Ion Irradiation Conditions Research Articles

Extended metastable Al solubility in cubic VAlN by metal-ion bombardment during pulsed magnetron sputtering: film stress vs subplantation

Dynamic ion-recoil mixing of near-film-surface atomic layers is commonly used to increase the metastable solubility limit xmax in otherwise immiscible thin film systems during physical vapor deposition. Recently, Al subplantation achieved by irradiating the film growth surface with Al+ metal-ion flux was shown to result in an unprecedented xmax for VAlN, far above values obtained with gas ion irradiation. However, it is reasonable to assume that ion irradiation necessary for subplantation also leads to a compressive stress σ buildup. In order to separate the effects of Al+ bombardment on σ and xmax, and realize low-stress high-xmax nitride alloys, we grow metastable cubic V1-xAlxN (0.17 ≤ x ≤ 0.74) films using reactive magnetron sputtering under different ion irradiation conditions. Al and V targets are operated in Ar/N2 discharges employing (i) conventional DC (Ar+, N2+), (ii) hybrid High-power pulsed magnetron sputtering (HIPIMS)/DC processing with one type of metal ion present (Al+ or V+/V2+), and (iii) HIPIMS with concurrent Al+ and V+/V2+ fluxes. Comparison to the ab initio calculated Al solubility limit reveals that xmax = 0.55 achieved with V+/V2+ irradiation is entirely accountable for by stress. In contrast, Al+ fluxes provide a substantial increase in xmax to 0.63, which is 12% higher than that expected based on the stress-induced increase in metastable solubility. Correlative stress and atom probe tomography data confirm that the metastable Al solubility enhancement is enabled by Al+ subplantation. The here proposed processing strategy allows for growth of single-phase cubic nitride alloys with significantly increased Al concentrations embodying tremendous promise for substantial improvements in high temperature oxidation resistance and mitigates the risk of stress-induced adhesive or cohesive coating failure.

A mechanistic model for depth-dependent hardness of ion irradiated metals

A mechanistic model was developed for modeling the depth-dependent hardness in ion irradiated metallic materials. The model is capable of capturing the indentation size effect, ion irradiation induced damage gradient effect, and effect of unirradiated region acting as a soft substrate. A procedure was developed and described in detail to parametrize the model based on experimentally obtained hardness vs. indentation depth curves. Very good agreement was observed between our model predictions and experimental data of several different stainless steels subjected to various ion irradiation conditions. In addition, two hardening mechanisms are revealed in the new model. One is the well-known indentation size effect arising from the creation of geometrically necessary dislocations as the indenter pierces into the materials. The other is the irradiation hardening due to the presence of irradiation-induced defects. As a function of indentation depth h, the hardening due to indentation size effect is described by h¯∗/h, while the hardening due to irradiation first follows a power law form Phn, then changes to Z/h−Q/h3, where h¯∗, P, n, Z and Q>0 are constants. This transition occurs at the indentation depth when the plastic zone reaches the end of the irradiated layer.

Wafer-scale SiC rich nano-coating layer by Ar+ and Xe+ ion mixing

Abstract Ion irradiation of interfaces causes intermixing of the adjacent regions, which leads to compound formation in certain cases. With the aim of building, some nm thick protective coating at ambient temperature, C/Si/C/Si/C/Si substrate samples were irradiated with Ar + , Xe + , and Ga + ions in the energy and fluence ranges of 20–200 keV and 1–3 × 10 16 ion cm − 2 , respectively. The effect of ion irradiation was studied by Auger electron spectroscopy depth profiling and cross sectional transmission electron microscopy. All ion irradiations produced SiC rich regions the thickness of which, being some nm, could be tailored by changing the ion irradiation conditions. The chemical resistance of the SiC rich layer has been tested by polysilicon etchant. Rutherford Backscattering Spectrometry (RBS) analysis showed that etching rate of the SiC rich region was orders of magnitude lower than that of polysilicon on the whole irradiated area. It was also shown that Transport of Ions in Dynamic (TRIDYN) simulation combined with a simple compound formation rule provides a fair description of the resultant SiC distributions. Thus, it is possible to design and fabricate wafer-scale SiC for a given sample architecture by “TRIDYN simulation assisted” ion irradiation.

Microstructural evolution of Fe[sbnd]22%Cr model alloy under thermal ageing and ion irradiation conditions studied by atom probe tomography

Nanostructure evolution during ion irradiation of two thermally aged binary Fee22Cr alloys has been investigated using atom probe tomography. Specimens aged at 500 °C for 50 and 200 h were irradiated by 5.6 MeV Fe ions at room temperature up to fluences of 0.3 × 1015 ions/cm2 and 1 × 1015 ions/cm2. The effect of irradiation on the material nanostructure was examined at a depth of 1 μm from the irradiated surface. The analysis of Cr radial concentration functions reveals that dense α′-phase precipitates in the 200 h aged alloy become diffuse and thereby larger when subjected to irradiation. On the other hand, less Cr-enriched precipitates in the alloy aged for 50 h are less affected. The CreCr pair correlation function analysis shows that matrix inhomogeneity decreases under irradiation. Irradiation leads to a decrease in the number density of diffuse clusters, whereas in the case of well-developed precipitates it remains unchanged.

Defect microstructural equivalence in molybdenum under different irradiation conditions at low temperatures and low doses

Owing to its advantages such as higher dose rates and shorter time required, ion irradiation, including in-situ ion irradiation of nano-foils on electron microscopes, is being proposed as a surrogate for neutron/reactor irradiation in materials testing for the research of irradiation induced/enhanced degradation of reactor structural materials. This raises a key question: can the microstructural evolution be matched across different irradiation conditions? Here we report our recent study using a rate-theory based cluster dynamics approach on the time dependent defect accumulation in elemental molybdenum under varying ion and neutron irradiation conditions, within a low temperature and low dose regime. The approach solves a large system of coupled differential equations each equation describing the rate of change in the concentration of a particular defect/cluster (defined by its nature and number of constituent point defects) caused by direct production (for primary defects), diffusion flux across spatial grids (for mobile defects, under ion irradiation), and capturing and/or emission interactions with other defects/clusters. Our results suggest that defect evolution under different dose rates can be very well matched in either thin foil ion irradiation or bulk neutron irradiation, by using different irradiation temperatures to counteract the effect of the dose rate variation. Across the two types of irradiation, less perfect matching is obtained mainly due to the strong surface sink effect in the thin foil, but the matching can be improved by combining the temperature shift strategy with selection of a single depth in the foil (as opposed to all depths averaged) for matching, or a greater foil thickness.

Helium bubble evolution in ion irradiated Al/B4C metal metrix composite

Helium behavior in Al/B4C metal matrix composite with two different sets of ion irradiation conditions has been investigated by transmission electron microscopy. Helium bubbles in Al were found to be much larger than those in B4C after a helium fluence of 1.5×1017ions/cm2 at the room temperature. Also, bubbles at grain boundaries and their vicinity in aluminum are faceted. With additional proton irradiation, a bubble denuded zone along the aluminum grain boundary appears. The results are discussed in terms of the energetics of the material system.

Effect Of Heavy Ion Irradiation At Low Temperature In Fe-14Cr-0.2Ti-0.3Y2O3

Fe-14Cr-0.2Ti-0.3Y2O3, ODS alloy samples are irradiated with 880 keV Fe + ions at 230 K and 300 K upto a damage of 40 dpa at the surface. Transmission electron microscopy studies reveal a reduction in sizes of oxide dispersions in the ion irradiated alloys as compared to the as-prepared specimens; with greater diminution for samples irradiated at 230 K. Although the ion irradiation conditions (stage III) are favorable for vacancies to couple with solute atoms to cause precipitate growth, it is shown that such effects are less pronounced here and the ballistic effects dominate to cause oxide particle dissolution. Copyright © 2015 VBRI Press.

Investigation of SOL plasma interaction with graphite PFC

Morphological changes of graphite plasma facing component (PFC) were investigated with various ion irradiation conditions which may change the sputtering yield and the scrape-off layer (SOL) plasma property. The experiments were carried out by using electron cyclotron resonance deuterium plasma with the conditions of electron density range of 2.5–3.5×1011cm−3, electron temperature range of 3.3–4.1eV, and ion energy range of 17–100eV. The graphite morphology was changed from plane to conical tip with increasing ion energy and dose. In addition, morphological changes increase the sputtering yield due to the increase of local angle of ion incidence. The inflow of hydrocarbon causes the increase of electron density and the decrease of electron temperature due to its higher dissociation and ionization rates than those of deuterium. This result suggests that the morphological changes of graphite should be considered in the SOL plasma interaction with graphite PFC.

A combinatorial X-ray sub-micron diffraction study of microstructure, residual stress and phase stability in TiAlN coatings

The understanding of the relationship between structure and properties of thin coatings is one of the key requirements for their further improvement. Especially for metastable TiAlN, commonly used as a protective coating for cutting applications, detailed knowledge about the apparent microstructure, the resulting residual stresses and the accompanied decomposition behavior at elevated temperatures are of vital importance, as the subsequent high-temperature formation of the thermally stable wurtzite phase results in deteriorated mechanical properties. In this study, the recently introduced cross-sectional scanning X-ray diffraction method is applied as a combinatorial tool to investigate the depth evolution of the local microstructure and residual stresses and their effect on phase stability of a TiAlN coating synthesized by cathodic arc evaporation at stepwise increased bias voltages. The decomposition behavior of the coating during annealing is obviously given by the initial microstructure and stress state, which control the local stress relaxation as well as the formation of precipitates. Thus, the phase transformation is favored in the coating regions that developed under moderate ion-irradiation conditions, characterized by low stress and well-developed columnar grains, and retarded under the presence of high compressive stress. The observed non-linear dependency of phase decomposition on the initial microstructure and stress is interpreted by ab initio calculations.

Stability of MX-type strengthening nanoprecipitates in ferritic steels under thermal aging, stress and ion irradiation

The stability of MX-type precipitates is critical to retain mechanical properties of both reduced activation ferritic–martensitic (RAFM) and conventional FM steels at elevated temperatures above ∼500°C. The stability of TaC, TaN and VN nanoprecipitates under thermal aging (600 and 700°C), creep (600°C) and ion irradiation (Fe ion, 500°C) conditions was systematically studied in this work. The statistical particle evolution in density and size was characterized using transmission electron microscopy. Nanoprecipitate stability under the studied conditions manifested differently through either dissolution, reprecipitation, growth or fragmentation, with TaC exhibiting the greatest stability followed by VN and TaN in sequence. Nanoprecipitate evolution phenomena and mechanisms and the apparent disagreement of this interpretation with published literature on the subject are discussed. These findings not only help understanding the degradation mechanisms of RAFM and conventional FM steels at elevated temperatures and under stress and irradiation, but should also prove beneficial to the development of advanced RAFM steels.

Ion-beam simulation of radiation damage produced by fast neutrons in heterophase structures

3D Monte-Carlo algorithm and computer code have been developed that allows choosing and optimizing the conditions of ion irradiation needed for the adequate ion-beam simulation of radiation damage under fast neutron irradiation. It is established that, by the proper selection of energy and dose of Si+ ions, it is possible to reproduce well the effect of irradiation with fission neutrons of subsurface and buried layers of silicon or Si-based 2D and 3D-heterostructures. The results can be used for testing the radiation hardness of silicon-based electronic and optoelectronic device structures.

Ordered SrTiO3 Nanoripples Induced by Focused Ion Beam

Abstract Ordered nanoripples on the niobium-doped SrTiO3 surfaces were fabricated through focused ion beam bombardment. The surface morphology of the SrTiO3 nanoripples was characterized using in situ focused ion beam/scanning electron microscopy. The well-aligned SrTiO3 nanostructures were obtained under optimized ion irradiation conditions. The characteristic wavelength was measured as about 210 nm for different ion beam currents. The relationship between the ion irradiation time and current and SrTiO3 surface morphology was analyzed. The presented method will be an effective supplement for fabrication of SrTiO3 nanostructures that can be used for ferroelectric and electronic applications.

Modifying the structural phase state of fine-grained titanium under conditions of ion irradiation

The results from quantitative investigations into the structural phase state of finely dispersed titanium before and after implantation with aluminum ions are presented. Two types of α-Ti grains differing by phase composition, defect structure, and size are distinguished in the structure: fine grains in the range of 0.1–0.5 μm and coarse grains in the range of 0.5–5 μm. The presence of two types of TiO2 particles in the material, i.e., rounded particles found at dislocations in the bulk of the α-Ti grains and lamellar particles found only inside coarse α-Ti grains, is established. The formation of the Ti3Al phase is observed in the form of lamellar inclusions along the grain boundaries and rounded particles in triple joints. It is found that the particles of the TiAl3 phase are isolated with a smaller volume fraction than the Ti3Al phase; they are localized along the boundaries of coarse grains of the titanium matrix. It is established that the granular state and defect structure of the material change substantially after ion irradiation; i.e., the dislocation density and the fields of internal stresses in fine grains grow considerably, relative to the initial state of titanium.

Instability types at ion-assisted alloy deposition: From two-dimensional to three-dimensional nanopattern growth

Ion irradiation during film growth has a strong impact on structural properties. Linear stability analysis is employed to study surface instabilities during ion-assisted growth of binary alloys. An interplay between curvature-dependent ion-driven and deposition-driven instabilities is investigated. We demonstrate that ion irradiation of growing binary alloys leads to the formation of composition-modulated surface patterns. It is shown that the ion-to-atom arrival ratio R is the pattern control parameter. Close to the instability threshold we identify different regimes of instabilities driven by ion- or deposition-induced surface roughness processes, or roughness-composition feedback interactions. In particular, the synergistic effects of the curvature-dependent displacement and deposition coupling to the preferential sputtering or to the preferential diffusivity are found to induce instabilities and pattern formation. Depending on the film growth and ion-irradiation conditions, the instabilities show stationary or oscillating behavior. The latter one is exclusively connected with ion irradiation. The corresponding phase diagrams are presented in terms of experimentally accessible parameters. This shows an alternative way to control surface patterning and to grow three-dimensional laterally or vertically ordered nanostructures.

Effect of H and He irradiation on cavity formation and blistering in ceramics

Single- or poly-crystalline specimens of SiC, Si3N4, MgO, Al2O3 and MgAl2O4 were implanted with 0.4–1MeV H+ or He+ ion beams at room temperature and 650°C up to fluences of ∼1×1022/m2. This produced peak implanted gas and displacement damage levels as high as ∼50at.% and 34 displacements per atom (dpa). The specimens were subsequently examined optically, and in cross-section using transmission electron microscopy. Subsurface blistering occurred for specimens irradiated to H or He fluences greater than about 3×1021/m2 (∼15at.% peak implanted gas concentration), and surface exfoliation occurred for fluences above ∼1×1022/m2 (∼40at.% implanted gas). Both helium and hydrogen had comparable effectiveness for inducing blistering and exfoliation on an atomic basis. The threshold blistering and exfoliation fluences for both ions were weakly dependent on temperature between 25 and 650°C. Both H and He were found to be very effective in inducing matrix cavity formation, due to their low solubility in these ceramics. The implanted gas concentrations that resulted in visible cavity formation generally ranged from 1 to 5at.%. Visible cavity formation was readily induced during room temperature irradiation despite the limited vacancy mobility in these ceramics at room temperature. Three general types of cavity morphologies were observed: isolated cavities, clusters of small cavities (typically associated with dislocation loops), and two-dimensional platelets. Cavity formation was observed to initiate at the periphery of dislocation loops in some cases. During elevated temperature irradiation, cavity formation was often observed to be preferentially associated with certain low-index habit planes, particularly if the habit plane was oriented nearly parallel to the irradiated surface: (0001) and {11¯00} for Al2O3, (0001) for α–SiC, {001} and {110} for MgO, and {110} and {111} for MgAl2O4. The bubble formation and blistering behavior of the ceramics was similar to that observed in other studies of metals irradiated at comparable homologous temperatures. Ionization-induced diffusion effects associated with dual-beam light ion irradiation appeared to exert only a weak effect on cavity and dislocation loop growth compared to the single ion irradiation conditions.

Deuterium permeation in tungsten by mixed ion irradiation

Deuterium ion driven permeation was studied for mixed ion irradiation conditions with He and C. Addition of He greatly reduced permeation, while addition of C enhanced permeation. These phenomena are strongly temperature dependent, but both are significant around surface temperature of blankets (∼800K). Permeation flux has very weak dependence on microstructure. These results are important for evaluation of T behavior in blanket first walls.

Ionoluminescence induced by swift heavy ions in silica and quartz: A comparative analysis

Ionoluminescence (IL) of the two SiO2 phases, amorphous silica and crystalline quartz, has been comparatively investigated in this work, in order to learn about the structural defects generated by means of ion irradiation and the role of crystalline order on the damage processes. Irradiations have been performed with Cl at 10MeV and Br at 15MeV, corresponding to the electronic stopping regime (i.e., where the electronic stopping power Se is dominant) and well above the amorphization threshold. The light-emission kinetics for the two main emission bands, located at 1.9eV (652nm) and 2.7eV (459nm), has been measured under the same ion irradiation conditions as a function of fluence for both, silica and quartz. The role of electronic stopping power has been also investigated and discussed within current views for electronic damage. Our experiments provide a rich phenomenological background that should help to elucidate the mechanisms responsible for light emission and defect creation.

C/CrC nanocomposite coating deposited by magnetron sputtering at high ion irradiation conditions

CrC with the fcc NaCl (B1) structure is a metastable phase that can be obtained under the non-equilibrium conditions of high ion irradiation. A nano-composite coating consisting of amorphous carbon embedded in a CrC matrix was prepared via the unbalanced magnetron sputtering of graphite and Cr metal targets in Ar gas with a high ionized flux (ion-to-neutral ratio Ji/Jn = 6). The nanoscale amorphous carbon clusters self-assembled into layers alternated by CrC, giving the composite a multilayer structure. The phase, microstructure, and composition of the coating were characterized using x-ray diffraction, transmission electron microscopy, and aberration corrected scanning transmission electron microscopy coupled with electron energy loss spectroscopy. The interpretation of the true coating structure, in particular the carbide type, is discussed.

Radiation effects on film formation and nanostructural changes of iron disilicide thin film

Ion irradiation effects on the synthesis and modification of iron disilicide films have been investigated by cross-sectional transmission electron microscopy (TEM) observations in order to fabricate films with higher quality or unique properties. It has been observed that pre-treatment of the substrate surface by 0.8 keV Ne + irradiation affects the structure of the films and the interface. Highly oriented films with an atomically smooth interface with the substrate can be synthesized by optimizing the ion irradiation conditions. We also attempted to produce nanostructural changes by high-energy heavy-ion irradiation. In some cases, this led to the formation of columnar defects with an average diameter of a few nm, which appeared to be amorphous or heavily damaged. We found that the criterion determining whether such columnar defects were formed was the electronic stopping power.

快重离子辐照对非晶态SiO2薄膜光致发光谱的影响

Amorphous SiO2 thin films with about 500 nm in thickness were thermally grown on single crystalline silicon.These SiO2/Si samples were irradiated at room temperature(RT) by 853 MeV Pb-ions to 5×1011,1×1012,2×1012 or 5×1012 ions/cm2,and by 308 MeV Xe-ions to 1×1012 or 5×1012 ions/cm2,respectively.The variation of photoluminescence(PL) properties of these samples was investigated at RT using a fluorescent spectroscopy.The obtained results showed that Pb/Xe-ion irradiation led to significant changes of the PL properties and the variation of the PL properties depend strongly on the fluence of the Pb-ion irradiations and electronic energy loss of ions.For examples,huge PL peaks located at about 473 nm and 645 nm can be seen in PL spectra of 5×1012 Pb-ions/cm2 irradiated sample.Furthermore,with increasing of Pb-ion irradiation dose the intensity of these PL peaks increased.This implied that some micro-structure modifications like defects were induced by swift heavy ion irradiations,such as non-bridging oxygen defects(≡SiO·),oxygen-vacancies defects(≡Si—Si) and Si—O related defects(O—Si—O).Special light emitters will be achieved by using proper ion irradiation conditions,and it will be very useful for the synthesis of new type of SiO2-based light-emission materials.