Swift Heavy Ion Irradiation Research Articles

Effect of swift heavy ions irradiation on physicochemical and dielectric properties of chitosan and chitosan-Ag nanocomposites

Self-sustained films of biodegradable chitosan (CS) and chitosan-Ag nanocomposites (CSN) were prepared by chemical route followed by C+5 and Ni+7 ions irradiation with varying fluences. The crystallite size decreased from 11.1 to 2.7 nm for CS and 17.6 to 14.2 nm for CSN with increasing ions fluence as observed from the analysis of X-ray Diffraction (XRD) spectra. ATR-FTIR spectra revealed assorted vibrational modes and degradation of polymeric chains in both, CS and CSN matrices upon irradiation. The molecular interactions between main and side-chain functional groups impeded due to nanoparticles confining effects. MeV ions yield low-molecular-weight fragments with degassing of some volatile gaseous species during irradiation. An acute amendment in absorption spectra ascribed to change in surface color and differential absorbance at the wavelength of 370 nm showing blocking of UV radiation. The formation of conjugated linkages and carbonization of CS and CSN matrices lead to decrease in bandgap. Modifications in the physicochemical properties were found to be in persuasive association with changes in frequency-dependent dielectric responses. The shape parameter was moderately decreased and indicating non-Debye relaxation. The conductivity of CS and CSN matrices enhanced and follows the universal dielectric response. The amendment in surface morphology was also revealed upon irradiation.

Optical and structural modification in amorphous Ge24Se61Sb15 thin films under 80 MeV Silicon swift heavy ions for telecom and optical applications

Present study reports about the effect of 80 MeV Silicon swift heavy ions irradiation on linear and nonlinear optical properties of amorphous Ge24Se61Sb15 thin films. Optical changes are correlated with structural modifications for their utilization in telecom and optical applications. Optical transmission spectra were recorded from 200 nm to 1100 nm. Linear refractive index is calculated by optical transmission using Swanepoel envelope method. Dispersion in the linear refractive index of the thin films is described using Wemple-DiDomenico model. Nonlinear optical parameters are determined using semi-empirical relations. Optical band gap is calculated by extrapolating the Tauc's plot. The investigation shows that optical band gap decreases from 1.64 eV to 1.47 eV and linear refractive index increases from 2.50 to 2.59 till fluence 1 × 1012 ions/cm2. In addition, third-order nonlinear susceptibility increases from 8.178 × 10−10 [esu] to 11.43 × 10−10 [esu] and nonlinear refractive index increases from 1.742 × 10−10 [esu] to 2.698 × 10−10 [esu] till fluence 1 × 1012 ions/cm2. Raman measurements reveal that swift heavy ion irradiation converts homopolar Ge–Ge, Sb–Sb bonds into hetropolar Ge–Sb and Se–Sb bonds, which is responsible for observed optical changes. The changes are understood in terms of glass network structure and electronic energy loss for application point of view.

Nanopatterning surfaces by grazing incidence swift heavy ion irradiation

Nanopatterned surfaces play a key role for many applications exploiting unique features such as an enhanced surface area, long- and short-ranged morphology modulations or a spatial variation of electronic and chemical properties. Ion beam irradiation has been frequently used for nanostructuring bulk materials because it is efficient, fast, and cost-effective. In this paper we show that ion irradiation under extremely grazing incidence in conjunction with other scalable processing methods such as wet etching and thermal annealing, is a perfect tool for nanopatterning of dielectric surfaces. We demonstrate that by tuning ion energy and fluence, one can select different surface nanopattern morphologies like individual chains of nanohillocks, nanostripes, or nanoscaled ripples. Furthermore, chemical etching of the irradiated surface can be used to create a negative replica of the nanopattern as only the material making up the surface track is susceptible to the etching process and is thus removed. Also, a removal of the surface track can be achieved by thermal annealing in vacuum. All these presented strategies open up new ways for achieving control over nanoscale surface modifications using swift heavy ion beams.

OPTICAL AND STRUCTURAL PROPERTIES OF 100 MeV Ag SWIFT HEAVY ION IRRADIATED AMORPHOUS Ge24Se61Sb15 THIN FILMS

Present study reports about change in structural and linear/nonlinear optical properties of amorphous Ge24Se61Sb15 thin films using 100 MeV silver (Ag) swift heavy ion (SHI) irradiation. The thin films were irradiated under 100 MeV Ag SHI for six different fluences (3x1010, 1x10 11, 3x1011, 1x1012, 3x1012, and 1x1013 ions/cm2 ). The XRD images of the pristine and irradiated (3x1012 ions/cm2 ) thin films confirm the amorphous nature of thin films. The scanning electron microscopy (SEM) micrograph reveals that the fluence 1x1013 ions/cm2 is the upper limit of ion fluence. The loss of energy and stopping range of 100 MeV Ag SHI was calculated using SRIM-2006. The electronic energy loss dominates over nuclear energy loss, hence is mainly responsible for optical and structural changes. The optical transmission spectra of the pristine and irradiated thin films were recorded within the spectral range from 300 nm to 900 nm. The optical absorption coefficient was calculated by using the Lambert-Beer law. The optical band gap (Eg) was calculated by extrapolating the Tauc’s plot. The optical band gap (Eg) reduces from 1.59 eV (pristine) to 1.38 eV (3x1012 ions/cm2 ) and further increases to 1.48 eV (1x1013 ions/cm2 ). Linear and nonlinear refractive index were calculated using semi-empirical relations and both increases till fluence 3x1012 ions/cm2 , which is the consequence of bonding rearrangement as explained using Raman measurement.

Photoluminescence Quenching and Photo-Induced Charge Transfer Processes in Poly(3-octylthiophene) Polymer Based Hybrid Nano-composites by Ion Irradiation for Possible Optoelectronic Applications

Structural and spectroscopy studies have been carried out on conducting polymer poly(3-octylthiophene) (P3OT) and its copper-doped ZnO (Cu-ZnO/P3OT) hybrid nanocomposites (HNCs) under swift heavy ion (SHI) irradiation at different electronic energy depositions. The photoluminescence (PL) spectra of irradiated films exhibit a significant decrease in the intensity of emissions at higher ion fluences which is ascribed to the trapping of a photo-induced electron-hole by irradiation-induced free radicals and extrinsic non-radiative trap centers leading to the quenching effects. The generation of such free radicals and non-radiative recombination centers occurred through a chemical transformation of polymers in terms of polymer chain disordering, chain scission, chain aggregation, and bond breaking by ion irradiation depending upon the electronic energy depositions and ion fluences. The structural, vibrational, morphological, and optical properties of the irradiated P3OT and Cu-ZnO/P3OT HNCs films have been studied. Interestingly, the glancing-angle x-ray diffraction patterns of irradiated films reveal that the polymer and HNC films retain their chemical structures after high electronic deposition at lower ion fluences which leads to insignificant degradation of polymer and HNCs. However, a relative change in the intensity of characteristic peaks of polymer and ZnO was observed at higher ion fluences and is attributed to the disordering of polymer chains by high electronic depositions. Fourier transform infrared spectroscopy (FTIR) measurements also show similar observation, attributed to a decrease in the intensity of a few methyl and octyl functional groups of P3OT and HNCs. Further, optical study has shown a significant modification in the process of inter-chain and interfacial charge transfer. Finally, from these concurrent effects, PL quenching and photo-induced charge carrier transfer processes are understood by developing a schematic charge transfer diagram.

Modification of structure and surface morphology in various ZnO facets via low fluence gold swift heavy ion irradiation

The influence of low fluence high‐energy ion irradiation on the modification of the ZnO surface structure and optical properties has been studied. ZnO samples of various orientations, namely, c‐plane (0001), a‐plane (11–20) and m‐plane (10–10), have been implanted with 30‐MeV Au ions with fluences ranging from 5 × 109 to 5 × 1011 cm−2. Rutherford backscattering spectrometry in the channelling mode (RBS‐C) and Raman spectroscopy has shown the distinct damage accumulation in the irradiated surface layer about 1 μm depending on the ZnO facet being to larger extent evidenced in the m‐plane ZnO. Contrary, the a‐plane ZnO has been exhibited the lowest Zn disorder. Using atomic force microscopy (AFM), a complex morphology was detected on the irradiated samples containing grains and exhibiting increased roughness, both growing with the Au implantation fluence mainly in m‐plane ZnO. Positron annihilation spectroscopy (PAS) has shown distinct defect accumulation at the Au‐ion fluence of 5 × 1011 cm−2, where RBS‐C and Raman spectroscopy indicated sudden disorder increase in the irradiated layers, probably the creation of more complex clusters of Zn and O vacancies 4VZn + 8VO initiated in connection with an overlap of individual ion impacts. Photoluminescence measurements have shown a distinct near‐band‐edge (NBE) luminescence, developing with the increasing Au‐ion fluence in various ZnO orientations. The m‐plane ZnO had the most progressively suppressed NBE in comparison with the other orientations.

Intense ionizing irradiation-induced atomic movement toward recrystallization in 4H-SiC

An ultrafast thermal spike within a time interval of a few pico-seconds generated by intense ionizing energy deposited using 100 MeV Ag ions is utilized to study the atomistic details of damage recovery in 4H-SiC. Sequential single ion irradiations were performed using 300 keV Ar and 100 MeV Ag in ⟨0001⟩ 4H-SiC to invoke swift heavy ion (SHI) beam induced epitaxial recrystallization in samples with different degrees of pre-damaged conditions. SHI irradiation was carried out at both room temperature and a low temperature of ∼80K. Low-temperature irradiation was carried out to arrest thermal diffusion of defects and to isolate ionization-induced defect migration in 4H-SiC. Insights into the thermal spike generated by ionizing events in crystalline and amorphous regions at both the temperatures predict a SiC response to SHI. The results emphasize the role of different degrees of pre-damage induced physico-chemical conditions and irradiation temperatures against SHI-induced recrystallization as evaluated by Rutherford backscattering/channeling, Raman spectroscopy, and hard x-ray photoelectron spectroscopy. Understanding the dependence of ion-beam damage accumulation and their recovery on the inelastic to elastic energy loss ratio is important for the performance prediction of SiC intended for extreme environments such as space, defense, and nuclear radiation. We report substantial damage recovery even at a near liquid nitrogen temperature of ∼80K. The recovery gets impeded mainly by the formation of complex defects having homonuclear bonds. The results are explained in the framework of the inelastic thermal spike model, and the role of phonon in the damage recovery process is emphasized.

Tuning the properties of Fe-BTC metal-organic frameworks (MOFs) by swift heavy ion (SHI) irradiation

Impact of Swift Heavy Ion (SHI) irradiation is an effective way to tailor the properties of materials to enhance their applicability toward high-end applications. In the present investigation, hydrothermally synthesized Fe-BTC metal–organic frameworks (MOFs) were irradiated with 197Au8+ ion beam, 100 MeV at fluence range of 1 × 1011 ions/cm2 and 1 × 1012 ions/cm2. Hydrothermally synthesized Fe-BTC MOFs were characterized by X-ray diffractometer, UV-Visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), Raman spectroscopy, and Atomic Force Microscopy (AFM). The significant modifications were observed as ion fluence increases, viz. decrease of crystallite size, increase of energy bandgap, reduction in average surface roughness, and the formation of new functional group (C–H) at a higher fluences 1 × 1012 ions/cm2.

Swift heavy ion irradiation-induced modifications in the electrical and surface properties of β-Ga2O3

The electrical device characteristics of Ni/β-Ga2O3 vertical Schottky barrier diodes (SBDs) were measured in situ during the irradiation of 120 MeV Ag7+ swift heavy ions (SHIs). These devices exhibit SHI irradiation-induced degradation with 120 MeV Ag7+ ions in the ion fluence ranges of 1 × 1010 to 1 × 1012 ions/cm2. The height of the Schottky barrier is found to decrease from 1.11 to 0.93 eV, and the ideality factor increases from 1.16 to 2.06. These changes indicate the degradation of the device with SHI irradiation. A significant four orders increase is observed in the leakage current density from 4.04 × 10−8 to 1.98 × 10−4 A/cm2 at −1 V, and the series resistance also increases from 3.38 × 103 to 1.15 × 104 Ω. X-ray photoelectron spectroscopy measurements show that the Ga ions are present in divalent and trivalent states with the spectral features having the binding energies centered at 20.2 eV and 19.9 eV (Ga 3d core-levels) before and after ion irradiation. The O 2s peak shifts to 23.7 eV, and there is an increase in intensity and peak broadening due to the change in the trivalent to divalent state of Ga due to the irradiation. The O(I) peak appears at 530.7 eV in the pristine sample with the Ga–O bonding with the Ga3+ state in pure Ga2O3. Moreover, there is a significant change in the intensity and the peak width of O(II) centered at 533.0 eV after ion irradiation at the fluence of 1 × 1012 ions/cm2. This indicates that there is an increase in the surface adsorbed/lattice oxygen, resulting in GaO.

Swift heavy ion irradiation induced negative differential resistance and transport of charge carriers in conducting polymer-metal oxide hybrids

An intriguing phenomenon of the negative differential resistance (NDR) in conducting polymer-metal oxide hybrids is manifested upon measuring the In-situ current-voltage characteristics. Anomalous evolution of low current state leading to the electrical bistability has also been observed as an induced effect at low ion irradiation doses and explained by invoking ordering of the polymer chains and electric-field induced charge transfer mechanisms. Later, a disorder leading to damage is observed at higher doses by the diffusion of irradiation-induced electrically active free radicals and defect centers within the active region of the device. This leads to the device into a high current state of electrical bistability. Further, the observed NDR is attributed to the tunneling of carriers along with transient charging of molecular chains by trapping of charge carriers at the heterojunction interfaces induced by ion irradiation. It is further confirmed by anomalous response of voltage shifting in the conductance response upon incremented doses of irradiation. Efforts are envisaged to understand the processes of irradiation interactions and their influences on the transport of charge carriers by fitting experimental data using various conduction models such as Ohmic conduction, space-charge-limited conduction (SCLC), and trap-assisted SCLC. Thus, such low-cost and simple design devices have lots of potential applications for radiation harsh environments and could be easily integrated into the existing silicon-based technology.

Atomistic strain and structural analysis of 120 MeV Ni ions irradiated CdSe nanocrystals through molecular dynamics simulation method

Swift heavy ion (SHI) irradiation modifies the physical and chemical properties of semiconductor sample like CdSe nanocrystals by inducing vacancies and structural change in the lattice system. Here, the atomistic strain analysis has been performed using molecular dynamics (MD) simulation on the SHI irradiated CdSe nanocrystals by approximating interatomic interaction as (ZBL) potential. MD simulation based on LAMMPS package has been employed for better understanding the time response of the sample with swift heavy ion irradiation. The primary knock-on atom (PKA) method has been used for the simulation that starts the cascade of energy transfer, which triggers the displacement of atoms. Initial parameters of PKA have been obtained from the SRIM simulation of the irradiation effect of 120 MeV Ni ions. Finally, the time evolution of the system has been studied.

A versatile multifaceted resistive switching memory activated by light and ion irradiation in poly (3-octylthiophene)-zinc oxide hybrids

Abstract The resistive switching memory behavior activated by simulated solar light and swift heavy ion irradiation in poly (3-octylthiophene)-zinc oxide hybrid devices are reported. The current-voltage characteristics show the appearance of a remarkable hysteresis in reverse bias and a considerable in a forward bias upon illumination by simulated solar light results in memory behavior. Ion irradiation exhibits strong enhancement of the memory behavior under both dark and light illuminations. Thus, the memory response is activated and/or enhanced upon illumination by light and irradiation along with the cyclic endurance of the devices. This is attributed due to the formation of well built-in conducting filament pathways through the trapping of injected and photo-generated charges via irradiation-induced electrically active defect and trap states and well explained by a schematic energy band diagram. The defect density induced upon ion irradiation works as a dominant factor and thus the tailoring of the interfacial properties of the hybrid devices leads to the strong strengthening of memory formations. Thus, the hybrid devices can be activated and/or enhanced by light and irradiation for potential fast resistive switching memory applications.

Phase dependent radiation hardness and performance analysis of amorphous and polycrystalline Ga2O3 solar-blind photodetector against swift heavy ion irradiation

Solar-blind photodetectors are critically important for civil and military applications. Several of these applications, such as space exploration and nuclear energy infrastructure, demand the use of a photodetector under extreme environments. In this paper, we have studied the radiation hardness and device performance of amorphous and polycrystalline gallium oxide thin films against heavy ion (Ag7+) irradiation with a high energy of 100 MeV. Gallium oxide thin films show great tenacity against massive and highly energetic ions. The amorphous and polycrystalline phases undergo structural and morphological changes that initially induce degradation in the device performance. Nano-pore like structures are formed in the amorphous film, while the polycrystalline film shows the destruction of large crystallites. The responsivity of the photodetector device reduces fourfold in the amorphous phase; however, a sixfold reduction in the performance is observed in the polycrystalline phase of the gallium oxide photodetector. The degradation is attributed to the annealing of pre-existing optical defects that are otherwise responsible for the huge photoconductive gain in the detector and confirmed by photoluminescence studies. The effect of self-annealing at room temperature and annealing at moderate temperature is investigated to recover the irradiated photodetector devices. Partial recovery in the polycrystalline based photodetector and two orders of magnitude enhanced responsivity and an almost twice faster response time compared to the control photodetectors in the amorphous phase are observed. This work investigates the effect of heavy and energetic ions on the performance of gallium oxide based solar-blind photodetector and provides the guideline to use high energy irradiation as a tool for defect engineering.

Defects induced resistive switching behavior in Ca doped YMnO3–based non–volatile memory devices through electronic excitations

Defect induced structural, microstructural, resistive switching (RS) characteristics and related responsible charge conduction mechanisms of Y0·95Ca0·05MnO3 (YCMO) manganite films, grown on single crystalline (100) Nb:SrTiO3 (SNTO) substrates (0.2 wt% Nb doped at Ti–site in SrTiO3), are reported in this communication. Films were irradiated by 100 MeV O+7swift heavy ions (SHI) with different ion fluence. Structural studies were performed using X–ray diffraction (XRD) and XRD φ–scan measurements for all pristine and irradiated films. Atomic force microscopy (AFM) measurement was performed to understand the granular morphology and surface modifications in YCMO films due to SHI irradiation. Observed RS behavior has been ascribed to the trapping–detrapping processes, modifications in the depletion region, movement of oxygen vacancies and tunneling process across the interface barriers between YCMO and SNTO. Various models and mechanisms have been employed to understand the observed charge transport across the interfaces. All the films show endurance and retention behaviors that suggest the reproducibility, dynamic stability and reliability of presently studied films as non–volatile memory devices.

Physio-chemical influence of high electron-phonon coupling induced by 120 MeV Ag9+ SHI irradiation on exfoliated MoS2 - PVA nanocomposite films for achieving remarkable electrical conductivity for potential application in organic electronics

Swift heavy ion (SHI) irradiation technology is known to enhance the optical, electronic, mechanical, and electrical properties in polymer nanocomposites by the virtue of electron-phonon coupling. In the present work, Molybdenum disulphide (MoS2), a two-dimensional metal dichalcogenide, has been exfoliated via liquid-phase exfoliation using N-methyl-2- pyrrolidone (NMP) as the solvent that yielded nanosheets of around 2–4 layers as depicted by HR-TEM images. MoS2 - PVA free-standing films were prepared by wet chemical technique i.e. solution casting method and irradiated by focussed high-energy Ag9+ ion beam at fluence range of 1E10 - 3E11 ions/cm2. As a consequence, the structural modification was observed by X-Ray diffraction studies that showed the shift of (002) plane of MoS2 while Raman studies indicated the decrease of degree of disorderness at fluence 1E10 ions/cm2. SHI irradiation has found to induce a two-order increase in the electrical conductivity yielding a 9.7 E-3 S/cm against that of the pristine films at 2.6E-5 S/cm. The enhanced conductivity is attributed to the induced dispersion and annealing of MoS2 nanosheets in the PVA matrix due to the interaction of 120 MeV Ag9+ ion beam irradiation as explained by Thermal spike model.

Observation of exchange bias in nanoscale AuFe alloy film

We report on observation of the exchange bias effect in AuFe co-sputtered alloy films in the as-deposited state and following swift heavy ion irradiation. The Mössbauer spectrum for the as-deposited film shows a broad paramagnetic doublet together with a small contribution from hyperfine magnetic sextets. The magnetization behavior exhibits a spontaneous exchange bias effect at room temperature without application of an external triggering field. The magnitude of exchange bias in the as-deposited sample increases with decreasing temperature, at first gradually down to about 50 K and then more rapidly down to 5 K. Irradiation of AuFe film with 100 MeV Au9+ ions transforms the Mössbauer spectrum into a broad magnetic sextet, with asymmetric broadening characteristic of the formation of α-Fe magnetic nanoclusters surrounded by shells of reduced Fe concentration. At room temperature the exchange bias field is in the same sense as that for the as-deposited sample, but decreases with temperature until it reverse its sign at below about 50 K. In both the as-deposited and irradiated samples a well-defined uniaxial magnetic anisotropy, consequent on a stress induced texturing of the Fe precipitate distribution, is observed.

Highly Efficient Solid-State Intra-Track Polymerization of Ethynyl-Substituted Spirobifluorenes Triggered by Swift Heavy Ion Irradiations

Highly Efficient Solid-State Intra-Track Polymerization of Ethynyl-Substituted Spirobifluorenes Triggered by Swift Heavy Ion Irradiations

Issue Information

Cover Photograph: Small angle X‐ray scattering images of MgAl2O4 irradiated by swift heavy ions (SHI) of 100 MeV Xe to a fluence of 1 × 1013 cm–2. (a) The sample was set with the X‐ray beam incident parallel to the direction of SHI irradiation, whereas (b‐d) the sample was tilted to 1°, 5°, and 15°, respectively, with respect to the X‐ray beam. The two vertical lines and central spot without intensities visible in each image are gaps due to the detector module edge and the catcher for the incident X‐ray beam, respectively. Analyses on these images showed that the defects induced by the SHIs were cylindrical shape ones (ion tracks) with a diameter of 5.1±1.4 nm, and that cations at tetrahedral and octahedral sites inside the ion tracks were significantly disordered. Cover Credit: Satoru Yoshioka, Kyushu University. DOI;10.1111/jace.17101. image 2019 ACerS Ceramographic Exhibit & CompetitionCategory: Underrgraduate, 2nd Place image

Influence of 120 MeV Ag swift heavy ion irradiation on the optical and electronic properties of As-Se-Bi chalcogenide thin films

Ion beams of widely varying energies from keV to GeV have played a significant role in the modification of materials. The manuscript reports the influence of 120 MeV Ag swift heavy ion irradiation (SHI) at two different fluence on As40Se58Bi02 and As40Se45Bi15 thin films. The irradiation has shown strong impact on the optical constants like transmittivity, absorption coefficient, extinction coefficient, optical band gap and disorderness with no structural change. The optical transmittance decreased while absorption coefficient and extinction coefficient increased with increase in the fluence from 5 × 1012yions/cm2 to 5 × 1013ions/cm2. The decreased optical band gap with irradiation is explained on the basis of bond distribution model and density of defect states with increase in disorder. The p-type to n-type conductivity switching was observed at higher Bi content and the Hall measurement showed the increase in conductivity with irradiation. The Raman study on these ion irradiated films also confirmed no structural transformation. The surface morphological evolution of the films by Ag ion irradiation was studied by Field Emission Scanning Electron Microscopy.

Recrystallization effects in GeV Bi ion implanted 4H-SiC Schottky barrier diode investigated by cross-sectional Micro-Raman spectroscopy

It is especially important to study on the change of 4H-SiC physical properties by swift heavy ion irradiation (SHI) for the future application of SiC devices in extreme irradiation environment. Herein, 4H-SiC Schottky barrier diodes (SBDs) are irradiated by 1.9 GeV 209Bi ion beams without intentional heating. The cross-sectional Micro-Raman Spectroscopy (MRS) results clearly indicated that there are new vibration bands at low fluence. This is attributed to the formation of homonuclear bonds Si–Si and C–C within the SiC network to break down the Raman selection rules. At high fluence, there are only typical Raman data for 4H-SiC crystal and the disappearance of Si–Si and C–C bonds. In addition, it is observed that the interfacial structure is modified due to the silicon and carbon atomic migration during SHI process at the metal-semiconductor interface, and then reacting at high temperature annealing treatment. Furthermore, these results suggest that the evolution of recrystallization effect is varied with irradiation fluence by the cross-sectional MRS.