keV Ar Ions Research Articles

Damage kinetics in high-temperature irradiated Ni crystals

High-temperature (∼800 K) ion irradiation with 380 keV Ar ions was used to modify the surface of Ni single crystals in order to generate radiation defects and mimic the effect of neutrons avoiding sample activation. The modified 800 nm thick layer was analyzed regarding structural and mechanical properties utilizing a combination of experimental and simulation techniques. The ion implantation fluence ranged from 1 × 1014 cm−2 up to 1 × 1016 cm−2, which corresponds to values of displacements per atom from 0.25 to 25, respectively. The structural characterization was performed by Rutherford Spectroscopy in Channeling mode (RBS/C) associated with scanning (SEM) and transmission electron microscopy (TEM). The experimental results were supported by Monte Carlo (McChasy) and Molecular Dynamics (MD-LAMMPS) simulations. The simulations performed using the second generation of the McChasy code show that the influence of bubbles formed inside the material is not negligible and affects the quantitative analysis of defects in the simulated spectra. A second step in damage kinetics was revealed for the highest dose (i.e., 25 dpa) as a consequence of the entanglement of dislocations and agglomeration of noble gas bubbles, which was confirmed by TEM analysis. Moreover, nanomechanical results confirm that Ar bubbles deteriorate mechanical properties such as hardness.

Formation of partially embedded Au nanostructures: Ion beam irradiation on thin film.

The Au partially embedded nanostructure (PEN) is synthesized by ion irradiation on an Au thin film deposited on a glass substrate using a 50 keV Ar ion. Scanning electron microscopy results show ion beam-induced restructuring from irregularly shaped nanostructures (NSs) to spherical Au NSs, and further ion irradiation leads to the formation of well-separated spherical nanoparticles. Higuchi's algorithm of surface analysis is utilized to find the evolution of surface morphology with ion irradiation in terms of the Hurst exponent and fractal dimension. The Au PEN is evidenced by Rutherford backscattering spectrometry and optical studies. Also, the depth of the mechanism behind synthesized PEN is explained on the basis of theoretical simulations, namely, a unified thermal spike and a Monte Carlo simulation consisting of dynamic compositional changes (TRIDYN). Another set of plasmonic NSs was formed on the surface by thermal annealing of the Au film on the substrate. Glucose sensing has been studied on the two types of plasmonic layers: nanoparticles on the surface and PEN. The results reveal the sensing responses of both types of plasmonic layers. However, PEN retains its plasmonic behavior as the NSs are still present after washing with water, which demonstrates the potential for reusability. RESEARCH HIGHLIGHTS: Synthesis of PENs by ion irradiation Utilization of Higuchi's algorithm to explore the surface morphology. Unified thermal spike and TRIDYN simulations being used to explain the results. Glucose is only used as a test case for reusability of substrate.

Sputtering of silver nanoparticles bombarded with 3–100 keV Ar ions

Rutherford backscattering spectrometry and scanning electron microscopy were applied to obtain sputtering yields of Ag nanoparticles (5–30 nm in diameter) under 3–100 keV Ar+ ion irradiation. For low-energy ion irradiation, the diameter dependence of the sputtering yield was approximately 1.5 times higher than that of the bulk at diameters of a few nanometers, and then approached the bulk value at larger diameters. Under high-energy ion irradiation, especially for 100 keV Ar+ irradiation, the sputtering yields of Ag nanoparticles with diameters as small as a few nanometers were extremely higher than those predicted by the theoretical calculations. We concluded that such high sputtering yield originated in Ag cluster emission.

PKA Energy dependence of defect evolution in ion irradiated Fe-15Ni-15Cr alloy – a successive cascade study using molecular dynamics simulation

Molecular dynamics has been used to carry out successive cascade simulations on model alloy Fe-Ni-Cr for three distinct primary knock-on atom (PKA) energies to elucidate the earlier experimentally obtained results of ion irradiation studies on SS316 and its Ti-modified version. The PKA energies used for the simulations were calculated using the stopping and range of ions in matter (SRIM-2013) to represent the irradiation of SS316 using 145 MeV Ne, 35 MeV He and 315 keV Ar ions. The simulation has been carried out successively to emulate the progress of irradiation and obtain results as a function of dose. The results for each PKA energy have been analysed to obtain the evolution of defect clusters in terms of their size, different types of dislocations, stacking fault probabilities, etc., in all three cases. The simulation results have been compared with our earlier experimental studies.

An evaluation of Ar ion milling in TEM sample preparation by energy-filtered TEM technique

Irradiated materials impose unique challenges when it comes to sample preparation for transmission electron microscopy (TEM) analysis. After the preparation of TEM samples by electrolytic polish, Ar ion milling was usually used to remove the surface contamination, as well as to thin the samples to desired thickness. Therefore, it is necessary to evaluate the advantages and limitations of Ar ion milling technique. In this work, the optimum milling condition with minimal surface artifacts was determined by Ar ion milling with various incident angles and beam energies, and the high-resolution TEM (HR-TEM) examinations confirmed the optimum condition to be 4.0keV Ar ions with incident angles of ±4°. In addition, Ar ion milling and subsequent thickness measurement by energy-filtered TEM (EF-TEM) were conducted to determine the thinning rate. It is found that electrolytic polished TEM lamella has a wedge-shape structure with a very sharp edge, and the thinning rates varied from 9.7±1.4nm/minute to 5.0±2.3nm/minute across the TEM lamella for 4.0keV Ar ions. However, the thinning rates for 2keV and 1keV Ar ions were under the examination limit, and they were supposed not sufficient to thin the tungsten samples. Even though the exact thinning rate varies for different materials, the general trends for the Ar ion milling observed in this study can be used as a guidance.

Exploring wetting & scaling behavior of rough silicon surfaces

Here we study the roughening behavior, scaling properties and the wetting nature of the Silicon surfaces that have been irradiated with 3 keV Ar ions. These surfaces illustrate the formation of nanostructures and ripples, which evolve at higher fluences. The scaling studies have been applied to understand the evolution of the surfaces. Height- Height correlation method has been utilized to extract important scaling parameters, and the derived Hurst exponents (H) indicate these surfaces to be of self-affine type. The derived correlation lengths (ξ) reflect long ranged correlations on the surface and evolution of the nanostructures. The nano-patterned surfaces show near hydrophobic behavior, which gets further enhanced with increasing irradiation.

Study of surface morphology of Ag thin films prepared by sputtering and irradiation with keV Ar ion beam

In this paper, the possibility of preparing silver nanostructures with a high area density of nanoparticles of various shapes by the ion beam sputtering (IBS) method, using a glancing angle deposition (GLAD) configuration, and subsequent irradiation with heavy ions, was tested. In the experiment, keV Ar+ ions were used for both IBS and bombardment. The prepared nanostructures were analyzed by RBS and microscopic methods of SEM and AFM. It turned out that IBS/GLAD makes it possible to create silver nanostructures (networks of individual silver nanoparticles), but only with relatively low areal densities (∼ 70 µm2). The bombardment led to changes in the porosity only after high ion fluences, but also to disruption of the nanostructures. Even so, the IBS method with GLAD configuration has been shown to be a promising way to prepare high-porosity nanostructures. Nevertheless, further experimental efforts will be needed to find the optimal technology.

380-keV Ar+-irradiation effects on optical phonons in graphite studied with transient reflection measurement

In this work, we performed transient reflection measurements using the pump–probe protocol to investigate the influence of lattice defects induced by 380 keV argon (Ar) ions on the phonon dynamics of interlayer shearing (E2g1) and in-plane carbon stretching (E2g2) modes in highly oriented pyrolytic graphite (HOPG). The frequency and decay rate of E2g1- and E2g2-mode phonons were changed significantly at the fluence of 1×1014 ions/cm2. This indicated that significant structural changes in HOPG due to 380 keV Ar-ion irradiation were expressed as changes in the frequency and decay rate of phonons. In HOPG irradiated with 380 keV Ar+ at the fluence of 1×1014 ions/cm2, our measurement results indicated that compressive and tensile stresses contributed to in-plane and interlayer graphite structures, respectively.

Ion bombardment induced surface microstructural modification of aluminum alloy

Surface microstructural modifications of 2A12 aluminum alloy exposed to 60 keV Ar ion bombardment with the dose of 1 × 1017 ions/cm2 under vacuum were studied in detail. The amorphous layer with the thickness of ∼130 nm accompanied with polycrystalline aluminum was formed at the surface after Ar ion bombardment. Beneath the amorphous layer, Al2CuMg precipitates were observed. Dynamic recrystallization(DRX)and grain growth were observed with the increment of texture intensity. Surface residual compressive stress and strain were enhanced characterized by electron back-scattered diffraction. After ion bombardment, the contact angles of diiodomethane and DI water on aluminum alloy were increased, and a notable decrement of surface energy of aluminum alloy was measured from 32.5 mJ/m2 to 23.4 mJ/m2. The diffusion experiments indicated that the mutual diffusion of Cu and Al was inhibited due to the bombardment-induced amorphous layer at aluminum alloy surface, which is beneficial to its application as a structure material in aerospace field.

Monitoring of the recovery of ion-damaged 4H-SiC with in situ synchrotron X-ray diffraction as a tool for strain-engineering

In situ thermal annealing (673-1273 K) during X-ray diffraction synchrotron measurements was performed to monitor the strain level as a proxy to follow the recovery of 300 keV Ar ion irradiated 4H-SiC single crystals. Results show that, when exposed to Ar ions at a fluence of 6.7 $$\times$$ 10 $$^{14}$$ ions/cm $$^2$$ (0.7 dpa), the material suffers a maximum strain of 12 $$\%$$ that reduces to 2 $$\%$$ after the final anneal at 1273 K. In the same time, the disorder derived from the XRD data also demonstrates a thermal recovery of the crystalline structure. Hence, this work presents ion irradiation as a means to induce specific crystalline order and depth-controlled strain states within a few 100 s of nm window in 4H-SiC.

GaAs a model system to study the role of electron–phonon coupling on ionization stimulated damage recovery

The latent ion tracks observed in various materials after swift heavy ion (SHI) irradiation is often explained in the framework of thermal spike model (TSM). Dominantly, SHIs deposit most of their energy via intense ionization leading to a very high density of localized electronic excitations. The energy transfer from electrons to lattice, within a time of electronic cooling ∼100 fs, is governed by the ‘electron-phonon coupling’ parameter g. In this work, GaAs is used as a model system for studying ionization-stimulated damage recovery. Controlled damage is introduced using 300 KeV Ar ion irradiation, followed by successive irradiation using 100 MeV Ag ions at ∼80 K by varying the fluence (ions cm−2). The TSM is utilized to explain the observed recovery. Using the previously published value of 1012 W cm−3 K−1 for GaAs, the existing thermal spike code resulted in melting and quick quenching within ∼10 ps, suggesting the formation of SHI-induced tracks. However, experimental observations do not support the formation of tracks in pristine GaAs. Multiple simulation runs, for different g values, predict that for no melting in GaAs, g should be 1.4 × 1012 W cm−3 K−1. Finally, the 3D version of the TSM is used to simulate the temperature profiles after an impact of SHI irradiation on an amorphous nano-zone embedded in a crystalline GaAs matrix. Simulations predict that the thermal spike in this zone is confined, indicating melt-flow at the crystalline-amorphous interface that can promote recovery. This lattice recovery is further supported by both RBS/C and TEM results.

Mechanical behavior of ion-irradiated ODS RAF steels strengthened with different types of refractory oxides

One of the most promising candidates for constructing IV generation nuclear reactors is Oxide Dispersed Strengthening (ODS) Reduced Activation Ferritic (RAF) steel. It is known that introducing refractory oxides to the ferritic matrix makes it possible to obtain a brand-new kind of materials with an excellent set of properties. In the present work, the authors focused on verifying materials' structural and mechanical properties strengthened by three different types of refractory oxides submitted to ion-irradiation. Three materials with an elemental chemical composition of 12 %Cr, 2 %W, 0.3 %Ti, and strengthened with 0.3% Y2O3 or Al2O3 or ZrO2 were produced by mechanical alloying and subsequently consolidated by Spark Plasma Sintering technique. Manufactured materials have been submitted to high energy (500 keV) Ar-ion irradiation at room temperature with three fluences (up to 5x1015 ions/cm2). This procedure allowed to generate a thin, strongly damaged zone with approximate thickness of 230 nm. SEM/EBSD and TEM bservations, Grazing Incidence X-ray Diffraction analysis, and nanoindentation tests have been included in examination of modified layers. Implementation of these techniques allowed to reveal alteration of structural and mechanical features between unmodified material and radiation-affected layer. Obtained results showed a strong correlation between the strengthening oxide and materials' microstructural and mechanical behavior under radiation damage. It has been proved that below 1x1015 ions/cm2 mechanical properties in the modified layer of all materials are very similar. Reported behavior may be related to the efficient annealing of the radiation defect process. Above this limit, significant differences between the materials are visible. It is believed that described phenomenon is directly related to the presence of the structural features and their capacity to act as defect sinks. Consequently, type of dominant mechanisms occurring in modified layer is proposed.

Structural stability of β -Ga2O3 under ion irradiation

β-Ga2O3 was suggested to have excellent irradiation hardness which makes β-Ga2O3-based devices extremely attractive for nuclear and space applications. To discern the fundamental nano-scale structural changes with irradiation, an in situ irradiation experiment in a transmission electron microscope was carried out using 400 keV Ar ions of fluences up to 8 × 1015 cm−2 (equivalent to four displacements per atom). Contrary to previous works, which indicate a phase transition of β-Ga2O3 into the κ polymorph, the β-Ga2O3 structure was found to remain intact throughout except for (i) anisotropic lattice distortions, which are most significant at low levels of irradiation, and (ii) the appearance of additional weak reflections above 2 dpa irradiation. The origin of the extra reflections is discussed.

Ion beam figuring with focused anode layer thruster.

This work presents the peculiarities of cone ion beam formation with a focused thruster with anode layer (TAL) and its application to silicon carbide (SiC) ion beam figuring. Modeling results of Lorentz E × B force distribution in the discharge gap are presented. 3D particle tracing for keV Ar ions is carried out for the first time in the beam drift region of TAL with magnetic lens. Extracted ion beam full width at half maxima is about 2mm in the focal plane, where the SiC etching rate reaches 0.5 µm/min. The SiC sputter yields are measured as a function of the Ar ion impact energy and beam incidence angle. The maximum sputter yield of 2.8 atom/ion is observed at 45° of the beam-sample angle for the Si targets. Furthermore, the maximum sputter yield value of 1.7 atom/ion is measured at 30° of the beam-sample angle for the SiC targets. The novelty of present research is in the application of focused TAL keV Ar ion beam to the SiC ion beam figuring.

Surface microstructure and wetting of SiC ceramic modified by ion bombardment

Ion bombardment is one of the powerful methods to modify the surface characteristics of materials. In this study, SiC ceramic is bombarded under different fluences by 60 keV Ar-ion beam. The effects of Ar ion bombardment on the surface microstructure and subsequent wetting of SiC ceramic using AgCu-Ti filler metal are investigated. Ar ion bombardment can break the SiC bond of SiC cell, thus, SiCx(x < 1), SiCx(x < 1) twins and the amorphous layer are generated in the SiC surface with the increase of fluence from 1×1014/cm2 to 1×1017/cm2. With the increase of fluences, the contact angle decreases by the acceleration of interfacial reaction rate as a result of the break of SiC bond in SiC surface in the rapid spreading stage. The amorphous layer is gradually formed in the SiC surface, requiring more time to reach the equilibrium stage for droplets, while the bonding quality of the SiC/AgCu-Ti wetting interface is obviously improved. Significant modification in the microstructural and excellent wetting behavior are obtained by leveraging the ion bombardment technique.

Surface characterization of low energy Si ion implanted graphene

Heteroatom doping is a critical route to implement graphene-based applications. Ion implantation is an ideal method for its advantages of controllability and diversity, but limited in two-dimensional materials applications by the lack of dopants with appropriate energy. In this work, single-layer graphene is implanted with sputtered Si atoms, which are from a pure silicon target bombarded with 15 keV Ar ions. Si atoms are doped into graphene with concentration up to 8.9 at%, which can be accurately controlled by adjusting the ion fluence. The Raman spectra manifests that the irradiation damage of graphene are mainly substitutions and adsorptions, while the vacancies maintain in a low level. In addition, the work function of the doped graphene increases from 4.34 to 4.46 eV when the Si concentration varied from zero to 8.9 at%, showing promising potential in regulating the performance of related electrical applications. Our work provides a simple, controllable, and widely applicable approach for doping two-dimensional materials with nearly all the elements besides silicon.

Recovery of ion-damaged 4H-SiC under thermal and ion beam-induced ultrafast thermal spike-assisted annealing

The recovery effect of isochronal thermal annealing and inelastic energy deposited during 100 MeV Ag swift heavy ion (SHI) irradiation is demonstrated in the case of 4H-SiC pre-damaged by elastic energy deposition of 300 keV Ar ion. The Ar-induced fractional disorder follows a nonlinear two-step damage build-up. The fractional disorder level of 0.3 displacements per atom (dpa) is established as the threshold above which the lattice rapidly enters the amorphous phase, characterized by the presence of highly photo-absorbing defects. The SHI-induced recovery suggests that the damage annealing, in the pre-damaged region (∼350 nm) where the Se for 100 MeV Ag is almost constant (∼16.21 keV/nm), is more pronounced than the damage creation by SHI. This allows the disorder values to saturate at a lower value than the present initial disorder. Furthermore, the thermal effect due to SHI irradiation of an amorphous nano-zone embedded in a crystalline host matrix has been evaluated using the 3D implementation of the thermal spike. The recovery process by SHI is ascribed to the thermal spike-induced atomic movements resulting from the melting and the resolidification of the crystalline–amorphous interface.

Tuning the optical and electrical properties of magnetron-sputtered Cu–ZnO thin films using low energy Ar ion irradiation

Cu doped ZnO (Cu–ZnO) nanocomposite thin films were successfully synthesized at room temperature by RF magnetron sputtering. The signature of Cu in pristine ZnO thin films was confirmed by Rutherford Backscattering Spectroscopy (RBS) with atomic concentration of ~10%. The Cu–ZnO thin films were irradiated with 800 keV Ar ion beam at three different ion fluences viz. 5 × 1015, 7 × 1015 and 9 × 1015 ions/cm2. As characterized by X-ray diffraction, the pristine and irradiated films show a hexagonal wurtzite structure with remarkable intensities of (100), (002) and (101) orientations. The surface morphology of the pristine and irradiated films was recorded using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The images clearly show the grain growth near the surface of films with increasing the ion fluences. The surface plasmon absorption (380 nm onwards) indicating the formation of metal nanoparticles in oxide matrices was confirmed by UV–visible spectroscopy of ion irradiated films. The electrical properties of the pristine and irradiated films were deduced by current voltage (I–V) and Hall measurements. The conductivity of the film increases as irradiation proceeds, achieves a maxima and then decreases with further processing of the ion beam. This study explores ion beam irradiation as a versatile tool to tailor the physical properties of nanocomposite thin films. Further, the properties can be precisely controlled by optimizing ion fluences and incident ion energy as well.

300 keV Ar ion induced effects in GaAs and 4H-SiC

Radiation damage effects on the structures of GaAs and 4H-SiC single crystals are investigated after irradiation with 300 keV Ar ions at room temperature. It is found that despite having contrasting physical and chemical properties, 0.3 displacement per atom (dpa) is the threshold of fractional disorder above which there is a rapid damage build-up behavior exhibited by both GaAs and 4H-SiC. 1 dpa means that all atoms are displaced at least once from their respective lattice sites. This study reveals that disordering in irradiated binary semiconductor materials is a discontinuous two-step process wherein various stages of irradiation are marked by different damage growth mechanisms.

Restoration of ion beam irradiation induced metastable magnetic states and lattice structures of FeRh thin films by heat treatments at elevated temperatures

The restoration process of irradiation-induced metastable magnetic states of FeRh thin films during the heat treatments at 373–1073 K was investigated by measuring the magnetization-magnetic field (M−H) curves and the magnetization-temperature (M−T) curves for the FeRh thin films irradiated with 50 keV Ar ions to various fluences. The recovery of lattice structures accompanying the magnetic restoration was also examined by an x-ray diffraction (XRD) measurement. For the ferromagnetic state induced by low fluence irradiation, the magnetic restoration to the thermal equilibrium antiferromagnetic state occurs during the heat treatment. Whereas for the paramagnetic state induced by high fluence irradiation, it once changes to the ferromagnetic state, and then, is restored to the antiferromagnetic (i.e., thermal equilibrium) state during the heat treatment. The above magnetic transformation occurs by the heat treatments at higher temperatures for the higher fluence irradiation. Moreover, the magnetic transition temperature from the antiferromagnetic state, which has been thermally restored from the irradiation induced ferromagnetic or paramagnetic state, to the ferromagnetic state decreases with increasing the irradiation fluence. This result implies that the antiferromagnetic state with larger amount of lattice defects is more unstable against the thermal vibration of lattice atoms.