Low-temperature Radiation Damage Research Articles

Low-temperature radiation damage studies in single-walled carbon nanotube bundles by hopping conductance

The paper shows the results of studying radiation defects in single-walled carbon nanotube bundles at low temperatures. The data were obtained in a unique experiment that inseparably combines 1 MeV electron irradiation at a temperature of ∼10 K and electrical conductivity measurements over a wide temperature range of 5–300 K. The experiment allowed us to reveal and separate the influence of stable and unstable radiation defects on the electrical properties of SWCNTs. It is shown that the 2D Mott variable range hopping conduction regime exhibits resistance to electron irradiation. The hopping conductivity is the dominant charge transfer mechanism in the temperature range of 5–50 K in both the pristine and irradiated SWCNT samples. It was found that the parameters of hopping transport demonstrate high sensitivity to the introduction and annealing of radiation defects. The low-temperature electron irradiation revealed the possibility of the emergence of an additional conduction channel in the irradiated SWCNTs. This channel demonstrates thermally activated behavior with a low activation energy of ∼0.5 meV at temperatures of 5–50 K. The obtained data indicate that unstable radiation defects create conditions for the possibility of impurity band conduction in SWCNT bundles.

Self-Interstitial in Germanium

Low-temperature radiation damage in n- and p-type Ge is strikingly different, reflecting the charge-dependent properties of vacancies and self-interstitials. We find, using density functional theory, that in Ge the interstitial is bistable, preferring a split configuration when neutral and an open cage configuration when positively charged. The split configuration is inert while the cage configuration acts as a double donor. We evaluate the migration energies of the defects and show that the theory is able to explain the principal results of low-temperature electron-irradiation experiments.

Structural factor and effects of low-temperature radiation damage in structural materials

The effect of the structural and phase state of steels and alloys based on iron and nickel on the recombination of vacancies and interstitial atoms in the process of neutron irradiation at 300–350°C is estimated.

The annealing of interstitial-related optical centres in type Ib diamond

Defect centres produced by low-temperature radiation damage in type Ib diamond have been studied using optical spectroscopy and thermal annealing. The phenomena are interpreted in terms of the trapping and detrapping of the self-interstitial to form a family of nitrogen–interstitial complexes.

Survivability of high-T/sub c/ microwave devices in space radiation environments

In order to investigate the suitability of high-T/sub c/ devices for satellite applications, a High Temperature Superconductivity Space Experiment (HTSSE I) is due for launch in 1993. The purpose of the present study is to examine the effect of nonionizing radiation on the performance of high-T/sub c/ devices intended for deployment on HTSSE I. A low-temperature radiation damage study of first-generation passive microwave devices fabricated from high-temperature cuprate superconductors has been performed in order to examine the effects of nonionizing radiation damage. Changes in performance due to radiation-induced shifts in the transition temperature and to film erosion are discussed. The results show that if these relatively simple passive devices are reasonably well shielded, they should survive in typical five-year space applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low temperature radiation damage in silicon: II. Production rates and annealing studies on p-type material

The results of low-temperature electron irradiation (0.80–1.50 MeV) of B-doped p-type silicon are reported. For each sample measurements of capacitance and loss factor were carried out at different doses of irradiation and at different temperatures. The production rates of defects in the samples are estimated using two methods, based independently on hopping conductivity and Schottky barrier capacitance. Results of annealing experiments done on the samples are discussed in the light of known defect and impurity behaviour. A hole trap observed at ≈( E v+0.23±0.02) eV is ascribed to the divacancy (+/0) donor state.

Amorphous Fe-B alloys produced by ion implantation. II. Low-temperature radiation damage

For pt.I see ibid., vol.15, p.1229 (1985). The electrical properties of amorphous Fe1-xBx alloys produced by ion implantation at room temperature have been studied in a companion paper (I). This paper reports the results of 6K irradiation (with 100 keV 1H, 540 keV 86Kr and 209Bi ions) and subsequent annealing of the Fe0.76B0.24 alloy. The electrical resistivity measurements are analysed in terms of irradiation-induced 'point defects' and are compared with those reported previously for Fe-B alloys quenched from the melt. Both the spontaneous recombination volume ( nu 0=29+or-4 atomic volumes) and the intrinsic resistivity of induced defects ( rho d=133+or-20 mu Omega cm) are found to be lower than those measured in Fe-B alloys quenched from the melt. The displacement cascade effects induced by heavy-ion irradiation are also studied: the irradiation efficiency is found to be lower for 86Kr irradiation than for 1H irradiation, as in crystalline metals. However, in contrast to the case of crystalline metals, the increase in saturation resistivity is the same whether or not displacement cascades occur during irradiation.

Low-temperature radiation damage studies in phosphorus-doped silicon

Annealing studies of capacitance and dielectric loss on irradiated phosphorus-doped silicon specimens are reported. Evidence is presented of the migration of interstitials at 130K, and also of the formation of carbon-interstitial-silicon complexes under irradiation is about 10K.

Low-temperature radiation damage studies in boron-doped silicon

Capacitance bridge measurements at low temperature on irradiated specimens of boron-doped silicon are reported. An electronic level at Ev+0.16 eV is seen and attributed to the boron interstitial.

Low-temperature radiation damage studies in silicon by hopping conductance

Radiation damage studies at low temperatures are described, based on measurements of capacitance and dielectric loss on thin specimens with gold electrodes. Results on electron irradiated n- and p-type silicon are discussed in the light of known defect and impurity behaviour, and damage rates are evaluated for specimens of different impurity content.

Theoretical study of the distortion around F centres and the interaction between F centres in NaCl

The distortions around an F centre are studied using an elastic strength for the defect as given by the lattice statics theory of Kanzaki. The defect is simulated by imposing different types of forces on the neighbours, and the resultant displacements calculated. The displacement of the surrounding ions is found to be inward when the defect is considered purely as an elastic singularity, but the inclusion of Coulomb forces results in a small outward displacement of the neighbours. Similarly, the strain field contribution to the binding energy between two F centres in the ground state is comparable to experiment when only elastic forces are considered but is much smaller when Coulomb forces are included. These studies suggest a probable explanation for the non-random distribution of F centres created in low temperature radiation damage of alkali halide crystals.

Low-temperature radiation damage in Mn-doped RbMgF3

Defects introduced by high energy electron irradiation at low temperatures have been studied in manganese doped RbMgF3. At these low temperatures negative-ion vacancies are not mobile and only the various radiation induced interstitials and X2- (VK) centres are mobile. It is found that at 15K where X2- centres are not mobile the F band (due to negative vacancies which have trapped electrons) increases almost linearly with radiation dose and optical bands due to X2- centres and impurities yield the only obvious absorption between 200 nm and 1000 nm. No sign of radiation defect perturbed Mn2+ optical transitions can be observed for the radiation doses investigated. However, when the irradiation is done at 77K both F centres and radiation defect-Mn2+ complexes are formed. Since vacancies are not mobile at 77K it is suspected that interstitial defects perturb the Mn2+ ions.

A calorimetric investigation of the low-temperature radiation damage suffered by titanium diboride

1. Experiments have revealed the existence of a low-temperature range of heat evolution for titanium diboride irradiated with neutron fluxes of integral doses 1.20 · 1018 thermal neutrons/cm2 + 1.25 · 1018 fast neutrons/cm2 and 1.46 · 1017 thermal neutrons/cm2 + 1.52 · 1017 fast neutrons/cm2 at temperatures of 115 and 130°K. 2. It is shown that the total amount of heat evolved is much smaller in a material irradiated with a neutron flux without its thermal spectrum than in a material irradiated with the full spectrum. 3. The hypothesis is advanced mat the heat evolution effect observed is linked with the annealing-out of interstitial atoms released from traps such as impurities.

Resistometric study of defects in rhenium following 2.8 MeV electron irradiation at 4.5 K

Abstract The low temperature radiation damage in rhenium caused by 2.8 MeV electron irradiation at 4.5 K has been studied by means of electrical resistivity measurements. The samples were Marz Grade foils supplied by Materials Research Corporation (U.S.A.) with a thickness of 0.03 mm. After a 30 minutes pulse at 2100 K in a vacuum of 2·10−10 Torr, the electrical resistivity ratio amounted to about 800.

Application of high voltage electron microscopy to low‐temperature radiation damage studies in metals

SUMMARYThe paper briefly reviews the advantages of high voltage electron microscopy applied to low temperature radiation damage studies. Such studies may be performed inside the microscope provided a high resolution specimen cooling stage is available. The main features of a new type of cooling stage used in the experiments relevant to this paper are outlined. The applicability of the stage for post‐irradiation annealing experiments is emphasized.During electron irradiation to high doses at 8°K the formation of defect clusters was observed in nickel and copper. This is accompanied by pronounced changes in the diffraction pattern. Post‐irradiation annealing of samples irradiated at 8°K produces defect clusters which can be identified as dislocation loops.