MeV Ag Ions Research Articles

Electronic excitation induced phase transformation in FSMA thin film

The influence of 120 MeV Ag ion irradiation on the structural and magnetic properties of Ni–Mn–Sn ferromagnetic shape memory alloy thin film is investigated. X-ray diffraction data confirms the phase transformation from martensite to austenite phase at a fluence of 1 × 1013 ions/cm2, which is further supported by the change in surface morphology of the film with increasing fluence as evidenced by field emission scanning electron microscopy. Thermo-magnetic measurements reveal the increase in magnetization and decrease in phase transformation temperatures with increasing fluence. The maximum value of magnetization is ∼2.9 × 105 Amp/meter for the film irradiated at a fluence of 1 × 1013 ions/cm2. The results are explained on the basis of thermal spike model considering the core and halo regions of ion tracks in FSMA materials.

Energetic ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy thin film

The ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy (FSMA) thin film is investigated. Thin films of Ni–Mn–Sn FSMA synthesized by DC magnetron sputtering on Si substrate at 200 °C are irradiated by a beam of 120 MeV Ag ions at different fluence varying from 1 × 1012 to 6 × 1012 ions/cm2. X-ray diffraction pattern reveals that the pristine film grows in L21 cubic austenite phase with poor crystallinity and crystallinity of the film improves with increasing ion fluence, which is attributed to the strain relaxation by the energy deposited by incoming ions and promotes the grain growth. Grain growth is further confirmed by Atomic force microscopy. The temperature dependent magnetization measurements show improvement in the magnetic and shape memory properties of the films with increasing fluence, which is ascribed to the ordering of austenite phase. Nanoindentation measurements show that with increasing fluence of 120 MeV Ag ions, films exhibit a greater stiffness and smaller tendency towards plastic deformation.

Strain modification of AlGaN layers using swift heavy ions

Epitaxial AlGaN/GaN layers grown by molecular beam epitaxy (MBE) on SiC substrates were irradiated with 150 MeV Ag ions at a fluence of 5×1012 ions/cm2. The samples used in this study are 50 nm Al0.2Ga0.8N/1 nm AlN/1 μ m GaN/0.1 μ m AlN grown on SI 4H-SiC. Rutherford backscattering spectrometry/channeling strain measurements were carried out on off-normal axis of irradiated and unirradiated samples. In an as-grown sample, AlGaN layer is partially relaxed with a small tensile strain. After irradiation, this strain increases by 0.22% in AlGaN layer. Incident ion energy dependence of dechanneling parameter shows E 1/2 dependence, which corresponds to the dislocations. Defect densities were calculated from the E 1/2 graph. As a result of irradiation, the defect density increased on both GaN and AlGaN layers. The effect of irradiation induced-damages are analyzed as a function of material properties. Observed results from different characterization techniques such as RBS/channeling, high-resolution XRD and AFM are compared and complemented with each other to deduce the information. Possible mechanisms responsible for the observations have been discussed in detail.

Mesoscopic inhomogeneity creation in YBa2Cu3O7−y thin film by swift heavy ion irradiation at low temperature

In the present study, we report the modification of pulsed laser deposited c-axis oriented thin films of YBa2Cu3O7−y (YBCO) in a cylindrical region around the path of swift heavy ions (SHIs). Our in situ temperature-dependent resistivity measurement and in situ low-temperature X-ray diffraction (XRD) study on YBCO irradiated at liquid nitrogen temperature with 200 MeV Ag ions shows that the SHI-induced secondary electrons selectively create point defects at CuO basal chains of YBCO. Beyond a critical fluence (∼1012 ions/cm2), the radially strained region around the amorphous latent tracks estimated from full width at half-maximum of (00l) XRD peaks tends to overlap, and a two-step superconducting transition evolves instead of a single transition in the in situ resistivity measurement.

Swift heavy ion-induced surface nanopatterning of indium oxide films

In this study, indium oxide films are deposited by electron-beam evaporation and thermally annealed at 600°C in an oxygen atmosphere to form stoichiometric In2O3 films with a high transparency. They are then irradiated with 120 MeV Ag ions with different fluences (i.e. 1×1011, 1×1012 and 1×1013 ions/cm2). The morphology of the films as a function of fluence is studied by atomic force microscopy and the root mean square roughness values are obtained. The pristine film consists of uniformly-sized particles distributed over the sample surface. On irradiation with 1×1011 ions/cm2, fragmentation of these particles takes place. These fragmented particles start to agglomerate and align slightly in a particular direction at a fluence of 1×1012 ions/cm2. Morphology is further confirmed by scanning electron microscopy. A two-dimensional power spectral density analysis has been done to elucidate the topographical changes due to varying ion fluences. The growth exponent value of α>1 suggests that the growth is governed by surface diffusion.

Defect formation in GaN epitaxial layers due to swift heavy ion irradiation

GaN epitaxial layers were irradiated with 200 MeV Ag ions at various fluences. These samples were characterized ex situ by resistivity/Hall, XRD, and transmission electron microscopy (TEM). The resistivity of irradiated layers increased by eight orders of magnitude after irradiation with a fluence of 5×1012 ions/cm2. The increase in peak width (FWHM) with the incident ion fluence showed a reduction in the crystallinity of epitaxial layers. Cross-sectional TEM images confirmed that at the highest fluence (5×1012 ions/cm2), electronic energy loss caused structural defect formation in the GaN layer.

The effect of swift heavy ion irradiation on critical current density in YB2Cu3O7−δ thick film with Y2O3 addition

The effect of 200 MeV Ag ion irradiation on thick films of YBCO grown by the diffusion reaction technique has been studied. Magnetization at 40 K marks a substantial change in the critical current density (J c) of the irradiated sample when compared with unirradiated ones. The critical current density was estimated from the widths of magnetization loops using Bean's critical state model. The enhancement of J c from 1.06×105 to 2.5×105 A/cm2 with irradiation up to a fluence of 5×1011 ions/cm2 in YBCO samples is associated with an increase in the flux pinning created by the irradiation-induced columnar defects. In excess Y2O3 (10 wt%) to YBCO, the J c increases in the pristine sample to 1.33×105 A/cm2 but decreases with increasing fluence. This may be due to an excess of defects, overlapping of defected zones and weakening of the pinning barriers. Further studies using X-ray diffraction and a scanning electron microscope reveal microstructural changes in the irradiated samples.

Effects of SHI irradiation on the critical current density of Y1−x Ca x Ba2Cu3O7−δ thick film with Y2O3 composite

Y1−x Ca x Ba2Cu3O7−δ (x=0.1)+Y2O3 (10 wt%) composite thick film has been prepared by the diffusion reaction technique. Samples are irradiated with 200 MeV Ag ions. X-ray diffraction and scanning electron microscopy reveal microstructural changes in the irradiated samples. The enhancement of the critical current density (J c) from 1.4×104 to 6.7×104 A/cm2 with irradiation in YCaBCO samples is observed, indicating that flux pinning increases due to the creation of columnar defects induced by irradiation. On addition of Y2O3 to YCaBCO, J c increases to 8.3×104 A/cm2. The insulating inclusions of Y2O3 cause J c to increase by the process of flux pinning in the unirradiated YCABCO/Y2O3 composite. However, J c starts decreasing for YCABCO/Y2O3 composite with the increase in ion fluence. The main mechanism of the decrease in the critical current density is the reduction in the effective pinning potential, which is caused by an increase in the defect concentration.

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.

Nano/micro-structuring of oxide thin film under SHI irradiation

In the present work, we have studied the nano/micro-patterning of the surface of NiO thin films on different substrates (SiO 2, Si and Al) using 100 MeV Ag ions at LN 2 temperature and at an incidence angle of 75 ° with the beam axis. The surface morphology of the irradiated surface is observed by Atomic force microscopy (AFM). AFM images of ion beam irradiated samples show the restructuring of initially flat and coherent NiO film into an almost periodic NiO lamellae structure. The quite regular lamellae with width, height and average distance of hundreds of nm are oriented perpendicular to the beam direction. Section analysis of the AFM images reveal that the width of the lamellae is less in case of NiO films deposited on SiO 2 substrate in comparison to Al substrate. The cracking and the development of lamellae structure is observed at higher fluence in the case of Al substrate in comparison to other substrates.

Ion beam induced formation of nanocrystalline silicon in pulsed laser deposited SiO X thin films

Synthesis and structural studies of nanocrystalline silicon grown in pulsed laser deposited SiO X films is reported. The effect of high energy heavy ion beam irradiation on these films is studied using 100 MeV Ag ions. The structural studies were carried out using micro Raman spectroscopy, GAXRD, FTIR, TEM, HRTEM, SAED and EDX. The occurrence of phase separation in non-stoichiometric silicon oxide by means of ion beam irradiation leading to the formation of silicon nanocrystals in the films is confirmed by the results. HRTEM results reveal the structure of silicon phase formed after ion beam treatment and the particle size can be controlled up to 2–3 nm. A detailed analysis by micro Raman and HRTEM studies suggest the presence of crystallite size distribution. The results of GAXRD and SAED confirm the formation of cubic phase of silicon with two different lattice parameters. The studies conclude that the size of the nanocrystals can be controlled by varying deposition and ion irradiation parameters.

Evolution and tailoring of plasmonic properties in Ag:ZrO2 nanocomposite films by swift heavy ion irradiation

Ag:ZrO2 nanocomposite films have been synthesized by a sol-gel dip coating process at room temperature, followed by irradiation using swift heavy ions. The effect of electronic energy loss and fluences on the evolution and consequently on the tailoring of plasmonic properties of films has been studied. The optical study exhibits that color of films converts from transparent in pristine form into shiny yellow when films are irradiated by 100 MeV Ag ions at a fluence of 3×1012 ions/cm2. However, irradiation by 120 MeV O ions up to the fluence of 1 × 1014 ions/cm2 does not induce any coloration in films. The coloration is attributed to the evolution of plasmonic feature resulting in a surface plasmon resonance (SPR) induced absorption peak in the visible region. Increase in fluence from 3 × 1012 to 6 × 1013 ions/cm2 of 100 MeV Ag ions induces a redshift in SPR induced peak position from 434 to 487 nm. Microstructural studies confirms the conversion of Ag2O3 (in pristine films) into cubic phase of metallic Ag and the increase of average size of particles with the increasing fluence up to 6 × 1013 ions/cm2. Further increase in fluence leads to the dissolution of Ag atoms in the ZrO2 matrix.

Steady-state conduction behaviour of 100 MeV Ag ion-irradiated polyetherimide

The effect of high-energy ion irradiation on the steady-state conduction behaviour of polyetherimide (PEI) has been investigated. PEI samples of 25 μm thickness were irradiated with 100 MeV Ag ions (fluences of 5.6×1010, 1.8×1011 and 1.8×1012 ions/cm2) at the Inter University Accelerator Centre, New Delhi. Measurements under steady-state conditions at different temperatures (40–250 °C) were made at different electric fields ranging from 40 to 600 kV/cm. The ionic jump distance estimations indicate the possibility of ionic conduction at low and moderate temperatures. At high temperatures, the Schottky and Poole–Frenkel-type conduction mechanisms occur, depending on the fluence of irradiance. A decrease in charge carrier mobility (μ) with field has been associated with the radiation-induced disorders in PEI. An anomalous variation in μ with fluence shows the occurrence of a secondary radiation-induced crystalline phase. The activation energies were determined to be 0.05 and 2.3 eV below and above the glass transition, temperature, indicating the presence of more than one type of trapping centre in irradiated PEI.

Electronic stopping dependence of ion beam induced modifications in GaN

We report here Swift heavy ion induced effects in GaN samples grown by metal organic chemical vapor deposition (MOCVD) technique. These samples were irradiated with 80 MeV Ni and 100 MeV Ag ions at a fixed fluence of 1 × 10 13 ions/cm 2. Ion species and energies are chosen such that the difference in their electronic energy loss ( S e) would be 8 keV/nm. Effects of Ag on structural and optical properties over Ni ions have been discussed extensively. We employed different characterization techniques like High Resolution X-ray Diffraction (HRXRD) and Raman Spectroscopy for defect density calculations and for vibrational modes, respectively. Defect densities are calculated and compared using Williamson–Hall method from HRXRD. Change of strain and vibrational modes with S e has been discussed.

Selective disorder in the CuO basal planes of YBa 2Cu 3O 7−y by swift heavy ion induced secondary electrons

In situ temperature dependent resistivity, ρ( T) study on c-axis oriented YBa 2Cu 3O 7− y thin films irradiated with 200 MeV Ag ions at 79 K is shown to induce point defects in addition to amorphous ion tracks. Annealing characteristics of these defects indicate that the point defects are basically oxygen disorder selectively created in the CuO basal planes of YBa 2Cu 3O 7− y structure by secondary electrons emanating from the path of 200 MeV Ag ions. These electrons are shown to create defects by inelastic interaction process. Contrary to the general expectation, we show that the superconducting transition temperature, T c is suppressed at a rate two orders of magnitude faster at extremely low fluences where ion tracks are far apart from each other than at high fluences where tracks tend to overlap. The transition width on the other hand remains unaffected while resistivity shows a large increase at high fluences. At high fluences, a two-step superconducting transition emerged, which indicate the evolution of two types of superconducting regions with distinctly different T cs.

Influence of 190 MeV Ag+15 ion irradiation on electrical transport and magnetic properties of LaFe1−xNixO3 (x=0.3 and 0.4) thin films

In the present work we have studied the effect of 190 MeV Ag ion irradiation on the structural, electrical, and magnetic properties of LaFe1−xNixO3 (x=0.3 and 0.4) thin films. The films were grown on LaAlO3 ⟨001⟩ oriented substrates using pulsed laser deposition technique. The pristine and irradiated samples were investigated using x-ray diffraction, temperature dependent resistivity, and magnetic measurements. The x-ray diffraction patterns of the irradiated films show that the lattice of the composition strain relaxed with enhanced c-axis orientation. The temperature dependence of the resistivity indicates that all the films (pristine and irradiated) exhibit semiconducting behavior for entire studied temperature range (80–300 K). The pristine and irradiated samples show the activated variable range hopping behavior throughout the studied temperature range. The magnetization hysteresis measurements show ferromagnetic behavior at 300 K for all samples. The results are explained on the basis of the close interplay between the electrical and the magnetic properties.

XRD and SEM Investigation of Swift Heavy Ion-Irradiated Polyvinylidene Fluoride Thin Films

Polyvinylidene fluoride (PVDF) films of different thicknesses are irradiated with 100 meV Ag-ion and 75 meV Oxygen-ion beams at different fluences to study the effects of swift heavy ion (SHI) irradiation in PVDF. The change in physical, chemical, and surface morphological properties of irradiated films are investigated using x-ray diffraction, Field emission scanning electron microscopy (FESEM), and energy dispersive analysis by x-ray (EDAX) techniques by taking unirradiated (pristine) films as reference. The diffraction pattern shows that PVDF polymer is in semi-crystalline form and possesses crystalline α-, β-, and γ-phases. A decrease in the crystallinity and crystallite size has been observed when PVDF is irradiated with 100 meV Ag-, and also Oxygen ions at a higher fluence of 5.675 × 1012 ions/cm2. However, an increase in crystallinity and decrease in crystallite size are observed when PVDF is irradiated with oxygen-ion beam at lower fluence 5.625 × 1011 ions/cm2. The structural parameters such as degree of crystallinity, crystallite size, microstrain, and dislocation density have also been estimated. EDAX result shows that the chemical composition of PVDF is invariant under SHI irradiation, which is in agreement with our earlier results of FTIR. FESEM analysis shows granular microstructure with small porosity on SHI irradiation.

Fourier transform infrared and ultraviolet-visible investigation of swift heavy 100 MeV Ag-ion- and 75 MeV oxygen-ion-irradiated polyvinylidene fluoride thin films

Polyvinylidene fluoride (PVDF) polymer films (9, 12, and 20 μm) were irradiated with 100 MeV Ag ion (fluence: 1.875×1011 ions/cm2) and 75 MeV oxygen ion (fluences: 5.625×1011 and 5.675×1012 ions/cm2) using the PELLETRON facility at the Inter University Accelerator Centre, New Delhi, to study swift heavy ion (SHI) irradiation effects in thin films. The change in chemical, optical, and structural properties was analysed by comparing Fourier transform infrared (FTIR) and ultraviolet (UV)-visible spectra of pristine and irradiated films. The FTIR spectra show no major change in characteristic bands on irradiation, except that some weak bands appear because of the evolution of volatile species, unsaturated bond formation, decomposition of the free radicals, and subsequent cross-linking. The spectra of the irradiated films show some broadening and a decrease in intensity in characteristic bands when compared with the pristine samples. The FTIR results indicate that the overall chemical structure of PVDF is stable under SHI irradiation. The UV-visible absorption spectra of irradiated samples reveal hyperchromic shift, bathochromic shift, and hypsochromic shift. The spectra also estimate the direct optical band gap around 3.6 eV. The band gap decreases on irradiation, and the decrease is dependent on ion beam and fluence rate. The present study opens up the scope for the applicability of SHI-irradiated PVDF thin films as microsensors and actuators.

100 MeV Ag ions irradiation effects on the optical properties of Ag0.10(Ge0.20Se0.80)0.90 thin films

This paper reports the effect of 100 MeV Ag swift heavy ion (SHI) irradiation with fluences ranging from 1 × 1011 to 1 × 1013 ions cm−2 on the optical properties of Ag0.10(Ge0.20Se0.80)0.90 thin films. It has been observed that the SHI irradiation changes the refractive index (n) and the oscillator strength (Ed). The data on the dispersion of the refractive index, n(λ), have been determined using the single-effective-oscillator model. We observed an increase in Ed and refractive index (n) at lower ion fluence (1 × 1011 ions cm−2), followed by the reversal in the trend at higher fluences. The optical gap has been determined by Tauc's plot. The values of decrease with ion fluence. Results have been explained in terms of the structural changes in thin films.

Swift heavy ion irradiation induced modification of the microstructure of NiO thin films

Abstract NiO nanoparticle films (200 nm thick) grown on Si substrates by pulsed laser deposition method were irradiated by 200 MeV Ag 15+ ions. The films were characterized by glancing angle X-ray diffraction, atomic force microscopy and optical absorption spectroscopy. Though electronic energy loss of 200 MeV Ag ions in NiO matrix was higher than the threshold electronic energy loss for creation of columnar defects, films remained crystalline with the initial fcc structure even up to a fluence of 5 × 10 13 ions cm −2 , where ion tracks are expected to overlap. Irradiation however modified the microstructure of the NiO films considerably. The grain size decreased with increasing ion fluence, which led to reduced surface roughness and increased optical band gap due to quantum confinement. These results correlate well with variation of the power spectral density exponent with ion fluence, which indicate that at high ion fluences, the evolution of surface morphology is governed by surface diffusion.