Low-temperature Electron Irradiation Research Articles

The positive muon and the positron as probes of defects

A brief but hopefully general comparison has been made between muons and positrons as probes for the study of defects in metals. Since muon experiments are not only more demanding in manpower, cost and availability than positron experiments, they should be carefully designed in light of the knowledge that the muon is extremely sensitive to both intrinsic and extrinsic defects. Initial experiments should provide estimates of the muon diffusion coefficients as a function of sample temperature. High temperature hydrogen diffusion measurements do provide quidelines, although so far most of the observations of muon trapping have been made at low sample temperatures where hydrogen diffusion data do not exist. Given that the diffusion constant is known as a function of temperature, high-purity Fe26 after low temperature electron irradiation is therefore a good candidate to study with muons. Since the defect type and concentration can be controlled in electron irradiated samples, such investigations could confirm the stated values of the diffusion constants in Fe thereby providing a new method for evaluating diffusion coefficients below Stage III in different metals.

A magnetic relaxation occurring below 15 K in nickel-doped α-iron after low-temperature electron irradiation

A magnetic relaxation occurring below 15 K in nickel-doped α-iron after low-temperature electron irradiation

Disaccomodation measurements in Ni 3Fe after low temperature electron and neutron irradiation

Magnetic after-effect measurements have been made in the temperature range 10–300 K on ordered Ni 3Fe samples after low-temperature electron and neutron irradiation up to doses of 10 23 ē m −2 and 5 × 10 22 n m −2 respectively. The resulting relaxation spectra are discussed in terms of the relaxations of various intrinsic interstitial configurations.

Solid solution softening and hardening in the NbO system

It is demonstrated that, in niobium, the interstitial O atoms cause the softening and hardening effect similar to the self-interstitials generated by low temperature electron irradiation. The stress-strain curves of crystals with two tensile axis orientations are shown. Their deformation behavior was quite different. (FS)

Interstitial trapping by Ni, Ag, in impurities in electron irradiated copper

Abstract Samples of copper, pure and alloyed with very small amounts of Ni, Ag, In impurities have been submitted to isochronal recovery between 10K and 60K after low temperature electron irradiation. The capture radii of the self interstitial atoms by the impurities are found: R Ni ∽ 0, R Ag = 1, R In = 1.5 in units of rv, the average vacancy capture radius for migrating self-interstitials.

Effect of electron irradiation on the low temperature deformation of niobium

Preliminary results of low-temperature electron irradiation experiments with niobium are presented to examine the difference between the low-temperature deformation mechanisms of ion and niobium. (FS)

Trapping of defects at 111In impurities In e −-irradiated Al

The trapping and detrapping of interstitials and vacancies at 111In impurities in aluminium after low-temperature electron irradiation was observed. Using perturbed angular correlation of 111Cd the electric field gradients caused by nearby lattice defects were determined and used to monitor the formation and dissociation of impurity-defect complexes.

The configuration of atomic defects as determined from scattering studies

Atomic defects such as vacancies and interstitials in crystalline solids produce elastic diffuse scattering of X-rays or neutrons. The distribution in reciprocal space of the diffuse scattering intensity contains very direct information about the atomic structure of point defects, and it sensitively shows the formation of defect clusters. Three domains of the scattering are distinguished: (a) scattering in the forward direction (small-angle scattering); (b) scattering between the Bragg reflections; and (c) scattering close to the Bragg reflections (Huang scattering). The specific features of the information obtained from measurements in the different domains are discussed. Experimental results on the structure of interstitials in metals have been obtained after low temperature electron irradiation of the fcc metals Al and Cu, bcc Mo, and hcp Zn. In other metals (Au, Nb, Cd, Mg) the agglomeration of interstitials was observed during electron irradiation at 5 K.

Defect recovery in Zn after low temperature electron irradiation

Some new experimental results for Stage I and III recovery in electron-irradiated Zn are presented. Stage I (< 20 K) is found to consist of more sub-stages than previously resolved. There is little evidence for long range migration below 20 K although the possibility cannot be ruled out. Stage III (> 70 K) exhibits several features different from those reported previously. In particular, a sub-stage centered at 140 K, thought to be dose-dependent, exhibits no observable shift. A possible explanation is suggested. Several recovery models are investigated; the totality of available results cannot readily be explained fully by either of the two currently most widelyaccepted models. Es werden neue experimentelle Ergebnisse für Erholung der Stufen I und III in elektronenbestrahltem Zn mitgeteilt. Es wird gefunden, daß Stufe I (< 20 K) aus mehr Unterstufen besteht als früher angenommen. Nur geringe Hinweise für weitreichende Verlagerungen unterhalb 20 K werden gefunden, obwohl die Möglichkeit nicht ausgeschlossen werden kann. Stufe III (> 70 K) zeigt einige Merkmale, die von den früher berichteten unterschiedlich sind. Insbesondere zeigt ein bei 140 K gelegener Subzustand, von dem angenommen wird, daß er dosisabhängig ist, keine beobachtbare Verschiebung. Eine mögliche Erklärung wird vorgeschlagen. Einige Erholungsmodelle werden untersucht. Die Gesamtheit der vorhandenen Ergebnisse läßt sich von keinem der beiden zur Zeit am verbreitetsten akzeptierten Modelle vollständig erklären.

The magnetic after-effect spectrum of α-iron after low-temperature electron irradiation

The magnetic after-effect spectrum of α-iron after low-temperature electron irradiation

The effect of low-temperature electron irradiation on lutetium and its hydrogen solid solutions

Lutetium metal and several Lu(H) solid solutions are irradiated with electrons in the energy range 0·4 to 1·7 MeV at liquid-helium temperatures. The threshold energy for the displacement of a Lu atom is determined to Td = (17 ± 1) eV, corresponding to an incident electron energy of Ed = (780 ± 30) keV. Displacement cross sections are fitted to the experimental data, with ϱ ≈︁ (60 to 90) μΩ cm/at% F.P. as Frenkel-pair resistivity. The defect production rates at 0·4 MeV of Lu(H) depend on the H-concentration in the α-phase. From their fluence dependence, the concentration dependent defect formation cross sections, σH = (2.35 to 4.18) × 106 barns, are deduced and the defect resistivities, ΔϱH = (36 to 41) μΩ cm/atom H. A comparison with calculated electron-hydrogen scattering cross sections permits to determine a threshold energy for the H-defect formation, TH = (0.06 to 0·09) eV, which, consequently, also varies with the H-concentration. A possible model assuming a paired hydrogen configuration as the stable low-resistivity form at low temperatures is suggested. Le lutetium métal et plusiers solutions solides Lu(H) ont été irradiés par des électrons d'énergie comprise entre 0,4 et 1,7 MeV à la température de l'hélium liquide. L'énergie seuil de déplacement d'un atome Lu est déterminée, cette valeur Td = (17 ± 1) eV correspondant à l'énergie d'électrons incidents Ed = (780 ± 30) keV. Les sections efficaces de déplacement calculées ont été comparées aux données expérimentales en prenant ϱF ≈︁ (60 à 90) × 10−4 Ω cm/F.P. pour la résistivité d'une paire de Frenkel. A 0,4 MeV, les taux de production de défauts dans Lu(H) varient avec la concentration de H dans la phase α. De leur diminution en fonction du flux électronique on déduit des sections efficaces de formation de défauts, σH = (2,35 à 4,18) × 106 barns, et des résistivités de défauts, δϱH = (36 à 41) μΩ cm/atome H, variant avec la concentration. La comparaison avec les sections efficaces d'intéraction électron-hydrogène calculées permet de déterminer l'énergie seuil pour la création de défaut H, TH = (0,06 à 0,09) eV, qui varie done aussi avec la concentration de H. On envisage un modèle où la configuration des atomes H en paires est supposée la forme stable et peu résistante à basse température.

Anelastic relaxation due to clustered self-interstitial atoms in Al

Anelastic processes in Al single crystals present after low-temperature electron irradiation have been investigated using both internal-friction and elastic-aftereffect techniques. Several stress-induced relaxation processes have been observed, one due to the ${I}_{B}$ close-pair defect, and six others attributed to small interstitial clusters formed during long-range interstitial migration in recovery stage I. Details are presented concerning the creation, stability, symmetry, and relaxation kinetics of the various defects responsible for the anelastic processes. One of the processes exhibits all the characteristics expected for a configuration of the di-interstitial proposed by Johnson. A model is discussed which suggests how a small interstitial cluster may undergo reorientation without simultaneous migration of the defect center of mass.

The resistivity recovery of niobium following low temperature electron irradiation

Abstract High-purity niobium (residual resistance ratio 2000–8000) and oxygen and nitrogen-doped Mb samples were irradiated with electrons of 3.0 MeV at 4.5 K. The resistivity recovery and the kinetics of the main recovery stages were investigated. As in f.c.c. metals the recovery can be divided into recovery regions, stages I, II and III. An intrinsic stage III is observed at 250 K to 270 K. Unusual features are the small recovery in the proposed stages of correlated and uncorrelated recovery and a pronounced continuous back-ground recovery.

Influence of Fermi surface and defect structure on the lowfield galvanomagnetic properties of Al

Low-field Hall coefficient R and transverse magnetoresistance Delta rho / rho 0 were measured in Al single crystals. A definite defect structure (statistically distributed Frenkel pairs) was created in the specimens by low-temperature electron irradiation. This defect structure could then be changed in a controlled way by annealing at different temperatures. Eliminating the influence of defect concentration with the aid of the Kohler representation thus allowed the dependence of R and Delta rho / rho 0 on the defect structure to be investigated. Various effects of the Fermi surface geometry and of the scattering mechanism on R and Delta rho / rho 0 are discussed on the basis of simple equations for the low-field Hall coefficient and magnetoresistance.

Photoluminescence from Si irradiated with 1.5-MeV electrons at 100 °K

The effects which low-temperature electron irradiation have on the photoluminescence from Si provide new information regarding irradiation-induced defects which participate in radiative recombination. Previous identifications of the 0.8–1.0-eV band with the divacancy and the 0.6–0.8-eV band with the Si-G15 (or K) center are apparently in error. The 0.8–1.0-eV band appears only after anneals above ∼300 °K, whereas the 0.6–0.8-eV band can be detected after 100 °K anneals. The lower-energy band may be due to radiative recombination at an oxygen-modified divacancy or a carbon-oxygen-vacancy complex. The 0.8–1.0-eV band may involve a carbon-related defect. A band between 0.7 and 1.0 eV, which is seen only from boron-doped crystals, may arise from a defect involving boron and intrinsic defects.

Mobility changes in PbSnTe due to low-temperature electron irradiation

Electron irradiations of PbSnTe at 10 °K are found to produce mobility increases in n-type material, while mobility decreases are observed in p-type material. This behavior is shown to be directly related to the carrier addition which occurs during irradiation in n-type samples and the carrier removal which occurs in p-type samples, and is also shown to be dependent on the carrier degeneracy and heavily compensated state of the samples.

Diaelastic modulus change of aluminium after low temperature electron irradiation

The changes of the elastic shear moduli C44 and C'=(C11-C12)/2 have been measured after electron irradiation of aluminium at 4.5K. Aside from dislocation pinning, a diaelastic effect which is proportional to the radiation-induced defect density has been observed. From these data the diaelastic polarizabilities under an external shear strain of the radiation-induced interstitials can be extracted. The results are very similar to those of Cu. The observed polarizabilities of alpha =-23 and alpha '=-13 are unusually large (for point defects) and highly anisotropic i.e. alpha / alpha ' approximately=2. These findings can be understood quantitatively on the basis of a model calculation which takes into account the (100) split configuration of the interstitial and the effect of the highly compressed atomic arrangement within the interstitial core region on the interatomic force constants. Thermal annealing studies indicate that di-interstitials present at the end of stage I have an even higher diaelastic polarizability than single interstitials and that the diaelastic polarizability decreases strongly when the interstitials form dislocation loops.

Huang scattering from Frenkel defects in electron-irradiated f.c.c metals

Diffuse scattering of X-rays (Cu Kα1) has been investigated close to different Bragg reflections of Al and Cu after low-temperature electron irradiation (defect concentrations between 2 and 6 × 10−4) and results discussed.

High-field magnetoresistance and hall effect in aluminium single crystals. Influence of Fermi surface and defect structure

Abstract The influence of electron scattering on the high-field galvanomagnetic properties was investigated by measuring transverse magnetoresistance and Hall effect in an Al single crystal with different defect structures. A systematic variation of the number and the kind of defects was achieved by low-temperature electron irradiation and subsequent annealing at different temperatures. Obeying Kohler's rule, the high-field magnetoresistance does not change with defect concentration. However, it depends sensitively on the defect configuration. On the other hand the anisotropy of the magnetoresistance is observed to be independent of the defect configuration. That means the anisotropy is solely determined by the anisotropy of the Fermi surface. New evidence for explaining the linear high-field magnetoresistance by magnetic breakdown was found and orientation-dependent geometry effects on the transverse magnetoresistance are discussed.

Analysis of the recovery of dilute alloys of gold and silver in copper after low temperature electron irradiation

Abstract The influence of dilute concentrations of both Au and Ag atoms on the stage I and stage I1 annealing structure in copper has been investigated using electrical resistivity measurements. An excellent agreement of the stage Id and I, experimental data with the theoretical predictions of the SimpsonJosin full diffusional theory is obtained; this analysis determines the capture radius of solute Au atoms in Cu to be 1.7 ± 0.1 I.c. and that of solute Ag atoms in Cu to be 1.8 ± 0.1 I.c. (in comparison with an interstitial-vacancy capture radius of 3.2 1.c.). Four well-defined recovery substages are observed in the dilute alloys during stage I1 recovery. An interpretation of each of these substages, consistent with experimental results, is presented. The following processes were observed to occur during stage 11: The release of trapped interstitial atoms from trapping centers formed by the proximity of a gold atom near a vacancy; the rearrangement of trapped interstitials to new trapping positions at imp...