Low-temperature Electron Irradiation Research Articles

Ion-Selective Scattering Studied Using the Variable-Energy Electron Irradiation in the Ba0.2K0.8Fe2As2 Superconductor.

Low-temperature variable-energy electron irradiation was used to induce non-magnetic disorder in a single crystal of a hole-doped iron-based superconductor, Ba1-xKxFe2As2, x = 0.80. To avoid systematic errors, the beam energy was adjusted non-consequently for five values between 1.0 and 2.5 MeV when sample resistance was measured in situ at 22 K. For all energies, the resistivity raises linearly with the irradiation fluence suggesting the creation of uncorrelated dilute point-like disorder (confirmed by simulations). The rate of the resistivity increase peaks at energies below 1.5 MeV. Comparison with calculated partial cross-sections points to the predominant creation of defects in the iron sublattice. Simultaneously, superconducting Tc, measured separately between the irradiation runs, is monotonically suppressed as expected, since it depends on the total scattering rate, hence on the total cross-section, which is a monotonically increasing function of the energy. Our work experimentally confirms an often-made assumption of the dominant role of the iron sub-lattice in iron-based superconductors.

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.

Short-range order in Fe-Cr alloys irradiated with electrons at low temperatures and cr solubility in α-iron near 270 K

Chromium has limited solubility in -iron. It is shown that unsaturated Fe-Cr alloys should demonstrate short-range ordering (i.e. tendency to neighboring of Fe and Cr atoms). The type of short-range ordering in several Fe-Cr alloys is revealed from the data on the recovery of residual electrical resistivity after low temperature electron irradiation at sufficiently low temperatures. The combined consideration of the data on short-range ordering and chromium solubility at 570 K (Scr. Mater. 2014 v. 74, p. 48 and ibid 2016 v. 122, p. 31) gives the confidence interval for the solubility limit near 270 K equal to 8.8±0.4 at. % Cr.

Electron irradiation effects on superconductivity in PdTe2 : An application of a generalized Anderson theorem

Low temperature ($\sim$ 20~K) electron irradiation with 2.5 MeV relativistic electrons was used to study the effect of controlled non-magnetic disorder on the normal and superconducting properties of the type-II Dirac semimetal PdTe$_2$. We report measurements of longitudinal and Hall resistivity, thermal conductivity and London penetration depth using tunnel-diode resonator technique for various irradiation doses. The normal state electrical resistivity follows Matthiessen rule with an increase of the residual resistivity at a rate of $\sim$0.77$ \mu \Omega$cm/$(\textrm{C}/\textrm{cm}^2)$. London penetration depth and thermal conductivity results show that the superconducting state remains fully gapped. The superconducting transition temperature is suppressed at a non-zero rate that is about sixteen times slower than described by the Abrikosov-Gor'kov dependence, applicable to magnetic impurity scattering in isotropic, single-band $s$-wave superconductors. To gain information about the gap structure and symmetry of the pairing state, we perform a detailed analysis of these experimental results based on insight from a generalized Anderson theorem for multi-band superconductors. This imposes quantitative constraints on the gap anisotropies for each of the possible pairing candidate states. We conclude that the most likely pairing candidate is an unconventional $A_{1g}^{+-}$ state. While we cannot exclude the conventional $A_{1g}^{++}$ and the triplet $A_{1u}$, we demonstrate that these states require additional assumptions about the orbital structure of the disorder potential to be consistent with our experimental results, e.g., a ratio of inter- to intra-band scattering for the singlet state significantly larger than one. Due to the generality of our theoretical framework, we think that it will also be useful for irradiation studies in other spin-orbit-coupled multi-orbital systems.

Vacancy- and interstitial-mediated self-diffusion coefficients determined from the analysis of observed self-diffusion coefficients in silicon crystals

We clarify the mechanisms of self-diffusion mediated by both vacancies and interstitials in silicon crystals. Südkamp and Bracht published carefully measured self-diffusion data for silicon and determined the vacancy-mediated diffusion coefficients from the difference between their new data and previous data of metal diffusion under consideration of a correlation factor. Instead, we analyzed their data using the vacancy properties: the formation energy was obtained from quenching experiments of silicon crystals in a hydrogen atmosphere, and the migration energy determined from low-temperature electron irradiation. The self-diffusion coefficient is given by the sum of the diffusion coefficients of the vacancy mechanism, 0.90 exp (−4.30 eV/kBT), and the interstitial mechanism, 6.9 × 102 exp (−4.8 eV/kBT) cm2 s−1.

Effects of cold deformation, electron irradiation and extrusion on deuterium desorption behavior in Zr-1%Nb alloy

The present article introduces the data of analysis of ranges of ion-implanted deuterium desorption from Zr-1% Nb alloy. The samples studied underwent plastic deformation, low temperature extrusion and electron irradiation. Plastic rolling of the samples at temperature ∼300 K resulted in plastic deformation with the degree of ε = 3.9 and the formation of nanostructural state with the average grain size of d = 61 nm. The high degree of defectiveness is shown in thermodesorption spectrum as an additional area of the deuterium desorption in the temperature ranges 650–850 K. The further processing of the sample (that had undergone plastic deformation by plastic rolling) with electron irradiation resulted in the reduction of the average grain size (58 nm) and an increase in borders concentration. As a result the amount of deuterium desorpted increased in the temperature ranges 650–900 K. In case of Zr-1% Nb samples deformed by extrusion the extension of desorption area is observed towards the temperature reduction down to 420 K. The formation of the phase state of deuterium solid solution in zirconium was not observed. The structural state behavior is a control factor in the process of deuterium thermodesorption spectrum structure formation with a fixed implanted deuterium dose (hydrogen diagnostics). It appears as additional temperature ranges of deuterium desorption depending on the type, character and defect content.

Differing behaviors of point defects in Fe–36Ni alloy during annealing after low-temperature deformation and irradiation

Fe–36Ni alloy is studied in states in which it is quenched, irradiated with electrons at 70 K, and deformed at 77 K. It is shown that similar structure-phase transformations occur in the investigated alloy during annealing at the temperature range of 70–570 K both after preliminary low-temperature electron irradiation and after preliminary low-temperature deformation. Migration of interstitial atoms (70–140 K) and vacancies (180–570 K), which induce phase transformations and are the results of atomic separation and ordering of zones with increased nickel content, is observed. Mechanisms of structure-phase changes under deformation and annealing are discussed.

Reprint of: Effects of cold deformation, electron irradiation and extrusion on deuterium desorption behavior in Zr-1%Nb alloy

Abstract The present article introduces the data of analysis of ranges of ion-implanted deuterium desorption from Zr-1% Nb alloy. The samples studied underwent plastic deformation, low temperature extrusion and electron irradiation. Plastic rolling of the samples at temperature ∼300 K resulted in plastic deformation with the degree of e = 3.9 and the formation of nanostructural state with the average grain size of d = 61 nm. The high degree of defectiveness is shown in thermodesorption spectrum as an additional area of the deuterium desorption in the temperature ranges 650–850 K. The further processing of the sample (that had undergone plastic deformation by plastic rolling) with electron irradiation resulted in the reduction of the average grain size (58 nm) and an increase in borders concentration. As a result the amount of deuterium desorpted increased in the temperature ranges 650–900 K. In case of Zr-1% Nb samples deformed by extrusion the extension of desorption area is observed towards the temperature reduction down to 420 K. The formation of the phase state of deuterium solid solution in zirconium was not observed. The structural state behavior is a control factor in the process of deuterium thermodesorption spectrum structure formation with a fixed implanted deuterium dose (hydrogen diagnostics). It appears as additional temperature ranges of deuterium desorption depending on the type, character and defect content.

Effects of Cr and W on defects evolution in irradiated F82H model alloys

The effects of Cr and W solute atoms on the evolution of irradiation-induced defects in Fe-8Cr and Fe-8Cr-2W alloys upon annealing after low-temperature neutron and electron irradiation were investigated by using positron annihilation lifetime measurements. Vacancy defects behavior at elevated temperatures showed that added solute Cr and W in Fe clearly suppress void growth. The void swelling suppression by Cr was explained using configuration-trapping model. For the W solute effects, the results of two types of irradiation support the solute and dislocation interaction model. Related results are important for the fabrication of improved radiation-resistant materials for fission or fusion reactors.

Effect of titanium doping on accumulation and annealing of radiation defects in austenitic steel 16Cr15Ni3Mo(0-1)Ti at low temperature (80 K) electron irradiation

The effect of titanium doping on accumulation and annealing of radiation defects was investigated in austenitic stainless steel 16Cr15Ni3Mo under low temperature (80 K) electron irradiation. Steel has been taken in the quenched, aged and separation of solid solution states. The data obtained on the accumulation of radiation defects and their evolution during isochronous annealing. The types of defects and its complexes and the activation energy of the processes taking place with their participation is identified. The mechanisms of radiation- induced processes and the effect of titan doping is discussed.

Accumulation and annealing of radiation defects and the hydrogen effect thereon in an austenitic steel 16Cr15Ni3Mo1Ti upon low-temperature neutron and electron irradiation

The effect of hydrogen, accumulation and annealing of radiation defects on the physicomechanical properties of an austenitic Kh16N15M3T1 steel (16Cr15Ni3Mo1Ti) has been investigated upon low-temperature (77 K) neutron and electron irradiations. It has been shown that, when its concentration is about 300 at ppm, hydrogen reduces plasticity by 25%. The presence of helium (2.0–2.5 at ppm) introduced by the tritium-trick method exerts an effect on the yield strength and hardly affects embrittlement. Upon both electron and neutron irradiation, there is a linear relation between the increment of the yield strength and the square root of the increment of the residual electrical resistivity (the concentration of radiation defects). The annealing of vacancies occurs in the neighborhood of 300 K (energy for vacancy migration is 1.0–1.0 eV). Vacancy clusters dissociate near 480 K (energy for dissociation is 1.4–1.5 eV).

Accumulation and annealing of radiation defects under low-temperature electron and neutron irradiation of ODS steel and Fe-Cr alloys

The processes of accumulation and annealing of radiation defects at low-temperature (77 K) electron and neutron irradiation and their effect on the physicomechanical properties of Fe-Cr alloys and oxide dispersion strengthened (ODS) steel have been studied. It has been shown that the behavior of radiation defects in ODS steel and Fe-Cr alloys is qualitatively similar. Above 250 K, radiation-induced processes of the solid solution decomposition become conspicuous. These processes are much less pronounced in ODS steel because of specific features of its microstructure. Processes related to the overlapping of displacement cascades under neutron irradiation have been considered. It has been shown that, in this case, it is the increase in the size of vacancy clusters, rather than the growth of their concentration, that is prevailing. Possible mechanisms of the radiation hardening of the ODS steel and the Fe-13Cr alloy upon irradiation and subsequent annealing have been discussed.

Impact of irradiation-induced point defects on electronically and ionically induced magnetic relaxation mechanisms in titano-magnetites

This report deals with the analysis of point-defect-induced magnetic after-effect (MAE) processes occurring in as-grown, single-crystalline titano-magnetite (Fe2.8–DTi0.2O4), containing B-site vacancies (D < 0.005). In a foregoing experiment, these processes, situated near 450 K, 200 K and 65 K, have been completely recovered in the course of systematic annealing up to Ta ≤ 1200 K. Analysis of respective annealing kinetics suggested to associate them with vacancy- (450 K) and interstitial-based (200 K) defect reorientations, including modified electron hopping (65 K). The present study was performed in order to check the previously developed relaxation model by low-temperature (80 K) electron (e–) irradiation of the prerecovered crystal and investigating if thereby the point-defect relaxations of the initial, as-grown, state could be reconstituted. MAE analyses, based on systematic sample annealing in the temperature range 80 K ≤ Ta ≤ 1200 K prove, indeed, radiation-induced reproduction of related processes. Partial modifications of respective process genealogies may be conveniently assigned to the alternative techniques of defect induction, i.e. high-temperature crystal growth in thermal equilibrium or out-of-equilibrium, low-temperature e–-irradiation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

On the migration and trapping of single self-interstitial atoms in dilute and concentrated Fe–Cr alloys: Atomistic study and comparison with resistivity recovery experiments

Atomistic simulations have been used to characterize the mobility of single self interstitial atoms (SIAs) in Fe–Cr alloys of different compositions. Density functional theory (DFT) results concerning the interaction energies between an SIA and Cr atoms in different configurations and relative positions have been extended to concentrated alloys by using an empirical potential (EP). This EP, fitted to a set of DFT data so as to provide a correct heat of mixing and point defect features, has been further validated. Static calculations using the EP allowed the existence of configuration traps for SIAs to be identified and their strength and concentration to be assessed. Dynamic simulations were used to estimate the diffusion coefficient of the SIA, as well as to characterize the primary damage state after low-temperature electron irradiation (1–5MeV), in Fe–Cr alloys of different Cr content. The results correlate with available experimental data and provide a qualitative and partially also quantitative explanation for the observed differences in the resistivity recovery stages in diluted and concentrated Fe–Cr alloys of different composition.

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.

Self-interstitials and Frenkel pairs in electron-irradiated germanium

First principles calculations were used to study the structures and electrical levels of the self-interstitial in Ge. We considered the possibility of structural changes consequent with change in charge state and show these have important implications in the mobility and electrical activity of the defect. The theoretical model is compared to the results of low temperature electron irradiation in germanium reported in the literature.

Electron spin resonance in thin film silicon after low temperature electron irradiation

Paramagnetic defects in amorphous and microcrystalline silicon (a-Si:H and μc-Si:H) with various structure compositions and doping levels were investigated by electron spin resonance (ESR). Samples were prepared by PECVD. The defect density was varied with 2 MeV electron bombardment at 100 K and stepwise annealing in the range of 80 K–433 K. In intrinsic material the spin density of the dominant ESR signal, presumably originating from dangling bonds (db), increases by up to 3 orders of magnitude after irradiation. In doped μc-Si:H material the pronounced conduction electron (CE) resonance disappears after irradiation and is replaced by the db resonance like in the irradiated intrinsic material. Generally the initial spin density and the line shape can be restored upon annealing at 433 K. Additional features at g-values of g ≈ 2.010 and g ≈ 2.000 in the ESR spectra are observed after irradiation together with the strongly enhanced Si db line at about g = 2.004–2.005. These features decrease rapidly on the first annealing steps and cannot be observed after the final annealing stage.

Migration energies of point defects during electron irradiation of hydrogenated Si crystals

To study both generation rates and mobilities of point defects due to electron irradiation, we measured and analyzed optical-absorption spectra of complexes of hydrogen and point defects generated by low-temperature electron irradiation of hydrogenated Si crystals. Specimens were doped with H by heating in ${\mathrm{H}}_{2}$ gas at 1300 \ifmmode^\circ\else\textdegree\fi{}C followed by quenching. They were then irradiated with 6-MeV electrons at 270, 200, 130, and 77 K. We measured their optical-absorption spectra at 7 K with an Fourier transform infrared spectrometer. We observed many optical absorption peaks which are due to localized vibrational modes of H bound to various point defects. The irradiation temperature dependence of concentrations of some H-point defect complexes was not monotonic contrary to the prediction of metastable Frenkel pair models. Relative intensities of those peaks depended on the irradiation temperature and were interpreted to be due to the relative mobilities of various point defects. The migration energies of a self-interstitial and a Frenkel pair relative to that of a vacancy were determined.

On-line DLTS investigations of the mono- and di-vacancy in p-type silicon after low temperature electron irradiation

Using deep level transient spectroscopy (DLTS) and Laplace-DLTS, we have investigated vacancy-related defects created in boron-doped epitaxial Si by 2 MeV electron irradiations at low temperatures (⩽ 40 K) . The vacancy level is found at E v +0.12 eV together with a DLTS peak at E v +0.20 eV which anneals at ∼140 K and is tentatively identified as a vacancy in a different configuration. The emission rate of the dominant vacancy-related deep level in the temperature range from 200 to 550 K, namely the (0/+) transition of the di-vacancy (V 2), displays a very large dependence of the emission rate on the electric field strength in the depletion region of the diodes. This dependence is unexpected in terms of the classical Poole–Frenkel effect, given the neutral charge state of V 2 before hole capture. The effect of high fields appears to be caused by phonon assisted tunneling. When V anneals around 200 K, a new complex assigned to a vacancy–boron pair gives rise to two charge states. Quenching experiments with reverse bias show that the complex is bistable. It anneals at 260 K.

Self-Organized Nanostructures Generated on Au, Ag and Cu Surfaces by Low-Temperature Electron Irradiation

We describe a new type of self-organized nanostructure for Au, Ag and Cu thin foils irradiated with high-energy electrons at around 100 K. The nanostructure appears on the electron exit surface and consists of aligned grooves which developed parallel to the surface, and nanoholes and hillocks which grew parallel to the electron beam. The groove pattern depends on the irradiation direction, the surface orientation, and the kind of metal. After about 1000 s of irradiation, penetration of the foil by grooves and holes occurs, finally leading to the formation of nanoslits or nanoparticles. These structures are probably the smallest ones generated so far on each metal surface. It is suggested that some irradiation-induced effects are closely related to the generation of nanostructures.