Increasing Irradiation Fluence Research Articles

Investigation of structural stability and magnetic properties of Fe/Ni multilayers irradiated by 300 keV Fe10+

The effects of irradiation on the structural stability and magnetic properties of Fe/Ni multilayers, which are promising candidate magnet materials in fusion reactors, were investigated. Three types of Fe/Ni multilayers with different modulation periods ranging from 2nm to 10nm were deposited on Si (100) substrate through direct current magnetron sputtering. The multilayered samples were irradiated by 300keV Fe10+ ions in a wide fluence range of 1.7×1018/m2 to 2×1019/m2. Magnetic hysteresis loops of pre- and post-irradiation samples were obtained using a vibrating sample magnetometer, and structural stability were analyzed by X-ray diffraction. Magnetic measurements showed that the coercive force of Fe/Ni multilayers remained stable with increasing irradiation fluence. However, saturation magnetization increased with increasing irradiation fluence. The samples with 5nm modulation period were the least affected by irradiation among the three types of Fe/Ni multilayers. The effects of temperature during irradiation were also discussed to explore the optimum temperature of multilayers.

Phase transformation of ZnMoO4 by localized thermal spike

We show that ZnMoO4 remains in stable phase under thermal annealing up to 1000 °C, whereas it decomposes to ZnO and MoO3 under transient thermal spike induced by 100 MeV Ag irradiation. The transformation is evidenced by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Thin films of ZnMoO4 were synthesized by thermal evaporation and subsequent annealing in oxygen ambient at 600 °C for 4 h. XRD results show that as the irradiation fluence increases, the peak related to ZnMoO4 decreases gradually and eventually disappear, whereas peaks related to ZnO grow steadily up to fluence of 3 × 1012 ions/cm2 and thereafter remain stable till highest fluence. This indicates that polycrystalline ZnMoO4 film has transformed to polycrystalline ZnO thin film. The Raman lines related to ZnMoO4 are observed to have disappeared with increasing irradiation fluence. XPS results show modification in bonding and depletion of Mo from near surface region after the ion irradiation. Cross-sectional transmission electron microscopy result shows the formation of ion track of diameter 12–16 nm. These results demonstrate that ion beam methods provide the means to control phase splitting of ZnMoO4 to ZnO and MoO3 within nanometric dimension along the ion track. The observation of phase splitting and Mo loss are explained in the framework of ion beam induced thermal spike formalism.

Separation of Ionization Traps in NPN Transistors Irradiated by Lower Energy Electrons

Effects of oxide-trapped charge and interface traps induced by ionizing radiation, on the degradation of the electrical properties in NPN bipolar junction transistors (BJTs), are identified in this paper. Ionization traps in 3DG110 NPN BJTs are caused by 110 keV electron irradiations for various fluences, and the key electrical parameters are measured in situ during irradiation. In order to separate the effects of the interface traps and oxide charge on the radiation response in BJTs, the isochronal and isothermal annealing are performed after irradiations. Behavior of the radiation-induced defects is detected by DLTS after the irradiation and the postirradiation annealing. Measurement results indicate that when the change in reciprocal of the gain (Δ(1/ β)) tends to level off, the concentration of oxide-trapped charge increases with increasing irradiation fluence, while that of the interface traps keeps unchangeable. A comparison of DLTS signals with changes in excess base current (ΔI <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) versus base-emitter voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BE</sub> ) is conducted to show the role of oxide-trapped charge and interface traps on the excess base current, illustrating that the DLTS analysis is suitable to separate the ionization traps in BJTs.

Formation of Ge nanocrystals from ion-irradiated GeO2 nanocrystals by swift Ni ion beam

GeO2 nanocrystal (NC) thin films were deposited on Si substrate using a magnetron sputtering method and irradiated with swift heavy ions of 80MeV Ni at various fluences ranging from 5×1012 to 1×1014ions/cm2. Grazing incidence X-ray diffraction measurements indicate the decrease in average size of NCs with increase in fluence of ion irradiation. Micro-Raman spectroscopy studies show clearly the formation of Ge NCs with the increase of irradiation fluence. Field emission scanning electron microscopy was employed to study the morphology and modifications in NCs due to ion irradiation. Transmission electron microscopy measurement of the ion-irradiated sample at 1×1014ions/cm2 confirmed the presence of few nm-sized Ge NCs, which were not observed in as-deposited sample. The overall results suggest that GeO2 NCs are reduced in size and few of them are converted into Ge NCs due to the effects of electronic energy deposition by the irradiating ions. This formation of Ge NCs in the ion-irradiated GeO2 NC thin films has been understood on the basis of irradiation-induced separation of oxygen from GeO2 NCs.

Swift heavy ion irradiation acts as a size filter to Ag nanoparticles embedded in silica glass

The swift heavy ion (SHI) irradiation using as a tool for the ion-beam-shaping technique has attracted much attention in recently years, which can transform spherical metal nanoparticles (Nps) to prolate spheroids, nanorods or nanowires, with the elongation along the beam direction. In the present paper, we show that SHI irradiation can also act as a size filter to Ag Nps embedded in silica glass. In experiment, Ag Nps were introduced into silica glass by Ag ion implantation. Subsequently, 73MeV Ca ions were used to irradiate the samples contained Ag Nps to different fluences. The direction of incident ions is perpendicular to sample surface. The surface plasmon resonance (SPR) absorbance peak of Ag Nps shifts to short wavelength with increase of irradiation fluence, meanwhile, the full width at half maximum (FWHM) of SPR peak decreases with increase of irradiation fluence. The decrease of FWHM indicates the reduction of Ag Nps size dispersion. TEM results show that Ag Nps smaller than 2.0nm dissolve during irradiation, only Ag Nps larger than 2.0nm survive and distribute in a narrow region. High energy Ca ion irradiation seems to act as a size filter. From TEM micrographs the size dispersion of Ag Nps is reduced comparing with that before irradiation, which is consistent with optical results.

Ion beam irradiation effects on Ge nanocrystals synthesized by using RF sputtering followed by RTA

Here we report the effects of ion beam irradiation on Ge nanocrystals (NCs) embedded in SiO2 matrix. The Ge NCs embedded in silicon oxide matrix have been synthesized using RF magnetron co-sputtering technique followed by rapid thermal annealing. Eventually, Ge NCs were irradiated by 120MeV Ag ions with various fluences at room temperature. X-ray diffraction patterns indicate the decrease in average size of Ge NCs with increase in irradiation fluence. Raman scattering spectra showed a peak of Ge–Ge optical phonon vibrational mode shifted towards lower wavenumber side upon irradiation with respect to its bulk value, which is due to quantum confinement of optical phonons in the NCs. This blue shift also reflects decrease in the size of NCs upon irradiation. Change of NC size with the increase of irradiation fluence can be explained on the basis of energy deposited by incident ion inside the target material.

Dielectric and conductivity studies of 90 MeV O7+ ion irradiated poly(ethylene oxide)/montmorillonite based ion conductor

In the present work effect of 90 MeV O7+ ions with five different fluences on poly(ethylene oxide) (PEO)/Na+-montmorillonite (MMT) nanocomposites has been investigated. PEO/MMT nanocomposites were synthesized by solution intercalation technique. With the increase in irradiation fluence, gallery spacing of MMT increases in the composite and an exfoliated nanostructure is obtained at the fluence of 5 × 1012 ions/cm2 as revealed by X-ray diffraction results. Highest room temperature ionic conductivity of 4.2 × 10−6 S cm−1 was found for the fluence 5 × 1012 ions/cm2, while the conductivity for unirradiated polymer electrolyte was found to be 7.5 × 10-8 S cm−1. The increase in intercalation of PEO chains inside the galleries of MMT results in the increase in interaction between Na+ cation and oxygen heteroatom leading to the increase in ionic conductivity of the composites. Surface morphology and interactions among the various constituents in the nanocomposites at different fluence have been examined by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The appearance of peak for each fluence in the loss tangent suggests the presence of relaxing dipoles in the polymer nanocomposite electrolyte films. With the increase in ion fluence the peak shifts towards higher frequency side, suggesting decrease in the relaxation time.

On the optical properties of Ag+15 ion-beam-irradiated TiO2 and SnO2 thin films

The effects of 200-MeV Ag+15 ion irradiation on the optical properties of TiO2 and SnO2 thin films prepared by using the RF magnetron sputtering technique were investigated. These films were characterized by using UV-vis spectroscopy, and with increasing irradiation fluence, the transmittance for the TiO2 films was observed to increase systematically while that for SnO2 was observed to decrease. Absorption spectra of the irradiated samples showed minor changes in the indirect bandgap from 3.44 to 3.59 eV with increasing irradiation fluence for TiO2 while significant changes in the direct bandgap from 3.92 to 3.6 eV were observed for SnO2. The observed modifications in the optical properties of both the TiO2 and the SnO2 systems with irradiation can be attributed to controlled structural disorder/defects in the system.

Structural properties of embedded Ge nanoparticles modified by swift heavy-ion irradiation

Silica-embedded Ge nanoparticles (NPs) of different sizes irradiated with swift heavy ions (SHIs) at a given energy may reportedly elongate along the incident ion direction, perpendicular to it, or not at all. Here, for a given NP size distribution, we have investigated the SHI energy dependence of the elongation process. Higher-energy irradiation generally yielded elongation along the ion track (as previously observed), but for lower-energy irradiation, elongation both parallel and perpendicular to the ion direction was observed. We demonstrate that NP size and electronic energy loss together govern the elongation process, reinforcing the proposed model where elongation perpendicular to the ion direction is only expected for Ge NPs bigger than the mean ion track diameter in silica. Here, a wide fluence range is also probed, enabling us to follow in more detail the transition from spherical unirradiated Ge NPs to Ge NPs elongated either parallel or perpendicular to the ion beam. X-ray absorption spectroscopy (XAS) measurements are utilized for the quantification of crystalline, amorphous, and oxidized environments around Ge atoms. Combining such results with transmission electron microscopy (TEM) observations shows the Ge NPs are rendered amorphous prior to elongation, potentially via a melt-and-quench process. Thereafter, stronger electron-phonon coupling in amorphous Ge compared to crystalline Ge may potentially influence the elongation process. The Ge NP amorphization occurs at lower fluences for higher irradiation energies, indicating electronic energy loss---and not ballistic effects---governs the amorphization. Subsequent to amorphization and elongation, TEM and XAS results also show the NPs gradually intermix with SiO${}_{2}$ and dissolve within the matrix as the irradiation fluence increases. We discuss the impact of such results in the ion beam tailoring of Ge NPs for technological applications.

Evolution of superconducting and normal state properties of YBa2Cu3O7−y thick films under 200 MeV Ag ion irradiation

Temperature dependent resistivity of YBa2Cu3O7−y (YBCO) thick films irradiated with 200MeV Ag ions has been investigated. The YBCO thick films were prepared by solid state diffusion reaction technique. In contrast to the general perception that the energetic ion induces defects and disorders, which lead to decrease of Tc and increase of normal state resistivity in a superconductor, 200MeV Ag ions in the present case led to an increase in Tc and decrease in normal state resistivity at low ion fluence (1011 ions cm−2) in YBCO. At this fluence, the electronic energy loss, Se induced amorphous ion tracks are well separated from each other and hence are not expected to influence the Tc. The observed changes in transport properties is explained as being caused by irradiation-induced chain oxygen ordering of the oxygen defects in the CuO chains. Subsequent increase of irradiation fluence leads to decrease of Tc and increase of normal state resistivity.

Surface analysis of high performance carbon/bismaleimide composites exposed to electron irradiation

The aim of this article was to investigate the effects of electron irradiation in ultrahigh vacuum environment on the surface properties of high‐performance carbon/bismaleimide (BMI) composites used in aerospace. The changes in surface chemical composition with increasing irradiation fluence were studied by XPS. The evolution of surface morphology and surface roughness were observed by atomic force microscopy (AFM). The mass loss behavior occurring in the surface layer of the composites was examined. The results indicated that the electron irradiation in high vacuum caused rupture of chemical bonds and cross‐linking process in the surface layer, thereby leading to the mass loss behavior and the formation of carbonification layer in the surface of the carbon/BMI composites. The changes in the surface chemical composition were determined by a competing effect existing between the rupture of chemical bonds and the cross‐linking process at lower irradiation fluence, and by a degradation process only at higher fluence of electron irradiation. The surface morphology was altered and the surface roughness was increased significantly after electron irradiation. The mass loss ratio first increased obviously at lower fluences, and then reached a plateau value of 0.45% beyond 5 × 1015 cm−2 fluence of electron irradiation. Copyright © 2011 John Wiley &amp; Sons, Ltd.

A study on damage effects of

The changes in optical properties and damage mechanism of ZnO/silicone white paint caused by <200 keV protons in space were investigated in terms of ground-based simulation testing. The energies of protons were chosen as 50, 90, and 110 keV. The results show that the change in solar absorptance s increases with increasing irradiation fluence as well as the proton energy. On the basis of photoluminescence spectroscopy, it is revealed that with increasing proton fluence, the 660-nm emission band related to the interstitial Zn-ions changes little, the 405-nm emission band related to the Zn vacancies decreases and tends to disappear, the 460-nm emission band related to the double ionized oxygen vacancies VO  decreases, and the emission band

Defect engineering in GaAs using high energy light ion irradiation: Role of electronic energy loss

We report on the application of high energy light ions (Li and O) irradiation for modification of defects, in particular, for annihilation of point defects using electronic energy loss in GaAs to minimize the defects produced by nuclear collisions. The high resolution x-ray diffraction and micro-Raman spectroscopy have been used to monitor that no lattice damage or amorphization take place due to irradiating ions. The effects of irradiation on defects and their energy levels have been studied using thermally stimulated current spectroscopy. It has been observed that till an optimum irradiation fluence of 1013 ions/cm2 there is annihilation of native defects but further increase in irradiation fluence results in accumulation of defects, which scales with the nuclear energy loss process, indicating that the rate of defects produced by the binary collision process exceeds rate of defect annihilation. Defect annihilation due to electronic energy loss has been discussed on the basis of breaking of bonds and enhanced diffusivity of ionized native defects.

Optical and electrical properties of electron-irradiated Cu(In,Ga)Se 2 solar cells

The optical and electrical properties of electron-irradiated Cu(In,Ga)Se 2 (CIGS) solar cells and the thin films that composed the CIGS solar cell structure were investigated. The transmittance of indium tin oxide (ITO), ZnO:Al, ZnO:Ga, undoped ZnO, and CdS thin films did not change for a fluence of up to 1.5 × 10 18 cm − 2 . However, the resistivity of ZnO:Al and ZnO:Ga, which are generally used as window layers for CIGS solar cells, increased with increasing irradiation fluence. For CIGS thin films, the photoluminescence peak intensity due to Cu-related point defects, which do not significantly affect solar cell performance, increased with increasing electron irradiation. In CIGS solar cells, decreasing J SC and increasing R s reflected the influence of irradiated ZnO:Al, and decreasing V OC and increasing R sh mainly tended to reflect the pn-interface properties. These results may indicate that the surface ZnO:Al thin film and several heterojunctions tend to degrade easily by electron irradiation as compared with the bulk of semiconductor-composed solar cells.

Surface molecular degradation of high performance carbon/bismaleimide composites induced by proton irradiation

This work aims to identify and describe the effects of proton irradiation in ultra high vacuum environment on the surface degradation of high performance carbon/bismaleimide composites used in aerospace. The changes in surface molecular structure and surface chemical composition with increasing irradiation fluence were studied by Attenuated total reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively. The evolution of surface morphology and surface roughness were characterized by atomic force microscopy. The results indicated that the proton irradiation caused surface degradation of the carbon/bismaleimide composites by altering their surface chemical structure and surface morphology. The surface chemical bonds were broken largely and the extent of carbonification at the surface layer of the composites was enhanced with increasing irradiation fluence. The increment in the carbon concentration and the sharp reduction in the oxygen and nitrogen concentration with increasing irradiation fluence were caused by the emission of some oxygen-containing and nitrogen-containing small molecules from the material surface under high vacuum environment. The surface roughness firstly increased under the fluence lower than 5 × 10 15 cm −2, and then decreased after the irradiation fluence increased to some extent.

Optical property modification of ZnO: Effect of 1.2 MeV Ar irradiation

AbstractWe report a systematic study on 1.2 MeV Ar8+ irradiated ZnO by X‐ray diffraction (XRD), room temperature photoluminescence (PL) and ultraviolet‐visible (UV‐Vis) absorption measurements. ZnO retains its wurtzite crystal structure up to maximum fluence of 5 × 1016 ions/cm2. Even, the width of the XRD peaks changes little with irradiation. The UV‐Vis absorption spectra of the samples, unirradiated and irradiated with lowest fluence (1 × 1015 ions/cm2), are nearly same. However, the PL emission is largely quenched for this irradiated sample. Red shift of the absorption edge has been noticed for higher fluence. It has been found that red shift is due to at least two defect centers. The PL emission is recovered for 5 × 1015 ions/cm2 fluence. The sample colour is changed to orange and then to dark brown with increasing irradiation fluence. Huge resistivity decrease is observed for the sample irradiated with 5 × 1015 ions/cm2 fluence. Results altogether indicate the evolution of stable oxygen vacancies and zinc interstitials as dominant defects for high fluence irradiation. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Swift heavy ion irradiation induced modification of BiFeO3 thin films prepared by sol-gel method

We report the preparation of multiferroic BiFeO3 thin films on ITO coated glass substrates through sol-gel spin coating method followed by thermal annealing and their modification by swift heavy ion (SHI) irradiation. X-ray diffraction and Raman spectroscopy studies revealed amorphous nature of the as deposited films. Rhombohedral crystalline phase of BiFeO3 evolved on annealing the films at 550°C. Both XRD and Raman studies indicated that SHI irradiation by 200 MeV Au ions result in fragmentation of particles and progressive amorphization with increasing irradiation fluence. The average crystallite size estimated from the XRD line width decreased from 38 nm in pristine sample annealed at 550°C to 29 nm on irradiating these films by 200 MeV Au ions at 1 × 1011 ions cm−2. Complete amorphization of the rhombohedral BiFeO3 phase occurs at a fluence of 1 × 1012 ions.cm−2. Irradiation by another ion (200 MeV Ag) had the similar effect. For both the ions, the electronic energy loss exceeds the threshold electronic energy loss for creation of amorphized latent tracks in BiFeO3.

Effect of 100 MeV O7+ ion beam irradiation on structural, optical and electronic properties of SnO2 thin films

In this paper, we present the impact of swift heavy ion beam irradiation on the structural, optical and electronic properties of SnO2 thin films. Thin films were deposited using the pulsed laser deposition technique on Al2O3 substrates. Atomic force microscopy, X-ray diffraction, UV–visible absorption and temperature-dependent resistivity measurements were performed to explore the morphological, structural, optical and electronic properties of the as-deposited and irradiated samples. The peak intensity of the (200) peak was found to decrease monotonously with increasing irradiation fluence. The band gap energy of the 1×1011 ion/cm2 irradiated sample was found to increase. The electrical resistivity of the samples showed a continuous increase with the irradiation fluence.

Micro-Raman studies of swift heavy ion irradiation induced structural and conformational changes in polyaniline nanofibers

Polyaniline (PAni) nanofibers doped with camphor sulfonic acid have been irradiated with 90 MeV O 7+ ions at different fluences (3 × 10 10−1 × 10 12 ions/cm 2) using a 15UD Pelletron accelerator under ultra-high vacuum. XRD studies reveal a decrease in the domain length and an increase in the strain upon SHI irradiation. The increase in d-spacing corresponding to the (1 0 0) reflection of PAni nanofibers with increasing irradiation fluence has been attributed to the increase in the tilt angle of the chains with respect to the ( a, b ) basal plane of PAni. Decrease in the integral intensity upon SHI irradiation indicates amorphization of the material. Micro-Raman (μR) studies confirm amorphization of the PAni nanofibers and also show that the PAni nanofibers get de-doped upon SHI irradiation. μR spectroscopy also reveals a benzenoid to quinoid transition in the PAni chain upon SHI irradiation. TEM results show that the size of PAni nanofibers decreases with the increase in irradiation fluence, which has been attributed to the fragmentation of PAni nanofibers in the core of amorphized tracks caused by SHI irradiation.

Swift heavy ion irradiation induced enhancement in the antioxidant activity andbiocompatibility of polyaniline nanofibers

Polyaniline (PAni) nanofibers doped with HCl and CSA have been irradiated with 90 MeVO7 + ions withfluence of 3 × 1010, 3 × 1011 and 1 × 1012 ions cm − 2. TEM micrographs show a decrease in the fiber diameter with increasing irradiation fluence,which has been explained on the basis of the Coulomb explosion model. XRD analysis reveals adecrease in the crystalline domain length and an increase in the strain. The increase ind-spacing for the (100) reflection with increasing irradiation fluence is ascribed to the increase inthe tilt angle of the polymer chain, which is also evident from micro-Raman spectra. UV–visspectra of the PAni nanofibers exhibit blue-shift in the absorption bands attributed toπ–π* band transitions indicating a reduction in particle size after SHI irradiation; as alsoobserved in TEM micrographs. Micro-Raman spectra also reveal a transition from thebenzenoid to quinoid structures in the PAni chain as the fluence is increased. Although thequinoid unit has no hydrogen for DPPH scavenging, the antioxidant activity of PAninanofibers is found to increase with increasing fluence. This has been attributed to theavailability of more reaction sites as a result of fragmentation of the PAni nanofibers whichcompensates for the benzenoid to quinoid transition after irradiation. The biocompatibilityof the PAni nanofibers is also found to increase with increasing irradiation fluence,indicating the possibility of employing swift heavy ion irradiation as an effective techniquein order to modify conducting polymer nanostructures for biomedical applications.