Formation Of Radiation Defects Research Articles

Radiation resistance and generation of pinning centers in composite HTSC under heavy ion irradiation

AbstractThe effect of irradiation with heavy ions 40Ar8+ (48MeV), 132Xe27+ (167MeV) and 84Kr17+ (107 MeV) on the critical temperature (Tc) and critical current (Ic) of YBCO(123) composite tapes was investigated. It was found that threshold values were 5 × 1012 and 1 × 1013 ion/cm2 for 132Xe27+ and 84Kr17+ irradiation, correspondently. Critical current measured at T = 77 K increased for the lower 40Ar8+ and 84Kr17+ fluencies compared to the initial values.The formation of radiation defects that could be effective pinning centers of Abrikosov vortices resulted in the increase of the critical current. The calculations of track diameters produced by 84Kr17+ ions with energy 1.2 MeV/amu in the composite YBCO tape showed the good agreement with the experimental ones. Transmission electron microscopy (TEM), high resolution TEM and scanning TEM were used to study defects induced by irradiation. The diameter of defects obtained from TEM was in the range from 3 to 5 nm. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Configurational instability at the excited impurity ions in alkaline earth fluorites

The formation of intrinsic defects by ionizing radiation in some ionic crystals in the anion sublattice is only associated with the instability of the self-trapped exciton up to now. In this paper, on the basis of an analysis of experimental evidence already in the literature, we want to show that there are phenomena in the ionic crystals doped with some cations, which cannot be explained on the basis of existing models of the formation of radiation defects. A new mechanism for the formation of the defects in the anion sublattice associated with the Jahn–Teller instability occurring near the cation impurities in the excited state is proposed. The instability occurs when the degenerate excited state of the impurity ion is localized in the conduction band. We believe that the configuration interaction between the discrete impurity level and host continuum (effect Fano) plays an important role in this process.

Features of changes in electrical parameters of silicon p-n structures upon high-temperature electron irradiation

The effect of the temperature mode of 4-MeV electron irradiation on the change in the basic electrophysical characteristics of silicon diffused p +-n-n + structures has been studied. It has been shown that the temperature of the crystal and integrated intensity during irradiation have a significant effect on the parameters of formation of radiation defects and the pattern of their distribution in different regions of silicon p +-n-n + structures.

Deep level studies in high‐temperature annealed silicon wafers for layer transfer in thin‐film solar cells

AbstractDeep‐level transient spectroscopy (DLTS) has been applied to high‐temperature annealed n‐ and p‐type Si wafers. The aim is to identify the deep levels responsible for the observed minority carrier lifetime degradation after thin‐film transfer to a glass substrate. Anneals have been performed at 1150 °C in H2 or Ar. Care has been taken to avoid radiation defect formation during the fabrication of the Al Schottky barriers used for DLTS. It is shown that besides a change in the carrier doping density and profile, an annealing‐induced electron trap at 0.43 eV below the conduction band edge can be found, which is related to a vacancy–impurity complex.

Formation and annealing of radiation defects in tin-doped p-type germanium crystals

The effect of tin on the formation and annealing of radiation defects in p-type germanium crystals irradiated with 6-MeV electrons at a temperature of 80 K is studied. It is shown that acceptor complexes SnV with a hole ionization enthalpy of 0.16 eV are dominant in irradiated Ge:(Sn, Ga) crystals after their heating to a temperature of 300 K. These complexes disappeared as a result of the annealing of irradiated crystals in the temperature range 30–75°C. Annealing of irradiated crystals at temperatures in the range 110–150°C brings about the formation of deep-level centers with a donor level at Ev + 0.29 eV; this center is presumably related to a complex consisting of a tin atom and an interstitial gallium atom.

Symmetry of crystals with diamond structure and formation of radiation defects induced by negative muon

Positive and negative muons (μ+ and μ−) are widely used for study condensed matter at present. Negatively charged muon is captured by nuclei rapidly at 1s-state and forms μ-atom. Because of the muon mass is at 207 time grater than the electron mass, negatively charged muon screens effectively a nucleus with a charge Z and so models a single atomic isotope with the charge equal to Z – 1. To interpret experimental results one supposes as usual that muons are thermalized in a condensed matter for a time shorter than an equipment resolution time. Experimental technique development showed that this suggestion is not true for some targets.A neutralization process of a radiation defect induced by negative muon in crystals with diamond structure (Diamond, Silicon and Germanium) is considered in this work. Estimates of the velocity of neutral acceptor center (μA)0 formation connected with radiation transitions are obtained. Radiation transitions take place when a neutral atom (μA)0 changes it's configuration and formes chemical links with nearest neighbours in hybrid states. Symmetry of crystals with diamond structure allows us to express the velocity of neutral acceptor center formation in terms of one matrix element only

In situTEM Ion Irradiation and Atmospheric Heating of Cladding Materials

ABSTRACTOver the course of use, both in-service and during storage, fuel claddings for nuclear reactors undergo complex changes that can drastically change their material properties. Exposures to irradiation, temperature changes, and stresses, as well as contact with coolant, storage pool, and dry storage environments, may induce microstructural changes, such as formation of radiation defects, precipitate dissolution, and chemical segregation, that can ultimately result in failure of the cladding if pushed beyond its limit. In order to predict the performance of cladding in-service and during storage, understanding of the dominant processes related to these changes and their consequences is essential. In situ transmission electron microscopy (TEM) allows dynamic observation, at the nanoscale, of microstructural changes under a range of stimuli, making it an excellent tool for deepening our understanding of microstructural evolution in claddings. This proceeding presents details of the new in situ ion irradiation TEM and in situ gas cell TEM capabilities developed at Sandia National Laboratories. In addition, it will present the initial results from both systems investigating radiation tolerance of potential Generation IV cladding materials and understanding degradation mechanisms in Zr-based claddings of importance for dry storage.

Atomistic and Kinetic Simulations of Radiation Damage in Molybdenum

ABSTRACTA new Mo potential, developed recently by using an ab initio quantum mechanics theory, was used to study formation and time evolution of radiation defects, such as self-interstitial atoms (SIAs), vacancies, and small clusters of SIAs, using molecular dynamics (MD). MD models were developed for calculation of the diffusion coefficients of vacancies, self-interstitials, and small dislocation loops containing 2 to 37 SIAs; and the rate constants were calculated. Interactions of small SIA loops with SIAs were simulated. The results show that rotation of SIA from one <111> to another equivalent direction is an important mechanism that significantly contributes to kinetic coefficients.

In-Situ Study of Silicon Single Crystals Conductivity under Electron Irradiation

The influence of electron radiation on the properties of semiconducting silicon single crystals (Si)—both n- and p-types (currently one of the most widely applied material in the electronic technology) was studied under the electron irradiation process in-situ in air (in common conditions). Higher value of electro-conductivity (σ) during the irradiation process with respect to after irradiation was observed, which was explained by ionization and capture mechanisms resulting in the formation of non-equilibrium carriers (hole-electron pairs). The kinetics of radiation defects generation, their physical nature, temperature stability and relaxation are examined. Structural radiation defects formation: point and complexes, their influence on the silicon conductivity are considered.

Effect of ionizing irradiation on the mechanism of current passage in TlInSe2 single crystals

The temperature dependence of the electrical conductivity and current-voltage characteristics of γ-irradiated TlInSe2 single crystals with an electrical resistivity of ∼108 Ω cm have been investigated. It has been established that the anomalies of the conductivity observed in weak electric fields and at low dozes of irradiation are related to the decomposition of neutral complexes containing an interstitial cation atom. In strong electric fields, a thermal-field ionization of traps occurs. The main mechanism of radiation defect formation is the formation of complexes [VIn−Ini+], [VSe−Sei−], and others with the structural defects characteristic of unirradiated crystals. The activation energy, trap concentrations, and the potential well shape near the traps have been determined.

Picosecond-laser-induced structural modifications in the bulk of single-crystal diamond

Arrays of through laser-graphitized microstructures have been fabricated in type IIa single-crystal 1.2-mm-thick diamond plates by multipulse laser irradiation with 10-ps pulses at λ=532 nm wavelength. Raman and photoluminescence (PL) spectroscopy studies of the bulk microstructures have evidenced the diamond transformation to amorphous carbon and graphitic phases and the formation of radiation defects pronounced in the PL spectra as the self-interstitial related center, the 3H center, at 504 nm. It is found that the ultrafast-laser-induced structural modifications in the bulk of single-crystal diamond plates occur along {111} planes, known as the planes of the lowest cleavage energy and strength in diamond.

Implantation of helium and deuterium ions into tungsten-coated composite structures

Various processes occurring in tungsten coatings deposited on composite substrates under ion irradiation have been analyzed. Processes leading to formation of radiation defects of a crystal lattice, helium and deuterium accumulation, and their thermodesorption from samples are compared. Possible mechanisms behind these processes are discussed.

Specific features of formation of radiation defects in the silicon layer in “silicon-on-insulator” structures

Specific features of formation of radiation defects in thin silicon layer of silicon-on-insulator (SOI) structures have been studied. It is shown that there are differences between variations in the structural and electrical properties of the thin silicon layer and those in bulk silicon crystals (with similar electrical characteristics) subjected to the same radiation effect. It is established that the embedded insulator in the SOI structure represents a barrier for motion of radiation-induced intrinsic interstitial silicon atoms, which brings about an increase in the dose of bombarding ions, which leads to the loss of single-crystallinity of the silicon layer in a SOI structure. It is shown that γ-ray irradiation with doses unaffecting the electrical conductivity of bulk silicon crystals appreciably affects the conductivity of the silicon layer in the SOI structures. In addition, variation in the conductivity of silicon layer is related to variation in the density of surface states at the interface between the silicon layer and the built-in insulator, rather than to generation of conventional radiation-induced structural defects in silicon.

Vacancy generation in silicon in the temperature range 100–633 K under electron irradiation

The processes of radiation defect formation in Si with 1 MeV electron irradiation in the temperature range 100–633 K have been investigated. It is established that the generation efficiency of vacancies λV increases with temperature, then starts to saturate at temperatures of 250 K and finally stays constant at T>300 K. It is shown that at high temperatures, the λV dependence can be caused by the additional scattering of “hot” interstitial atoms on acoustical and optical phonons, the numbers of which increase with the temperature. An explanation, based on the creation of quasi-molecule of “hot” interstitial and lattice atoms, is proposed.

Ion implantation and ion milling in MBE Hg 1−xCd xTe films

Direct comparison of the effects of ion implantation with energy E = 20–150 keV (B + ions) and ion milling ( E = 0.5 keV, Ar + ions) on p-type HgCdTe (MCT) molecular-beam epitaxy-grown films with and without graded band-gap surface layers was performed. Both treatments were found resulting in formation of multi-layer n +–p or n +–n–p structures, comprising a radiation-damaged n + -layer with high electron concentration and, optionally, a deeper n-layer with low electron concentration. Basic processes, which occur in MCT under implantation and milling appear to be similar, and include formation of primary radiation defects, their interaction, and in-diffusion of interstitial mercury atoms with their interaction with defects already present in the crystal. The difference in energy and fluence typically used for ion implantation and ion milling in MCT results in different mechanisms of the formation of the n + - and n-layers. The presence of the graded band-gap surface layer was found to affect the thickness of the n-layer via internal electric field associated with the energy gap gradient.

Energy distribution of recoil atoms and formation of radiation defects in silicon carbide films under proton irradiation

Proton scattering in a silicon carbide film has been numerically simulated. Distribution histograms of the energy imparted to recoil atoms are obtained. Two energy ranges are considered when analyzing the histograms. In the first range of “low” energies, individual Frenkel pairs with closely spaced components are created. In the second range, recoil atoms have energies sufficient for generating a cascade of displacements. This gives rise to microscopic regions with high density of vacancies and vacancy complexes of various kinds.

The effect of neutron irradiation and annealing temperature on the electrical properties and lattice constant of epitaxial gallium nitride layers

Effect of irradiation with high reactor-neutron fluences (Φ = 1.5 × 1017-8 × 1019 cm−2) and subsequent heat treatments in the temperature range 100–1000°C on the electrical properties and lattice constant of epitaxial GaN layers grown on an Al2O3 substrate is considered. It is shown that, with the neutron fluence increasing to (1–2) × 1018 cm−2, the resistivity of the material grows to values of about 1010 Ω cm because of the formation of radiation defects, and, with the fluence raised further, the resistivity passes through a maximum and then decreases to 2 × 106 Ω cm at 300 K, which is accounted for by the appearance of a hopping conductivity via deep defects in the overlapping outer parts of disordered regions. With the neutron fluence raised to 8 × 1019 cm−2, the lattice constant c increases by 0.38% at a nearly unchanged parameter a. Heat treatment of irradiated samples at temperatures as high as 1000°C does not fully restore the lattice constant and the electrical parameters of the material.

The calculation of the radiation-defect distribution profiles in mct exposed to powerful pulsed laser beams

The results of calculation of radiation-defect distribution profiles and thermal-mechanical characteristics under the action of powerful laser beams on semiconductor MCT samples are reported. The calculations were performed within the physical-mathematical model of radiation defect formation. The calculated profiles are compared with the theoretical and experimental data.

Comparative study of changes in electrical properties of silicon and silicon carbide upon proton irradiation

Rates of carrier removal from the conduction band in n-type FZ-Si and 4H-SiC irradiated with 8- and 15-MeV protons at room temperature are discussed. Calculated rates of formation of primary radiation defects (Frenkel pairs) in these materials are presented and compared with the corresponding experimental values. Protons create defects in collision cascades involving recoil atoms formed in the crystal lattice itself. The results are compared with similar data previously obtained in irradiation of n-type FZ-Si and 4H-SiC with 900-keV electrons, in which case isolated so-called close Frenkel pairs are absolutely dominant among primary radiation defects. It has been found that the E-center model adequately describing the decrease in the electrical conductivity of n-FZ-Si upon electron irradiation is inapplicable to interpretation of experimental data for proton-irradiated materials. It is suggested that a pronounced annealing of “simple” radiation defects of the type of close Frenkel pairs occurs during irradiation at room temperature.

ACTION OF MAGNETIC AND X-RAY FIELDS ON ELECTRO-PHYSICAL PROPERTIES OF TEMPERATURE SENSORS

The influence of X-ray and magnetic fields on the formation of radiation defects in silicon temperature sensors is investigated by the method of capacitance spectroscopy. It is shown that the defects which are generated by X-ray radiation are more sensitive to weak magnetic fields in comparison with structural defects. Effects of weak magnetic fields (B=0.17 Tl) on the pattern changes VFC of barrier structures are opposite to the action of X-ray radiation.