs irradiation, coercivity exhibits opposite trends for different thicknesses of Fe/Cr/Al multilayers due to different interface mixing. Fe K-edge XAFS is used for quantitative analysis of the Fe-Cr and Fe-Al phases as a function of multilayer thickness and ion fluence. The inelastic thermal spike (i-TS) model with size effect is used to explain the observed thickness-dependent intermixing due to the SHIs irradiation. The lattice temperature evaluation calculated by i-TS model shows longer spike duration in thinner film resulting in higher mixing.

Experimental study and thermal spike modeling of sputtering in SiO2 thin films under MeV Auq+ heavy ion irradiation

The sputtering of silicon dioxide (SiO2/Si) thin films deposited onto silicon substrates and irradiated by swift Auq+ heavy ions (q = +4 to +9) has been investigated both by experiment and via numerical modeling by varying the kinetic energy from 10 to 40 MeV. The induced sputtering yields were determined experimentally via the Rutherford backscattering spectrometry (RBS) technique using a 2‐MeV He+ ion beam. The obtained experimental results were first plotted versus the target electronic stopping power together with previous data available for the same projectile‐target system at high kinetic energies, indicating increased sputtering yields with increasing electronic energy loss. Then, the whole data were compared with numerical sputtering yield values derived both from the inelastic thermal spike model and the SRIM‐2013 simulation code by including, respectively, nonlinear elastic spikes and linear elastic collision cascades. A good agreement was observed between the measured sputtering yield data and i‐TS predicted values over higher incident energies used by using refined parameters of the ion slowing down with reduced thermophysical properties of the SiO2 thin film. Finally, the synergy between electronic and nuclear energy loss processes inducing sputtering at low incident energies was discussed through the comparison between experimental and numerical yield data.

Surface erosion of BaF2 thin films under SHI irradiation: Angular distribution and role of different substrates

In the present report, the surface erosion of the thin films of barium fluoride (BaF2) deposited on different substrates (Glass, Silicon, and Aluminum) using the electron beam evaporation method, has been investigated under swift heavy ions irradiation employing experimental and theoretical aspects. The experiments have been carried out at room temperature using normally incident 100 MeV Au+28 ions. Rutherford backscattering spectrometry has been employed to estimate the sputtering yield and angular distribution of sputtering yield has been obtained using the unique catcher technique approach. The variation of sputtering yield at different angles shows an isotropic distribution superimposed with enhanced sputtering at surface normal. The sputtering studies in the thin films on different substrates show that the maximum sputtering takes place for glass (insulator) substrate while minimum sputtering occurs for the aluminum (metal) substrate. Simulations based on the inelastic thermal spike model have been performed to compare the observed experimental findings. The temperature spike generated in Al will smear out more efficiently and quickly because of its high thermal conductivity as compared to Si and glass substrates resulting in less contribution to the temperature spike generated in the film and thus causing lower sputtering yield for Al substrate.

Structural modifications of boron carbide irradiated by swift heavy ions

Boron carbide (B4C) behavior under irradiation is widely studied in order to predict the lifetime of this material in future (Generation IV) nuclear fission reactors. This paper is focused on the effects of high electronic stopping powers (Se) on B4C structure modifications. Sintered B4C samples were irradiated at room temperature with swift heavy ions (between 0.5 and 3 MeV·u − 1) corresponding to Se values in the 4.1 to 15.4 keV·nm−1 range at the sample surface. In order to investigate the structural changes as a function of depth, transmission electron microscopy and Raman mapping were performed on the irradiated samples along the path of the incident ions. For the highest Se values, damage results in the creation of large hillocks at the sample surface along with the amorphization of the bulk. These results are explained, in the frame of the inelastic thermal spike model, by local melting in latent tracks that are created only when irradiations are performed above a Se threshold evaluated at around 9 keV nm−1.

Intense ionizing irradiation-induced atomic movement toward recrystallization in 4H-SiC

An ultrafast thermal spike within a time interval of a few pico-seconds generated by intense ionizing energy deposited using 100 MeV Ag ions is utilized to study the atomistic details of damage recovery in 4H-SiC. Sequential single ion irradiations were performed using 300 keV Ar and 100 MeV Ag in ⟨0001⟩ 4H-SiC to invoke swift heavy ion (SHI) beam induced epitaxial recrystallization in samples with different degrees of pre-damaged conditions. SHI irradiation was carried out at both room temperature and a low temperature of ∼80K. Low-temperature irradiation was carried out to arrest thermal diffusion of defects and to isolate ionization-induced defect migration in 4H-SiC. Insights into the thermal spike generated by ionizing events in crystalline and amorphous regions at both the temperatures predict a SiC response to SHI. The results emphasize the role of different degrees of pre-damage induced physico-chemical conditions and irradiation temperatures against SHI-induced recrystallization as evaluated by Rutherford backscattering/channeling, Raman spectroscopy, and hard x-ray photoelectron spectroscopy. Understanding the dependence of ion-beam damage accumulation and their recovery on the inelastic to elastic energy loss ratio is important for the performance prediction of SiC intended for extreme environments such as space, defense, and nuclear radiation. We report substantial damage recovery even at a near liquid nitrogen temperature of ∼80K. The recovery gets impeded mainly by the formation of complex defects having homonuclear bonds. The results are explained in the framework of the inelastic thermal spike model, and the role of phonon in the damage recovery process is emphasized.

Latent Tracks in Ion-Irradiated LiTaO3 Crystals: Damage Morphology Characterization and Thermal Spike Analysis

Systematic research on the response of crystal materials to the deposition of irradiation energy to electrons and atomic nuclei has attracted considerable attention since it is fundamental to understanding the behavior of various materials in natural and manmade radiation environments. This work examines and compares track formation in LiTaO3 induced by separate and combined effects of electronic excitation and nuclear collision. Under 0.71–6.17 MeV/u ion irradiation with electronic energy loss ranging from 6.0 to 13.8 keV/nm, the track damage morphologies evolve from discontinuous to continuous cylindrical zone. Based on the irradiation energy deposited via electronic energy loss, the subsequently induced energy exchange and temperature evolution processes in electron and lattice subsystems are calculated through the inelastic thermal spike model, demonstrating the formation of track damage and relevant thresholds of lattice energy and temperature. Combined with a disorder accumulation model, the damage accumulation in LiTaO3 produced by nuclear energy loss is also experimentally determined. The damage characterizations and inelastic thermal spike calculations further demonstrate that compared to damage-free LiTaO3, nuclear-collision-damaged LiTaO3 presents a more intense thermal spike response to electronic energy loss owing to the decrease in thermal conductivity and increase in electron–phonon coupling, which further enhance track damage.

Ion shaping of single-layer Au nanoparticles in amorphous silicon dioxide, in silicon nitride, and at their interface

We present the shape transformation of a single layer of Au nanoparticles (NPs) when embedded in, and at the interface of, amorphous $\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ and $\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$ ($\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ and $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$) thin films upon irradiation with 185-MeV Au ions to fluences ranging from 0.3 to $30\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$. Transmission electron microscopy (TEM) and high angular annular dark field microscopy were used to study the ion-shaping process. The former allows us to follow the overall change in geometry, size, and structure, while the latter reveals information about the relative position with respect to the interface. For Au NPs embedded in a single material, a lower elongation rate for $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ was found in comparison to $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$. When at the interface of the two materials, TEM reveals a preferential elongation towards $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$. The latter demonstrates the use of $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ for confining the ion-shaping process within an intermediate $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$ layer. The simulation of the temperature evolution during a single-ion impact was used to understand the difference in elongation rates between $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{N}}_{\mathrm{x}}$ and $\mathrm{a}\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{\mathrm{x}}$, as well as the asymmetric behavior when located at the interface using the three-dimensional inelastic thermal spike model with bulk thermophysical properties. The calculations show good agreement with the experimental observations and reveal a correlation between the thermal profile and the resulting NP geometry.