The interaction of energetic ions with the electronic and ionic system of target materials is an interesting but challenging multi-scale problem and understanding of the early stages after impact of heavy, initially charged ions is particularly poor. At the same time, energy deposition during these early stages determines later formation of damage cascades. We address the multi-scale character by combining real-time time-dependent density functional theory for electron dynamics with molecular dynamics simulations of damage cascades. Our first-principles simulations prove that core electrons affect electronic stopping and have an unexpected influence on the charge state of the projectile. We show that this effect is absent for light projectiles, but dominates the stopping physics for heavy projectiles. By parameterizing an inelastic energy loss friction term in the molecular dynamics simulations using our first-principles results, we also show a qualitative influence of electronic stopping physics on radiation-damage cascades.
The recombination of Frenkel pairs resulting from low energy recoils in 3C-SiC has been investigated using first principles and Nudged Elastic Band calculations. Several recombination mechanisms have been obtained, involving direct interstitial migration, atoms exchange, or concerted displacements, with activation energies ranging from 0.65 eV to 1.84 eV. These results are in agreement with experimental activation energies. We have determined the lifetime of the $V_{Si}+Si_{TC}$ Frenkel pair, by computing phonons and the Arrhenius prefactor. The vibrational contributions to the free energy bar…
Raman spectroscopy has been used to identify defective bonding in neon and silicon ion irradiated single crystals of 6H-SiC. Observable differences exist in the C-C bonding region corresponding to different defect structures for neon and silicon ion implantations. Raman spectra of ion irradiated SiC show less tensile strain than neutron irradiations, explained by a residual compressive stress caused by the swelling constrained by the undamaged substrate. Evidence of oxidation during high temperature ion implantation is observed as C-O and Si-O Raman signals. Annealing irradiated SiC while acqu…
It is shown for the first time, that room temperature Ultrasonic Defect Manipulation (UDM) can significantly reduce the concentration of radiation defects in high resistivity silicon. Secondary Ion Mass Spectroscopy revealed that oxygen- and hydrogen- related chemical reactions in silicon are likely to occur under UDM at room temperature. Ultrasonically stimulated chemical reactions in solids can be an important source of energy, which is required for UDM.
Electron-beam (e-beam) lithography is commonly used in fabricating metal-oxide-silicon (MOS) quantum devices but creates defects at the Si/SiO$_2$ interface. Here we show that a forming gas anneal is effective at removing shallow defects ($\leq$ 4 meV below the conduction band edge) created by an e-beam exposure by measuring the density of shallow electron traps in two sets of high-mobility MOS field-effect transistors (MOSFETs). One set was irradiated with an electron-beam (10 keV, 40 $μ$C/cm$^2$) and was subsequently annealed in forming gas while the other set remained unexposed. Low tempera…
A negative kink in excess conductivity is observed in p-type non-degenerate (moderate dopant concentration) silicon wafers when excited by a very narrow pulse of 532 nm laser appearing just after the complete positive decay of dark conductivity voltage. Most of the Si samples are pristine, and 3 of them are irradiated with gamma, proton, and chlorine ion beams respectively. These transients were examined using a time-resolved millimeter-wave conductivity apparatus (TRmmWC ) and the radiofrequency (RF) voltage response (after laser cut-off) consistently reveals a positive peak with nominal deca…
We present a model for the effect of stress on thin amorphous films that develop atop ion-irradiated silicon, based on the mechanism of ion-induced anisotropic plastic flow. Using only parameters directly measured or known to high accuracy, the model exhibits remarkably good agreement with the wavelengths of experimentally-observed patterns, and agrees qualitatively with limited data on ripple propagation speed. The predictions of the model are discussed in the context of other mechanisms recently theorized to explain the wavelengths, including extensive comparison with an alternate model of s…
We have carried out scanning tunneling microscopy experiments under ultrahigh vacuum condition to study the morphology of ultrathin Ge films eposited on pristine Si(100) and ion-irradiated Si(100) self-affine fractal surfaces. The pristine and the ion-irradiated Si(100) surface have roughness exponents of alpha=0.19+/-0.05 and alpha=0.82+/-0.04 respectively. These measurements were carried out on two halves of the same sample where only one half was ion-irradiated. Following deposition of a thin film of Ge (~6 A) the roughness exponents change to 0.11+/-0.04 and 0.99+/-0.06, respectively. Upon…
Silicon Carbide (SiC) ceramic matrix composite (CMC) cladding is currently being pursued as one of the leading candidates for accident-tolerant fuels. To enable an improved understanding of SiC-SiC composite performance, the development of non-destructive evaluation techniques to assess critical defects is needed. Three-dimensional (3D) X-ray imaging, also referred to as X-ray computed tomography (CT), is a non-destructive, data-rich characterization technique that can provide surface and subsurface spatial information. This paper discusses the design and implementation of a fully automatic wo…
Crystal defects in magnesium and magnesium based alloys like AZ31 are of major importance for the understanding of their macroscopic properties. We have investigated defects and their chemical surrounding in Mg and AZ31 on an atomic scale with Doppler broadening spectroscopy of the positron annihilation radiation. In these Doppler spectra the chemical information and the defect contribution have to be thoroughly separated. For this reason samples of annealed Mg were irradiated with Mg-ions in order to create exclusively defects. In addition Al- and Zn-ion irradiation on Mg-samples was performe…
Defect microstructures formed in ion-irradiated metals, for example iron or tungsten, often exhibit patterns of spatially ordered nano-scale dislocation loops. We show that such ordered dislocation loop structures may form spontaneously as a result of Brownian motion of loops, biased by the angular-dependent elastic interaction between the loops. Patterns of spatially ordered loops form once the local density of loops produced by ion irradiation exceeds a critical threshold value.
Helium-ion-induced swelling and blistering of single-crystal tungsten is investigated using a Helium Ion Microscope for site-specific dose-controlled irradiation (at 25 keV) with analysis by Helium Ion Microscopy, Atomic Force Microscopy and Transmission Electron Microscopy (cross-sectioning by Focused Ion Beam milling). Our measurements show that the blister cavity forms at the depth of the helium peak and that nanobubbles coalesce to form nanocracks within the envelope of the ion stopping range, causing swelling of the blister shell. These results provide the first direct experimental eviden…
Elastic interactions play an important role in controlling irradiation damage evolution, but remain largely unexplored experimentally. Using transmission electron microscopy (TEM) and high-resolution on-axis transmission Kikuchi diffraction (HR-TKD), we correlate the evolution of irradiation-induced damage structures and the associated lattice strains in self-ion irradiated pure tungsten. TEM reveals different dislocation loop structures as a function of sample thickness, suggesting that free surfaces limit the formation of extended defect structures found in thicker samples. HR-TKD strain ana…
Co-sputtered Au-Ni thin films having thickness of 30 nm were deposited on Si(100) substrates and irradiated with 160 keV ^{40}Ar^{+} under ambient condition at a number of fluences and analyzed using Rutherford backscattering spectrometry (RBS). The variation of Au signal counts in the RBS spectra with ion dose has been investigated. The distribution of Au, Ni and Si atoms over various depths within the as deposited and irradiated samples have been computed using the backscattering data by means of a direct analytical method. Au and Si profiles have been fitted with error function and the rela…
Hexagonally arranged Au nano particles (NPs) exhibiting a broad size distribution ranging from 30 nm to 80 nm with a Gaussian shape were deposited on Si substrates and irradiated with Ar+ and Ga+ ions with various energies from 20 to 350 keV and 1 to 30 keV, respectively. The size and energy dependence of the sputter yield were measured using high resolution scanning electron microscopy image analysis. These results were compared to simulation results obtained by iradina, a Monte Carlo (MC) code, which takes the specifics of the nano geometry into account. The experimental obtained sputter yie…
Photoluminescence of Femtosecond Laser-irradiated Silicon Carbide
RPTU University Kaiserslautern-Landau（凯泽斯劳滕-兰道莱布尼茨技术大学）；Universität des Saarlandes（萨尔兰州立大学）；Luxembourg Institute of Science and Technology (LIST)（卢森堡科学与技术研究所）；University of Luxembourg（卢森堡大学）；Institut für Oberflächen- und Schichttechnik GmbH（表面与薄膜技术研究所有限公司）
Understanding the mechanisms of plasticity in structural steels is essential for the operation of next-generation fusion reactors. Elemental composition, particularly the amount of Cr present, and irradiation can have separate and synergistic effects on the mechanical properties of ferritic/martensitic steels. The study of ion-irradiated FeCr alloys is useful for gaining a mechanistic understanding of irradiation damage in steels. Previous studies of ion-irradiated FeCr did not clearly distinguish between the nucleation of dislocations to initiate plasticity, and their propagation through the …
Using _in situ_ transmission electron microscopy (TEM), we have observed nanometre scale dislocation loops formed when an ultra-high-purity tungsten foil is irradiated with a very low fluence of self-ions. Analysis of the TEM images has revealed the largest loops to be predominantly of prismatic 1/2<111> type and of vacancy character. The formation of such dislocation loops is surprising since isolated loops are expected to be highly mobile, and should escape from the foil. In this work we show that the observed size and number density of loops can be explained by the fact that the loops are _…
In this paper, we discuss the results of our study of the synthesis of endohedral iron-fullerenes. A low energy Fe+ ion beam was irradiated to C60 thin film by using a deceleration system. Fe+-irradiated C60 thin film was analyzed by high performance liquid chromatography and laser desorption/ionization time-of-flight mass spectrometry. We investigated the performance of the deceleration system for using a Fe+ beam with low energy. In addition, we attempted to isolate the synthesized material from a Fe+-irradiated C60 thin film by high performance liquid chromatography.
Based on the parameters from published ab-inito theoretical and experimental studies, and combining Molecular Dynamics (MD) and kinetic Monte Carlo (KMC) simulations, a framework of multi-scale modeling is developed to investigate the long-term evolution of displacement damage induced by heavy-ion irradiation in cubic silicon carbide. The isochronal annealing after heavy ion irradiation is simulated, and the annealing behaviors of total interstitials are found consistent with previous experiments. Two annealing stages below 600K and one stage above 900K are identified. The mechanisms for those…
Mechanism of Oxygen Reduction via Chemical Affinity in NiO/SiO2 Interfaces Irradiated with keV Energy Hydrogen and Helium Ions for Heterostructure Fabrication
Precise and scalable defect engineering of 2D nanomaterials is acutely sought-after in contemporary materials science. Here we present defect engineering in monolayer graphene and molybdenum disulfide (MoS$_2$) by irradiation with noble gas ions at 30 keV. Two ion species of different masses were used in a gas field ion source microscope: helium (He$^+$) and neon (Ne$^+$). A detailed study of the introduced defect sizes and resulting inter-defect distance with escalating ion dose was performed using Raman spectroscopy. Expanding on existing models, we found that the average defect size is cons…
Sintered samples of monoclinic zirconia (alpha-ZrO2) have been irradiated at room temperature with 6.0-GeV Pb ions in the electronic slowing down regime. X-ray diffraction (XRD) and micro-Raman spectroscopy measurements showed unambiguously that a transition to the 'metastable' tetragonal phase (beta-ZrO2) occurred at a fluence of 6.5x10^12 cm-2 for a large electronic stopping power value (approx 32.5 MeV $μ$m-1). At a lower fluence of 1.0x10^12 cm-2, no such phase transformation was detected. The back-transformation from beta- to alpha-ZrO2 induced by isothermal or isochronal thermal annealin…
Ion-beam irradiation of an amorphizable material such as Si or Ge may lead to spontaneous pattern formation beyond some critical angle of the beam versus the surface. It is known from experimental results that this critical angle varies according to beam energy, ion species and target material. However, most prevailing theoretical analyses predict a critical angle of $45^{\circ}$ independent of energy, ion and target, disagreeing with experiment. In this second part of a set of papers, we consider the influence of the relationship between the upper and lower interfaces of the amorphous thin fi…
Damage dose dependence of deuterium retention in high-temperature self-ion irradiated tungsten
Max Planck Institute for Plasma Physics（马克斯·普朗克等离子体物理研究所）；Karlsruhe Institute of Technology (KIT), Institute for Applied Materials - Applied Materials Physics（卡尔斯鲁厄理工学院应用材料研究所）
Data available in the literature of lattice parameter changes in Ni, Cu and MgO single crystals irradiated in neutron reactors are tentatively reproduced using ad hoc ion irradiation experiments. The nature and energy of the ions were selected so that their weighted average recoil spectrum matches at best that of the neutron flux inside the reactor. The ion fluence was calculated to obtain similar, average displacements per atom (dpa) levels. The lattice parameters of the irradiated samples were determined using X-ray diffraction. We show that, for the metals, it is not possible to reproduce t…
The field emission properties of ion irradiated multiwalled carbon nanotubes (MWCNTs) and doublewalled carbon nanotubes (DWCNTs) have been studied. The carbon nanotubes synthesized by a chemical vapor deposition method were irradiated by high energy (90 MeV) Au ions with different ion fluence from 4x1011 to 1x1013 ions/cm2 . After ion irradiation, the field emission properties of MWCNTs and DWCNTs were greatly influenced. The change in the emission characteristics is due to structural defects caused by the high energy ion irradiation. The emission characteristic of MWCNTs was improved and turn…
We report on a nanoscale patterning method on Si substrates using self-assembled metal islands and low-energy ion-beam irradiation. The Si nanostructures produced on the Si substrate have a one-to-one correspondence with the self-assembled metal (Ag, Au, Pt) nanoislands initially grown on the substrate. The surface morphology and the structure of the irradiated surface were studied by high-resolution transmission electron microscopy (HRTEM). TEM images of ion-beam irradiated samples show the formation of sawtooth-like structures on Si. Removing metal islands and the ion-beam induced amorphous …
Space-grade Si and GaAs solar cells were irradiated with 15 and 40 MeV lithium ions. Dark-IV analysis (with and without illumination) reveals differences in the effects of such irradiation on the different cell types
The studies of interaction of the UV photons with bulk and nanocristalline silicon by time-of-flight (TOF) mass-spectrometry allowed to reveal two populations of Si ion monomers. The first rapid population ejected even at low laser fluences is attributed to Colombian repulsion between the surface charges which are induced by emission of the photoelectrons. When the laser fluence increases, the second slow ion population appears. This population originates from the thermal processes in the irradiated material. The original result of this work is the observation of the non-thermal ion population…
Hydrogen isotopes are retained in materials for fusion power applications, changing both hydrogen embrittlement and tritium inventory as the microstructure undergoes irradiation damage. But modelling of highly damaged materials - exposed to over 0.1 displacements per atom (dpa) - where asymptotic saturation is observed, for example tungsten facing the plasma in a fusion tokamak reactor, is difficult because a highly damaged microstructure cannot be treated as weakly interacting isolated defect traps. In this paper we develop computational techniques to find the defect content in highly irradia…
Ion-irradiated FeCr alloys are useful for understanding and predicting neutron-damage in the structural steels of future nuclear reactors. Previous studies have largely focused on the structure of irradiation-induced defects, probed by transmission electron microscopy (TEM), as well as changes in mechanical properties. Across these studies, a wide range of irradiation conditions has been employed on samples with different processing histories, which complicates the analysis of the relationship between defect structures and material properties. Furthermore, key properties, such as irradiation-i…
Pure Fe and model Fe-Cr alloys containing 5, 10 and 14%Cr were irradiated with Fe+ ions at a maximum energy of 2MeV to the same dose of 0.6dpa at temperatures of 300 C, 400 C and 500 C, and at dose rates corresponding to 6 x 10-4 dpa/s and 3 x 10-5 dpa/s. All materials exhibited an increase in hardness after irradiation at 300 C. After irradiation at 400 C, hardening was observed only in Fe-Cr alloys, and not in the pure Fe. After irradiation at 500 C, no hardening was observed in any of the materials tested. For irradiations at both 300 C and 400 C, greater hardening was found in the Fe-Cr al…
We use first-principles calculations to uncover and explain a new type of anomalous low-velocity stopping effect in proton-irradiated graphene. We attribute a shoulder feature that occurs exclusively for channeling protons to enhanced electron capture from $σ$+$π$ orbitals. Our analysis of electron emission indicates that backward emission is more sensitive to proton trajectory than forward emission and could thus produce higher contrast images in ion microscopy. For slow protons, we observe a steep drop in emission, consistent with predictions from analytical models.
In electron irradiated Ge$_{0.98}$Si$_{0.02}$, In-vacancy and In-interstitial complexes were observed in analogy with defects in pure Ge. Isochronal annealing measurements reveal that the temperature of dissociation of In-defect complexes deviate from pure Ge subjected to identical e-irradiation, which is explained on the basis of strain induced by undersized silicon atoms affecting the binding energy of In-V and In-I complexes. Besides the pairing with intrinsic defects the interaction of In with Si atoms is observed resulting in several different configurations. Complementary experiments per…
In this paper, we investigate plasticity in irradiated FeCrAl nanopillars using discrete dislocation dynamics simulations (DDD), with comparisons to transmission electron microscopic (TEM) in situ tensile tests of ion and neutron irradiated commercial FeCrAl alloy C35M. The effects of irradiation-induced defects, such as a/2 111 and a 100 type loops and composition fluctuations representative of phase separation in irradiated FeCrAl alloys, are investigated separately as well as superposed together in simulations. We explore the effects of defects on the stress-strain behavior, specifically yi…
Graphene grown by chemical vapor deposition and supported on SiO2 and sapphire substrates was studied following controlled introduction of defects induced by 35 keV carbon ion irradiation. Changes in Raman spectra following fluences ranging from 10^12 cm^-2 to 10^15 cm^-2 indicate that the structure of graphene evolves from a highly ordered layer, to a patchwork of disordered domains, to an essentially amorphous film. These structural changes result in a dramatic decrease in the Hall mobility by orders of magnitude while, remarkably, the Hall concentration remains almost unchanged, suggesting …
In this brief review we discuss the transient processes in solids under irradiation with femtosecond X-ray free-electron-laser (FEL) pulses and swift-heavy ions (SHI). Both kinds of irradiation produce highly excited electrons in a target on extremely short timescales. Transfer of the excess electronic energy into the lattice may lead to observable target modifications such as phase transitions and damage formation. Transient kinetics of material excitation and relaxation under FEL or SHI irradiation are comparatively discussed. The same origin for the electronic and atomic relaxation in both …
The effects of 200-MeV Ag^{+15} ion irradiation on the optical properties of TiO_{2} and SnO_{2} thin films prepared by using the RF magnetron sputtering technique were investigated. These films were characterized by using UV-vis spectroscopy, and with increasing irradiation fluence, the transmittance for the TiO_{2} films was observed to increase systematically while that for SnO_{2} was observed to decrease. Absorption spectra of the irradiated samples showed minor changes in the indirect bandgap from 3.44 to 3.59 eV with increasing irradiation fluence for TiO_{2} while significant changes i…
Space-grade Si and GaAs solar cells were irradiated with 15 & 40 MeV Li ions. Illuminated (AM0 condition) and unilluminated I-V curves reveal that the effect of high-energy Li ion irradiation has produced similar effects to that of proton irradiation. However, an additional, and different, defect mechanism is suggested to dominate in the heavier-ion results. Comparison is made with proton-irradiated solar-cell work and with non-ionizing energy-loss (NIEL) radiation-damage models.
In recent years, observations of highly-ordered, hexagonal arrays of self-organized nanostructures on binary or impurity-laced targets under normal-incidence ion irradiation have excited interest in this phenomenon as a potential route to high-throughput, low-cost manufacture of nanoscale devices or nanostructured coatings. The currently-prominent explanation for these structures is a morphological instability driven by ion erosion discovered by Bradley and Shipman; however, recent parameter estimates via molecular dynamics simulations suggest that this erosive instability may not be active fo…
Predicting the dramatic changes in material properties caused by irradiation damage is key for the design of future nuclear fission and fusion reactors. Self-ion implantation is an attractive tool for mimicking the effects of neutron irradiation. However, the damaged layer of implanted samples is only few microns thick, making it difficult to estimate macroscopic properties. Here we address this challenge using a combination of experimental and modelling techniques. We concentrate on self-ion-implanted tungsten, the front-runner for fusion armour components and a prototypical bcc material. To …
A stack of titanium foils was irradiated with 136 MeV 136Xe to study microstructure damage and phase stability of titanium upon irradiation. X- ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and atomic force microscopy were used to study the resulting microstructure damage and phase stability of titanium. We observed the phase transfor- mation of polycrystalline titanium from alpha-Ti (hexagonally closed packed (hcp)) to face centered cubic (fcc) after irradiation with 2.2 x 1015 ions/cm2. Irradiation of Ti with 1.8 x 1014-2.2 x 1015 ions/cm2 resulted in the forma…
Fe/Co bilayers were made using ion beam sputtering and then were subjected to nitrogen-ion irradiation to explore the influence of irradiation on their magnetic properties. Magnetization studies of Fe/Co bilayers along with their irradiated counterparts were then performed. The magnetization and coercivity of the as-deposited sample exhibited a two-fold uniaxial symmetry while the behavior for high temperature irradiated sample depicts a small shift in the two fold behavior. The magnetization data measured with the magnetic field perpendicular to the plane of the film exhibited a hysteresis in…
Present study explores the observation of topological non-hexagonal rings (NHR) and Stone Wale (SW) defects by Raman experiments in both single (SLG) and multi-layer graphene (MLG) after they are irradiated with 100- 300 eV Ar ions. Although predicted by theoretical studies, here it is experimentally shown for the first time that graphene SW/NHR defects have a signature in Raman. Broad bandwidth of the pertinent Raman features suggests the presence of more than one SW/NHR defect mode, in agreement with the DFT studies. Variations in the SW/NHR related Raman mode intensities demonstrate the ann…
Distribution of black spot defects and small clusters in 1 MeV krypton irradiated 3C-SiC has been investigated using advanced scanning transmission electron microscopy (STEM) and TEM. We find that two thirds of clusters smaller than 1 nm identified in STEM are invisible in TEM images. For clusters that are larger than 1 nm, STEM and TEM results match very well. A cluster dynamics model has been developed for SiC to reveal processes that contribute to evolution of defect clusters and validated against the (S)TEM results. Simulations showed that a model based on established properties of point d…
As it is known from visible light experiments, silicon under femtosecond pulse irradiation can undergo the so-called 'nonthermal melting' if the density of electrons excited from the valence to the conduction band overcomes a certain critical value. Such ultrafast transition is induced by strong changes in the atomic potential energy surface, which trigger atomic relocation. However, heating of a material due to the electron-phonon coupling can also lead to a phase transition, called 'thermal melting'. This thermal melting can occur even if the excited-electron density is much too low to induc…
We propose and study a continuum model for the dynamics of amorphizable surfaces undergoing ion-beam sputtering (IBS) at intermediate energies and oblique incidence. After considering the current limitations of more standard descriptions in which a single evolution equation is posed for the surface height, we overcome (some of) them by explicitly formulating the dynamics of the species that transport along the surface, and by coupling it to that of the surface height proper. In this we follow recent proposals inspired by ``hydrodynamic'' descriptions of pattern formation in aeolian sand dunes …
