Effect Of High-energy Ion Irradiation Research Articles

Investigation of structural and optical properties of ZnTiO3 thin films irradiated with 50 MeV oxygen ions

This paper aims to investigate the effects of high-energy ion irradiation on the structural, morphological, optical, and luminescent characteristics of ZnTiO3 (ZTO) films. ZTO films were grown on silicon and quartz substrates via RF magnetron sputtering in pure argon ambiance and annealed at 800 °C for crystallization. The annealed (pristine) samples were irradiated with 50 MeV oxygen ions at three distinct fluences: 1 × 1012, 5 × 1012, and 1 × 1013 ions/cm2. X-ray diffraction (XRD) data demonstrates that the intensity of highly oriented (311) peak first increases with fluence up to 5 × 1012 and then decreases at 1 × 1013 ions/cm2. The root mean square roughness (RMS) increases initially from 8.22 (pristine) to 9.10 nm (1 × 1012 ions/cm2) and decreases to 8.25 nm for 1 × 1013 ions/cm2 fluence. Transmittance spectra indicate an enhancement in the transmission of irradiated films. The calculated band gap of pristine and irradiated films lies in the range of 3.93–3.84 eV. X-ray photoelectron spectroscopy (XPS) analysis reveals a reduction in oxygen vacancies up to a fluence of 5 × 1012 and then rises at 1 × 1013 ions/cm2. The enhancement of peak intensity is observed in photoluminescence (PL) spectra on increasing the ion fluence due to a reduction in the non-radiative recombination centers.

The Influence of the Structural Parameters of Nanoporous Alumina Matrices on Optical Properties

In this work, two types of nanoporous alumina membranes were prepared and tested. Structural features of the samples obtained by using different acids were investigated by scanning electron microscopy (SEM). And further SEM-images were analyzed by different types of fractal dimension estimation methods. The transmission and scattering of accelerated He+ ions were studied in experiments on the ion irradiation of dielectric channels based on porous alumina. An ion accelerator was used as a source of the He+ beam with an energy of 1.7 MeV. Ion scattering was studied by Rutherford backscattering spectrometry. Helium transition through nanoporous alumina at various angles between the normal to the sample and the beam direction were observed. It is shown that the porous structure of anodic aluminum oxide is excellent as a dielectric matrix of nanocapillaries. Owing to the small angle scattering, it allows for the transportation of the accelerated charged particles through the dielectric capillaries, and, as a result, the localization of high energy ion irradiation effects. Additionally, according to the transmission of UV–V is spectra, the energy gaps of samples obtained were calculated.

A novel method to enhance the catalytic activity of PtRu on the support using CeO2 by high-energy ion-beam irradiation

As a novel method for the preparation of highly-active anode catalysts for direct methanol fuel cells (DMFCs), the effect of high-energy ion irradiation on the CeO2 embedded carbon nanofiber support (CECNF) of the PtRu/CECNF catalyst, that has been reported as a very active catalyst, on the methanol oxidation activity as well as the crystalline structure of the support materials were investigated. PtRu/CECNFs were prepared using the CECNFs that were irradiated by high-energy ion-beams under the different conditions, i.e., using 127 MeV Ar ions, 310 MeV Kr ions and 350 MeV Xe ions with different ion-fluences from 5 × 1011 ions cm−2 to 1 × 1013 ions cm−2. A change in the activity was observed at the low electrode potentials below 0.7 V vs RHE. An almost two times higher current density at 0.6 V vs RHE compared to that without irradiation was obtained by the Ar ion irradiation with the ion-fluence at around 5 × 1011 ions cm−2, while a higher ion-fluence reduced the activity. The reduction of the CeO2 crystalline size with the increase in the ion-fluence was observed by XRD measurements. The change in the catalytic activity roughly correlated with the increase in the lattice distance of CeO2 suggesting that the generated oxygen atom vacancies enhanced the activity.

Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te).

Maximizing the sustainable supercurrent density, J C, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because J C amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSe x Te1-x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or "columnar defects," plus a higher density of single atomic site "point" defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields.

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.

Effects of High-Energy Ion Irradiation on the Conduction Characteristics of HfO2-based MOSFET Devices

MOSFET devices with HfO2 gate oxides were irradiated with high-energy (120 MeV) Au ions. It was observed that the irradiation ca n cause both little or severe damage to the structures under test. We associate these effects with the soft and hard breakdown failure modes occurring in ultra-thin oxides. In both cases there is a large increment of the transistor off current. If the damage is not catastrophic a decrease of the transconductance and drain current characteristics can also be detected. This indicates that the transistor is still operational but with worst performance parameters.

Mechanism of the swift heavy ion induced epitaxial recrystallization in predamaged silicon carbide

Although silicon carbide has attracted extensive investigations of ion irradiation effects at low energy owing to its potential use in harsh environments, very few works were carried out in the field of ion irradiation at high energy. A recent preliminary study exploring the combination of low and high energy ion irradiation effects in silicon carbide revealed that the damaged layer formed by low energy ion irradiation can undergo an epitaxial recrystallization under subsequent swift heavy ion irradiation. The present paper is devoted to the investigation of the mechanisms at the origin of this phenomenon by performing additional experiments. A detailed analysis of the kinetics of this recrystallization effect demonstrates that the latter cannot be explained by the models proposed for the well-known ion-beam-induced epitaxial crystallization process. Furthermore, it is found that this effect can be accounted for by a mechanism combining the melting within the ion tracks of the amorphous zones through a thermal spike process and their subsequent epitaxial recrystallization initiated from the neighboring crystalline regions wherever the size of the latter surpasses a certain critical value.

Transient current kinetics in the time range of 0.05–2 s for pristine and 100 MeV Ag ion irradiated polyetherimide

High energy ion irradiation effects on the transient current behaviour in the range of 0.05–2 s have been investigated. Polyetherimide samples of 25 µm thickness were irradiated with 100 MeV Ag + beam (fluences: 5.6 × 10 10, 1.8 × 10 11, 1.8 × 10 12 10 12 ions/cm 2). The transient currents were obtained in the temperature range 40–250 °C for step fields ranging from 40 to 600 kV/cm. The half decay time of the transient currents is field dependent and increases from 0.15 s at 40 kV/cm to 0.30 s at 600 kV/cm. The dipolar relaxation strength, estimated from transient current data, reveals the demerization of carbonyl groups and formation of radiation induced subpolar groups due to irradiation. The charge carrier mobility for pristine and ion irradiated samples at different temperatures and fields have been calculated. The charge carrier mobility is governed by several factors like nature of trapping sites and trap density, crystallinity, backbone conjugation and operating temperature etc.

High-energy ion irradiation effects on atomic structures and optical properties of copper oxide and electronic sputtering

We have investigated high-energy ion irradiation effects on atomic structures and optical properties of copper oxide (Cu2O) film on MgO substrate. X-ray diffraction shows that the diffraction intensity decreases to half of as-deposited film for 100MeV Xe ion irradiation at 3×1012cm−2 and no amorphization has been observed, while the optical absorption shows little change and no shift of the bandgap has been observed under high-energy ion irradiation. The electronic sputtering yields are also presented.

Multiple relaxation processes in high-energy ion irradiated kapton-H polyimide: Thermally stimulated depolarization current study

High-energy ion irradiation effects on the thermally stimulated depolarization current (TSDC) behaviour of kapton-H samples (12.5 μm) irradiated with 50 MeV Li ion (fluence 5 × 10 4, 10 5 and 5 × 10 5 ions/cm 2) have been investigated. The TSDC spectra of the irradiated samples reveal that the β-peak (appearing around 80–110 °C) associated with dipolar relaxation has been significantly affected owing to the demerization of carbonyl groups due to irradiation. The TSDC spectra also reveal a new relaxation process (termed as γ-relaxation) around 30 °C, due to increased water absorptivity in irradiated samples. The peak around 200 °C (α-peak) associated with space charge relaxation process also shows a behavioural change with ion irradiation. The peak not only shifts towards the higher temperature with increasing fluence but also show an increase in its activation energy (0.33–0.99 eV) with increasing polarizing field. The creation of new deep energy trap centers due to the formation of conjugated bonds after irradiation is responsible for this modification. The Cole–Cole distribution curves show the formation of new sub-polar group with different characteristic relaxation time.

Effect of high-energy ion irradiation on magnetic properties in Fe–Pt invar alloys

Measurements of AC-susceptibility versus temperature curves were made in thin plates of both ordered and disordered Fe-28.3at.%Pt invar alloys before and after swift heavy ion irradiation. In disordered Fe–Pt invar alloy the Curie temperature decreased about 15K by the irradiation of 200MeV Xe-ions to the fluence of 1014ions/cm2. In ordered Fe–Pt invar alloy the Curie temperature decreased about 128K to the value just coincide with that of irradiated disordered alloy. By comparing these data to the previous one for Fe–Ni invar alloys, it was concluded that there exist at least two mechanisms having opposite contribution.

Effect of high-energy heavy ion irradiation on dielectric relaxation behaviour of kapton-H polyimide

High-energy ion irradiation effects on the thermally stimulated depolarization current (TSDC) behaviour and dielectric constant (ε′)/loss factor have been investigated. Kapton-H samples of 25 μm thickness were irradiated with 50 MeV Si + beam (fluence 2.3×10 12 and 1.38×10 13 ions/cm 2). The TSD currents and dielectric constant/loss factor (frequency 1 and 100 kHz) have been investigated from room temperature to 250 °C, following the usual method. The TSDC spectrum of the irradiated samples reveal that the β-peak (appearing at ≈80 °C) associated with dipolar relaxation has been largely affected due to irradiation. At higher fluence, β-peak almost vanishes. The peak appearing at approximately 180 °C (α-peak) is due to space charge relaxation. The peak magnitude increases in samples irradiated with higher fluence. This is mainly due to the creation of new energy traps by irradiation. The ion irradiation results in a large increase in low temperature dielectric constant (30–70 °C) ascribed to the increase in water absorption capacity. The dielectric constant in temperature range 70–180 °C is mainly governed by dipolar relaxation and space charge relaxation. It is suggested that though the space charge relaxation tends to increase ε′, a major loss in carbonyl groups due to high-energy ion irradiation results in a decrease in ε′. In high temperature region (180–250 °C) the dominance of interfacial polarization increases the ε′ value. The loss peaks appearing at approximately 50, 180 and 250 °C are representative of the various relaxation processes. The findings of the TSDC data are in conformity with the dielectric constant data.

Damage and substitution anomalies for MeV Sb implantation in Si(1 0 0) after high-energy irradiation

We have studied the dopant substitution and the lattice damage after 1.5 MeV Sb implantation in Si(1 0 0). The effects of high-energy ion irradiation (HEII) on the Sb substitution and the Si damage have also been investigated. Vacancy super-saturation after HEII promotes high Sb substitution as well as stimulates Si regrowth after 400 °C anneal. The crystallinity of Si lattice as well as the Sb substitution however deteriorates after higher temperature anneals. In addition an inward Sb diffusion is also observed. With low-temperature annealing treatment prior to HEII, a good Sb substitution is observed after 800 °C. In addition, no dopant diffusion and a reduced overall damage is evidenced after 800 °C anneal. Techniques of RBS/C have been applied to investigate the dopant substitution and lattice damage for different irradiation conditions. Multiple scattering formalism has been utilized to extract the damage profiles from RBS/C data.

Metastable defects in SI-GaAs: Effect of high energy ion-irradiation

The intrinsic deep donor level, known as EL2, is responsible for semi-insulating behavior of undoped GaAs. EL2 is the most extensively studied point defect in GaAs. The most important property related to EL2 is the metastability under sub-bandgap light exposure at low temperature. The microscopic origin of EL2 and its photo-induced metastability is still under debate. We present an experimental investigation on unirradiated and irradiated semi-insulating GaAs using thermally stimulated current spectroscopy and photo-current quenching. In addition to EL2, we have discovered some other metastable defects in semi-insulating GaAs. Li ions of 48 MeV were used to irradiate semi-insulating GaAs with fluences between 10 11 and 10 13 ions/cm 2. The energy loss of 48 MeV Li ions in GaAs is dominantly due to electronic processes because the energy loss due to nuclear collision processes is much less than the lattice binding energy of GaAs. Extended range of 48 MeV Li ions in GaAs has been used to modify the defect levels by electronic energy loss processes. Several modifications of defect levels, including the metastable levels in semi-insulating GaAs observed after irradiation, are discussed.

Substitution and diffusion behaviour of MeV implanted Sb in Si(1 0 0) after carbon irradiation

We investigate the effect of high-energy ion irradiation (HEII) on the dopant behaviour for a 1.5 MeV Sb implantation in Si(1 0 0). For HEII, 8 MeV carbon ions were utilized. In addition to exploring the Sb substitution, distribution and diffusion, after HEII, Si lattice damage has also been studied. Effects of annealing, both prior to and after HEII, have also been investigated. Techniques of Rutherford backscattering spectrometry and channeling (RBS/C) have been applied to understand the dopant behaviour as well as the damage and crystallization of Si lattice. The results show that the vacancy (V) supersaturation created during HEII promotes a high (93%) Sb substitution and a low Si damage after a 400 °C anneal. This is an anomalous result as the SPEG of Si is expected at 600 °C. Enormous redistribution of Sb is observed indicating that the dopant defect interactions become crucial after HEII. In-diffusion of Sb is noticed at higher temperatures. Sb diffusion or redistribution is not observed in the absence of HEII. Results indicate that the excess V after HEII can control the dopant behaviour as well as the Si lattice damage.

Effects of High-Energy Ion Irradiation in Bismuth Thin Films at Low Temperature

ABSTRACTWe have studied high-energy ion irradiation effects in bismuth by measuring the electrical resistivity at low temperature in relation to its structural change. Bismuth thin films (330–520 Å thick) are irradiated below ∼10 K with energetic (150–200-MeV) heavy ions. The resistivity of the specimen is measured in situ below ∼7.2 K during the irradiation. After the irradiation, annealing behavior of the resistivity is observed up to ∼30 K. The temperature dependence of the resistivity during annealing shows an abrupt increase around 20 K, implying re-crystallization of irradiation-induced amorphous regions. We have tried to detect a superconducting transition which may take place as a result of irradiation-induced amorphization. In the range of the measuring temperature down to ∼4.9 K, resistivity decrease due to superconducting transition has not been observed in the temperature dependence of the resistivity after 200-MeV 197Au ion irradiation up to a fluence of 3.1×1012 cm-2.

High-energy ion irradiation effects on thin oxide p-channel MOSFETs

P-channel MOSFETs of a commercial 0.25 /spl mu/m CMOS technology have been irradiated by high linear energy transfer (LET) iodine (I) and low LET silicon (Si) ions up to 300 Mrad(Si) and 500 Mrad(Si), respectively. Threshold voltage variations (/spl Delta/V/sub TH/) up to -0.46 V and -0.44 V have been measured at the highest I and Si doses. Both oxide positive trapped charge (/spl Delta/V/sub OX/) and interface states (/spl Delta/V/sub IT/) contribute to /spl Delta/V/sub TH/ with a ratio /spl Delta/V/sub IT///spl Delta/V/sub OX/ /spl ap/ 1 ( 1.6 V (> 3.4 V).

Electrical conduction behaviour of high energy ion irradiated Kapton-H polyimide film

High energy ion irradiation effects on the conduction behaviour of Kapton-H polyimide have been investigated. Kapton-H samples of 125 μm thickness were irradiated with 100 MeV Si + beam for fluences 2.3×10 11, 4.3×10 11 and 1.15×10 12 ions/cm 2 at Nuclear Science Center (PELLETRON FACILITY), New Delhi. Measurements under both transient and the steady state conditions at different temperatures were made at different electric fields ranging from 24 to 160 kV/cm. The transient current behaviour is hyperbolic in nature up to 423 K. Above 423 K the currents are transient free. The decay rate decreases with increasing fluence. The transient currents have mainly been attributed to the formation of free radicals in irradiated Kapton-H polyimide. Non-linear nature of field-current plots is temperature and fluence dependent and an attempt has been made to explain these curves taking into account the various conduction processes. The ionic jump distance estimations do not support ionic hopping as a conduction process. The Poole-Frenkel and Schottky coefficient estimations show that both Poole-Frenkel and Schottky conduction mechanisms are the possible mechanisms operative at high and intermediate temperatures, respectively. The activation energies were determined to be 0.2 and 1.5 eV in the temperature regions below and above 393 K indicating the presence of more than one type of trapping centres in irradiated Kapton-H.

High energy ion irradiation effects on polymer materials–Changes in mechanical properties of PE, PSF and PES

The change in mechanical properties induced by irradiation of electron (2MeV), proton (10 and 20MeV), He2+ (20 and 50MeV), and 220MeV C5+ ions were studied for polymer films of polyethylene (PE), bis-phenol A based polysulphone (PSF) and polyethersulphone (PES). There is no difference between the irradiations of proton and electron in the mechanical properties for PE compared by absorbed dose. On the contrary, in aromatic polymers as PES and PSF, the decrement in the tensile strength and elongation with dose is extremely depressed in the irradiation of ion. It was found from the measurements of gel fraction and glass transition temperature that the probability of crosslinking and/or chain scission depends on linear energy transfer (LET).

High energy ion irradiation effects on polymer materials—Let dependence of G value of scission of polymethylmethacrylate (PMMA)

Linear energy transfer (LET) dependence of the probability of main chain scission of polymethylmethacrylate (PMMA) was investigated. The probability was obtained from decreases in molecular weight measured by gel permeation chromatography (GPC), and LET was evaluated by TRIM code. The scission probability was almost constant for low LET radiation, but decreased for high LET ion irradiation. The mechanism was interpreted from the model of spur overlapping along an ion's path.