Mechanical properties of polymer matrix composites at 77 K and at room temperature after irradiation with 60Co γ-rays

Ten different polymer matrix composites were irradiated with ⁶⁰Co γ-rays at room temperature, and were examined with regard to the mechanical properties at 77 K and at room temperature. The radiation-induced degradation of these composites is observed much more significantly in the ultimate strength and in the shear modulus than in the Young's modulus. The radiation resistance of these composites depends primarily on the radiation resistance of matrix resins, which increases in the order diglycidyl ether of bisphenol A < tetraglycidyl| diaminodiphenyl methane < Kerimid 601. Comparison of the mechanical properties tested at 77 K and at room temperature demonstrates that the extent of radiation-induced decrease in the composite strength is appreciably greater in the 77 K test than in the room temperature test. Interpretation of these results is based on the competition between the two opposing effects due to the hardness and brittleness of matrix resins.     

Formation de “whiskers” et de “hillocks” sur la surface des couches minces de Cu/Sn

The external morphology of free surfaces of Cu/Sn thin films was studied using scanning electron microscopy, electron microprobe analysis and X-ray diffraction. It was shown that the aging of samples of type A (films deposited at room temperature) and type B (copper underlayer deposited at 623 K) at room temperature leads to the formation of hillocks and whiskers; however, the annealing of as-prepared samples at temperatures in the range 363–483 K leads to hillock formation only. The density of hillocks and whiskers in type A samples is two times higher than that in type B samples. The length of the whiskers in type A films (about 4 × 10^-6 m) is one order of magnitude lower than that of the whiskers in type B samples (about 3 × 10^-5 m). This large difference is due to the texture {200} of tin films in type B samples. In type C samples, after aging at room temperature, we observed only hillocks whose diameter could reach 10 × 10^-6 m. Whiskers and hillocks are composed essentially of tin, and the matrix is composed of the Cu₆Sn₅ phase.     

Irradiation induced effects on Ni3N/Si bilayer system

The irradiation effect in Ni₃N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10¹⁴ ions/cm² was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni₂Si and Si₃N₄ phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni₃N thin films. It was observed that after irradiation (Ni 2p_3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10⁻⁴ torr, were examined using Au ions. In-situ I–V measurements on Ni₃N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.     

Thermoluminescence response of CaS:Bi nanophosphor exposed to 200 MeV Ag ion beam

A study of the thermoluminescence (TL) parameters has been performed on swift heavy ion exposed Bi³⁺ doped CaS nanophosphors prepared by the chemical co-precipitation method. All the samples have been exposed to 200 MeV Ag⁺¹⁵ ions in a fluence range of 1 × 10¹²–1 × 10¹³ ions/cm². The prominent TL glow peak at 403 K (observed for the γ-irradiated sample) appeared at the same position in the 200 MeV Ag⁺¹⁵ ion beam irradiated samples, while the other peak at 466 K disappeared and the broad peak normally measured at 534 K split into two peaks at 535 K and 582 K for the Ag⁺¹⁵ ion beam irradiated samples. The effect of different Bi³⁺ concentration has been investigated and it was found that the maximum TL intensity was measured for the 0.08 mol% sample. The effect of different heating rates on the TL response has also been determined. The trapping parameters (i.e. activation energy, frequency factor, order of kinetic) of all the individual peaks of the glow curves have been analysed by using Chen’s formulae. The low fading and linear TL response in the range of 1 × 10¹²–1 × 10¹³ ions/cm² will be helpful to explore the potential use of this material for heavy ion dosimetry.     

Structural and electrical properties of swift heavy ion beam irradiated Fe/Si interface

The present work deals with the mixing of iron and silicon by swift heavy ions in high-energy range. The thin film was deposited on a n-Si (111) substrate at 10⁻⁶ torr and at room temperature. Irradiations were undertaken at room temperature using 120 MeV Au⁺⁹ ions at the Fe/Si interface to investigate ion beam mixing at various doses: 5 × 10¹² and 5 × 10¹³ ions/cm². Formation of different phases of iron silicide has been investigated by X-ray diffraction (XRD) technique, which shows enhancement of intermixing and silicide formation as a result of irradiation. I-V measurements for both pristine and irradiated samples have been carried out at room temperature, series resistance and barrier heights for both as deposited and irradiated samples were extracted. The barrier height was found to vary from 0·73–0·54 eV. The series resistance varied from 102·04–38·61 kΩ.     

Anisotropy of radiation-induced degradation in mechanical properties of fabric-reinforced polymer-matrix composites

Four kinds of fabric-reinforced polymer-matrix composites (filler: E-glass or carbon fabric; matrix: epoxy or polyimide resin) were irradiated with⁶⁰Co-rays or 2 MeV electrons at room temperature. Three-point bend tests were then carried out at 77 K and at room temperature in a 45° direction from warp to fill. Comparison of the degradation behaviour among these composites reveals that the glass-epoxy and glass-polyimide composites are quite similar to each other in the dose dependence of the ultimate interlaminar shear strength at each test temperature. This result suggests that the radiation damage at the fibre-matrix interface decreases the contribution of the chemical bond mode to the total bond strength at the interface, thus decreasing the composite shear strength with increasing dose. For the carbon-epoxy and carbon-polyimide composites, on the other hand, the shear strength at room temperature changes little even after irradiation up to 140 MGy, while the shear strength at 77 K decreases monotonically with increasing dose. These findings suggest that the fibre-matrix bond strength due to the friction force mode is quite insensitive to radiation, thus resulting in the dose-independent shear strength at room temperature. At 77 K, however, the friction force mode fails to function properly because of the brittleness of the matrix resin, and consequently the composite shear strength decreases with increasing dose owing to a resulting increase in the matrix brittleness.     

Radiation hardness of cryogenic silicon detectors

We shall review test results which show that silicon detectors can withstand at 130 K temperature a fluence of 2×10¹⁵ cm^–2 of 1 MeV neutrons, which is about 10 times higher than the fluence tolerated by the best detectors operated close to room temperature. The tests were carried out on simple pad devices and on microstrip detectors of different types. The devices were irradiated at room temperature using reactor neutrons, and in situ at low temperatures using high-energy protons and lead ions. No substantial difference was observed between samples irradiated at low temperature and those irradiated at room temperature, after beneficial annealing. The design of low-mass modules for low-temperature trackers is discussed briefly, together with the cooling circuits for small and large systems.     

Research into mechanical properties of reaction-bonded SiC composites at cryogenic temperatures

The mechanical properties of reaction-bonded silicon carbide (RBSC) composites at cryogenic temperatures have been reported for the first time. The results show that the flexural strength and fracture toughness increase from 277.93 ± 23.21 MPa to 396.74 ± 52.74 MPa and from 3.69 ± 0.45 MPa·m^1/2 to 4.98 ± 0.53 MPa·m^1/2 as the temperature decreases from 293 K to 77 K, respectively. The XRD analysis of the phase composition reveals that there is no phase transformation in the composites at cryogenic temperatures, indicating cryogenic mechanical properties are independent of phase composition. The enhancement of mechanical properties at 77 K over room temperature could be explained by the transition of fracture mode from predominant transgranular fracture to intergranular fracture and stronger resistance to crack propagation resulting from higher residual stress at 77 K. The above results demonstrate that such composites do not undergo similar deteriorations in the fracture toughness as other materials (some kinds of metals and polymers), so it is believed that such composites could be a potential material applied in cryogenic field.     

Electron-beam irradiation effects on mechanical properties of PEEK/CF composite

Carbon fibre-reinforced composite (PEEK/CF) using polyarylether-ether-ketone (PEEK) as a matrix material was prepared and electron-beam irradiation effects on the mechanical properties at low and high temperatures were studied. The flexural strength and modulus of the unirradiated PEEK/CF were almost the same as those of carbon fibre-reinforced composites with epoxide resin. The mechanical properties at room temperature were little affected by irradiation up to 180 MGy, but in the test at 77 K the strength of the specimens irradiated over 100 MGy were slightly decreased. The mechanical properties of the unirradiated specimen decreased with increasing testing temperature, but the high-temperature properties were improved by irradiation, i.e. the strength measured at 413 K for the specimen irradiated with 120 MGy almost reached the value for the unirradiated specimen measured at room temperature. It was apparent from the viscoelastic measurement that the improvement of mechanical properties at high temperature resulted from the high-temperature shift of the glass transition of the matrix PEEK caused by radiation-induced cross-linking.     

Mechanism of adhesion improvement in ion-beam mixed Cu/SiO2

A thin copper layer (35 nm) deposited on SiO₂ has been subjected to ion-beam mixing with 80 keV Ar⁺ at room temperature, 550 and 650 K. Interfacial properties of irradiated samples were investigated using Rutherford backscattering spectroscopy, grazing-angle X-ray diffraction, X-ray photo-electron spectroscopy and scratch testing. The adhesion of the copper film was improved by a factor of three at a dose of 1.5 × 10¹⁶ Ar⁺ cm^–2 by the ion-beam mixing at room temperature, while the high-temperature ion-beam mixing enhanced the adhesion by a factor of five. Ballistic mixing plays a role in the improvement of adhesion for the room-temperature ion mixing, and the creation of Cu₂O phase induced by ion-beam mixing contributes to the enhancement of adhesion at high temperature.     

Electrical and morphological properties of poly(3-hexyl thiophene) irradiated with 100 MeV silver ions

Poly(3-hexyl thiophene) has been prepared by a chemical oxidation process. The pristine polymer was irradiated with various fluences of (silver (Ag⁸⁺)) swift heavy ions viz. 10¹⁰, 10¹¹, and 10¹² ions/cm². All the samples, irradiated and without irradiation, have been characterized by various techniques such as surface electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), FT-IR and UV spectroscopy. The dc conductivity of all the samples has been investigated in 77-300 K. The room temperature conductivity of pristine samples is 2.39 × 10⁻⁸ which increases to 1.65 × 10⁻⁶ Ohm⁻¹ cm⁻¹ at the fluence of 10¹¹ ions/cm². The observed conduction mechanism for all the samples could be explained in terms of Mott's variable range hopping model.     

Annealing behavior of single mode planar waveguide in YVO4 produced by He ion implantation

We report, for the first time to our knowledge, the formation of single mode planar waveguide in z-cut YVO₄ by 400 keV, 500 keV He ion implantation in fluence of 3 × 10¹⁶ ions/cm² at room temperature or at liquid nitrogen temperature (77 K). We investigated annealing behavior of the guiding mode and near-field image in the waveguide by prism-coupling method and end-face coupling method respectively. We found that the effective refractive index of the TE₀ mode was different before and after annealing for the samples implanted at room temperature, while, annealing had nearly no influence on the effective refractive index of the TE₀ mode of the samples implanted at liquid nitrogen temperature (77 K). After annealing at 600 K for 1 h, no guiding mode was observed in the sample implanted by 400 keV He ion in fluence of 3 × 10¹⁶ ions/cm² at room temperature. The Rutherford backscattering/channeling technique was used to investigate the damage reduction after annealing treatments. The minimum yield of the implanted, annealed sample was 5.43%. We reconstructed the refractive index profiles in the waveguide under different condition by applying intensity calculation method.     

Ab initio molecular dynamics simulation for structural transition of Zr during rapid quenching processes

We report the results of ab initio molecular dynamics simulation for the structural transition of Zr during two distinct quenching processes (Q1: 4.3 × 10¹³ K/s, Q2: 2.0 × 10¹⁴ K/s). In both the quenching processes, structural transition details have been analyzed by pair correlation functions g(r) and bond pair analysis technique. It is shown that the liquid Zr transforms to a metastable bcc phase (β-Zr) at the temperature about 1000 K as quenched at the rate of 4.3 × 10¹³ K/s. When quenched at 2.0 × 10¹⁴ K/s, however, the crystallization is suppressed and the liquid Zr is frozen into a glass state. The bond pair analysis reveals that the dominant bond pairs in the liquid and glass states are the 1551, 1541, 1431, 1661 and 1441, indicating that the short range order in both states mostly consists of icosahedral, tetrahedral and bcc clusters.     

Comparative studies of defect production in heavily doped silicon under fast electron irradiation at different temperatures

Production processes of electrically active defects in degenerate silicon subjected to 2.5 MeV electron irradiation at T = 4.2 K and T = 300 K have been studied. The production rates of primary and secondary defects in irradiated samples are analyzed on the basis of the known properties of radiation-produced defects in Si. It has been demonstrated that a striking difference in the production rates of electrically active defects in n- and p-Si under irradiation at cryogenic temperatures may be related to the different fate of Frenkel pairs in both materials. The production rate of primary defects in degenerate Si was found to be between 1.5 cm⁻¹ and 2 cm⁻¹.     

Mechanical and thermal expansion properties of glass fibers reinforced PEEK composites at cryogenic temperatures

Polyetheretherketone (PEEK) has been widely used as matrix material for high performance composites. In this work, 30% chopped glass fibers reinforced PEEK composites were prepared by injection molding, and then the tensile, flexural and impact properties were tested at different temperatures. The modulus, strength and specific elongation of glass fibers reinforced PEEK at room temperature, 77 K and 20 K have been compared. And the fracture morphologies of different samples were investigated by scanning electron microscopy (SEM). The results showed a dependence of mechanical properties of glass fibers reinforced PEEK composites on temperature. The coefficient of thermal expansion of unfilled PEEK and glass fibers reinforced PEEK were also investigated from 77 K to room temperature. The results indicated that the thermal expansion coefficient (CTE) of PEEK matrix was nearly a constant in this temperature region, and it can be significantly decreased by adding glass fibers.     

Electrical properties of thin PbTe films on Si substrates

An attempt was made to reduce the carrier concentration in thin PbTe films on Si substrates by optimizing deposition conditions. A modified hot-wall method was used for reproducible growth ofp-type films with 5 × 10¹⁵ < p(77 K) < 5 × 10¹⁷ cm^-3 andn-type films with 3 × 10¹⁵ < n(77 K) < 5 × 10¹⁶ cm^-3. The IR irradiation was found to have a significant effect on the temperature variation of film resistance. The activation energy of the IR-sensitivity centers was determined to be 0.11 ± 0.005 eV at room temperature and 0.18 ± 0.005 eV between 150 and 180 K.     

Photoinduced polarization investigations in 75 MeV oxygen ion irradiated kapton-H polyimide

The photoinduced polarization in 75 MeV oxygen ion irradiated (fluence: 1.8 × 10¹¹, 1.8 × 10¹² and 1.8 × 10¹³ ions/cm²) kapton-H polyimide has been investigated by analyzing charge decay characteristics for different polarizing parameters viz. electric fields (40 to 600 kV/cm), temperature (40 to 250 °C) and illumination intensity (1200 to 2800 1x). The fields induced as well as thermal ionization of excitons under illumination are the main causes which provide photopolarization. The charge decay spectra reveal the presence of both shallow and deep trapping sites in pristine and irradiated kapton-H polyimide. The variation in the photopolarization with fluence shows the occurrence of secondary radiation induced crystallinity (SRIC). The SRIC is also responsible for the increase in initial current (I_0P) with intensity of illumination in low fluence irradiated samples. A decrease in I_0P with intensity of illumination in high fluence irradiated samples has been associated to the conversion of trapping sites into recombination centers.     

Mechanism of radiation-induced degradation in mechanical properties of polymer matrix composites

Four kinds of polymer matrix composites (filler, E-glass or carbon fibre cloth; matrix, epoxy or polyimide resin) and pure epoxy and polyimide resins were irradiated with ⁶⁰Co -rays or 2 MeV electrons at room temperature. Mechanical tests were then carried out at 77 K and at room temperature. Following irradiation, the Young's (tensile) modulus of these composites and pure resins remains practically unchanged even at 170 MGy for both test temperatures. The ultimate strength, however, decreases appreciably with increasing dose. The dose dependence of the composite strength depends not only on the combination of fibre and matrix in the composite but also on the test temperature. A relationship is found between the composite ultimate strain and the matrix ultimate strain, thus indicating that the dose dependence of the composite strength is virtually determined by a change in the matrix ultimate strain due to irradiation. Based on this finding, we propose a mechanism of radiation-induced degradation of a polymer matrix composite in order to explain the dose dependence of the composite strength measured at 77 K and at room temperature.     

Characterisation of vacancy-like defects in III–V compound semiconductors using positron annihilation technique

Single crystals of GaP and InSb were irradiated by 3 MeV electrons at 20 K to a total dose of 4 × 10¹⁸ e ⁻/cm². Isochronal annealing in the temperature region 77–650 K followed the irradiation. In GaP, the positron lifetime measurement indicated the presence of irradiation-induced vacancies in the Ga-sublattice. The vacancies disappeared at two stages observed in temperature ranges 200–300 and 450–550 K. In InSb the positron lifetime was found to increase by 8 ps compared to that in as-grown crystals (i.e. 282±2 ps) after irradiation. The increase indicated the presence of irradiation-induced defects; the crystal was found to recover until 350 K with a sharp annealing stage at 250–350 K.     

High temperature fracture of boron carbide: experiments and simple theoretical models

The mechanical properties of theoretically dense boron carbide with a grain size of about 10μm have been investigated as a function of temperature. It was found that the fracture toughness remained constant at ∼3.7 MPa m^1/2 up to 1500 K and there was little or no decrease in strength from its room temperature value of ∼350 MPa. Both the order of magnitude and the temperature dependence of the fracture energy, calculated from the fracture toughness and elastic data, can be explained in terms of simple theoretical models.