Incident Ion Fluence Research Articles

Influence of energetic heavy ion sputtering on lifetime of alloy target

When energetic heavy ions are incident on negatively charged structure that collects and deposits ions, ion sputtering will occur. Metal wire is a structure commonly used for accelerating ions, the incidence of continuous high-throughput ions can cause surface loss of metal wire, affecting the service performance and lifespan of the metal wire. The SRIM software commonly used for calculating sputtering yield cannot consider the multi-body interaction problem contained in the alloy crystal structure. so, there is a significant error in calculating the sputtering yield of high-energy ions incident on alloy target. Based on the molecular dynamics method and Langevin temperature control model, the calculation model of ion sputtering parameters of energetic metal ions incident on alloy target is established in this work. The model is used to calculate the sputtering yield under the conditions of intact surface lattice of the target material and long-term incident surface lattice damage. The damages to the cathode metal wire under different incident ion fluences are further calculated, and the cross-sectional characterization of the metal wire is carried under typical working condition. The results show that the discrepancy between the experimental value and the theoretical value is less than 10%, which verifies the accuracy and applicability of the theoretical model. Based on this model, the search direction for sputtering resistant materials is proposed, meanwhile, a theoretical optimization is carried out to improve the service life of metal wire, and a method of using Ni-Ti alloy to improve the service life of metal wires is proposed, which is of great significance for predicting the service life of the metal wire under different conditions.

Molecular dynamics simulation of phase transition by thermal spikes in monoclinic ZrO<sub>2</sub>

Owing to its excellent corrosion, radiation and high temperature resistance, ZrO<sub>2</sub> has been considered as a strong candidate material for inert fuel for the incineration of actinides. In this paper, a combination of thermal spike model and molecular dynamics is used to simulate the phase transition process of ZrO<sub>2</sub> in the nuclear radiation environment. Based on the thermal spike model, two coupled diffusion equations are established with considering the multiple physical process of energy deposition and transmission after the implantation of swift heavy ions into target material. The space-time evolution characteristics of ZrO<sub>2</sub> lattice temperature are obtained by solving the coupled diffusion equations numerically. Then the phase transformation of ZrO<sub>2</sub> form monoclinic phase to tetragonal phase under the thermal spike is investigated on an atomic scale by means of molecular dynamics. It is found that a cylindrical track with a radius of 7 nm is generated in the center of ZrO<sub>2</sub> after the implantation of swift heavy ion with an electronic energy loss of 30 keV·nm<sup>–1</sup>. The lattice melts immediately in the center of track, accompanied with the coordination number of Zr decreasing from 7 to 4–6. Then at about 2 ps, the melting zone gradually turns cool and recrystallized. And in the center of the melting zone, voids begin to form and are surrounded by a highly disordered amorphous region. Meanwhile, tetragonal phase of ZrO<sub>2</sub>, whose coordination number of Zr is 8, is formed at the periphery of the amorphous region, which is also confirmed by the XRD calculation results. As energy transfers from track center to the surround, the tetragonal region gradually develops into the whole system, accompanied with the increase of voids size. The simulation results indicate that the irradiation of ZrO<sub>2</sub> with swift heavy ions can lead to a transformation from the monoclinic to the tetragonal phase when the deposited electronic energy loss exceeds an effective threshold ~21 keV·nm<sup>–1</sup>, greater than the experimental value (12 keV·nm<sup>–1</sup>), which was mainly due to the large difference between the simulated and measured incident ion fluences and the accuracy of the force field used in the molecular dynamics.

Size distribution of nano-tendril bundles with various additional impurity gases

Abstract Nano-tendril bundles (NTBs) are generated on a tungsten surface by helium plasma exposure with various additional impurity gases, such as argon, nitrogen and neon. In this study, the formation condition of NTBs and the effect of incident ion energy, Ei, and impurity gas ratio, λg, are explored in detail. It is found that NTBs are easily formed at where the incident ion flux and fluence is enhanced, such as the periphery of the sample. The confocal laser scanning microscopy reveals that the area and the height distributions of NTBs greatly depend on Ei, which plays a dominant role in determining the birth of new NTBs and the growth of existing NTBs. The number density of NTBs is found to depend on the net erosion yield, Y, regardless of gas species, indicating that the balance between Ei and λg is important for the favorable growth of NTBs. The preferential growth of NTBs in the radius direction appears and the cause of the limited growth in height is discussed.

Dependence of the far-field optical response of ion beam sculpted Cu thin films on their surface correlations

Recent studies involving the properties of metallic nanostructures for potential technological applications are fundamentally rooted in their optical absorption and scattering properties. In this study, we report the far-field optical behavior of self organized copper (Cu) nanoripples on a glass substrate fabricated using low energy Ar+ ion beam irradiation for varying ion fluences. The optical characterization was performed by measuring the specular as well as the diffuse component in wavelength dependent transmittance spectra for the irradiated samples. Quantitative analyses has been performed on the morphology of the nanostructured films in order to extract the surface statistical parameters like roughness, wavelength, aspect ratio and correlation length. Optical responses from the nanostructured surfaces exhibit additionally strong characteristic spectra arising out of diffuse scattering as compared to the specular ones for increasing incident ion fluences. The peak intensity and sharpness observed in the transmittance spectra was found to depend largely on the surface height correlations which showed variation with increasing ion fluences. Finally, we demonstrate the dependencies of the local surface slope and the autocorrelation function in regulation of the optical transmittance of the nanoripple structured Cu thin films.

Performance of Eurofer97 under deuterium plasma exposure with seeded impurities at elevated temperature

Eurofer97, P92 and Fe samples were exposed simultaneously in the linear plasma device PSI-2 to deuterium plasma and with addition of He, Ar or Kr at elevated temperature in the range of 800–950 K. Samples were exposed to plasma with an incident ion energy of 60–80 eV and an incident ion fluence of 5 × 1025 m−2. Surface morphology investigation of exposed samples reveals formation of fuzz-like structures on the surface steels when exposed to D and D+He plasma. Tungsten enrichment on the surface of the steels was observed after all exposures, but the average tungsten concentration varied from 4 to 18 at.%, depending on plasma composition. The highest tungsten enrichment on the surface was observed for samples exposed to D+He plasma. Addition of He to the plasma increased D retention, which was attributed to near-surface bubble formation, confirmed by transmission electron microscopy studies.

Molecular Dynamics Simulation of Physical Sputtering of Nanoporous Silicon-Based Materials with Low Energy Argon

The process of the physical sputtering of the (001) surface of continuous and nanoporous crystalline silicon by 100- and 200-eV Ar ions is simulated using the molecular dynamics method. The features of the process in porous materials are revealed. The dependences of the sputtering yield on the fluence and energies of incident ions are obtained. The structural changes under ion bombardment are described. The dissimilarity between the sputtering mechanisms for materials differing in pore radii and the degree of porosity is demonstrated.

Irradiation effects of MeV protons on dry and hydrated Brassica rapa seeds

Although space radiation is a known risk for space travel and eventual colonization of Moon or Mars, relatively few data exist on radiation effects on potential crop plants. We studied Brassica rapa to assess the tolerance of seeds and seedlings to radiation by exposing dry and hydrated B. rapa seeds to 1, 2 and 3 MeV proton ions of various fluences and examined the effect on germination and root growth. Modeling penetration depth with SRIM code indicated that the applied energy was insufficient to penetrate the seeds; therefore, all energy was deposited into the tissue. Subsequent germination varied based on the incident ion energy and fluence (dose). Dry and hydrated seeds germinate after ion fluence (1013 ions cm−2) irradiation, but the germination percentage decreased with increasing fluence for ions that could penetrate the seed coat (> 1 MeV). Despite their greater volume and mass, hydrated seeds were more sensitive to irradiation than dry seeds. Damage of the seed coat after irradiation led to faster germination and initial seedling growth. Our results suggest that the seed coat represents a valuable natural radiation protection and that low energy protons, the prevailing solar radiation, are suitable for studying radiation effects in seeds and plants.

Impact of SHI on structural and mechanical behavior of intermetallic NiTi thin films

In the present investigation, nanocrystalline thin films of NiTi are grown on Si substrate by dc-magnetron co-sputtering using Ni and Ti sputtering targets. These as- grown NiTi thin films are irradiated by 90 MeV Ni ions with fluences 1 × 1012, 3 × 1012, 9 × 1012 and 1 × 1013 ions/cm2, respectively. The elemental composition and depth profile of the pristine film are analyzed by Rutherford backscattering spectrometry. Further, structural, surface morphology and mechanical properties of these films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation techniques, respectively. X-ray diffraction result shows the presence of both austenite and martensite phases in the pristine film with the preferred growth of (110) orientation. The crystallite size is decreased with increase in the ion fluence as compared to pristine film. The AFM images confirm the variation in surface roughness values with the change in the incident ion fluence. The nanoindentation investigation has revealed the enhancement in the mechanical behavior of the NiTi films with ion fluences. The irradiated NiTi film at a fluence of 3 × 1012 ions/cm2 exhibits higher hardness, elastic modulus and depth recovery ratio and therefore better wear-resistance as compared to other films. This result of nanoindentation indicates the higher ductility of NiTi film in comparison of pristine film and their applicability for Micro-electromechanically system applications (MEMS).

Enhanced effect of a plasma‐irradiated titanium substrate on the photocatalytic activity of a TiO2 film

To improve the photocatalytic activity of TiO2 film, Ti substrates are irradiated by He ions with different incident ion energy, temperature, and fluence. Anatase TiO2 films are then coated on the plasma‐irradiated substrates via chemical vapor deposition followed by calcination. Photocurrent tests and photocatalytic oxidation (PCO) of formaldehyde are used to assess photocatalytic performance. The optimal plasma‐irradiated samples showed a four times higher photocurrent and a three fold increase in the rate constant of the PCO reaction compared to the TiO2 coated, untreated control sample. It is found that the enhanced photocatalytic activity and photocurrent are related to the changes of Ti crystal structure and surface morphology through plasma irradiation.

Sputtering of bismuth thin films under MeV Cu heavy ion irradiation: Experimental data and inelastic thermal spike model interpretation.

The sputtering of bismuth (Bi/Si) thin films deposited onto silicon substrates and irradiated by swift Cuq+ heavy ions (q = +4 to +7) was investigated by varying both the ion energy over the 10 to 26‐MeV range and the ion fluence ϕ from 5.1 × 1013 cm−2 to 3.4 × 1015 cm−2. The sputtering yields were determined experimentally via the Rutherford backscattering spectrometry technique using a 2‐MeV He+ ion beam. The measured sputtering yields versus Cu7+ ion fluence for a fixed incident energy of 26 MeV exhibit a significant depression at very low ϕ‐values flowed by a steady‐state regime above ~1.6 × 1014 cm−2, similarly to those previously pointed out for Bi thin films irradiated by MeV heavy ions. By fixing the incident ion fluence to a mean value of ~2.6 × 1015 cm−2 in the upper part of the yield saturation regime, the measured sputtering yield data versus ion energy were found to increase with increasing the electronic stopping power in the Bi target material. Their comparison to theoretical predicted models is discussed. A good agreement is observed between the measured sputtering yields and the predicted ones when considering the contribution of 2 competitive processes of nuclear and electronic energy losses via, respectively, the SRIM simulation code and the inelastic thermal spike model using refined parameters of the ion slowing down with reduced thermophysical proprieties of the Bi thin films.

The microstructure of reduced activation ferritic/martensitic (RAFM) steels exposed to D plasma with different seeding impurities

EUROFER, P92 steel and iron samples were exposed in the linear plasma generator PSI-2 at a sample temperature of about 470–500 K with an incident ion flux of about 3–5 × 1021 m−2 s−1, an incident ion fluence of 1 × 1026 m−2 and an incident ion energy of 60–70 eV. Samples were exposed to deuterium plasma and with additional seeding impurities of He, Ar, Ne, Kr or Kr + He. Laterally averaged surface W enrichment varied between 0.6 and 6 at.%, depending on the exposure conditions, measured by energy dispersive x-ray spectroscopy with low energy electron beam and Rutherford backscattered spectroscopy. Microstructure observation revealed a complex morphology depending on the plasma composition. W enrichment was mostly located in the spike nano structures. Addition of He to the plasma rounded and enlarged the spikes on the surface whereas addition of heavier species to the plasma resulted in smoothing the steels surface. In case of steel samples exposed to D + He plasma, fine nano-bubbles with sizes below 3 nm were found near the sample surface. Sputtering rate increases by one order of magnitude by Ar and Ne seeding and by two orders of magnitude by Kr seeding for both types of steels. Measured D retention increases with He addition and decreases with higher-Z species seeding.

Erosion and deuterium retention of CLF-1 steel exposed to deuterium plasma

In recent years reduced activation ferritic martensitic steel has been proposed as the plasma-facing material in remote regions of the first wall. This study reports the erosion and deuterium retention behaviours in CLF-1 steel exposed to deuterium (D) plasma in a linear experimental plasma system as function of incident ion energy and fluence. The incident D ion energy ranges from 30 to 180 eV at a flux of 4 × 1021 D m−2 s−1 up to a fluence of 1025 D m−2. SEM images revealed a clear change of the surface morphology as functions of incident fluence and impinging energy. The mass loss results showed a decrease of the total sputtering yield of CLF-1 steel with increasing incident fluence by up to one order of magnitude. The total sputtering yield of CLF-1 steel after 7.2 × 1024 D m−2 deuterium plasma exposure reduced by a factor of 4 compared with that of pure iron, which can be attributed to the enrichment of W at the surface due to preferential sputtering of iron and chromium. After D plasma exposure, the total deuterium retention in CLF-1 steel samples measured by TDS decreased with increasing incident fluence and energy, and a clear saturation tendency as function of incident fluence or energy was also observed.

Influence of high energy ion irradiation on fullerene derivative (PCBM) thin films

The modifications produced by 55MeV Si4+ swift heavy ion irradiation on the phenyl C61 butyric acid methyl ester (PCBM) thin films (thickness∼100nm) has been enlightened. The PCBM thin films were irradiated at 1×1010, 1×1011 and 1×1012ions/cm2 fluences. After ion irradiation, the decreased optical band gap and FTIR band intensities were observed. The Raman spectroscopy reveals the damage produced by energetic ions. The morphological variation were investigated by atomic force microscopy and contact angle measurements and observed to be influenced by incident ion fluences. After 1011ions/cm2 fluence, the overlapping of ion tracks starts and produced overlapping effects.

Swift heavy ion induced optical and structural modifications in RF sputtered nanocrystalline ZnO thin film

In the present study, 100 MeV Ag7+ ion beam-induced structural and optical modifications of nanocrystalline ZnO thin films are investigated. The nanocrystalline ZnO thin films are grown using radio frequency magnetron sputtering and irradiated at fluences of 3 × 1012, 1 × 1013 and 3 × 1013 ions/cm2. The incident swift heavy ions induced change in the crystallinity together with the preferential growth of crystallite size along the c axis (002) orientation. The average crystallite size is found to be increased from 10.8 ± 0.7 to 20.5 ± 0.3 nm with increasing the ion fluence. The Atomic force microscopy analysis confirms the variation in the surface roughness by varying the incident ion fluences. The UV–visible spectroscopy shows the decrement in transmittance of the film with ion irradiation. The micro-Raman spectra of ZnO thin films are investigated to observe ion-induced modifications which support the increased lattice defects with higher fluence. The variation in crystallinity indicates that ZnO-based devices can be used in piezoelectric transduction mechanism.

The microstructure of tungsten exposed to D plasma with different impurities

In this study the effect of impurities in deuterium plasma on the tungsten microstructure is investigated. W samples were exposed in the linear plasma generator PSI-2 at a sample temperature of 500K with an incident ion flux of about 1022m−2s−1, an incident ion fluence of 5×1025m−2 and an incident ion energy of 70eV. Samples were exposed to pure D+ plasma and with additional impurities of He (3%), Ar (7%), Ne (10%) or N (5%). After the PSI-2 exposure a part of each sample was additionally loaded with tritium to measure the tritium uptake using the imaging plate technique.The surface morphology was investigated using scanning electron microscope (SEM) combined with a focused ion beam (FIB) utilized for cross-sectioning and thin lamella preparation for the transmission electron microscope (TEM) analysis.Blistering with grain orientation dependence was observed on all exposed samples. Most pronounced blistering is reported for grains with orientation close to (111). The addition of Ar or Ne results in surface erosion with different yields depending on grain orientation. Highest erosion yield is observed for grains with orientation close to (100). Large blisters are present but show signatures of erosion. Less pronounced erosion is visible when adding N. The highest uptake of tritium was reported for the sample exposed to D+He plasma which corresponds to the largest – 18nm, near surface damage zone revealed by TEM. Lowest tritium accumulation was observed for samples exposed to D+Ar and D+Ne plasmas, which corresponds to the shallowest near surface damage zone, as confirmed by TEM.

Molecular dynamics study of radiation damage and microstructure evolution of zigzag single-walled carbon nanotubes under carbon ion incidence

The radiation damage and microstructure evolution of different zigzag single-walled carbon nanotubes (SWCNTs) were investigated under incident carbon ion by molecular dynamics (MD) simulations. The radiation damage of SWCNTs under incident carbon ion with energy ranging from 25eV to 1keV at 300K showed many differences at different incident sites, and the defect production increased to the maximum value with the increase in incident ion energy, and slightly decreased but stayed fairly stable within the majority of the energy range. The maximum damage of SWCNTs appeared when the incident ion energy reached 200eV and the level of damage was directly proportional to incident ion fluence. The radiation damage was also studied at 100K and 700K and the defect production decreased distinctly with rising temperature because radiation-induced defects would anneal and recombine by saturating dangling bonds and reconstructing carbon network at the higher temperature. Furthermore, the stability of a large-diameter tube surpassed that of a thin one under the same radiation environments.

Impact of surface morphology on sputtering during high-fluence plasma exposure

The erosion behavior of beryllium targets subjected to deuterium, or argon, plasma is compared. Erosion by deuterium plasma results in the development of a cone-like surface morphology and the resultant measured erosion rate is almost an order of magnitude less than expected from sputtering calculations. The morphology that develops has been characterized as a function of incident ion energy and fluence to the target. The sputtering yield measured from targets exposed to argon plasma agrees with sputtering calculations and no surface morphology is observed after the exposure. A simulation of the sputtered atoms ejected into the plasma column is developed in order to understand the changing axial penetration distance measured spectroscopically as the morphology emerges. Redeposition of atoms sputtered at shallow angles on adjacent cone structures can result in a lower erosion rate and can account for an increase in the axial penetration distance of atoms into the plasma.

Ion-induced luminescence and damage process of LiTaO3

In order to examine the basic characteristics of light emission and damage accumulation in lithium tantalate (LiTaO3), ion-induced luminescence was measured. A broad peak centered at about 540nm was observed under ion bombardment. The ion-induced luminescence was essentially the same as the luminescence under UV photon irradiation. The initial intensity of the luminescence was proportional to the projected range of the incident ions and independent of the electronic energy loss. The shape of the spectra was independent of the species, energy, and fluence of incident ions. The luminescence monotonically decreased with an increase in ion fluence. Assuming first-order kinetics in the annihilation and recovery process of the luminescent centers, the annihilation rate was proportional to the nuclear energy stopping power. It was considered that the luminescent center was mainly damaged by nuclear collisions, and the recovery of the damaged luminescent center was caused by local heating by the ion beam.

Effects of energetic ion irradiation on the magnetism of Fe–Ni Invar alloy

The magnetic properties of Fe–Ni Invar alloys are significantly affected by ion irradiation. Au3+ with the energy of 16MeV irradiation effects on the magnetism of Fe66Ni34 have been reported in this paper. Considering from the temperature variations of AC susceptibility of irradiated Fe66Ni34, Curie temperature of a part of sample increase with increasing incident ion fluence, and the magnetization of irradiated Fe66Ni34 is also increase. The FCC structure of Fe66Ni34 is not changed by ion irradiation; however peaks become broader with increasing ion fluence. It means that lattice fluctuations are generated owing to ion irradiation. However it cannot be considered that lattice fluctuations observed X-ray diffraction measurements are enough to increase the Curie temperature observed in AC susceptibility measurements. Then, we suggest as the considerable origin of increasing TC, atomic mixing effects owing to the ion irradiation. It might change the chemical ordering reported in the diffused scattering, such as Fe–Fe coupling.

Nanoscale Track Diameter and Hydrogen Yield: Dependence upon Charge State of Incident Ion on Polystyrene

The study of radiation damage of high- molecular weight substances due to MeV ion interactions is of interest for engineering and scientific applications. In the present study polystyrene (PS) was irradiated with 107Ag ions of three different charge states (q) 11+, 14+ and 25+ and of 130 MeV energy. The emission of hydrogen from PS was monitored as a function of the incident ion fluence. The experimental results showed that the hydrogen depletion per incident ion from PS varies as qn, where n was found to be 2.1 as compared to the value 2.7 to 3.0 reported in the literature. Radii of the nanometric damaged zones or ion tracks formed were analyzed from the slope of the hydrogen depletion versus ion fluence curves as a function of charge state of incident ion. These have values between 3.2 - 6.8 nm. These radii were found to depend upon the charge state of the incident ion and vary as qm, where m has the value 0.9.