Lattice Damage Research Articles

Study on the uniaxial tensile mechanical behavior of two-dimensional single-crystal aluminum nitride

Abstract To investigate the tensile behavior and mechanical properties of single-crystal aluminum nitride (AlN) at the microscopic level, molecular dynamics simulations were used to study the effects of crystal orientation, strain rate, environmental temperature, and hole defect size on fracture strength, fracture mechanism, and potential energy during uniaxial tensile. The results show that the tensile strength of AlN in the [100] crystal direction is stronger. The anisotropic behavior characteristics of Al-N bonds fracture mechanism, crack growth rate, and cracking degree are significant when stretched along the [100], [010], and [110] crystal directions. Under high temperature condition, the lattice structure undergoes changes, causing grain boundaries to move and slip. This facilitates the breaking of bonds, leading to a decrease in tensile strength and a reduction in stored potential energy. Hole defects cause more lattice damage, reducing the energy required for Al-N bonds breakage and facilitating the propagation of microcracks. Additionally, it was found that the strain rate affects the stress-strain behavior of the model. An increase in strain rate leads to an increase in breaking stress, and the rapid deformation of AlN results in more energy being stored in the lattice in the form of potential energy. Therefore, the tensile strength and potential energy are improved.

Modification of microstructural, mechanical and optical properties with carbon ion irradiation in Y2SiO5 crystals

Yttrium orthosilicate Y2SiO5 crystals, a member of the silicate family, are versatile and multifunctional materials when doped with rare earth or transition metal ions. However, there have been limited investigations into the impact of ion irradiation on the crystal structure of Y2SiO5 crystals to date. In this paper, the effect of microstructure, mechanical and optical properties of Y2SiO5 crystal before and after different fluences of carbon ions irradiation was investigated utilizing complementary characterization techniques. The results indicate that carbon ion irradiation caused lattice disorder and damage, which resulted in structural deterioration and changes in optical properties, such as decrease in the optical band gap energy (from5.77 eV to 5.44 eV), changes in the effective refractive index (neff) which resulted in the formation of “well + barrier” type and “barrier” type waveguides. In addition, elastic modulus increased after carbon ion irradiation. The results will be helpful for understanding the damage study of the Y2SiO5 crystal with carbon ion irradiation and proving that ion beam techniques can be used for material modification.

Sampling Confined Fission Tracks for Constraining Geological Thermal Histories

Fission-track modeling rests on etching, counting and measuring the lattice damage trails from uranium fission. The tools for interpreting fission-track data are advanced but the results are never better than the data. Confined-track samples must be an adequate size for statistical analysis, representative of the track population and consistent with the model assumptions and with the calibration data. Geometrical and measurement biases are understood and can be dealt with up to a point. However, the interrelated issues of etching protocol and track selection are more difficult to untangle. Our investigation favors a two-step protocol. The duration of the first step is inversely proportional to the apatite etch rate so that different apatites etch to the same Dpar. A long immersion reveals many more confined tracks, terminated by basal and prism faces. This allows consistent length measurements and permits orienting each track relative to the c-axis. Long immersion times combined with deep ion irradiation reveal confined tracks deep inside the grains. Provided it is long enough, the precise immersion time is not important if the effective etch times of the selected tracks are calculated from their measured widths. Then, whether the sample is mono- or multi-compositional, we can, post hoc, select tracks with the desired properties. The second part of the protocol has to do with the fact that fossil tracks in geological samples appear to be under-etched compared to induced tracks etched under the same conditions. This should be assumed if the semi-axes of a fitted ellipse plot above the induced-track line. In that case, an additional etch can increase the track lengths to a point where they are consistent with the model based on lab-annealing of induced tracks, a condition for valid thermal histories. Here too, it is possible to select a subset of tracks with effective etch times consistent with the model if the widths of confined tracks are measured along with their lengths and orientations.

Synthesis and Properties of CaMgSi2O6 - SrO Bioceramics for Enhanced Hydroxyapatite Formation and Cell Viability in Bone Regeneration

This study aims to synthesize and evaluate the properties of diopside (CaMgSi2O6) and strontium modified diopside (CaMgSi2O6-SrO) bioceramics for potential bone regeneration applications. The substitution of strontium for calcium leads to the formation of solid solutions: Sr-CaMgSi2O6, Ca-SrMgSi2O6, and a single phase of SrMgSi2O6, along with secondary phases of Ca-Sr2MgSi2O7 and Sr2MgSi2O7. This study is the first to examine the physical and biological properties of SrMgSi2O6 and its solid solutions. Microstructural analysis reveals that the pure diopside exhibits uniformly packed fine particles, while the SrO substitution results in lattice distortion and structural damage, thus weakening the mechanical properties and biodegradation resistance. The in vitro hydroxyapatite (HAp) formation ability of CaMgSi2O6-SrO bioceramics is comprehensively investigated, revealing that the re-adsorption of Mg2+/Sr2+ is a crucial factor. Pure diopside and Sr0.25 demonstrate effective HAp formation after immersion in simulated body fluid (SBF), with Sr0.25 showing finer particles and more uniform distribution due to appropriate Sr2+ re-adsorption. In contrast, SrO-rich samples show reduced HAp formation due to excessive re-adsorption of Mg2+ and Sr2+ ions, hindering HAp nuclei development. The cell viability test reveals that SrO substitution enhances cell viability due to increased surface area and the release of beneficial ions. Overall, Sr0.25 demonstrates excellent potential for bone regeneration applications by promoting HAp uniformity.

Analysis of Lattice Damage in 4H-SiC Epiwafers Implanted with High Energy Al Ions at Elevated Temperatures

4H-SiC wafers with 12 µm epilayers were blanket implanted to a depth of 12 µm with 5 x 1016 cm-3 Al ions via Tandem Van de Graaff accelerator located at Brookhaven National Laboratory with energy range of 13.8 to 65.7 MeV at room temperature, 300 °C and 600 °C. High resolution X-ray diffraction measurements reveal the implanted layers are characterized by tensile strains. However, the dynamic annealing process reduces the level of tensile strains as the temperature of implantation is increased. Analysis indicates that the implant temperature of 600 °C is not sufficient to minimize lattice damage due to implantation and a higher implantation temperature will be required. This preliminary experiment will guide the optimization of implantation conditions for fabricating superjunction devices.

Evolution of the Substitutional Fraction on Post-Implantation Annealing in Al/4H-SiC Systems

The problem of crystal damage recovery and of impurity substitution in implanted semiconductors is considered from a statistical mechanical viewpoint. This is done by resorting to a thermodynamic pseudo-potential originally developed for cooperative structural rearrangements in disordered systems close to their glass transition. The dependence of the substitutional fraction φ on the post-implantation annealing temperature Tann in Al/4H-SiC systems is discussed in the light of these ideas. After completion of the annealing process, an Arrhenius plot of φ(Tann) shows a slope in the order of 1 eV or less, depending on the amount of lattice damage initially produced by the implantation. Slopes ∼4 eV are found after incomplete annealing, indicating that substitution occurs mainly in damaged crystal cells. These concepts are suggested to be used for optimization of the doping procedure by ion implantation.

Breakdown up to 12 Kv in NiO/β-Ga2O3 Vertical Heterojunction Rectifiers

Vertical heterojunction NiO/β n-Ga2O/n+ Ga2O3 rectifiers fabricated on 15 µm thick drift layers with carrier concentration 8.8 x1015 cm-3 and employing simple dual-layer PECVD SiNx/SiO2 edge termination demonstrate breakdown voltages (VB) up to 12 kV, on-voltage (VON) of ~2.2V and on-state resistance RON of 11.1-12 mΩ.cm2 . The breakdown field is ~8 MV. cm-1, close to the commonly accepted theoretical value. The associated power figure-of-merit, VB 2/RON is 13 GW·cm-2 . By sharp contrast, Schottky rectifiers concurrently fabricated on the same drift layers had maximum VB of 2.9 kV, but lower VON of 0.71-0.75 V. Transmission electron microscopy showed an absence of lattice damage between the PECVD and sputtered films within the device and the underlying epitaxial Ga2O3. The key advances are thicker, lower doped drift layers and optimization of edge termination design and deposition processes. Figure 1

Transfer learning-based Gaussian process classification for lattice structure damage detection

This study presents a novel approach for real-time vision-based structural health monitoring, focusing on evaluating the deformation state of lattice structures. The structures are renowned for their remarkable recovery capabilities and exhibit similar mechanical responses under compressive loads. Despite these characteristics, quickly assessing the health status of the applied structure using knowledge from another related lattice structure is usually time-consuming and impractical. To address this, we propose to combine Gaussian process classification with transfer learning, termed TL-GPC, to detect damage states under compressive loads while also achieving uncertainty quantification. By employing structural deformations captured via the optical flow algorithm as inputs, the internal transfer kernel factor in TL-GPC is tailored to model knowledge transfer between source and target domain inputs. Experimental results show that the proposed TL-GPC model can deliver higher damage detection accuracy while ensuring stable uncertainty quantification in scenarios with limited and unbalanced experimental data.

H+ implantation induced defects distribution in 4H-SiC single crystal film fabricated by Crystal-Ion-Slicing and its effects on electrical behavior: A multiple characterization study

The composite substrate of SiC single crystal films fabricated by Crystal-Ion-Slicing (CIS) is acknowledged as an excellent material platform for the realization of electronic devices with specific functions. In CIS technology, the transferred monocrystalline films can retain good monocrystalline quality close to the virgin monocrystalline quality, but the lattice damage caused by ion implantation and crystal cleavage is still not negligible. The distribution of H+ implantation induced defects is studied in this paper, according to which the transferred film can be divided into lattice distortion region, moderately damaged region and application region. The lattice distortion region has serious lattice defects and stacking faults, while the moderately damaged layer is dominated by high lattice stress and high density point defects. For application region, in addition to the defect morphology, its influence on the electrical behavior is also investigated, which indicate the defects are mainly vacancy defects introduced by the H+ penetration, which act as carrier traps and recombination centers in electronic behavior. The research work is helpful to further understand the microstructure and defect distribution of the films of various materials fabricated by the common technology CIS, and can provide a theoretical basis for further defect layer removal and defect repair.

Deep-level defects induced by implantations of Si and Mg ions into undoped epitaxial GaN

The properties and concentrations of deep-level defects induced by implantations of Si and Mg ions into unintentionally doped (UID) epitaxial GaN have been revealed by using the Laplace-transform photoinduced transient spectroscopy (LPITS) and molecular dynamics (MD) calculations. The material lattice damage, produced by the Si ions implanted at room temperature in the single process at the energies of 200 and 340 keV, is compared with that produced by the Mg ions implanted in the similar process at the energies of 150, 210, and 270 keV. The LPITS results indicate that the same deep traps with the activation energies of 396, 512, 531, 587, 635, and 736 meV are present in the tail regions of the semi-insulating Si- and Mg-implanted films. It is argued that the predominant implantation-induced point defects in the tail region of the Si-implanted films are nitrogen vacancies, whose concentration is 7.7 × 1017 cm−3. In the Mg-implanted films, the predominant implantation-induced point defects are gallium interstitials, whose concentration is 1.2 × 1 018 cm−3.

Strength of bulk aluminum-boron alloys containing helium produced by 10B(n,α)7Li reaction in nuclear reactor

The study of metals and alloys containing helium has garnered significant attention within the nuclear energy community. However, there is limited research on the mechanical behavior of bulk alloys implanted with helium. This study investigates the mechanical properties of several Al-Boron alloys implanted with helium using controlled manipulation of helium doses via boron content under a consistent neutron dose. Results show that HemVn may contribute to strength by approximately 8.4–15 MPa and 16.8–23 MPa for helium doses 3.08 × 1019/cm3 and 6.84 × 1019/cm3, respectively, while lattice damages due to neutron-aluminum reaction contribute to strength by 24∼27 MPa. Subsequent annealing leads to the formation of helium bubbles, resulting in a slightly higher strengthening effect compared to HemVn. Additionally, the work hardening behavior of the alloys can be explained by the Voce model, drawing inspiration from the resemblance between helium bubbles and nanoprecipitates in 7xxx alloys. These findings provide insights to the nuclear energy community.

Transition‐Metal‐Doped TiO2 Nanorods with High‐Visible‐Light Response via a Simple Hydrothermal Method

Transition‐metal‐ion doping is an effective method to shorten bandgap and enhance visible‐light absorption of TiO2, but there are still some serious challenges for most doping technologies, such as nonuniform doping, severe lattice damages, metal atoms agglomeration, and inactivated impurities. Herein, a simple and universal hydrothermal method is developed to realize the effective transition‐metal ions doping of TiO2 (including Fe, Co, Mn, Cu, V, and Cr). The photoelectrochemical water splitting performances of Cr‐doped TiO2 nanorods with multifarious Cr ion valence states (Cr3+ or Cr6+ ions), various Cr‐ion concentrations, with or without oxygen vacancy activation are emphatically and systematically studied. Experiments and theoretical calculations demonstrate that the remarkably enhanced carrier separation and injection efficiencies are the key factors to improve the visible‐light photoactivity, benefiting from the homogeneous distribution of impurity atoms and the incorporation of oxygen vacancies. The Cr3+‐ion‐doped TiO2 nanorod arrays with oxygen vacancy activation (Cr3+/Ov–TiO2) displays an impressive incident photon‐to‐electron conversion efficiency of 5.4% at 450 nm visible light, far superior to the pure TiO2 of 0.03%. Furthermore, no obvious photocurrent decay is observed in the Cr3+/Ov–TiO2 photoanode after 12 h continuous light illumination.

Microstructural changes induced in advanced tungsten grades under high temperature neutron irradiation

Recent studies addressing the change of mechanical properties after high temperature irradiation of tungsten have reported substantial increase of the ductile to brittle transition temperature as well as increase of the hardness. In this work, we performed microstructural analysis by means of transmission electron microscopy (TEM) on various tungsten grades earlier exposed to high temperature neutron irradiation at 1200 °C up to 1 dpa. The latter corresponds to the expected irradiation temperature on the surface of a tungsten monoblock during the steady state operation in ITER. TEM was applied to five tungsten (W) materials including ITER specification pure W and precipitate strengthened W alloys. The analysis of TEM data coupled with its discussion led to a number of important conclusions regarding the damage induced at 1200 °C neutron irradiation such as: (i) weak effect of recrystallization on the accumulation of the lattice damage; (ii) promising results on the tolerance of damage accumulation in W-Y2O3 grade and (iii) internal oxidation of TiC particles which may contribute to the huge increase of the irradiation induced hardening.

The radiation resistance and chemical stability optimization of analog actinide nuclides incorporated Gd2Zr2O7 ceramics via grain size control

Gd2Zr2O7 is considered a promising host material for immobilizing high-level radioactive waste. However, its interplay between grain sizes, radiation resistance and chemical stability is not well understood yet. Herein, Gd1.7Nd0.3Zr0.5Ce1.5O7 ceramics with defect-fluorite phase and three different grain sizes (96, 390 and 1959 nm) were successfully fabricated and irradiated by 140 keV He ion beam up to a fluence of 8 × 1017 ions/cm2. Phase evolutions, microstructure changes and chemical stabilities were investigated. The nano-grained ceramic exhibits the lowest degree of amorphization and a delayed irradiation-induced lattice expansion and damage evolution process, demonstrating an enhanced ability in suppressing the coalescence of He bubbles inside the grain. Grain boundaries parallel to the surface were found to be more favorable sinks for irradiation-induced defects. Chemical stability tests showed that the 42 days leaching rates of all elements were between 10−7∼10−5 g/m2·d. All samples have maintained this superior chemical stability even after irradiation. Interestingly, the leaching test results also suggested that grain size may be not the primary factor influencing the long-term leaching rate.

Atomistic analysis on implantation effects of hydrogen ions and copper ions into 4H-SiC

The microstructure evolution of 4H-SiC under the implantation of hydron ions and copper ions was investigated using molecular dynamics (MD) simulations and experimental analysis. MD models were developed to simulate the implantation of single Cu2+ and H+ ions into SiC, analyzing lattice damage, amorphous defects, and temperature distribution. H+ ion implantation resulted in a higher number of amorphous atoms compared to Cu2+ ions. The maximum atomic temperature during Cu2+ ion implantation was significantly higher (1635 K) than during H+ ion implantation (950 K), although the volume of the temperature rise region was larger in the H+ model. Cu2+ ions induced more severe lattice vibrations than H+ ions. Atom movement along regions of weak lattice binding energy was observed. The study also examined overlapping multiple ion implantations, considering ion type, initial energy, and incident angle. Cu2+ ions exhibited smaller sputtering yield, projection range, number of amorphous atoms, and energy increment compared to H+ ions. A 0° incident angle resulted in higher sputtering yield and increased amorphous structure formation due to the channeling effect, which was more pronounced in the H+ model. The experimental results demonstrate that compared to Cu2+ ions, H+ ions have a greater impact on the surface peak roughness, sub-surface damage depth, and surface damage of SiC samples. It can provide a reliable guidance for selecting process parameters and the types of ions to implant.

Disorder induced in GaN thin films by 200 MeV silver ions

GaN is a material of strategic importance due to its versatility in high temperature, radiation prone and chemical environments. The present study explores evolution of defects in GaN thin films in swift heavy ion radiation regime. GaN thin films grown by metal organic chemical vapour deposition techniques were irradiated with 200 MeV Ag ions at various fluences starting from 5 × 1010 to 5 × 1012 ions/cm2. Structural analysis revealed accumulation of lattice damage with increasing fluence. XRD analysis reveals that swift heavy ions of silver (Ag) deposit more energy into the target lattice, inducing localized damage at higher fluences, leading to broader peaks in irradiated samples. Recrystallization becomes evident at fluences of 1 × 1011 ions/cm2 of Ag 200 MeV ion irradiation, as indicated by a decrease in Full Width at Half Maximum (FWHM). The compressive stress identified in Raman analysis is associated with the c-axis and elevates the wavenumber of the E2(H) mode following Ag ion irradiation. Meanwhile, the pristine sample exhibits narrow A1 (LO) phonon mode peaks, indicating good crystallinity. Photoluminescence investigations demonstrate that Ag ions induce point defects in GaN, evident through analysis of YL, GL, and BL defect-related emission peaks following irradiation at various fluences.

The near surface damage and recovery of low nitrogen diamond implanted with MeV phosphorus ions

The purpose of this work is to provide a novel perspective for investigating the damage of diamond surfaces implanted by MeV phosphorus (P) ions and recovery of the surfaces after high-temperature annealing. SRIM simulation and low-temperature luminescence spectroscopy were performed to analyze the properties of the samples comprehensively. The results revealed that a certain degree of diamond lattice damage was caused without graphitization by the irradiation of 1 MeV P ions with a fluence value of 1015 ions/cm2. The SRIM simulation revealed that the ions that were implanted into the lattice collided with carbon atoms. These ions stopped at a depth of approximately 0.55 μm and generated intrinsic diamond defects on the diamond near the surface. The simulated defects were confirmed by the appearance of neutral single vacancy (GR1) centers in the photoluminescence (PL) spectrum after annealing at 400 °C. In addition, the annealing behavior of optical centers at 900 °C indicated significant damage recovery, including the disappearance of GR1 centers, combined with the increased intensity, slightly blue-shifted peak position, and narrowed FWHM of the nitrogen-vacancy (NV) center.

Impact of Dual-Gate Configuration on the Endurance of Ferroelectric Thin-Film Transistors With Nanosheet Polycrystalline-Silicon Channel Film

This work explores the characteristics of ferroelectric thin-film transistors (FeTFTs) utilizing an asymmetric dual-gate (DG) structure in both single-gate (SG) and DG operation modes. In the transfer characteristics, DG mode exhibits a memory window (MW) of 1.075 V, smaller than SG mode’s MW of 1.402 V, attributed to the back-gate bias effect causing a reduction in the device’s threshold voltage. However, DG mode demonstrates superior endurance characteristics with 106 cycles compared to SG mode’s 105 cycles. Additionally, the increase in erase pulse voltage (VERS) exacerbates the polycrystalline-silicon channel lattice damage of FeTFT, resulting in subthreshold swing (SS) degradation. Nevertheless, the extent of SS degradation from DG mode operation is significantly lower than that of SG mode, contributing to the superior endurance of DG mode. The elevation of program pulse voltage (VPRG) induces imprint and charge-trapping effects in the top-gate ferroelectric dielectric, leading to reduced endurance. Due to the use of SiO2 as the back-gate dielectric in FeTFT, DG mode exhibits lower impacts of charge-trapping effects from the top-gate ferroelectric dielectric layer, resulting in better endurance compared to SG mode. The asymmetric DG structure provides greater tolerance in the selection of VPRG and VERS.

Breakdown up to 13.5 kV in NiO/β-Ga2O3 Vertical Heterojunction Rectifiers

Vertical heterojunction NiO/β n-Ga2O/n+ Ga2O3 rectifiers with 100 μm diameter fabricated on ∼17–18 μm thick drift layers with carrier concentration 8.8 × 1015 cm−3 and employing simple dual-layer PECVD SiNx/SiO2 edge termination demonstrate breakdown voltages (VB) up to 13.5 kV, on-voltage (VON) of ∼2.2 V and on-state resistance RON of 11.1–12 mΩ.cm2. Without edge termination, the maximum VB was 7.9 kV. The average critical breakdown field in heterojunctions was ∼7.4–9.4 MV. cm−1, within the reported theoretical value range from 8–15 MV.cm−1 for β-Ga2O3. For large area (1 mm diameter) heterojunction deives, the maximum VB was 7.2 kV with optimized edge termination and 3.9 kV without edge termination. The associated maximum power figure-of-merit, VB 2/RON is 15.2 GW·cm−2 for small area devices and 0.65 GW.cm−2 for large area devices. By sharp contrast, small area Schottky rectifiers concurrently fabricated on the same drift layers had maximum VB of 3.6 kV with edge termination and 2.7 kV without edge termination, but lower VON of 0.71–0.75 V. The average critical breakdown field in these devices was in the range 1.9–2.7 MV. cm−1, showing the importance of both the heterojunction and edge termination. Transmission electron microscopy showed an absence of lattice damage between the PECVD and sputtered films within the device and the underlying epitaxial Ga2O3. The key advances are thicker, lower doped drift layers and optimization of edge termination design and deposition processes.

Intense optical activation of Eu-doped KTiOAsO4 crystal induced by ion implantation

We report on the optical activation of Eu-doped KTiOAsO4 (KTA) by ion implantation and the effect on luminescence activity during lattice recovery. Optical activation of KTA crystals implanted with 400 keV Eu ions at an ion fluence of 5 × 1015 ions/cm2 is investigated. Despite a high damage level induced by the implantation, doping of Eu into KTA results in a strong photoluminescence in the temperature range from 4 K to 300 K, the strongest peak appears at 612 nm, which corresponding to the 5D0-7F2 transition. The lattice strain and Raman spectroscopy of the implanted KTA before and after annealing at 600°C and 700°C showed that the lattice defects are effectively recovered under annealing. Furthermore, the lattice damage effect on photoluminescence of ion-implanted Eu-doped KTA is negligible, indicating that ion implantation is an important method to obtain intense photoluminescence. The results reveal the optical activation properties of Eu implanted KTA and the attractiveness of its applications in waveguide quantum reservoirs.