Ion-induced Damage Research Articles

Depth-resolved deuterium retention analysis in displacement-damaged tungsten using laser-induced breakdown spectroscopy

Fuel retention in plasma-facing components (PFCs) is a critical issue in future nuclear fusion reactors operating with Deuterium-Tritium (DT) regarding nuclear safety and fulfillment of the T cycle. However, during DT plasma operation, highly energetic neutrons will induce damage in the lattice of W PFCs causing enhanced fuel retention in defects or traps. Laser-Induced Breakdown Spectroscopy (LIBS) is a potential tool to monitor the T-content in situ in PFCs of future nuclear fusion devices. This article presents an ex situ study on pre-damaged W material after D plasma exposure to qualify the method and mimic conditions expected in a reactor. ITER grade W samples were displacement-damaged by 10.8 MeV W ions to a damage dose of 0.23 dpa and exposed to low temperature deuterium plasma at low energy in PlaQ. The resulting deuterium concentration was analyzed by using 3He Nuclear Reaction Analysis (depth resolution of ≈150 nm) as a well-established method, and LIBS (picosecond laser pulses, depth resolution of 15 nm). The sample with the highest deuterium concentration showed a deuterium-rich zone up to a depth of 1.13 μm using both techniques. This is close to the expected W ion-induced damage depth of ≈1 μm. The results imply that LIBS as an in situ technique for tritium monitoring could be a viable option for a reactor.

Thinner is not always better: Optimizing cryo-lamellae for subtomogram averaging.

Cryo-electron tomography (cryo-ET) is a powerful method to elucidate subcellular architecture and to structurally analyze biomolecules in situ by subtomogram averaging, yet data quality critically depends on specimen thickness. Cells that are too thick for transmission imaging can be thinned into lamellae by cryo-focused ion beam (cryo-FIB) milling. Despite being a crucial parameter directly affecting attainable resolution, optimal lamella thickness has not been systematically investigated nor the extent of structural damage caused by gallium ions used for FIB milling. We thus systematically determined how resolution is affected by these parameters. We find that ion-induced damage does not affect regions more than 30 nanometers from either lamella surface and that up to ~180-nanometer lamella thickness does not negatively affect resolution. This shows that there is no need to generate very thin lamellae and lamella thickness can be chosen such that it captures cellular features of interest, thereby opening cryo-ET also for studies of large complexes.

Ion beam processing of DNA origami nanostructures.

DNA origami nanostructures are emerging as a bottom-up nanopatterning approach. Direct combination of this approach with top-down nanotechnology, such as ion beams, has not been considered because of the soft nature of the DNA material. Here we demonstrate that the shape of 2D DNA origami nanostructures deposited on Si substrates is well preserved upon irradiation by ion beams, modeling ion implantation, lithography, and sputtering conditions. Structural changes in 2D DNA origami nanostructures deposited on Si are analyzed using AFM imaging. The observed effects on DNA origami include structure height decrease or increase upon fast heavy ion irradiation in vacuum and in air, respectively. Slow- and medium-energy heavy ion irradiation results in the cutting of the nanostructures or crater formation with ion-induced damage in the 10 nm range around the primary ion track. In all these cases, the designed shape of the 2D origami nanostructure remains unperturbed. Present stability and nature of damages on DNA origami nanostructures enable fusion of DNA origami advantages such as shape and positioning control into novel ion beam nanofabrication approaches.

Normalization Indicator of Ion-Induced Radiation Damage in Power VDMOS Transistors

Normalization Indicator of Ion-Induced Radiation Damage in Power VDMOS Transistors

Dynamics of plasma atomic layer etching: Molecular dynamics simulations and optical emission spectroscopy

Atomic layer etching is intrinsically dynamic as it involves sequential and repeated exposures of a surface to be etched with different species at different energies. The composition and structure of the near surface region change in both time and depth. Full understanding of this process requires resolving both temporal and spatial variations. In this work, we consider silicon (Si) atomic layer etching (ALE) by alternating exposure to chlorine gas (Cl2) and argon ions (Ar+). Molecular dynamics (MD) simulations are compared to experimental measurements with the aim of better understanding the dynamics of ALE and to test the simulation procedure. The simulations help to more fully interpret the experimental measurements. Optical emission measured just above the surface being etched can be related to etch products and can, therefore, be directly compared to simulation predictions. The simulations capture the measured initial product distribution leaving the surface and match the measured etch per cycle reasonably well. While simulations demonstrate the importance of ion-induced surface damage and mixing into a layer below the surface, the depth of which depends mainly on ion energy, the experiments suggest there is more Cl mixed into the layer than the MD procedure predicts.

Calibration and data-analysis routines for nanoindentation with spherical tips

Instrumented spherical nanoindentation with a continuous stiffness measurement has gained increased popularity in microphysical investigations of grain boundaries, twins, dislocation densities, ion-induced damage, and more. These studies rely on different methodologies for instrument and tip calibration. Here, we test, integrate, and re-adapt published strategies for tip and machine-stiffness calibration for spherical tips. We propose a routine for independently calibrating the effective tip radius and the machine stiffness using standard reference materials, which requires the parametrization of the effective radius as a function of load. We validate our proposed workflow against key benchmarks and apply the resulting calibrations to data collected in materials with varying ductility to extract indentation stress–strain curves. We also test the impact of the machine stiffness on recently proposed methods for identification of yield stress. Finally, we synthesize these analyses in a single workflow for use in future studies aiming to extract and process data from spherical nanoindentation.Graphic abstract

Estimation of different calculation models for evaluating heavy ion-induced damage in plasma facing materials

In a fusion reactor, plasma-facing materials are bombarded by various energetic particles (such as neutrons) from fusion reactions, leading to inevitable irradiation damages. These damages can significantly affect the material servicing life time and threaten the safety of fusion reactors. Accurate and consistent evaluation of irradiation damage is quite important to investigate the evolution mechanism of irradiation defect. In this study, the irradiation damage of tungsten caused by high-energy particles were evaluated using the SRIM code and molecular dynamics simulations. The accuracy of three atomic displacements calculation models, i.e., VAC model, NRT model, and arc-dpa model, under two computational modes of SRIM (the K-P mode and F-C mode) were discussed. It was found that with the increase of the incident particle atomic number, the peak depth of displacement moved to the shallow layer and increased in peak height, while the trend was opposite with the increase of the incident particle energy. As to the different calculation modes, the F-C and K-P modes produced a ratio of vacancies of about 1.8 times in the VAC model. What's more, the VAC model and NRT model predicted results consistent with molecular dynamics simulation results at lower energy ranges (approximately <100 eV), but deviated from them as the energy increased. In contrast, the arc-dpa model exhibited good consistency with the molecular dynamics simulations and had higher accuracy. Therefore, it is recommended to use the arc-dpa model under the K-P mode for the calculation of atomic displacement. This model can accurately and quickly calculate the irradiation damage level caused by high-energy particle irradiation in fusion reactors.

Fabrication of triangular pits in barium fluoride single crystals by localized electronic excitations

Ion beam technology is considered as one of the most effective and unique techniques for materials engineering. Here, we show that the selective chemical etching is used successfully for the fabrication of pyramidal etch pits by revealing the ion-induced damage in the surface and below surface regions of barium fluoride single crystals. The size of ion-induced pits is increasing by etching the ion impacted zones for longer time. Moreover, the types of the induced defects are probed using optical absorption spectroscopy. The presented findings are discussed in terms of the peculiarities of ion energy deposition as well as the comparison with the induced structures using different type of ions, namely slow highly charged ions. Furthermore, they might be of importance in today’s nano and microelectronics applications, where the fabrication of size-controlled surface structures is of high necessity.

High-throughput SiN ALE: surface reaction and ion-induced damage generation mechanisms

Atomic layer etching (ALE) has been practically implemented as a technique to achieve atomic/molecular level control. However, its main disadvantage is that it involves long process time. The surface reaction mechanism required to realize high-throughput (HT) SiN ALE was investigated. CH3F/Ar plasma was applied in the adsorption step, while Ar plasma was used in the desorption step. Finally, an additional O2 ashing step was applied. To reduce process time, HT ALE was performed at high ion energy, and the amount of etched SiN was evaluated. HT SiN ALE conducted at short time intervals and at high ion energy underwent a quasi-self-limited reaction, which is a characteristic of ALE, and the process time decreased. However, HT ALE using CH3F in the adsorption step caused an increase in the extent of the damage. Thus, the use of C4F8 (without H) can significantly reduce damage even under HT ALE conditions.

Sidewall Electrical Damage in β-Ga2O3 Rectifiers Exposed to Ga+ Focused Ion Beams

The energy and beam current dependence of Ga+ focused ion beam milling damage on the sidewall of vertical rectifiers fabricated on n-type Ga2O3 was investigated with 5–30 kV ions and beam currents from 1.3–20 nA. The sidewall damage was introduced by etching a mesa along one edge of existing Ga2O3 rectifiers. We employed on-state resistance, forward and reverse leakage current, Schottky barrier height, and diode ideality factor from the vertical rectifiers as potential measures of the extent of the ion-induced sidewall damage. Rectifiers of different diameters were exposed to the ion beams and the “zero-area” parameters extracted by extrapolating to zero area and normalizing for milling depth. Forward currents degraded with exposure to any of our beam conductions, while reverse current was unaffected. On-state resistance was found to be most sensitive of the device parameters to Ga+ beam energy and current. Beam current was the most important parameter in creating sidewall damage. Use of subsequent lower beam energies and currents after an initial 30 kV mill sequence was able to reduce residual damage effects but not to the point of initial lower beam current exposures.

Ion-Induced Lateral Damage in the Focused Ion Beam Patterning of Topological Insulator Bi2Se3 Thin Films

Focused Ion Beam patterning has become a widely applied technique in the last few decades in the micro- and nanofabrication of quantum materials, representing an important advantage in terms of resolution and versatility. However, ion irradiation can trigger undesired effects on the target material, most of them related to the damage created by the impinging ions that can severely affect the crystallinity of the sample, compromising the application of Focused Ion Beam to the fabrication of micro- and nanosized systems. We focus here on the case of Bi2Se3, a topological material whose unique properties rely on its crystallinity. In order to study the effects of ion irradiation on the structure of Bi2Se3, we irradiated with Ga+ ions the full width of Hall-bar devices made from thin films of this material, with the purpose of inducing changes in the electrical resistance and characterizing the damage created during the process. The results indicate that a relatively high ion dose is necessary to introduce significant changes in the conduction. This ion dose creates medium-range lateral damage in the structure, manifested through the formation of an amorphous region that can extend laterally up to few hundreds of nanometers beyond the irradiated area. This amorphous material is no longer expected to behave as intrinsic Bi2Se3, indicating a spatial limitation for the devices fabricated through this technique.

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.

Investigation of ion-induced etch damages on trench surface of Ge2Sb2Te5 in high density Ar/SF6 plasma

Ion-induced etch damage on trench surfaces of Ge2Sb2Te5 (GST) by reactive ion etching (RIE) is investigated with Ar/SF6 capacitively coupled plasma (CCP). Etch damage on the sidewall increases with higher plasma density and decreases with the bias power. The roughness of the bottom decreases with the bias power due to the ion sputtering. It is demonstrated that the optimum process condition to minimize the ion-induced damage can be obtained from the feature analysis of the virtual metrology, which was developed with plasma information parameters named PI-VM, and it predicted the GST etch rate and surface roughness. It reveals that the energetic ions play a crucial role in removing the halogenated surfaces by high-energy ion sputtering. In addition, the sidewall damage by the lower F radicals is significant because the collisional diffused F radicals are enhanced in the high-density plasma. It explains the control of bias power required to achieve the profiling etch in the high-density plasma.

Dependency of Ag wetting on the oxygen nonstoichiometry of oxide surfaces

Oxide substrates are frequently modified to have either an oxygen deficiency or excess to synthesize a completely continuous, ultrathin metal layer on them by strengthening the metal–oxide adhesion. However, conventional surface treatments using ionic irradiation inevitably induce detrimental structural irregularities, along with chemical modification, on the surface of oxide substrates. This study explores the dependency of Ag wetting on the oxygen deficiency and excess on the surface of a ZnO substrate. The favorable contribution of the increased oxygen deficiency and excess of ZnO surfaces in improving Ag wetting during the inceptive growth stages is evidenced by both experimental results and numerical interpretations. This improved Ag wetting is attributed to a significant reduction in free energy at the Ag–ZnO interfaces, whereas pinholes remain in thicker Ag layers on the ZnO surfaces. This finding extends earlier studies, reporting a favorable role of an increased oxygen deficiency on Ag wetting, with the point that oxygen excess beyond a threshold value is also helpful in improving Ag wetting. Our findings redefine the underlying Ag wetting mechanisms of the nonstoichiometric surface of oxide substrates. Moreover, the study provides guidelines for implementing a continuous ultrathin Ag layer while avoiding ion-induced damage to the oxide substrates.

Structural and electrical characteristics of ion-induced Si damage during atomic layer etching

Abstract Damage to the underlying Si substrate during the over-etching step of SiN atomic layer etching (ALE) was investigated. CH3F/Ar plasma was applied in the adsorption step, and Ar plasma in the desorption step. ALE increased interface trap density (D it), whereas Ar plasma did not affect D it. C, H, and F in the hydrofluorocarbon polymer, knocked-on by Ar, penetrated the Si substrate, which resulted in an increase in D it. Additionally, H in the polymer layer had a negligible impact on the damage caused by ALE. The H-penetration depth was shallow because the energy transferred from Ar to the H component in the polymer was low. Damage occurred only in the first cycle of ALE because a thick polymer layer, deposited after the second cycle, protected the substrate from additional damage. Thus, precise control of incident ion energy, adsorbed polymer thickness, and polymer composition are required to realize low-damage ALE.

Comparative study of radiation tolerance of GaN and Ga2O3 polymorphs

The mechanisms of ion-induced defect formation and physical characteristics promoting radiation tolerance of wide and ultra-wide bandgap semiconductors are not well-studied and understood. In contrast to gallium nitride (GaN), gallium oxide (Ga2O3) can be crystallized in several polymorphs having different crystal structures and physical properties. In the preset paper, the damage buildup in wurtzite GaN as well as in corundum (α-) and monoclinic (β-) Ga2O3 polymorphs bombarded at room temperature with 40 keV P+ ions is studied by Rutherford backscattering/channeling spectrometry. We demonstrate that ion-beam-induced damage formation in Ga2O3 is different from that observed in GaN and dramatically depends on the polymorph type. Both Ga2O3 polymorphs cannot be rendered amorphous and exhibit considerably higher damage saturation at ∼90% of the full amorphization as compared to that of GaN. Intriguing enough the metastable α-Ga2O3 demonstrates considerably higher radiation resistance as compared to the most thermodynamically stable β-Ga2O3 polymorph. Furthermore, our results indicate that the sample surface and dynamic annealing play a significant role in the ion-induced damage formation processes in all Ga-based compounds studied.

Effects of Ion-Induced Displacement Damage on GaN/AlN MEMS Resonators

Gallium nitride (GaN) has attracted great attention as a structural material for advanced microelectromechanical systems (MEMS), thanks to its excellent ensemble of electrical and mechanical properties. Here, we report on studying the effects of ion radiation-induced displacement damage on resonant MEMS made of GaN film grown on aluminum nitride (AlN) buffer layer. We design and fabricate GaN/AlN heterostructure doubly-clamped microstring resonators with length <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L \,\, =100$ </tex-math></inline-formula> , 200, 300, 400, 500, 600, and 700 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> , and irradiate the devices with 440-keV Ar <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{+}$ </tex-math></inline-formula> ions, to probe the effects of ion radiation-induced displacement damage on the resonance behavior. The ion energy and range have been selected so that the ions would stop within the GaN layer, thus allowing diagnostics to show the effects of damage in the structure. The multimode resonance frequencies of the devices decrease significantly ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \Delta f\vert /f &gt;50$ </tex-math></inline-formula> %) with the increase of fluence beyond 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> . According to scanning electron microscopy (SEM) imaging, the irradiated GaN/AlN resonators are visibly deformed at high fluence, where the amount of curvature increases monotonically with the fluence. The deformation of the structures can be ascribed to the change in both Young’s modulus and built-in stress resulting from ion radiation-induced displacement damage. The results extend the understanding of radiation-induced damage mechanisms in resonant MEMS.

Raman and photoluminescence evaluation of ion-induced damage uniformity in ThO2

Nuclear reactor conditions can be emulated in part by exposing potential fuel materials, such as ThO2, to ion beam radiation. Changes in properties can then provide invaluable insight into how the material will perform as a fuel. Here, a hydrothermally grown single crystal of ThO2 is irradiated with 2 MeV H+ and the crystallographic and electronic structure homogeneity and damage extent is investigated. μ-Raman spectroscopy shows that the damage to the crystal face directly exposed to the irradiation is heterogeneous, with the intensity of irradiation-induced peaks altering substantially in relation to the T2g structural peak. Damage on orthogonal faces is more uniform and the damage depth profile is investigated with Raman spectroscopy. The damage as a function of depth is compared to stopping range of ions in matter simulations. Photoluminescence spectroscopy is also employed to investigate the depth profiles and exhibits clear signs of damage, which are discussed.

Reconditioning of Diamond Coated Tools and Its Impact on Cutting Performance for CFRP Laminates

In recent years, CVD diamond-coated tungsten carbide (WC-Co) tools have been widely utilized due to their benefits in the machining of non-ferrous alloys and polymer composite materials, especially carbon-fiber-reinforced plastics (CFRPs). The reconditioning of such coated tools is economically attractive due to their high cost and short tool life. The decoating of the remaining diamond film from the used tools and the subsequent surface preparation by wet chemical pretreatment are essential steps for new CVD diamond film formation. Previously, it was shown that reactive ion beam etching (RIBE) could effectively remove CVD diamond films. However, some degree of WC-Co tool substrate damage is expected due to the high ion energy in RIBE and the chemical activity in wet etching. This study addresses the effects of RIBE decoating and surface pretreatment steps on WC-Co tools with a complex shape in terms of the ion-induced surface damage, geometry alteration, and adhesion of a subsequently re-applied CVD diamond film. Moreover, the cutting performance of the tools subjected to the RIBE decoating and repeated film deposition was studied via CFRP cutting tests. It has been shown that the RIBE decoated and recoated tools had a high level of cutting performance comparable to the new tools.

Lithium niobate microring with ultra-high Q factor above 108

We demonstrate integrated lithium niobate (LN) microring resonators with Q factors close to the intrinsic material absorption limit of LN. The microrings are fabricated on pristine LN thin-film wafers thinned from LN bulk via chemo-mechanical etching without ion slicing and ion etching. A record-high Q factor up to 108 at the wavelength of 1550 nm is achieved because of the ultra-smooth interface of the microrings and the absence of ion-induced lattice damage, indicating an ultra-low waveguide propagation loss of ∼0.0034 dB/cm. The ultra-high Q microrings will pave the way for integrated quantum light source, frequency comb generation, and nonlinear optical processes.