Types Of Radiation-induced Defects Research Articles

Inductive Type Impedance of Mo/<i>n</i>-Si Barrier Structures Irradiated with Alpha Particles

In silicon microelectronics, flat metal spirals are formed to create an integrated inductance. However, the maximum specific inductance of such spirals at low frequencies is limited to a value of the order of tens of microhenries per square centimeter. Gyrators, devices based on operational amplifiers with approximately the same specific inductance as spirals, are also used. Despite the fact that such solutions have been introduced into the production of integrated circuits, the task of searching for new elements with high values of specific inductance is relevant. An alternative to coils and gyrators can be the effect of negative differential capacitance (i.e., inductive type impedance), which is observed in barrier structures based on silicon.The purpose of the work is to study the low-frequency impedance of Schottky diodes (Mo/n-Si) containing defects induced by α-particles irradiation and determination of the parameters of these defects by methods of low-frequency impedance spectroscopy and DLTS (Deep Level Transient Spectroscopy).Unpackaged Schottky diodes Mo/n-Si (epitaxial layer of 5.5 μm thickness and resistivity of 1 Ohm∙cm) produced by JSC “Integral” are studied. Inductance measurements were carried out on the as manufactured diodes and on the diodes irradiated with alpha particles (the maximum kinetic energy of an αparticle is 5.147 MeV). The impedance of inductive type of the Schottky diodes at the corresponding DC forward current of 10 µA were measured in the AC frequency range from 20 Hz to 2 MHz. DLTS spectra were used to determine the parameters of radiation-induced defects. It is shown that irradiation of diodes with alpha particles produces three types of radiation-induced defects: A-centers with thermal activation energy of E1 ≈ 190 meV, divacancies with activation energies of E2 ≈ 230 meV and E3 ≈ 410 meV, and Ecenters with activation energy of E4 ≈ 440 meV measured relative to the bottom of c-band of silicon.

New insights into microstructure of neutron-irradiated tungsten

The development of appropriate materials for fusion reactors that can sustain high neutron fluence at elevated temperatures remains a great challenge. Tungsten is one of the promising candidate materials for plasma-facing components of future fusion reactors, due to several favorable properties as for example a high melting point, a high sputtering resistivity, and a low coefficient of thermal expansion. The microstructural details of a tungsten sample with a 1.25 dpa (displacements per atom) damage dose after neutron irradiation at 800 °C were examined by transmission electron microscopy. Three types of radiation-induced defects were observed, analyzed and characterized: (1) voids with sizes ranging from 10 to 65 nm, (2) dislocation loops with a size of up to 10 nm and (3) W–Re–Os containing σ- and χ-type precipitates. The distribution of voids as well as the nature of the occurring dislocation loops were studied in detail. In addition, nano-chemical analyses revealed that the σ- and χ-type precipitates, which are sometimes attached to voids, are surrounded by a solid solution cloud enriched with Re. For the first time the crystallographic orientation relationship of the σ- and χ-phases to the W-matrix was specified. Furthermore, electron energy-loss spectroscopy could not unambiguously verify the presence of He within individual voids.

Luminescence and electron-phonon interaction characteristics of radiation-induced point defects in magnesium fluoride nanocrystals

Nanocrystals of magnesium fluoride have been irradiated by γ-rays at 77 K or electrons at room temperature. Three types of radiation-induced defects (color centers) with previously unknown characteristics, such as luminescence and excitation luminescence spectra, luminescence lifetime, and Huang-Rhys parameters, have been observed and studied in these nanocrystals. It has been established that the luminescence excitation spectra of these centers contain two closely spaced bands with slightly different intensities. It was shown that pre-irradiation annealing of nanocrystals at temperatures above 823 K for one hour leads to the impossibility of observing all three new types defects in irradiated samples. It has been found that during the post-radiation annealing of samples, one of the new types of color centers is transformed into a well-known defect described earlier in the literature. It is concluded that new types of defects are generated near the nanoclusters which are formed during nanocrystals production. It has been found that defects previously known and referred to as M (C1) consist of two modifications which differ in luminescence and excitation luminescence spectra, and in dependencies of their concentrations upon temperature annealing.

Investigation of the thermo-mechanical behavior of neutron-irradiated Fe-Cr alloys by self-consistent plasticity theory

The thermo-mechanical behavior of non-irradiated (at 223 K, 302 K and 573 K) and neutron irradiated (at 573 K) Fe-2.5Cr, Fe-5Cr and Fe-9Cr alloys is studied by a self-consistent plasticity theory, which consists of constitutive equations describing the contribution of radiation defects at grain level, and the elastic-viscoplastic self-consistent method to obtain polycrystalline behaviors. Attention is paid to two types of radiation-induced defects: interstitial dislocation loops and solute rich clusters, which are believed to be the main sources of hardening in Fe-Cr alloys at medium irradiation doses. Both the hardening mechanism and microstructural evolution are investigated by using available experimental data on microstructures, and implementing hardening rules derived from atomistic data. Good agreement with experimental data is achieved for both the yield stress and strain hardening of non-irradiated and irradiated Fe-Cr alloys by treating dislocation loops as strong thermally activated obstacles and solute rich clusters as weak shearable ones.

Irradiation effect on physico-chemical properties of clay minerals

The purpose of the present work was to study the exposure of various doses of γ-irradiation (10 5, 10 6, 10 7, 3×10 7 Gy) on types and concentration of radiation-induced defects, deuteration, changes in specific surface and solubility of minerals irradiated in D 2O solution in closed capsules. Some clay minerals (perfect and imperfect kaolinites, palygorskite, montmorillonite), muscovite, synthetic gibbsite and brucite were investigated. A sharp increase of the A- (Si–O −) and B-centres (Al VI–O −–Al VI bridge) concentration in the dose interval 10 5–10 7 Gy in both investigated kaolinites has been established. These concentrations are higher both in the initial and irradiated samples of well-ordered kaolinite. In irradiated palygorskite, montmorillonite and muscovite, such concentration is considerably lower than in kaolinites. The concentration of the A-centres and their stabilization are determined by the composition of the tetrahedral structural fragment of a mineral: kaolinite ([Si 4O 10])>montmorillonite, palygorskite ([Al 0.5Si 3.5O 10])>muscovite ([AlSi 3O 10]), and also by the presence of mobile water molecules on the surface and in the interlayer space of a mineral: perfect kaolinite (water molecules are practically absent)>imperfect kaolinite>montmorillonite (the maximum amount of water molecules). Concentration of the B- and B′-centres is even more sensitive in the presence of mobile water molecules in mineral like the A-centres concentration. In irradiated montmorillonite, the B′-centre was not found. The B-centre model has been refined: an unpaired electron in the B-centre in kaolinite (1:1 structure) is located on an oxygen ion of an outer OH-group, and in the B′-centre in minerals with 2:1 structure—on an inner OH-group. The deuteration begins at lower irradiation doses in those minerals, in which the maximum amount of the radiation-induced centres appears. The lower limit of the beginning of deuteration at small irradiation doses rises in the following sequence: brucite<kaolinite<montmorillonite<palygorskite<gibbsite. The irradiation dose growth leads to the increase of specific surface and change of solubility of the irradiated samples of clay minerals: the going out degree of the Al 3+ ions from kaolinite increases, but that of Si 4+ ions—decreases, for montmorillonite and palygorskite the inverse dependence takes place. It can be explained by the increase in the amount of the different types of radiation-induced defects in these minerals.

Defect states in transmutation-doped γ-irradiated Cz-Si crystals under high uniaxial pressure

In order to identify tensoeffect mechanisms in neutron transmutation doped (NTD) n-Si(P), the tensoresistive and tenso-Hall effects were investigated in highly strained crystals with phosphorous concentration 3×10 13–7.2×10 14 cm −3 and under different doses of γ-radiation (up to 8×10 17 quanta/cm 2). It was determined that according to the defect structure and its corresponding energy level within the band gap, an appreciable decrease of the activation energy of different types of radiation-induced defects and accompanied increase of the concenration of free electrons occur in different range of uniaxial pressure. The mechanism indicated above together with the intervalley redistribution of electrons (Smith–Herring mechanism) and pressure dependence of the f-scattering probability determine tensoeffect peculiarities which were investigated in highly strained NTD and γ-irradiated Si(P).

Radiation-induced paramagnetic defects in natural kaolinites: Alpha dosimetry with ion beam irradiation

Three types of paramagnetic radiation-induced defects (RID), namely A, A′ (Si-O−-centers) and B (Al-O−-Al center), had been identified in natural kaolinites by means of electron paramagnetic resonance spectroscopy. The A-center, stable at the scale of geological periods, was thought to be of particular relevance to quantify past transits of radionuclides in the geosphere. Alpha radiation being likely the main source of RID in kaolinite, the objective of this paper is to define the role of α-particles on the creation of RID and to test the use of A-centers for an α-dosimetry. Three kaolinites with different crystalline order and containing other clays as impurities were irradiated with He+ ion beams. The radiation dose range (0–750 MGy) was consistent with natural radioactivity in environments from the Earth's surface. Irradiation drastically enhanced the original signals due to RID. An important increase of concentration of the unstable B-center, partly due to unrealistic dose rate provided by accelerator ion beam, was observed from the lower doses. The most stable defects remained of the Atype all along experimental irradiations. The contribution of ancillary phyllosilicates to EPR spectra was negligible. The concentration of the three types of RID was related to radiation doses up to 30 MGy. Dosimetry growth curves for the A-centers exhibited variable efficiencies and saturation levels that were related to the structural order and the chemical purity of the kaolinites: the more ordered and purer the kaolinite, the higher the efficiency and the lower the saturation plateau. Moreover, these results are of geochemical significance: dosimetry based on A-centers could be directly used to quantify past migrations of radioelements in the geosphere, by determination of the naturally-cumulated doses (paleodose) of kaolinites.