Ion Irradiation Fluence Research Articles

Defects and Interfaces on PtPb Nanoplates Boost Fuel Cell Electrocatalysis.

Nanostructured Pt is the most efficient single-metal catalyst for fuel cell technology. Great efforts have been devoted to optimizing the Pt-based alloy nanocrystals with desired structure, composition, and shape for boosting the electrocatalytic activity. However, these well-known controls still show the limited ability in maximizing the Pt utilization efficiency for achieving more efficient fuel cell catalysis. Herein, a new strategy for maximizing the fuel cell catalysis by controlling/tuning the defects and interfaces of PtPb nanoplates using ion irradiation technique is reported. The defects and interfaces on PtPb nanoplates, controlled by the fluence of incident C+ ions, make them exhibit the volcano-like electrocatalytic activity for methanol oxidation reaction (MOR), ethanol oxidation reaction (EOR), and oxygen reduction reaction (ORR) as a function of ion irradiation fluence. The optimized PtPb nanoplates with the mixed structure of dislocations, subgrain boundaries, and small amorphous domains are the most active for MOR, EOR, and ORR. They can also maintain high catalytic stability in acid solution. This work highlights the impact and significance of inducing/controlling the defects and interfaces on Pt-based nanocrystals toward maximizing the catalytic performance by advanced ion irradiation strategy.

He ion irradiation effects on multiwalled carbon nanotubes structure

Samples of multi-walled carbon nanotubes (MWNTs) were irradiated with 80 keV He ions. Scanning electron microscopy (SEM) inspection showed that the average outer diameters of the tube decreased as a result of ion irradiation. The samples were also characterized using Raman spectrometry by analysis of the intensity of main bands in the spectra of virgin and irradiated MWNT samples. Modifications of the disorder mode (D-band) and the tangential mode (G-band) were studied as a function of irradiation fluences. Raman spectra showed that as the fluence increases, the MWNTs first show disorder due to the produced defects, and then amorphization under still higher fluence of ion irradiation. Thermal and athermal mechanisms of the radiation induced MWNTs modifications are discussed.

Diamond single crystal-surface modification under high- fluence ion irradiation

The modification of (111) face of synthetic diamond has been studied experimentally for high-fluence 30 keV argon bombardment. It has been found that ion irradiation leads to the electrically conductive layer formation the sheet resistance of which decreases more than 100 times while changing the temperature of the irradiated diamond from 70 to 400 oC. This effect, as well as significant changes of optical transmittance after ion irradiation are associated with ion-induced structural changes of irradiated diamond obtained by the methods of Raman spectroscopy.

Swift heavy ion induced structural phase generation and enhanced luminescence from CdS based nanocomposites

Abstract Synthesis and modification of CdS:SiO 2 and Cd 0.99 Ag 0.01 S:SiO 2 nanocomposite thin films grown at substrate temperature 200 °C by pulsed laser deposition (PLD) followed by swift heavy ion irradiation (SHII) using 120 MeV Ag 9 + ions is reported. The structural evolution of CdS phase in SiO 2 after SHII is illustrated by glancing angle x-ray diffraction patterns and micro-Raman spectra. Transmission electron microscopy (TEM) images clearly show the growth of CdS/Cd 0.99 Ag 0.01 S nanoparticles in SiO 2 matrix under the influence of SHII. Photoluminescence (PL) spectra show two emission peak at ~ 2.34 eV and ~ 3.05 eV assigned for green emission (GE) and violet emission (VE) respectively. The VE assumed to be originated due to the band edge emission and GE identified as the trap levels located between conduction band and valence band. The presence of emission from pristine films indicates that the crystalline domains are very small in films rather than the particles are amorphous in nature. A systematic increment in PL emission intensity corresponding to trap emission as a function of ion irradiation fluence is observed from the two nanocomposite systems. However, the behavior of band edge emission induced by SHII is quite different in two nanocomposite systems. SHII induced phase formation and emission intensity variation as a function of ion fluence are explained on the basis of thermal spike model.

Cluster ion beam assisted fabrication of metallic nanostructures for plasmonic applications

We report a high-throughput, single-step method for fabricating rippled plasmonic nanostructure arrays via self-assembly induced by oblique angle cluster ion beam irradiation of metal surfaces. This approach does not require lithographic or chemical processes and has the prominent advantage of possible large surface area coverage and applicability to different starting materials. The polarization dependent plasmonic property of the gold nano-ripple is due to their one dimension structure. The localized plasmon resonance frequency of synthesized nano-ripple arrays is tunable by changing nano-ripple dimensions that can be engineered by changing the cluster ion beam irradiation parameters. In this specific case presented, using 30keV Ar-gas cluster ion beam, we fabricate gold nano-ripple arrays that show localized plasmon resonance in the visible range through near IR range, tunable by varying cluster ion irradiation fluence.

Compositional, structural and optical changes of polyimide irradiated by heavy ions

Polyimide (PI, (C22H10O5N2)n) foil, 8 µm thick, was irradiated with 9.6‐MeV C4+ and O4+ ions at fluences of 1010–1013 cm−2. Compositional and structural changes related to the ion species, ion irradiation fluence and the type of polymer were studied and discussed in connection with energy‐loss measurement. The knowledge of these changes of polymers after the irradiation is very important for the estimation of the influence of these effects on the experimentally determined ion‐energy losses. Rutherford back‐scattering (RBS) and elastic recoil detection analysis (ERDA) were used for the elemental composition study, atomic force microscopy (AFM) for the detection of the changes in surface roughness and UV–Visible spectral study (UV–Vis) for variation in the absorbance and the optical band gap. The chemical and structural changes, new radical appearance, and polymeric chain crosslinking especially at ion fluencies above 1013 cm−2 were observed and discussed in the frame of energy stopping experimental determination. Copyright © 2016 John Wiley & Sons, Ltd.

Structural and magnetic properties of zinc ferrite thin films irradiated by 90 keV neon ions

The effects of 90keV neon beam irradiation on the structure and magnetic properties of zinc ferrite thin films have been investigated through several methods, namely, X-ray diffraction technique, Vibrating Sample and SQUID magnetometers. Beforehand, the pristine have also been characterized using profilometry and microscopy techniques. In particular single-phase formation of the thin films deposited on monocrystalline Si (111) substrate by pulsed laser deposition technique was confirmed. Crystal lattice, coercivity, saturation magnetization have been studied for the first time, as a function of ion penetration depth and irradiation fluence. The chemical composition and the crystallinity of the films are not affected with the ion impact acting as a mechanical stress relief. On the contrary, both magnetization and coercivity are sensitive to Neq+ ion irradiation and exhibit different behaviours depending on the ion fluence range.

Structural, surface potential and optical studies of AlGaN based double heterostructures irradiated by 120 MeV Si9+ swift heavy ions

The Al0.33Ga0.77N/Al0.14Ga0.86N based double heterostructure was irradiated using Si9+ ion at room temperature (RT) and liquid nitrogen temperature (LNT) with four dissimilar ion fluence. The effect of Si9+ ion irradiation in dislocation densities and in-plane strain of GaN layer were discussed. The in-plane strain values of AlxGa1-xN layers were calculated from asymmetric reciprocal space mapping (RSM). The surface modification and the variation in phase shift on Al0.33Ga0.77N surfaces due to the irradiation were measured by Electrostatic Force Microscopy (EFM). The capacitance of the tip-sample system was determined from EFM. The band edge emissions of heterostructures were measured by the room temperature phototluminescence (PL) and the shift in the Al0.14Ga0.86N active layer emission peaks towards the low energy side at low fluence ion irradiation has been noted.

Effect of ion beam parameters on engineering of nanoscale voids and their stability under post-growth annealing

Swift heavy ion (SHI) irradiation of damaged germanium (d-Ge) layer results in porous structure with voids aligned along ion trajectory due to local melting and resolidification during high electronic energy deposition. The present study focuses on the irradiation temperature- and incident angle-dependent growth dynamics and shape evolution of these voids due to 100 MeV Ag ions irradiation. The d-Ge layers were prepared by multiple low-energy Ar ion implantations in single crystalline Ge with damage formation of ~7 displacements per atom. Further, these d-Ge layers were irradiated using 100 MeV Ag ions at two different temperatures (77 and 300 K) and three different angles (7°, 30° and 45°). After SHI irradiation, substantial volume expansion of d-Ge layer is detected which is due to formation of nanoscale voids. The volume expansion is observed to be more in the samples irradiated at 77 K as compared to 300 K at a given irradiation fluence. It is observed that the voids are of spherical shape at low ion irradiation fluence. The voids grow in size and change their shape from spherical to prolate spheroid with increasing ion fluence. The major axis of spheroid is observed to be aligned approximately along the ion beam direction which has been confirmed by irradiation at three different angles. The change in shape is a consequence of combination of compressive strain and plastic flow developed due to thermal spike generated along ion track. Post-SHI irradiation annealing shows increase in size of voids and reversal of shape from prolate spheroid towards spherical through strain relaxation. The stability of voids was studied with the effect of post-growth annealing.

Tuning the antiferromagnetic to ferromagnetic phase transition in FeRh thin films by means of low-energy/low fluence ion irradiation

Ion irradiation induced modifications of the thermomagnetic properties of equiatomic FeRh thin films have been investigated. The application of 20keV Ne+ ions at different fluencies leads to broadening of the antiferromagnetic to ferromagnetic phase transition as well as a shift of the transition temperature towards lower temperatures with increasing ion fluence. Moreover, the ferromagnetic background at low temperatures generated by the ion irradiation leads to pronounced saturation magnetisation at 5K. Complete erasure of the transition, i.e. ferromagnetic ordering through the whole temperature regime was achieved at a Ne+ fluence of 3×1014ions/cm2. It does not coincide with the complete randomization of the chemical ordering of the crystal lattice.

Impact of 100 MeV Ag7+ SHI irradiation fluence and N incorporation on structural, optical, electrical and gas sensing properties of ZnO thin films

In the present study, we have investigated the influence of Ag7+ ion irradiation fluence and N incorporation on structural, optical, electrical and gas sensing properties of ZnO thin films. The X-ray diffraction analysis reveals the retainment of ZnO wurtzite structure even at higher fluence irradiation with slight decrease in crystallinity. Photoluminescence and Hall effect measurement analysis showed an increase in density of defects for high ion fluence irradiation. Atomic force microscope analysis shows that the films irradiated at high ion fluence have vertical standing needle-like morphology and also have high value of roughness compared with the films irradiated at low ion fluence. The ammonia and methanol gas sensing properties of the films have been studied at different operating temperature and gas concentration. It conveys that the films have selectivity towards ammonia than methanol and also that the films irradiated at high ion fluence exhibit better sensitivity, low response and recovery times compared with the films irradiated at low ion fluence. The film grown in oxygen ambience and irradiated at high ion fluence showed good sensing characteristics at all temperatures even at room temperature.

Pre and Post Effect of Swift Heavy Ion Irradiation on Infrared Spectral Evolution of Y<sub>3+</sub><i><sub>x</sub></i>Fe<sub>5-</sub><i><sub>x</sub></i>O<sub>12</sub> (<i>x</i> = 0.0 - 1.0) System

Present work aims to investigate the effect of Y3+ - substitution and 50 MeV, Li3+ ion irradiation (fluence: 5 x 1013 ions/cm2) on infrared spectral evolution of Y3+xFe5-xO12 (x = 0.0, 0.2 0.4, 0.6, 0.8 and 1.0) garnet system. Infrared absorption spectra for x = 0.0 – 0.6 compositions show three absorption bands while x = 0.8 – 1.0 compositions are characterized by two absorption bands, identical with IR spectra of rare earth ortho ferrites. The position and intensity of bands are found to be influenced by Y3+ - substitution. The intensity of absorption bands for x = 0.0 – 0.4 compositions is found to increase, while for x = 0.6 – 1.0 compositions no effect of swift heavy ion irradiation has been observed. The results have been explain in the light of SHII induced defect states, partial removal of un-wanted YFeO3 phase and change in structural parameters. It seems that YFeO3 phase is irradiation hard phase.

Pre and Post Effect of Swift Heavy Ion Irradiation on Infrared Spectral Evolution of Y<sub>3+</sub><i><sub>x</sub></i>Fe<sub>5-</sub><i><sub>x</sub></i>O<sub>12</sub> (<i>x</i> = 0.0 - 1.0) System

Present work aims to investigate the effect of Y3+ - substitution and 50 MeV, Li3+ ion irradiation (fluence: 5 x 1013 ions/cm2) on infrared spectral evolution of Y3+xFe5-xO12 (x = 0.0, 0.2 0.4, 0.6, 0.8 and 1.0) garnet system. Infrared absorption spectra for x = 0.0 – 0.6 compositions show three absorption bands while x = 0.8 – 1.0 compositions are characterized by two absorption bands, identical with IR spectra of rare earth ortho ferrites. The position and intensity of bands are found to be influenced by Y3+ - substitution. The intensity of absorption bands for x = 0.0 – 0.4 compositions is found to increase, while for x = 0.6 – 1.0 compositions no effect of swift heavy ion irradiation has been observed. The results have been explain in the light of SHII induced defect states, partial removal of un-wanted YFeO3 phase and change in structural parameters. It seems that YFeO3 phase is irradiation hard phase.

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.

Effects of the deep ion-induced modification of highly oriented pyrolytic graphite

The capabilities of in situ ion-electron emission monitoring of the effects of deep modification for surfaces of highly oriented pyrolytic graphite at high ion irradiation fluences and determining the threshold radiation damage level of these effects are demonstrated experimentally.

150 MeV Au ion induced modification of Si nanoparticles prepared by laser ablation

We have investigated in detail the effects of 150MeV Au ions irradiation on Si nanoparticles (NPs) synthesized by picosecond laser ablation of single crystal Si wafers in acetone. The formation of Si NPs was confirmed by Raman spectroscopy, transmission electron microscopy (TEM) and field emission scanning electron microscope (FESEM) measurements. The size distribution of synthesized NPs was found to be in the range of few nm to 80nm. These samples were then irradiated with 150MeV Au ions at various fluences ranging from 1×1013 to 1×1014ions/cm2. The effects of ion irradiation on the size and shape of Si NPs were further investigated using TEM, FESEM and micro Raman spectroscopy. From TEM data, we have noticed the reduction in size of NPs with increasing ion irradiation fluence. Furthermore with the increasing fluence we also observed the nucleation of 6–9nm NPs in the vicinity of bigger NPs where there were no such NPs before ion irradiation. The increase in the FWHM of the Raman peak and its shift towards lower wave number side also suggests that the decrease in NP size is a result of increase in the fluence of irradiation.

Swift heavy ion irradiation-induced modifications in structural and electrical properties of Y3+-substituted yttrium iron garnet

The consequences of 50 MeV Li3+ ion irradiation (fluence: 5×1013 ions/cm2) on the structural and electrical properties of the Y3+xFe5−xO12 (x=0.0, 0.2, 0.4 and 0.6) garnet system have been investigated over the temperature range of 300–673 K. It is found that the percentage formation of an additional yttrium orthoferrite phase observed along with the bcc garnet phase considerably reduces for x=0.4 and 0.6 compositions after swift heavy ion (SHI) irradiation. The nature of thermal variation of DC resistivity curves for x=0.0 and 0.2 compositions is different from that for x=0.4 and 0.6 compositions. The SHI irradiation influences the magnitude of DC resistivity and conduction mechanism for the single-phase compositions while for mixed-phase compositions they remain unaffected. The results have been explained in the light of replacement of magnetic (5μB), smaller (0.64 Å), Fe3+ ion by nonmagnetic (0μB), larger (0.89 Å), Y3+ ion, the presence of the yttrium orthoferrite phase and swift heavy ion irradiation-induced paramagnetic centers in the system.

Phonon transport assisted by inter-tube carbon displacements in carbon nanotube mats

Thermal transport in carbon nanotube (CNT) mats, consisting of randomly networked multi-walled carbon nanotubes (MWNTs), is not as efficient as in an individual CNT because of the constrained tube-to-tube phonon transport. Through experiments and modeling, we discover that phonon transport in CNT mats is significantly improved by ion irradiation, which introduces inter-tube displacements, acting as stable point contacts between neighboring tubes. Inter-tube displacement-mediated phonon transport enhances conductivity, while inter-tube phonon-defect scattering reduces conductivity. At low ion irradiation fluence, inter-tube thermal transport enhancement leads to thermal conductivity increase by factor > 5, while at high ion irradiation fluence point defects within tubes cause a decrease in thermal conductivity. Molecular dynamics simulations support the experimentally obtained results and the proposed mechanisms. Further conductivity enhancement in irradiated mats was obtained by post-irradiation heat treatment that removes majority of the defects within the tubes without affecting thermally stable inter-tube displacements.

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.

Ion-induced modification of glassy carbon structure and morphology

The temperature dependences of ion-induced electron emission yield γ (T) under 10–30keV Ar+ high-fluence ion irradiation of glassy carbon SU-2500 at normal ion incidence have been analyzed to trace the structure and morphology changes depending on the irradiation temperature and the level of radiation damage ν measured in dpa (displacements per atom).It has been found that high fluence ion irradiation can result in changes of pristine structure of glassy carbon to amorphous structure at relatively low temperatures (T⩽100oC) and to ordering till polycrystalline graphite structure at elevated temperatures (T⩾250oC) The amorphization at room temperature is started at the mean radiation damage level <ν>∼50 dpa and finished at <ν>≈75 dpa. The graphitization at T>250°C begins at <ν>≈75 dpa.