Swift Heavy Ion Irradiation Research Articles

Insights into nanoparticle shape transformation by energetic ions

Shape modification of embedded nanoparticles can be achieved by means of swift heavy ion irradiation. During irradiation, the particles elongate and align with the direction of the ion beam, presumably due to nanometer-scale phase transitions induced by individual ion impacts. However, the details of this transformation are not fully understood. The shape of metal nanoparticles embedded in dielectric matrices defines the non-linear optical properties of the composite material. Therefore, understanding the transformation process better is beneficial for producing materials with the desired optical properties. We study the elongation mechanism of gold nanoparticles using atomistic simulations. Here we focus on long-timescale processes and adhesion between the nanoparticle and the matrix. Without the necessity of ad-hoc assumptions used earlier, our simulations show that, due to adhesion with the oxide, the nanoparticles can grow in aspect ratio while in the molten state even after silicon dioxide solidifies. Moreover, they demonstrate the active role of the matrix: Only explicit simulations of ion impacts around the embedded nanoparticle provide the mechanism for continuous elongation up to experimental values of aspect ratio. Experimental transmission electron microscopy micrographs of nanoparticles after high-fluence irradiation support the simulations. The elongated nanoparticles in experiments and their interface structures with silica, as characterized by the micrographs, are consistent with the simulations. These findings bring ion beam technology forward as a precise tool for shaping embedded nanostructures for various optical applications.

The SHI irradiation induced transition to negative dielectric constant phase in K2Bi4Ti4WO18

In present communication, a new Aurivillius family compound K2Bi4Ti4WO18 was synthesized, and the impact of swift heavy ion (SHI), Ni+11 irradiation on its surface and dielectric properties has been studied in detail. The phase formation in this complex oxide, and crystallization to B2cb symmetry was confirmed by the X-ray diffraction. However, post irradiation the XRD, SEM and AFM studies shows the surface amorphization, in agreement with the theoretical calculations. Furthermore, the effect of irradiation was also observed in the bulk dielectric properties as the system transform to a phase with negative dielectric constant above 350 K in the radio frequencies. This transition is in correlation with significant change in other dielectric parameters such enhancement in AC conductivity, a helical Nyquist plot and multiple dielectric relaxations. This conspicuous changes in the dielectric response post irradiation is attributed to the SHI induced defect formation, modification of energy barriers and their consequences on the electronic structure. Thus, current study suggests that the dielectric properties of Aurivillius K2Bi4Ti4WO18 could be tailored by ion irradiation and opens a new possibility of tuning functional properties.

Modelling of nanocrystalline insulators response to swift heavy ion irradiation

We apply a hybrid multiscale model to describe structural damage in nanocrystalline insulators irradiated with swift heavy ions. The approach couples Monte Carlo code TREKIS tracing excitation of the electron ensemble and energy transfer to target atoms with the molecular dynamics simulating the lattice kinetics during its relaxation. We compare response of amorphizable and non-amorphizable nanocrystalline targets to strong perturbations initiated by an ion impact. The recrystallization processes observed in non-amorphizable MgO and Al2O3 strongly affects the grain boundaries that may result in association and enlargement of nanoparticles. Strong material heating and expansion in the track core can form voids near the grain boundaries. In contrast, swift heavy ion passage in the amorphizable sample almost do not affect the grains morphology forming amorphous tracks, similarly to the damage in the bulk.

Enhancement of Luminescence of PET Films after Swift Heavy Ion Irradiation

The novelty of the study is that the ordering that occurs in a PET film under the action of SHI irradiation manifests itself as an increase in the integral intensity of intrinsic luminescence. The Urbach behaviour of the red shift of the absorption edge is used as a baseline for further analysis of experimental optical transmission spectra of PET films irradiated by swift heavy ions (SHI) previously published by the authors. Negative deviations of the experimental spectra from the Urbach baseline in the visible and UV parts of the spectrum are attributed to enhanced by SHI irradiation intrinsic luminescence. The observed dependence of the integral intensity of luminescence of irradiated PET films on the SHI fluence and ion charge provides further confirmation of the presence of SHI-induced ordering of the molecular structure in SHI latent tracks.

120 MeV swift Au9+ ion induced phase transition in ZrO2: monoclinic to tetragonal and cubic to tetragonal structure

This study reports the effect of 120 MeV swift Au9+ ion irradiation on the structures of monoclinic, tetragonal and cubic ZrO2, probed through x-ray diffraction (XRD) and Raman spectroscopy. Three phases of ZrO2 were prepared using the solution combustion method. The tetragonal and cubic phases of ZrO2 were stabilized at room temperature by adding 6% and 10% of yttrium ions, respectively. Both the XRD and Raman results confirm the partial phase transition from monoclinic to tetragonal, which was approximately 74%. Tetragonal ZrO2 is stable under 120 MeV Au9+ ion irradiation. Interestingly, a phase transition from cubic to tetragonal ZrO2 was observed under 120 MeV Au9+ ion irradiation. The roles of transient temperature, defects and strain in the lattice induced by swift heavy ions are discussed. This study reveals the structural stability of different phases of ZrO2 under swift heavy ion irradiation and should be helpful in choosing potential hosts for various applications such as inert fuel matrix inside the core of nuclear reactors, oxygen sensors and accelerators, and radiation shielding.

On the effect of oxygen on the creation of colour centres in swift heavy ion-irradiated AlN

We readdress the nature and creation mechanism of the defects absorbing at 4.7 eV in Swift Heavy Ion (SHI)-irradiated AlN semiconductor. Irradiations are performed in different controlled atmospheres (vacuum, oxygen, helium or argon partial pressure) to investigate the coupled effects of (i) the synergy between electronic excitations (Se) and nuclear collisions (Sn) for point defect creation and (ii) SHI-induced impurity introduction/diffusion into the AlN layer. We found that the synergy, previously reported, between Se and Sn for defect formation must also be related to the presence of oxygen during irradiation. At the same Se, the synergy parameter is indeed increased by up to two orders of magnitude during irradiation under O2 compared to irradiation under vacuum. By SHI irradiation and by a fine-tuning of the irradiation atmosphere, we then control the activation or inhibition of these light-emitted point defects (oxygen-vacancy complexes) which can be used as qubits for applications in quantum computing.

Latent track PET membranes for high-performance Li+/Mg2+ selectivity assisted with trivalent ion

Selective ionic transport in sub-nanometer pores attracts strong interest. It is still limited by the difficulties in large-scale production of uniform membranes with well-defined sub-nanometer pores. The polymer membranes with latent track are excellent candidate materials. However, the Li+/Mg2+ selectivity in latent track polymer membranes is not high. Herein, we optimize the fabrication process and introduce the trivalent coexisting ions to achieve high selectivity. The polyethylene terephthalate membranes are prepared using the sequential steps of swift heavy ion irradiation, UV illumination, and DMF treatment. The DMF extraction can well control the pore diameters ranging from 2.96 to 5.19 Å as a moderate treatment of membranes. It generates high selectivity in latent track membranes. More interestingly, the ionic transport behavior can be significantly regulated by coexisting ions. By optimizing the experimental conditions, the high selectivity of Li+/Mg2+ of 773 can be achieved in the mixture solutions.

Tuning of charge carriers in Bi2Te3 thin films via swift heavy ion irradiation

Tuning of charge carriers in Bi2Te3 thin films via swift heavy ion irradiation

<i>In situ</i> study of light emission from SiO<sub>2</sub> irradiated by 645 MeV Xe<sup>35+</sup> ions

Silicon dioxide (SiO<sub>2</sub>) is an important component of nuclear reactor optical fiber and is also a candidate material for wast solidification. Owing to its special physical and chemical characteristics, it is used in many different technology fields like optics, electronics, energy orspace. Swift heavy ion irradiation can modify the crystal structure and optical property of optical material SiO<sub>2</sub>. Swift heavy ions deposit their energy mainly by inelastic interaction. Highly ionized lattice atoms may be formed along the trajectory, and a fraction of their electrical energy can be converted directly into the kinetic energy of the ions. The irradiation experiment is performed with Xe<sup>q+</sup> ions at the irradiation terminal of the sector-focused cyclotron at heavy-ion research facility in Lanzhou (HIRFL). The on-line spectral measurement experiment is carried out during irradiation. In the darkroom, the UV-visible light emission from the target is focused into optical fiber by a collimating lens, and then is analyzed with the Sp-2558 spectrometer equipped with a 1200 g/mm optical grating blazed at 500 nm. In the present work, SiO<sub>2</sub> single crystals are irradiated with 93–609 MeV Xe<sup>q+</sup> ions with a dose in a range of 1×10<sup>11</sup>–3×10<sup>11</sup> ions/cm<sup>2</sup>. During irradiation, the emission spectra, in a range of 200–800 nm, from SiO<sub>2</sub> irradiated by 93, 245, 425 and 609 MeV Xe<sup>q+</sup> ions, are obtained. Two emission bands centered at 461 and 631 nm are observed. These emission bands are produced by Frenkel exciton radiation de-excitation and their intensities are closely related to the irradiated ion energy and radiation dose. The results show that the light intensity increases with the electron energy loss index increasing. And owing to crystal damage caused by ion irradiation, the intensity of emission spectrum decreases with the augment of irradiation dose. Ion loses its energy throughout the ion track via Sn and Se interacting with target atoms and electrons respectively, and the energy lost by the ion is estimated by using SRIM code. The SRIM simulated ion ranges and recoil atom distribution, target ionization (energy loss to target electrons), damage production in SiO<sub>2</sub> are presented. Based on the energy deposition process, the emission bands related to the crystal structure itself are discussed. It indicates that electron energy loss plays a leading role in the process of light emission. In-situ measurement of the optical emission is of great significance in studying the irradiation modification and can help to understand the process of crystal damage caused by ion irradiation.

Elongation and plasmonic activity of embedded metal nanoparticles following heavy ion irradiation.

Shape modification of embedded nanoparticles by swift heavy ion (SHI) irradiation is an effective way to produce nanostructures with controlled size, shape, and orientation. In this study, randomly oriented gold nanorods embedded in SiO2 are shown to re-orient along the ion beam direction. The degree of orientation depends on the irradiation conditions and the nanorod's initial size. SHI irradiation was also applied to modify spherical metallic nanoparticles embedded in Al2O3. The results showed that they elongate due to the irradiation comparably to those embedded in SiO2. Metallic nanostructures embedded in dielectric matrices can exhibit localized surface plasmon (LSP) modes. The elongated nanoparticles investigated by means of dark-field spectroscopy showed two discrete peaks which correspond to longitudinal and transverse modes.

Influence of swift heavy ion irradiation on bimetallic gold-silver nanoparticles in dielectric matrices and their optical properties

Nanosized gold-silver (AuAg) alloy nanoparticles (NPs) of sizes, 2 nm -25 nm embedded in fused quartz are synthesized using sequential implantation and post annealing at 900℃ for 1 h in Argon environment. The post annealed film is irradiated using swift heavy ions (SHI), 120 MeV Ag ions to investigate the effect of electronic energy deposition, (Se×ϕ), on size, shape and composition of the alloy NPs. Transmission electron microscopy (TEM) analysis of the as- implanted AuAg film reveals the formation of small sized, 1.8 nm-3.5 nm, bimetallic AuAg NPs. Rutherford backscattering spectroscopy (RBS) spectra along with its fitted graph convey the annealing induced out diffusion, mixing and formation of larger sized, 2 nm -25 nm, alloy NPs through Ostwald ripening. SHI irradiation results in deformation in shape from spherical to ellipsoidal alloy NPs with major axis align along the beam direction and the average aspect ratio is about 1.20. RBS analysis results convey the formation of Ag enriched alloy NPs after irradiation. The smaller nanoparticles are found dissolved while larger ones grow and elongate along the ion beam direction. SPR properties are modified by SHI induced processes of melting, sputtering and re-precipitation in the ion tracks.The un-irradiated film exhibits a single intense SPR peak at 536 nm, while the irradiated film gives rise two SPR peaks: Ist, a blue shifted SPR peak from 536 nm to 515 nm with significantly reduced intensity and much wider FWHM; and, IInd, a small SPR peak around 460 nm. SHI induced modifications on the NPs are understood in terms of thermal spike model. The detailed analysis shows that SHI can be used as a tool to tailor size, shape and composition of the bimetallic AuAg alloy NPs and their SPR properties.

Investigation of heavy ion irradiation effects on a charge trapping memory capacitor by C–V measurement

Heavy ion irradiation effects on charge trapping memory (CTM) capacitors with TiN/Al2O3/HfO2/Al2O3/HfO2/SiO2/p-Si structure have been investigated. The ion-induced interface charges and oxide trap charges were calculated and analyzed by capacitance–voltage (C–V) characteristics. The C–V curves shift towards the negative direction after swift heavy ion irradiation, due to the net positive charges accumulating in the trapping layer. The memory window decreases with the increase of ion fluence at high voltage, which results from heavy ion-induced structural damage in the blocking layer. The mechanism of heavy ion irradiation effects on CTM capacitors is discussed in detail with energy band diagrams. The results may help to better understand the physical mechanism of heavy ion-induced degradation of CTM capacitors.

Formation of light-emitting defects in silicon by swift heavy ion irradiation and subsequent annealing

High-resistivity floating-zone silicon (FZ-Si) and n-type (4.5 Ohm·cm) Czochralski silicon (CZ-Si) wafers were irradiated at room temperature with 167 MeV Xe ions to fluences ranging from 5·1010 to 5·1011 cm−2. Temperature dependent photoluminescence (PL) measurements were performed to characterize the as-implanted and annealed silicon wafers. It was found that irradiation with swift heavy ions (SHI) leads to the formation of light-emitting defects in both types of silicon wafers. Low-temperature annealing (400 °C) leads to a significant increase of the photoluminescence intensity. In addition, the photoluminescence decreases for increasing measurement temperatures and eventually quenching is observed for temperatures larger than 80 K. The type of silicon wafer (FZ or CZ) does not significantly influence the defect-related light-emitting properties. This implies that low fluence SHI irradiation is a promising method for creation of light-emitting defects in silicon.

Effects of swift heavy ion irradiation on the InAs and Zn-based nanoparticles ion-beam synthesized in silica

Till now, a shape elongation effect under swift heavy ions (SHI) irradiation was observed predominantly for metal nanoparticles (NPs). We report this effect for InAs and Zn(core)/ZnO(shell) NPs embedded in silica matrix. In case of InAs NPs, SHI irradiation results in the formation of nanorods. A diversity of elongated features is observed for Zn-based NPs: chains of small ZnO clusters, elongated (Zn)core/(ZnO)shell structures and drop-like elongated Zn particles. The intense silica sputtering due to electronic excitations has been found for the “SiO2 + Zn-based NPs” composite. Photoluminescence (PL) spectroscopy reveals an emission in the visible range for both nanocomposites before SHI irradiation. This emission is attributed to the oxygen excess-related defect (NBOHC) as well as to the oxygen deficiency-related centres created in silica matrix during the implantation of cluster-forming ions (In + As or Zn). An intensive band in the spectral region of 2.8–3.1 eV is observed in PL spectrum of annealed “SiO2 + InAs NPs” composite. SHI irradiation results in its quenching and formation of an asymmetrical band centred at 1.9 eV. In case of “SiO2 + Zn-based NPs”, SHIs irradiation results in substantial increase of PL in orange spectral range.

Single graphene nanopore for biomimetic ion channel via tunably voltage-modulated ion transport

Biological ion channels possess a remarkable ability to selectively modulate ionic flux and play an irreplaceable role in many life processes. The modulation of ion transport through nanopores or nanochannels has received considerable attention due to the similar transport mechanism of biological ionic channels. Graphene has become the most promising membrane material because of its good permeability, mechanical strength and chemical stability. Based on its excellent electrical conductivity, it is possible to apply the gate voltage on the graphene to modulate ion transport through the graphene nanopore. Herein, the graphene/polyethylene terephthalate (G/PET) composite nanochannel was prepared by swift heavy ion irradiation, and gate voltage was applied on it. The results exhibited that the transport of cations (K+, Na+, Li+, Mg2+) can be electrostatically modulated by the applied gate voltage. The G/PET nanochannel imitated the K+ ions biological nanochannel and impeded the transport of divalent ions with K+/ions selectivity up to ∼4.2. Furthermore, it was confirmed that the applied gate voltage can change the electric potential around the graphene nanopore and the surface of the graphene through simulation. Therefore, the changed potential caused the accumulation and depletion of anions and cations near the graphene nanopore and has the ability to modulate cations transport through the graphene nanopore. This work demonstrated that the graphene nanopore with applied gate voltage can effectively modulate ion transport and exhibit significant selectivity of monovalent and divalent cations.

Structure Formation and Regulation of Au Nanoparticles in LiTaO3 by Ion Beam and Thermal Annealing Techniques.

The size uniformity and spatial dispersion of nanoparticles (NPs) formed by ion implantation must be further improved due to the characteristics of the ion implantation method. Therefore, specific swift heavy ion irradiation and thermal annealing are combined in this work to regulate the size and spatial distributions of embedded Au NPs formed within LiTaO3 crystals. Experimental results show that small NPs migrate to deeper depths induced by 656 MeV Xe35+ ion irradiation. During thermal annealing, the growth of large Au NPs is limited due to the reductions in the number of small Au NPs, and the migrated Au NPs aggregate at deeper depths, resulting in a more uniform size distribution and an increased spatial distribution of Au NPs. The present work presents a novel method to modify the size and spatial distributions of embedded NPs.

Effects of swift heavy ion irradiation and annealing on the microstructure and recrystallizationof SiC pre-implanted with Sr ions

Polycrystalline SiC wafers were implanted with 360 keV strontium (Sr) ions at room temperature (RT)to a fluence of 2 × 1016 cm−2. Some of the implanted samples were irradiated with xenon (Xe) ions of 167 MeV to a fluence of 3.4 × 1014 cm−2 and 8.4 × 1014 cm−2at RT. The as-implanted and implanted then irradiated samples were vacuum annealed (isochronally) at temperatures ranging from 1,100 to 1,400°C in steps of 100°C for 5 h. Annealing induced modification of the microstructure of the implanted and swift heavy ions (SHIs) irradiated SiC was studied by Raman spectroscopy, scanning electron microscopy (SEM) and backscattering spectrometry (RBS). Sr ions bombardment caused formation of an amorphous layer in SiC, while irradiation by Xe ions led to partial recrystallization of the amorphized layer. After annealing at 1,100°C, the samples with low Sr retained ratio showed full recrystallization, while the samples with high Sr retained ratio showed poor recrystallization. This suggests that the presence of Sr within the implanted region inhibited the recrystallization of SiC. Annealing of the as-implanted samples at temperatures from 1,100°C and 1,200°Cresulted in larger average crystal size compared to the SHIsirradiated samples annealed in the same temperature range. The difference in the average crystal sizes between the as-implanted and SHIs irradiated samples was due to the differences in the nucleation rate per amorphous area in the two samples. Ramanspectroscopy results showedthat the intensity of the LO mode of SiC increases with increasing crystal size. However, several factors such as pores and defects in SiC play a role in the decrease of the LO mode intensity of SiC (even if the average crystal size is large).

Swift heavy ion irradiation of thymine at cryogenic temperature

Thymine (C5H6N2O2) is a basic N-heterocyclic nucleobase in all known organisms, and this molecule is also found in meteoritic materials. This study aims to investigate thymine's physical and chemical modifications under ion irradiation in cryogenic conditions. Space radiation was simulated by exposing thymine at 27 K to 230 MeV 48Ca10+ ions. Fourier transform infrared spectroscopy (FTIR) was employed to monitor the degradation of a 2.8 μm thick sample film under irradiation. From the intensity decrease of the infrared absorptions as a function of ion fluence, the destruction cross-section (σ), required to dissociate or eject a thymine molecule, is deduced by an exponential function. The physical and chemical modifications induced by energetic projectiles can be related to the electronic stopping power Se as σ=Se/D0, where D0=9.6±0.4 eV/molecule is the effective mean dose needed to destroy the thymine molecule at 27 K. Also, new molecular species formed under irradiation are observed and, based on infrared spectra, identified as CN−, OCN−, HCNO, and CO.

Electrical Characteristics and Defect Dynamics Induced by Swift Heavy Ion Irradiation in Pt/PtO/-Ga₂O₃ Vertical Schottky Barrier Diodes

In situ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> measurements were performed on Pt/PtOx/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga2O3 vertical Schottky barrier diodes (SBD) during 120 MeV Au9+ swift heavy ion (SHI) irradiation in a fluence range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10^{{10}}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 10^{{12}}$ </tex-math></inline-formula> ions/cm2. The reverse leakage current density increased from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.21\times 10^{-{10}}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.69\times 10^{-{4}}$ </tex-math></inline-formula> A/cm2 at −1 V. The Schottky barrier height (SBH) remains close to ~1.8 eV up to the fluence of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times 10^{{11}}$ </tex-math></inline-formula> ions/cm2, and however, at the fluences of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10^{{12}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 10^{{12}}$ </tex-math></inline-formula> ions/cm2, the SBH increased to 1.93 and 2.03 eV, respectively. Also, the ideality factor (IF) increased from 1.07 to 1.38. The in situ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> measurements showed a similar trend, as the SBH decreased from 2.04 to ~1.88 eV until <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times 10^{{11}}$ </tex-math></inline-formula> ions/cm2, but it increased to 2.14 and 2.56 eV at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 10^{{12}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 10^{{12}}$ </tex-math></inline-formula> ions/cm2, respectively. In addition, the doping concentration decreased from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.01\times 10^{{16}}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.27\times 10^{{16}}$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{3}}$ </tex-math></inline-formula> as the defects increased significantly at the fluence of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 10^{{12}}$ </tex-math></inline-formula> ions/cm2. The cathodoluminescence measurements revealed various Ga and O defects produced during SHI irradiation. Cross-sectional transmission electron microscopy measurements confirmed the formation of tracks within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga2O3 along the SHI path, and these results are explained with the inelastic thermal spike model.

GaAs a model system to study the role of electron–phonon coupling on ionization stimulated damage recovery

The latent ion tracks observed in various materials after swift heavy ion (SHI) irradiation is often explained in the framework of thermal spike model (TSM). Dominantly, SHIs deposit most of their energy via intense ionization leading to a very high density of localized electronic excitations. The energy transfer from electrons to lattice, within a time of electronic cooling ∼100 fs, is governed by the ‘electron-phonon coupling’ parameter g. In this work, GaAs is used as a model system for studying ionization-stimulated damage recovery. Controlled damage is introduced using 300 KeV Ar ion irradiation, followed by successive irradiation using 100 MeV Ag ions at ∼80 K by varying the fluence (ions cm−2). The TSM is utilized to explain the observed recovery. Using the previously published value of 1012 W cm−3 K−1 for GaAs, the existing thermal spike code resulted in melting and quick quenching within ∼10 ps, suggesting the formation of SHI-induced tracks. However, experimental observations do not support the formation of tracks in pristine GaAs. Multiple simulation runs, for different g values, predict that for no melting in GaAs, g should be 1.4 × 1012 W cm−3 K−1. Finally, the 3D version of the TSM is used to simulate the temperature profiles after an impact of SHI irradiation on an amorphous nano-zone embedded in a crystalline GaAs matrix. Simulations predict that the thermal spike in this zone is confined, indicating melt-flow at the crystalline-amorphous interface that can promote recovery. This lattice recovery is further supported by both RBS/C and TEM results.