Electrically active defect annealing in neutron and in ion-damaged Si

Hall effect and electrical conductivity measurements of defect annealing in 1 ohm-cm n-type and 2 ohm-cm p-type silicon were made following neutron irradiation at ～50°C. Measurements were also made following 400-keV B¹¹ ion implantation into a 100 ohm-cm n-type Si substrate. As the neutron fluence is increased the electrical effects of the damage eventually outweigh those of the chemical dopants, and further changes in the electrical properties become small. Conversely, significant electrical recovery upon annealing begins only when the electrical effects of the remaining damage become comparable to those of the chemical dopants. This condition will occur at higher anneal temperatures for higher fluence irradiations. The neutron fluence dependence of the damage and the annealing is interpreted in terms of the neutron energy per cm³. E, spent in atomic processes divided by the number/cm³, N, of electrically active dopants. When E/N ≤ 0.5 keV the electrical measurements show that the predominant defect annealing occurs below 400°C. However, when E/N > 0.5 keV electrical measurements emphasize the annealing at temperatures > 400°C. After 500°C annealing, energy levels in neutron damaged Si are observed at E_v +0.1 and E_v +0.15 eV in p-type and at E_c -0.33 eV in n-type Si. Application of the E/N criteria to room temperature implant-doped Si predicts that the electrical effects will be dominated by lattice damage even if all the implanted ions are substitutional.     

The atkermal stress component in neutron irradiated mild steel

Abstract

The temperature dependence of the tensile lower yield stress of an annealed aluminium grain size controlled mild steel has been investigated in the range 23–250 °C and at a strain rate of 1.67 × 10^?4 sec^?l before and after neutron irradiation to 2.3 × 10¹⁸ n/cm² (fission). The yield stress of the irradiated steel decreases with increasing temperature due to thermal activation of the radiation damage and is predicted to reach asymptotically that of the unirradiated steel at ～285 °C; the maximum test temperature was below that at which thermal annealing of the damage occurs. This implies that the athermal stress component due to irradiation is zero and hence there is negligible long range interaction between dislocations and radiation-induced defects.     

Radiation hardening in niobium-dependence of the yield stress on neutron dose

Abstract

Niobium samples were neutron-irradiated at reactor ambient temperatures (approximately 50 °C for polycrystals and 90°C for single crystals) to doses from 4 × 10¹⁵ to 8 × 10¹⁸ neutrons/cm² (E> 1 MeV). The density and size distribution of radiation-produced defect clusters, observed by transmission electron microscopy, were measured in polycrystalline niobium over a range of doses from 2 × 10¹⁷ to 4.4 × 10^l8 neutrons/cm². The TEM results were correlated with yield stress measurements as a function of dose. The radiation hardening was analyzed on the basis of a planar dispersed barrier model. It was found that the observed increases in yield stress at low doses were consistent with the measured density and size distribution of the defect clusters, with a cluster strength of (0.5–0.8) Gb² (G, shear modulus; b, Burgers vector). This corresponds to strong barrier hardening. At doses above about 10¹⁸ neutrons/cm², the hardening rate decreased sharply; this apparent saturation is discussed in terms of the coarsening of defect clusters, dislocation channeling, and the effect of interstitial impurities.     

Kinetics of the radiation-induced hardening of EP-823 steel after Ni++ ion irradiation, annealing, and re-irradiation

The ferritic-martensitic steel 12Cr-MoWSiVNbB (EP-823) was irradiated with Ni⁺⁺ ions with the energy 7 MeV, and fluences of 2.7 × 10²⁰ and 3.9 × 10²⁰ ion/m² at 380 C. The irradiated samples were annealed at 600°C and then re-irradiated under the same conditions. After re-irradiation, the microhardness increased to the maximum value and achieved about 70% of the value corresponding to that after primary irradiation. After primary and secondary irradiation with increasing doses, the hardening reaches its saturation level at approximately similar damaging doses and behaves similar to that obtained in the case of the neutron irradiation of ferritic chromium steels.     

<Emphasis Type="Italic">I-V,C-V</Emphasis> and deep level transient spectroscopy study of 24 MeV proton-irradiated bipolar junction transistor

This paper describes the effect of 24 MeV proton irradiation on the electrical characteristics of a pnp bipolar junction transistor 2N 2905A. I-V, C-V and DLTS measurements are carried out to characterize the transistor before and after irradiation. The properties of deep level defects observed in the bulk of the transistor are investigated by analysing the DLTS data. Two minority carrier levels, E _C − 0.27 eV and E _C − 0.58 eV and one majority carrier level, E _V +0.18 eV are observed in the base collector junction of the transistor. The irradiated transistor is subjected to isochronal annealing. The influence of isochronal annealing on I-V, C-V and DLTS characteristics are monitored. Most of the deep level defects seem to anneal out above 400°C. It appears that the deep level defects generated in the bulk of the transistor lead to transistor gain degradation. A comparison of proton- and electron-induced gain degradation is made to assess the vulnerability of pnp transistor as against npn transistors.     

Positron annihilation study of voids in a neutron irradiated aluminum single crystal

We have measured the lifetimes of positrons in an aluminum single crystal which was irradiated to a fast neutron fluence of 1.5·10²¹ n/cm² (>0.18 MeV) at 50°C. These irradiation conditions produced 4.2·10¹⁴ voids/cm³ with a mean diameter of 330 ?, as determined by both small-angle x-ray scattering and transmission electron microscopy. The positron lifetime spectra were resolved into three lifetime components of 100, 300, and 500 ps. The short lifetime component is a result of fast trapping of positrons by the voids; the long lifetime components result from annihilations within the voids. The intensity of the long lifetime components increases with temperature in the range 80 to 300 K and supports the model of a positron state at the void surface. The positron diffusion coefficient appears to have aT ^1/2-dependence. A magnetic quenching experiment shows no indication of positronium formation. Finally, an isochronal heat treating sequence shows that the voids anneal out between 200 and 300°C, and that the lifetime spectrum after annealing is described by a single component of 170 ps, the observed lifetime in unirradiated aluminum. Research sponsored in part by the U.S.Atomic Energy Commission under contract with the Union Carbide Corporation.     

Gettering of implanted Au in MeV?C implanted Si

The gettering behavior of 1 MeV?C implantation induced defects for Au (1.5 MeV, 2.2×10¹⁵ cm^-2), implanted into FZ Si(111), has been investigated using Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy. The gettering efficiency of the C implanted layer has been studied as a function of C dose, annealing temperature and time. For a C dose of 2×10¹⁶ cm^-2, a 2 h anneal at 950 °C has been found to result in a gettering efficiency going beyond ?90%. Thermal stability of the gettered Au in the C implanted layer has subsequently been investigated over a temperature range of 950–1150 °C using isochronal annealing. The gettered amount has been found to be stable up to 1050 °C beyond which there is a release. We have observed nanovoids in the C implanted layer surrounded by ?-SiC precipitates along with patches of a-SiC. Up to about 1050 °C, these nanovoids act as efficient gettering centers beyond which they seem to release the trapped Au. Four distinct regimes in annealing temperature with different mechanisms for Au gettering have been observed.     

Defect recovery behavior of neutron irradiated molybdenum and tungsten of two purity levels

Abstract

The recovery behavior of radiation-induced defects during post-irradiation annealing was studied on molybdenum and tungsten specimens of two different purity levels. An electrical resistivity measurement technique at liquid nitrogen boiling temperature (～77°K) was used. Irradiation of both materials was conducted in Oak Ridge Research reactor at reactor ambient temperature (～70°C). The accumulative neutron fluence received was 7.3E+19 neutrons cm^?2 (E_n>l MeV) and 5.1E+20 neutrons cm^?2 (thermal). It was found that the number of recovery stages appeared to be independent of either the material or the impurity content. The stages are then believed to be due to the recovery of intrinsic defects and the recovery mechanisms are most likely the same for molybdenum and tungsten on the homologous temperature scale.     

Plasticization of neutron-irradiated LiF crystals upon thermal stimulation of a single-system dislocation glide

It has been shown that post-radiation annealing of LiF crystals irradiated by high neutron fluences (10¹⁵–10¹⁸ neutrons/cm²) at comparative low temperatures (300–400°C) creates optimal conditions for single-system dislocation glide, which favors a complete recovery of the plasticity with conservation of a significant fraction of radiation hardening.     

The 220°K defect in electron irradiated p-Type Germanium

Lattice defects introduced in p-type nondegenerate germanium by 1.5 MeV electron irradiation at liquid nitrogen temperature was investigated by means of electrical resistivity and Hall coefficient measurements. The annealing behavior of two kinds of defects, which anneal at about 220 °K, was investigated in detail. Each of them has an electron trap. Making use of trap-filling and emptying processes, the 220 °K defects are separated from other defects.     

Positron annihilation study of voids in a neutron irradiated aluminum single crystal

We have measured the lifetimes of positrons in an aluminum single crystal which was irradiated to a fast neutron fluence of 1.5·10²¹ n/cm² (>0.18 MeV) at 50°C. These irradiation conditions produced 4.2·10¹⁴ voids/cm³ with a mean diameter of 330 Å, as determined by both small-angle x-ray scattering and transmission electron microscopy. The positron lifetime spectra were resolved into three lifetime components of 100, 300, and 500 ps. The short lifetime component is a result of fast trapping of positrons by the voids; the long lifetime components result from annihilations within the voids. The intensity of the long lifetime components increases with temperature in the range 80 to 300 K and supports the model of a positron state at the void surface. The positron diffusion coefficient appears to have aT ^1/2-dependence. A magnetic quenching experiment shows no indication of positronium formation. Finally, an isochronal heat treating sequence shows that the voids anneal out between 200 and 300°C, and that the lifetime spectrum after annealing is described by a single component of 170 ps, the observed lifetime in unirradiated aluminum.     

Field ion microscopy of cascades of atomic displacements in metals and alloys after various types of irradiation

Experimental results on atomic-spatial investigation of radiative defect formation in surface layers of materials, initiated by neutron bombardment (of Pt, E > 0.1 MeV) and ion implantation (in Cu₃Au: E = 40 keV, F = 10¹⁶ ion/m², j = 10^?3 A/cm²), are considered. Quantitative estimates are obtained for the size, shape, and volume fraction of cascades of atomic displacements formed under various types of irradiation in the surface layers of the materials. It is shown that the average size of radiation clusters after irradiation of platinum to a fast neutron fluence of 6.7 × 10²² m^?2 (E > 0.1 MeV) is about 3.8 nm. The experimentally established average size of a radiation cluster (disordered zone) in the alloy after ion bombardment is 4 × 4 × 1.5 nm.     

The bulk effect of point defects on young's modulus in electron irradiated copper

Abstract

Pairs of copper samples—one for electrical resistivity, the other for Young's modulus measurements - were irradiated simultaneously at 120°K with 3 MeV electrons up to an integrated dose of 2 × 10²⁰ el/cm². The effect of dislocation pinning and the bulk effect of point defects on Young's modulus E could clearly be separated. The following relation between the bulk effect ΔE/E and the resistivity increase Δρ[Ωcm] was found: ΔE/E = ?25 × 10⁴ × Δρ. Besides strong annealing in stages II and III (180–300°K) and some annealing between 300–500°K, stage V annealing (500–600°K) also was found. In stage III the resistivity annealed more than Young's modulus. whereas the converse occurred in stage V. These measurements are discussed in connection with the electron microsopical observation of point defect clusters after electron irradiation at 120°K and heating to room temperature.

Probenpaare, bestehend aus einer Widerstandsprobe und einer Probe zur Messung des Elastizitätsmoduls, wurden gleichzeitig bei 120°K mit 3 MeV-Elektronen bis zu einer Dosis von 2 × 10²⁰ el/cm² bestrahlt. Die direkte Reein-flussung des E-Moduls durch die im Gitter verteilten Punktdefekte (Volumeneffekt) konnte getrennt von der Beeinflussung durch Versetzungsverankerung gemessen werden. Es ergab sich dabei folgende Beziehung zwischen relativer Modulanderung ΔE/E und strahlungsinduziertem Widerstand Δρ[Ωcm]: ΔE/E = ?25 × 10⁴ × Δρ. Neben starker Erholung in den Stufen II und III (180–300 °K) und schwacher Erholung zwischen 300–500°K wurde auβerdem Stufe V (500–600°K) beobachtet. In Stufe III erholte sich der Widerstand starker als der E-Modul, wahrend in Stufe V das umgekehrte der Fall war. Die Messungen werden diskutiert in Zusammenhang mit der elektronenmikroskopischen Beobachtung von Punktdefektclustern nach Elektronenbestrahlung bei 120°K und anschlieβender Erwärmung auf Raumtemperatur.     

Small-angle neutron scattering investigation of the nanostructure of ferritic-martensitic 12%-chromium steels

The nanostructure (nanoparticle distribution) of ferritic-martensitic 12%-chromium steels EK-181 (Fe-12Cr-2W-V-Ta-B) and ChS-139 (Fe-12Cr-2W-V-Ta-B-Nb-Mo) subjected to different modes of mechanical and heat treatments and neutron irradiation has been investigated using small-angle neutron scattering. The samples have been studied in the initial state and after neutron irradiation (IVV-2M reactor) at a temperature of 80°C with fluences of 10¹⁸, 10¹⁹, and 5 × 10¹⁹ cm^?2 (E ≥ 0.1 MeV). The nanostructure of the steels is characterized by precipitations of nanoparticles with two characteristic sizes of 1.0–1.5 and 7–8 nm. The dependence of the nanostructure parameters on the composition of the steels and on the conditions of heat treatment and irradiation has been discussed.     

Dimpling—A new manifestation of ion-produced lattice damage

Abstract

Bombardment of thin (1–10 μ) single crystal targets with energetic ion beams has been found to result in macroscopic distortion of the thin film in the bombarded region. This effect, which has been euphemistically termed a ‘dimple’, is readily observed with the naked eye even at relatively low particle fluence. A useful first-order model has been developed which interprets the dimpling as an expansion of the bombarded region. For very thin samples, this expansion can be accommodated by bowing of the crystal out of the original crystal plane. For this simple model, the fractional expansion is proportional to (δ/d)² where δ is the maximum displacement from the original crystal plane and d is the diameter of the bombarded area. This measurement allows expansioh to be determined with a sensitivity comparable to or better than the most sensitive existing methods.

For silicon about 3 μ thick bombarded by 1.8 MeV He ions, the expansion increases essentially linearly with fluence at the lowest fluence (below about 10¹⁵ to 10¹⁴ cm^?2). In this region about 0.001 atomic volumes are added per incident ion. As the fluence is increased, the apparent expansion begins to increase more rapidly than linearly but approaches a saturation value at the highest fluence (about 10¹⁸ cm^?2). The effect of particle flux, incident energy, and bombardment temperature is discussed as well as some preliminary results on C ion produced dimples in Si and the behavior of Ge samples.

Thirty-minute isochronal annealing of silicon samples irradiated with He ions at room temperature shows reverse annealing for temperatures up to about 200–300°C. The dimple begins to anneal at 300°C and disappears after annealing to 600–700°C.

After irradiation, the dimpled region absorbs light more strongly in the visible and near IR region. This disappears with annealing before the dimple itself completely disappears and is felt to be largely due to scattering from defect clusters.     

Microstructural evolution and changes in mechanical property of irradiated Fe–0.6Cu alloy under uniaxial tension stress in reactor

Structural materials for commercial reactor are usually used under conditions of stress. However, the evaluation of the microstructural evolution and the changes in the mechanical property induced by the neutron irradiation in structural materials does not typically consider the effect of stress since it is difficult to carry out neutron irradiation testing under conditions of stress. In this study, a model alloy (Fe–0.6Cu) of reactor pressure vessels was irradiated by neutrons at 573?K with a dose of about 3.2?×?10²¹?neutrons/m² (E?>?0.1?MeV), corresponding to 5.2?×?10^?4?dpa (displacement per atom), with and without tension stress. The tension stress caused elastic deformation in the specimens. The size of microvoids in the irradiated sample with tension stress was larger than that in the sample without tension stress. However, the effects of stress on the formation of Cu precipitates and the changes in the mechanical property were not clear.     

Effects of neutron irradiation and subsequent annealing on the optical characteristics of sapphire

In this paper, the effect of neutron irradiation on sapphire single crystal with fast neutron of 1.0×10¹⁸ and 1.0×10¹⁹ neutrons/cm² has been investigated along with the effect of annealing temperature. It is found that the colorless transparent sapphire single crystals were turned yellow after 10 MeV fast neutron irradiation at room temperature. There are peaks at 206, 230, 258, 305, 358 and 452 nm after neutron irradiation. And the intensity of optical absorption bands decrease with wavelength and annealing temperature. A new absorption peak at 452 nm was found after isothermal annealing at 400 °C for 10 min, which was ascribed to F₂⁺ color center. Because of the recombination of interstitial ions and vacancies, color centers were almost removed after annealing at 1000 °C. The TL peaks were found to shift to higher temperature after neutron irradiation. And a higher fluence of the neutron irradiation would result in deep traps revealed as the new TL peaks at 176 and 227 °C.     

Low temperature photoconductivity in electron - irradiated p-type Si

The photoconductivity spectra of p-type silicon irradiated at ～15 °K with 1.2 MeV electrons were studied in the wavelength range from 1.2 to 5.5 μ at temperatures from 23 to 80 °K. The 3.9 μ photoconductivity band appears immediately after irradiation in all crystals already at low temperatures, giving further evidence that it is due to the divacancy formed directly during irradiation by electrons. Three main annealing stages of the photoconductivity have been observed; (a) below 160 °K, (b) 160–250 °K, and (c) 280–360 °K. A radiation-induced deep level at E_v , +(0.12±0.02 eV disappears upon annealing at stage b. The annealing behavior of the spectra depends strongly on the measuring temperature. The dependence of the spectra on chopper speed was also investigated.     

implantation of Bi into GaP. II. channeling studies

The channeling technique has been used to investigate the properties of Bi-implanted Gap. Measurements of the crystal disorder for 100 keV room temperature implants indicate a damage vs dose curve corresponding to ～13000 displacements/ion in the linear region and saturation at ～1.5 × 10¹³ Bi ions/cm². Annealing of the radiation damage has been observed and indicates two annealing steps at ～450°C for light damage and ～750°C for implants in the 1 × 10¹⁴/cm² range. Difficulties associated with the thermal decomposition of the implanted area have been overcome with the use of SiO _x coatings. The experimental details associated with the use of the SiO _x layer and with the use of a C¹² beam to obtain better depth and mass resolution in the backscattering spectrum are discussed. The lattice location measurements of the Bi impurity show ～50 per cent of the Bi atoms to be along the 〈110〉 string after a 900°C anneal for a 7.5 × 10¹³/cm² implant. In addition, the spectra show ～25 per cent of the Bi atoms have diffused to the surface. Correlations of these lattice location results with measurements of the photoluminescent intensity of the GaP (Bi) isoelectronic trap show an agreement in trend with anneal temperature but indicate a factor of ～10 more substitutional ions in the channeling measurement as compared to the photoluminescence results.     

Defect-annealing in neutron-damaged β-Ga2O3

A study is made of the effect of fast neutrons on the electrical conductivity and thermoelectric power and also the neutron-induced defects in β-Ga₂O₃. It is found that the conductivity decreases while the thermoelectric power increases after an irradiation of about 10¹⁷ nvt. This is explained by assuming that the defects introduced into the Ga₂O₃ lattices act as trapping centres for electrons. The defect anneal by thermally activated processes at temperatures up to about 1000 °K with an activation energy of about 2 eV. The defects are the most likely vacancies of the galium atoms.