Damage In SiC Research Articles

Generalized damage profile function for subsurface damage in SiC induced by helium focused ion beam under line scanning at different energies and doses

Silicon carbide is receiving increasing attention as a substrate due to its stability in harsh environments. At the same time, further minimization of sensors and micro devices requires new techniques for nanofabrication. In this context, the helium focused ion beam (He-FIB) is a promising candidate, due to its high resolution and capability of sub-10 nm fabrication, as well as its ability to modify the properties of the substrate via ion implantation. In this work, we consider previously reported experimental images of subsurface damage in both SiC and Si, as induced by He-FIB under line scanning, and provide a summary of the resulting amorphous and bubble regions as a function of the beam energy and dose. Based on empirical relations collectively encapsulated into a damage profile function (DPF) that was previously used to describe the contour of the amorphous region in Si, we focus on presenting a generalized damage profile function (GDPF) that enables describing the contours of both the amorphous and bubble regions in SiC simultaneously. In particular, the role of swelling, as a relatively small protruding region from the initial surface that eventually restricts the upward expansion of the bubble region, is fully considered. The parameters of the resulting mathematical model are related to measurements from the experimental cross-sectional images and are eventually optimized by using an evolutionary algorithm. Comparison to the experimental profiles concludes that the proposed GDPF captures both the amorphous and bubble region profiles with good precision.

Incessant tribo-layer formation supresses high temperature wear damage in SiC reinforced equi-volume ZrB2-HfB2 composite

The lift-off and re-entry expose space vehicles to kinetically sharp particles, necessitating the study of surface damage resistance of potential materials for this application. For this purpose, room temperature (RT) and high temperature (1000 °C) wear resistance of 20 vol% SiC reinforced ZrB2-HfB2 based composites is investigated. It is observed that usually microhardness follows the same trend as that of densification, which is reflected in room temperature wear performance. As a result, ZrB2-SiC (the most dense composite with % densification of ~98 and possessing the highest microhardness of ~14 GPa) yields lowest cof (0.412). At high temperature, SiC reinforced equi-volume ZrB2-HfB2 composite exhibits minimum wear. The lubricating effect of tribo-chemical product formed in SiC reinforced equi-volume ZrB2-HfB2 composite is manifested through lowering of cof (from 0.484 during RT wear test to 0.381 in wear test performed at 1000 °C) and thus wear rate (wear rate of 0.31 × 10−4 mm3N−1 m−1 compared to other composites (0.41–1.96 × 10−4 mm3N−1 m−1)). The counter body, composed of alumina, in each case showed resistance to any surface damage though elemental analysis confirmed material transfer between the two bodies.

Estimation of Residual Radioactivity and Radiation Damage in SiC After Neutron Irradiation

In the process of neutron transmutation doping (NTD), Si, C, and impurities in the SiC become radioactive nuclides by neutron capture reaction (n, $\gamma $ ) and several threshold reactions. The radiations emitted from the residual radionuclides constantly damage the SiC until they completely decay. The radiation damage can create many defects in the SiC, and the defects can reduce the electron mobility and distort the band structure. This radiation damage to the SiC should be evaluated in terms of quality management. In order to quantify the sources of radiation damage, time variations of the residual radionuclides’ radioactivity in 5-in cylindrical SiC ingot after neutron irradiation were calculated using the DCHAIN program linked to the particle and heavy ion transport code system (PHITS). In the calculation, it was assumed that the SiC ingot was irradiated in the NTD1 irradiation hole of the High-Flux Advanced Neutron Application Reactor (HANARO) at the Korea Atomic Energy Research Institute (KAERI). The energy spectrum of neutrons in the HANARO NTD1 irradiation hole calculated by using the Monte Carlo N-particle code version 6.1 (MCNP6.1) code was considered as a neutron source for the calculation. Based on the radioactivity data, the total flux and energy spectra of the electrons and gamma-rays in the SiC were calculated to analyze the properties of the radiation sources. Most of the radiations were emitted from the beta decay of 31Si, but they decayed early, and radionuclides with a relatively long half-life, such as 59Fe and 32P, became the major radiation sources. Finally, the radiation damage was calculated in the displacement per atom (DPA) unit. The time variations of the DPA rate and cumulative DPA in the SiC are presented.

Dose-rate dependence of damage buildup in 3C-SiC

The influence of the defect generation rate on radiation damage processes in SiC remains poorly understood. Here, we use a combination of ion channeling and transmission electron microscopy to systematically study the dose-rate dependence of damage buildup in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. The results reveal a pronounced dose-rate effect, whose magnitude increases close-to-linearly with temperature. When ion dose and temperature are held constant, the dose-rate dependence of the damage level is nonlinear, with saturation at high dose rates. Electron microscopy reveals that the average size of stable defect clusters increases with increasing dose rate. These findings have important implications for understanding and predicting radiation damage in SiC.

Effects of collision cascade density on radiation defect dynamics in 3C-SiC

Effects of the collision cascade density on radiation damage in SiC remain poorly understood. Here, we study damage buildup and defect interaction dynamics in 3C-SiC bombarded at 100 °C with either continuous or pulsed beams of 500 keV Ne, Ar, Kr, or Xe ions. We find that bombardment with heavier ions, which create denser collision cascades, results in a decrease in the dynamic annealing efficiency and an increase in both the amorphization cross-section constant and the time constant of dynamic annealing. The cascade density behavior of these parameters is non-linear and appears to be uncorrelated. These results demonstrate clearly (and quantitatively) an important role of the collision cascade density in dynamic radiation defect processes in 3C-SiC.

The Multiple Roles of Small-Angle Tilt Grain Boundaries in Annihilating Radiation Damage in SiC

Lattice defects generated by radiation damage can diffuse to grain boundaries (GBs) and be annihilated at GBs. However, the precise role of GBs in annihilating the segregated defects remains unclear. Here, we employed multi-scale models to determine how interstitials are annihilated at small-angle tilt GBs (STGBs) in SiC. First of all, we found the pipe diffusion of interstitials in STGBs is slower than bulk diffusion. This is because the increased interatomic distance at dislocation cores raises the migration barrier of interstitial dumbbells. Furthermore, we found both the annihilation of interstitials at jogs and jog nucleation from clusters are diffusion-controlled and can occur under off-stoichiometric interstitial fluxes. Finally, a dislocation line model is developed to predict the role of STGBs in annihilating radiation damage. This model includes defect flux to GBs, pipe diffusion in STGBs, and the interaction of defects with jogs. The model predicts the role of STGBs in annihilating defects depends on the rate of defects segregation to and diffusion along STGBs. STGBs mainly serve as diffusion channel for defects to reach other sinks when defect diffusivity is high at boundaries. When defect diffusivity is low, most of the defects segregated to STGBs are annihilated by dislocation climb.

Effective defect diffusion lengths in Ar-ion bombarded 3C-SiC

Above room temperature, SiC exhibits pronounced processes of diffusion and interaction of radiation-generated point defects. Here, we use the recently developed pulsed ion beam method to measure effective defect diffusion lengths in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal a diffusion length of ∼10 nm, which exhibits a weak temperature dependence, changing from 9 to 13 nm with increasing temperature. These results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions.

Time constant of defect relaxation in ion-irradiated 3C-SiC

Above room temperature, the buildup of radiation damage in SiC is a dynamic process governed by the mobility and interaction of ballistically generated point defects. Here, we study the dynamics of radiation defects in 3C-SiC bombarded at 100 °C with 500 keV Ar ions, with the total ion dose split into a train of equal pulses. Damage–depth profiles are measured by ion channeling for a series of samples irradiated under identical conditions except for different durations of the passive part of the beam cycle. Results reveal an effective defect relaxation time constant of ∼3 ms (for second order kinetics) and a dynamic annealing efficiency of ∼40% for defects in both Si and C sublattices. This demonstrates a crucial role of dynamic annealing at elevated temperatures and provides evidence of the strong coupling of defect accumulation processes in the two sublattices of 3C-SiC.

Combined effects of nuclear and electronic energy losses in solids irradiated with a dual-ion beam

Single and dual-beam irradiations of oxide (c-ZrO2, MgO, Gd2Ti2O7) and carbide (SiC) single crystals were performed to study combined effects of nuclear (Sn) and electronic (Se) energy losses. Rutherford backscattering experiments in channeling conditions show that the Sn/Se cooperation induces a strong decrease of the irradiation-induced damage in SiC and MgO and almost no effects in c-ZrO2 and Gd2Ti2O7. The healing process is ascribed to electronic excitations arising from the electronic energy loss of swift ions. These results present a strong interest for both fundamental understanding of the ion-solid interactions and technological applications in the nuclear industry where expected cooperative Sn/Se effects may lead to the preservation of the integrity of nuclear devices.

In-depth distribution of ion beam damage in SiC

In this paper we report on the ion beam bombardment-induced alteration of SiC measured at different ion energies (300–1700 eV) and at wide range of incident angle (43°–87°). Surface roughening was reduced by sample rotation during sputtering. The change of the concentration was characterized by Auger electron spectroscopy. Both low and high energy Auger peaks of Si were detected, which allowed us to estimate the depth distribution of the components. The observed alteration of Auger peak heights will be explained by simple model of the changed in-depth distribution. The model gives an estimate for the composition of top layer (the real surface) of SiC in different sputtering conditions, as well as the in-depth distribution of Si and C.

In situ X-ray microtomography characterization of damage in SiC f/SiC minicomposites

The purpose of the present study is to characterize matrix crack propagation and fiber breaking occurrences within SiC/SiC minicomposite in order to validate later on a multiscale damage model at the local scale. An in situ X-ray microtomography tensile test was performed at the European Synchrotron Radiation Facility (ESRF, ID19 beamline) in order to obtain 3-dimensional (3D) images at six successive loading levels. Results reveal a slow and discontinuous propagation of matrix cracks, even after the occurrence of matrix crack saturation. A few fiber failures were also observed. However, radiographs of the whole length (14 mm) of the minicomposites under a load and after the failure were more appropriate to get statistical data about fiber breaking. Thus, observations before the ultimate failure revealed only a few fibers breaking homogeneously along the minicomposite. In addition, an increase in fiber breaking density in the vicinity of the fatal matrix crack was observed after failure. These experimental results are discussed in regards to assumptions used in usual 1-dimensional (1D) models for minicomposites.

Effect of collision cascade density on radiation damage in SiC

The damage accumulation in 6H-SiC bombarded at room temperature with 1.3keV/amu atomic P+ ions and small cluster ions PFn+ (n=2 and 4) have been studied by Rutherford backscattering spectrometry in channeling mode. Results show that collision cascade density strongly affects damage buildup in SiC. The cluster ion bombardment of SiC produces more stable defects both near the surface and in the region between the surface and bulk defect peaks than irradiation by atomic ions.

MicroCT (microtomography) quantification of microstructure related to macroscopic behaviour: Part 2 – Damage in SiC–Al monofilament composites tested in monotonic tension and fatigue

The present paper reports results of monotonic tensile and of fatigue testing of an aligned monofilament composite SiC–Al. Macroscopic measures of damage (changes in unloading compliance and in unrecovered strain) correlate with noninvasive X-ray microCT (microtomography) quantification of microstructure (alteration of fibre separation, fibre misorientation relative to the load axis and amount of fibre fracture). Monotonic loading beyond yield (188 MPa) alters fibre arrangement and reduces fibre misorientation. Fracture of fibre carbon cores begins at 828 MPa and increases rapidly with rising stress concomitant with marked unloading modulus decreases and permanent strain increases. Fatigue at 621 MPa produces gradually increasing modulus and unrecovered strain with no evidence of fibre damage. At low cycles, the modulus, permanent strain and fraction of fractured C cores increase while fibre misorientation decreases; above 16 cycles, modulus decreases with gradual increases in the other quantities. Fracture in SiC could only be observed after the specimen broke.

TRIM Modeling of Displacement Damage in SiC for Monoenergetic Neutrons

Abstract Although silicon carbide is a very good semiconductor material for the fabrication of diode detectors for use as neutron power monitors in nuclear reactors, the electrical properties of the diodes may be altered because of interactions between energetic neutrons and SiC atoms. If the energy that is transferred from a neutron to an atom in a collision exceeds some threshold value, the atom will be moved from its original position, creating displacement damage. Accurately modeling displacement damage is a first step to finding ways to eliminate or decrease the amount of damage the displacements induce. The methodology that we have used to estimate the number of displacements per atom per fluence, using two codes (mcnp and trim) is presented in this paper, along with examples of the results of our calculations.

Pulsed electron beam annealing: A tool for post-implantation damage control in SiC

The possibility of reversing ion implantation damage in SiC using pulsed electron beam annealing is investigated. Using Raman spectroscopy, photo luminescence and infrared reflectance it is shown that good recovery can be obtained for an electron-energy fluence of 1.1 Jcm -2 .

Ion implantation-caused damage in SiC measured by spectroscopic ellipsometry

Since ion implantation-caused damage changes the complex refractive index of SiC significantly, optical methods can be used to measure the sample properties sensitively, non-destructively and quickly. In the present work the damage created by ion implantation into SiC and its change upon annealing was characterized by spectroscopic ellipsometry (SE). 4H SiC samples were implanted with 150 keV Al using doses between 4×l0 14 and 2×l0 15 cm −2 with current densities from 0.4 to 2.5 μA cm −2. They were subsequently annealed at 1100 °C in Ar for 1 h. SE measurements were made before and after annealing. The relative damage was measured using the Bruggeman effective medium approximation combining the dielectric function of single-crystalline and totally amorphized SiC. Therefore, the prerequisite of the proper interpretation of SE data measured on partially damaged SiC is the knowledge of the complex dielectric function of single-crystalline and completely ion implantation amorphized SiC. The complex dielectric function of ion implantation-amorphized SiC was determined from a high-dose implant. Different optical models and the influence of experimental conditions on the damage were investigated. The results were crosschecked by Rutherford backscattering spectrometry.

Displacement damage in silicon carbide irradiated in fission reactors

Calculations are performed for displacement damage in SiC due to irradiation in the neutron environments of various types of nuclear reactors using the best available models and nuclear data. The displacement damage calculations use recently developed damage functions for SiC that are based on extensive molecular dynamics simulations of displacement events. Displacements per atom (DPA) cross sections for SiC have been calculated as a function of neutron energy, and they are presented here in tabular form to facilitate their use as the standard measure of displacement damage for irradiated SiC. DPA cross sections averaged over the neutron energy spectrum are calculated for neutron spectra in the cores of typical commercial reactors and in the test sample irradiation regions of several materials test reactors used in both past and present irradiation testing. Particular attention is focused on a next-generation high-temperature gas-cooled pebble bed reactor, for which the high-temperature properties of silicon carbide fiber-reinforced silicon carbide composites are well suited. Calculated transmutations and activation levels in a pebble bed reactor are compared to those in other reactors.

Defect structure and evolution in silicon carbide irradiated to 1 dpa-SiC at 1100 °C

Transmission electron microscopy (TEM), swelling measurements, isochronal annealing, and thermal diffusivity testing were used to characterize the effects of radiation damage in SiC. Together, these techniques provided a comprehensive set of tools for observing and characterizing the structure and evolution of radiation-induced defects in SiC as a function of irradiation temperature and dose. In this study, two types of dense, crystalline, monolithic SiC were subjected to irradiation doses up to 1 dpa-SiC at a temperature of 1100 °C, as well as post-irradiation annealing up to 1500 °C. The microscopic defect structures observed by TEM were correlated to changes in the macroscopic dimensions, thermal diffusivity and thermal conductivity. The results demonstrated the value of using ultrapure β-SiC as an effective reference material to characterize the nature of expected radiation damage in other, more complex, SiC-based materials such as SiC/SiC composites.

Promise and challenges of SiC f/SiC composites for fusion energy applications

Silicon carbide fiber/silicon carbide matrix composites have been specified in several recent fusion power plant design studies because of their high operating temperature (1000–1100 °C) and hence high energy conversion efficiencies. Radiation resistance of the β-phase of SiC, excellent high-temperature fracture, creep, corrosion and thermal shock resistance and safety advantages arising from low induced radioactivity and afterheat are all positive attributes favoring the selection of SiC f/SiC composites. With the promise of these materials comes a number of challenges such as their thermal conductivity, radiation stability, gaseous transmutation rates, hermetic behavior and joining technology. Recent advances have been made in understanding radiation damage in SiC at the fundamental level through MD simulations of displacement cascades. Radiation stability of composites made with the advanced fibers of Nicalon Type S and the UBE Tyranno SA, where no change in strength was observed up to 10 dpa at 800 °C, in the development of materials with improved thermal conductivity, modeling of thermal conductivity, joining techniques and models for life-prediction. High transmutation rates of C and Si to form H, He, Mg, and Al continue to be a concern.

Study of the irradiation damage in SiC by ion channeling

The importance of silicon carbide as a wide band gap semiconductor is widely accepted and well documented. Its excellent physical properties (chemical inertness, high-temperature strength, low thermal expansion, extreme hardness) make it the most promising substitute for traditional semiconductors, especially when high-temperature, high-voltage power, and high-frequency devices are concerned. In the present work, the gradual amorphization of a SiC Lely (21R) crystal when irradiated with 8 MeV 7Li ions in a random direction up to a maximum dose of approximately 1×10 16 particles/cm 2, is being studied, using the progressive change of channeling parameters for different depths. The results refer to the energy region of ∼1 MeV/nucleon, and an attempt is made in order to explain the peculiarities of the experimental spectra and the mechanism of defect production in SiC. As in previous studies, a change in color was observed after irradiation in the random mode, indicating that the problem of irradiation damage in SiC caused by light ion beams needs further investigation.