MeV Ni Ions Research Articles

Effect of dose and post irradiation annealing in Ni implanted high entropy alloy FeCrCoNi using slow positron beam

Defect characterization of room temperature 1.5 MeV Ni ion implanted high entropy FeCrCoNi alloy for two fluences (1 × 1015 ions/cm2 and 5 × 1016 ions/cm2) was carried out using the variable low energy positron beam. The FCC solid solution remains robust and stable under 100 dpa irradiation and high temperature annealing. The change in the defect sensitive S-parameter upon implantation reveals the presence of monovacancies for both the doses. The changes in the defect microstructure upon thermal annealing are found to be dose dependent. The high dose shows the formation of stable stacking fault tetrahedrons (SFT's) from the aggregates of monovacancies at higher annealing temperatures while the low dose shows the annealing of monovacancies with temperature.

Ni ion damage structures and hardness changes in austenitic stainless steels and their model alloys

Defect structures of austenitic stainless steels and their model alloys after 6 MeV Ni ion irradiation were studied using positron annihilation lifetime measurements and Vickers hardness obtained from micro-hardness measurements. After irradiation at room temperature, a long lifetime of 150-180 ps was obtained and the Vickers hardness increased with increasing the irradiation dose. After irradiation at 573 K, all the alloys exhibited lifetime spectra that were not decomposed into two components. Their hardness also increased with the irradiation dose, but the enhancement was small compared with that at room temperature. Defects introduced by the ion irradiation could be detected near the surface using a Na-22 source. The hardness is correlated with the density and size of the defect clusters.

Investigation of defect clusters in ion-irradiated Ni and NiCo using diffuse X-ray scattering and electron microscopy

The nature of defect clusters in Ni and Ni50 Co50 (NiCo) irradiated at room temperature with 2–16 MeV Ni ions is studied using asymptotic diffuse X-ray scattering and transmission electron microscopy (TEM). Analysis of the scattering data provides separate size distributions for vacancy and interstitial type defect clusters, showing that both types of defect clusters have smaller sizes and higher densities in NiCo than in Ni. Diffuse scattering results show good quantitative agreement with TEM size distributions for cluster sizes greater than 2 nm in diameter, but we find that TEM under represents the number of defect clusters ≤ 2 nm, which comprise the majority of vacancy clusters in NiCo. Interstitial dislocation loops and stacking fault tetrahedra are identified by TEM. Comparison of diffuse scattering lineshapes to those calculated for dislocation loops and SFTs indicates that most of the vacancy clusters are SFTs.

Ion track diameter in fullerene C70 thin film using Raman active vibrational modes of C70 molecule

The effect of energy deposition in fullerene C70 (∼150 nm) thin film deposited by resistive heating method on glass, quartz and silicon substrates was investigated. The samples were irradiated with 90 MeV Ni ion beam at the fluences ranging from 1 × 1012 to 3 × 1013 ions/cm2. The pristine and Ni ion irradiated samples were examined for morphological and optical changes by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), UV–visible absorption spectroscopy and Raman spectroscopy. After ion irradiation, bigger grains are shown on surface as revealed by SEM analysis indicating the agglomeration of the smaller particles into bigger particles at the surface. UV–visible absorption studies reflect that the direct band gap of the film decreases with increase in ion fluence. At higher fluence, fullerene C70 is transformed into amorphous carbon (a-C) which is confirmed by Raman spectroscopy. The damage cross-section (σ) and radius of the damaged cylindrical zone (r) are approximated to be ∼1.72 × 10−13 cm2 and ∼2.3 nm, respectively using Raman active vibrational modes.

Ion irradiation studies on the void swelling behavior of a titanium modified D9 alloy

The sensitivity of Positron Annihilation Spectroscopy (PAS) for probing vacancy defects and their environment is well known. Its applicability in determination of swelling and the peak swelling temperature was put to test in our earlier work on ion irradiated D9 alloys [1]. Upon comparison with the peak swelling temperature determined by conventional step height measurements it was found that the peak swelling temperature determined using PAS was 50 K higher. It was conjectured that the positrons trapping in the irradiation induced TiC precipitation could have caused the shift. In the present work, D9 alloys have been implanted with 100 appm helium ions and subsequently implanted with 2.5 MeV Ni ions up to peak damage of 100 dpa. The nickel implantations have been carried out through a range of temperatures between 450 °C and 650 °C. The evolution of cavities and TiC precipitates at various temperatures has been followed by TEM and this report provides an experimental verification of the conjecture.

Predictive modeling of synergistic effects in nanoscale ion track formation.

Molecular dynamics techniques in combination with the inelastic thermal spike model are used to study the coupled effects of the inelastic energy loss due to 21 MeV Ni ion irradiation with pre-existing defects in SrTiO3. We determine the dependence on pre-existing defect concentration of nanoscale track formation occurring from the synergy between the inelastic energy loss and the pre-existing atomic defects. We show that the size of nanoscale ion tracks can be controlled by the concentration of pre-existing disorder. This work identifies a major gap in fundamental understanding on the role of defects in electronic energy dissipation and electron-lattice coupling.

Correlation between surface phonon mode and luminescence in nanocrystalline CdS thin films: An effect of ion beam irradiation

The influence of swift heavy ion irradiation (SHII) on surface phonon mode (SPM) and green emission in nanocrystalline CdS thin films grown by chemical bath deposition is studied. The SHII of nanocrystalline CdS thin films is carried out using 70 MeV Ni ions. The micro Raman analysis shows that asymmetry and broadening in fundamental longitudinal optical (LO) phonon mode increases systematically with increasing ion fluence. To analyze the role of phonon confinement, spatial correlation model (SCM) is fitted to the experimental data. The observed deviation of SCM to the experimental data is further investigated by fitting the micro Raman spectra using two Lorentzian line shapes. It is found that two Lorentzian functions (LFs) provide better fitting than SCM fitting and facilitate to identify the contribution of SPM in the observed distortion of LO mode. The behavior of SPM as a function of ion fluence is studied to correlate the observed asymmetry (Γa/Γb) and full width at half maximum of LO phonon mode and to understand the SHII induced enhancement of SPM. The ion beam induced interstitial and surface state defects in thin films, as observed by photoluminescence (PL) spectroscopy studies, may be the underlying reason for enhancement in SPM. PL studies also show enhancement in green luminescence with increase in ion fluence. PL analysis reveals that the variation in population density of surface state defects after SHII is similar to that of SPM. The correlation between SPM and luminescence and their dependence on ion irradiation fluence is explained with the help of thermal spike model.

Damage properties in ion-implanted YbVO4 crystals using RBS/Channeling study

YbVO4 crystals are implanted with 3.0MeV Ni ions and 600keV H ions with fluences of 2.0–10.0×1014cm−2 and 6.0×1016cm−2, respectively. In addition, post-implantation thermal annealing is performed at selected temperatures. The disorder induced by implantation and the effect of the annealing on the recovery of the crystal lattice are investigated by RBS/Channeling measurements with the help of simulation code RUMP.

Ion beam-assisted template synthesis of nanowires on semiconducting substrate

In this paper, we have studied the electrical properties of the randomly distributed metallic (Cu, Ni and Fe) nano-/micro wires on the silicon substrate. Deposition was carried out potentiostatically into the pores of the track-etch polycarbonate membrane spin coated onto the Si substrate. Spin coated films were irradiated with 150 MeV Ni (+11) ions at a fluence of 5E8 ions/cm2, followed by Ultra-Violet (UV) irradiation and chemically etching in aqueous NaOH (6N, at room temperature). The size, shape and morphology of the synthesized nano-/micro structures is strongly dependent on the preparation conditions such as deposition potential, current density, electrolyte and etching conditions. Later, morphological and electrical properties of the so-deposited nano-/micro structures were studied.

60 MeV Ni ion induced modifications in nano-CdS/polystyrene composite films

The cadmium sulfide (CdS) nanoparticles of size in the range 50–60nm were synthesized by micro-emulsion method. The polystyrene/CdS (PS/CdS) nanocomposites were doped with Ni and Cu metals. The pristine and doped samples were irradiated with 60MeV Ni ions. The effect of doping of metals and ion irradiation was studied for modifications in structural, optical and chemical properties of PS/CdS nanocomposites. The decrease in peak width of XRD spectra of irradiated PS indicated the decrease in the amorphous nature at higher fluences. The optical absorption peaks of the irradiated and doped samples shifted towards visible region. The shift in case of metal doped samples was more pronounced than those of pure polystyrene and PS/CdS matrix samples. The increase in absorption was attributed to the generation of a conjugated system of bonds. The decrease in band gap energy value in case of Ni doped PS/CdS was greater than that of Cu doped PS/CdS and the ion irradiation further decreased the band gap energy value. The vibrational absorption peak of the Cd–S bond was observed at 405cm−1 in FTIR spectra of metal doped PS/CdS composites. The intensity of styrene absorption lines decreased in all irradiated samples.

Study of 130 Mev Ni Ion Irradiation Induced Surface Modification of DLC Films Grown By Microwave Plasma CVD.

We report on the 130 MeV Ni ion irradiation induced modification of the surface roughness of DLC films grown by microwave plasma CVD method. The MWCVD system which was used to grow the DLC thin films was designed and developed in-house. The growth of thin films of DLC was studied with different substrate dc bias using Ar/H2 (2%) and Methane as feedstock. The deposited films were irradiated with 130 MeV Ni ion irradiation to doses of 3e, 3e and 1e ions/cm. Atomic force microscopy and Raman spectroscopy were used to study the 130 MeV Ni ion irradiation induced modification of surface topography and structure of the DLC films. Raman spectroscopy results of the deposited films show D and G bands at 1380 cm and 1558 cm characteristic of DLC films and indicate change in sp content with change in –dc bias. The Atomic force microscopy results show that the deposited DLC films have smooth surface and the RMS roughness decreased in the irradiated films relative to the pristine film which can be due to the electronic energy loss of 130 MeV Ni ions being lower than the energy loss threshold for track formation.

SHI irradiation induced effects in functionalized MWCNTs

Multi-walled carbon nanotubes (MWCNTs) have attracted extensive attention globally due to their applications in modern nanotechnology. It is very important to study the effects on these MWCNTs under swift heavy ion (SHI) irradiation since ion irradiation has been recognized as one of the best tools for nanostructuring of materials, in general. Here, we present the effects of 80 MeV Ni ions with a fluence ranging from 3×1012 to 3×1013 ions/cm2 on functionalized MWCNT mats. The properties of pristine and irradiated samples were studied using X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The effects of SHI irradiation on these samples are discussed in detail.

Irradiation induced nanotrack and property modification in Zn3P2

AbstractZn3P2 epilayers were grown on InP (100) substrates by liquid phase epitaxy (LPE) using In solvent. Zinc composition in the epilayers was varied by changing the zinc mole fraction in the growth melt and was confirmed by energy dispersive X‐ray analysis (EDAX). Stoichiometric Zn3P2 epilayers were subjected to 100 MeV Ni ion irradiation with various ion fluences of 1 × 1010 to 1 × 1013 ions/cm2 at 77 K. From the high resolution X‐ray diffraction (HRXRD) of 100 MeV Ni ion irradiated epilayers, the decrease in the peak intensities and increase in the FWHM values were observed. AFM analysis revealed the formation of nanotracks in the irradiated Zn3P2 epilayers. Hall measurements showed the decrease in carrier mobility with the increase of ion fluence. The absorption band edge of Zn3P2 gradually decreased from 1.49 eV to 1.42 eV upon increasing the ion fluence (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural phase diagram for ZnS nanocrystalline thin films under swift heavy ion irradiation

The synthesis of nanocrystalline ZnS thin films by pulsed laser deposition and their modification by swift heavy ions are presented. The irradiations with 150 MeV Ni ions at fluences of 1×10 11, 1×10 12 and 1×10 13 ions/cm 2 have been used for these studies. Irradiation results in structural phase transformation and bandgap modification of these films are investigated by using X-ray diffraction and UV–visible absorption measurements, respectively. Since stoichiometry changes induced by irradiation can contribute to the modification of these properties, elastic recoil detection analysis has been performed on pristine and 150 MeV Ni ions irradiated ZnS thin films using a 120 MeV Ag ion beam. The stoichiometry of the films has been found to be similar for pristine and ion irradiated samples. A structural phase diagram based on thermal and pressure spikes has been constructed to explain the structural phase transformation.

Photoluminescence and photoluminescence excitation studies in 80 MeV Ni ion irradiated MOCVD grown GaN

We report damage creation and annihilation under energetic ion bombardment at a fixed fluence. MOCVD grown GaN thin films were irradiated with 80 MeV Ni ions at a fluence of 1 × 10 13 ions/cm 2. Irradiated GaN thin films were subjected to rapid thermal annealing for 60 s in nitrogen atmosphere to anneal out the defects. The effects of defects on luminescence were explored with photoluminescence measurements. Room temperature photoluminescence spectra from pristine sample revealed presence of band to band transition besides unwanted yellow luminescence. Irradiated GaN does not show any band to band transition but there is a strong peak at 450 nm which is attributed to ion induced defect blue luminescence. However, irradiated and subsequently annealed samples show improved band to band transitions and a significant decrease in yellow luminescence intensity due to annihilation of defects which were created during irradiation. Irradiation induced effects on yellow and blue emissions are discussed.

Field emission and I–V characteristics of template synthesised nickel nanowires on semiconducting substrate

Ion track technology makes it possible to produce a low cost template for the synthesis of nanowires. In this article, spin-coated polycarbonate films have been irradiated by energetic 150 MeV Ni ion at a fluence of 8E7, followed by UV irradiation and chemical etching in aqueous NaOH (6N, 29°C). Ni nanowires were electrochemically synthesised in the pores created in the polycarbonate film. The nanostructures thus synthesised were morphologically analysed using scanning electron microscopy and further studied for their electrical and field emission properties.

Magnetic properties of ion irradiated epitaxial Fe films

Magnetic properties of a heavy-ion irradiated single crystalline iron film were investigated. A high quality Fe (001) film with a thickness of 250 nm was fabricated on MgO (001) using the molecular beam epitaxy technique. The film was irradiated by 3.2 MeV Ni ions at room temperature using a tandem accelerator. Formation of dislocation loops with nanometer size was observed by TEM observation, and that of sub-nanometer size vacancy clusters was confirmed indirectly from a resistivity increase. However, M-H hysteresis curves and magnetic domain structure did not change significantly. These results indicate the formation of irradiation defects of pure iron in nanometer scale range has little influence on the magnetization process of the iron.

Ion irradiation effects on tungsten-oxide films and charge state effect on electronic erosion

We have studied electronic- and atomic-structure modifications of polycrystalline WO 3 films (bandgap of ∼3 eV) by ion irradiation. WO 3 films were prepared by oxidation of W films on MgO substrates and of W sheets. We find disordering or amorphization, the lattice expansion of ∼1.5% and bandgap increase of 0.2 eV after 90 MeV Ni ion irradiation at ∼3 × 10 12 cm −2. A broad peak of optical absorption appears around 1.6 μm by ion irradiation. We also find that the erosion yield by high-energy ions with the equilibrium charge exceeds 10 4 and that the erosion yield under ion impact with non-equilibrium charge (90 MeV Ni +10) is ∼1/5 of that with the equilibrium charge (89 MeV Ni +19). Effects of depth dependence of the ion mean charge on the erosion yields are discussed. The erosion yield by low-energy ions is also presented.

Structural phase transformation in ZnS nanocrystalline thin films by swift heavy ion irradiation

Zinc sulfide (ZnS) thin films in zinc-blende (ZB) and wurtzite (W) phases have been fabricated by pulsed laser deposition. 150 MeV Ni ion beam irradiation has been carried out at different fluences ranging from 10 11 to 10 13 ions/cm 2 at room temperature for ion induced modifications. Structural phase transformation in ZnS from W to ZB phase is observed after high energy ion irradiation which leads to the decrease in bandgap. Generation of high pressure and temperature by thermal spike during MeV ion irradiation along the ion trajectory in the films is responsible for the structural phase transformation.

Comparative study of transient current induced in SiC p +n and n +p diodes by heavy ion micro beams

N +p and p +n diodes were fabricated on p- and n-type 6H–SiC substrates with epitaxial layers, respectively. The charge induced in the diodes by 9 MeV oxygen (O) and nickel (Ni) ions was measured using Transient Ion Beam Induced Current (TIBIC) to clarify the capability of these diodes as particle detectors. As a result of the TIBIC measurements using 9 MeV O, the Charge Collection Efficiency (CCE) of around 83% was obtained for both p +n and n +p diodes. Since the CCE value includes the consumption of incident ion energy in an Al electrode and the n + (p +) region as well as the decay of charge in the measurement system, the CCE value obtained in this study indicates that SiC n +p as well as p +n diodes are suitable for particle detectors. On the other hand, in the case of 9 MeV Ni ion irradiation, the CCE for both n +p and p +n diodes decreases due to the Auger recombination in dense electron–hole pairs.