Papers by Keyword: Dislocation Loops

Abstract: The average size and density evolution of dislocation loops in AL-6XN austenitic stainless steel, a candidate fuel cladding material for supercritical water-cooled reactor, under proton irradiation were simulated through a rate theory model. The simulation results exhibit relatively good agreement with the experimental results at 563 K. The size and density of defect clusters are calculated under irradiation temperature between 550 K and 900 K and irradiation doses up to 15 dpa which satisfies the working condition in supercritical water-cooled reactor. The fast nucleation between self-interstitials happens at the initial stage of irradiation. The average size of dislocation loops increases while the average density of these loops reduces with the increasing temperature, and the average density approaches to a constant when irradiated at higher irradiation doses. The mechanism is discussed based on the variation of rate constants of defect reactions and the variation of the diffusion coefficients of interstitials and dislocation loops with dose and temperature.

Abstract: Luminescence properties of silicon light emitting diodes with engineered dislocation loops were investigated. Dislocation loops were formed by Si+-ion implantation above and below metallurgical p+-n junction followed by an annealing step. The diodes showed characteristic dislocation (D-band) and band-to-band luminescence. Measurements of carrier-injection level dependence of the D-band signal intensity were performed. The results are in agreement with the model for dislocation luminescence, which suggests rediative transition between two, dislocation-related shallow levels. A gradual blue-shift of the D-band peak positions was observed with an increase in the carrier injection level in electroluminescence and photoluminescence. A supposition about existence of strong Stark effect for the excitonic dislocation states allows explaining the observations. Namely, in the build-in electric field of the p-n junction the exciton energies are red-shifted. The injected charge carriers lower the field and thus cause the blue-shift of the peak positions. A fitting of the data using the quadratic Stark effect equation suggests 795 meV for the spectral position of D1 peak at 300 K and 0.0186 meV/(kV/cm)2 for the characteristic constant.

Abstract: Characteristic features of radiation damage in insulators for fusion reactors are that those materials are exposed to synergistic radiation damage of elastic displacements and electric excitation with the presence of an electric field. This paper describes the nucleation-and-growth of radiation-induced defects and their stability in oxide ceramics, such as magnesium-aluminate spinel (MgAl2O4) and alpha-alumina (α-Al2O3). Microstructure evolution in these oxides is shown through transmission electron microscopy for the formation process of dislocation loops under synergistic irradiation with displacements and ionizing radiation, the stability of dislocation loops, and the nucleation-and-growth process of loops with an applied electric field.

Abstract: Irradiation of metals leads to the formation of point-defects (vacancies and selfinterstitials) that usually agglomerate in the form of dislocation loops. Due to the elastic interaction between SIA (self-interstitial atoms) and dislocations, the loops absorb in most cases more SIA than vacancies. That is why the loops observed by transmission electron microscopy are almost always interstitial in nature. Nevertheless, vacancy loops have been observed in zirconium following electron or neutron irradiation (see for example [1]). Some authors proposed that this unexpected behavior could be accounted for by SIA diffusion anisotropy [2]. Following the approach proposed by Woo [2], the cluster dynamics model presented in [3] that describes point defect agglomeration was extended to the case where SIA diffusion is anisotropic. The model was then applied to the loop microstructure evolution of a zirconium thin foil irradiated with electrons in a high-voltage microscope. The main result is that, due to anisotropic SIA diffusion, the crystallographic orientation of the foil has considerable influence on the nature (vacancy or interstitial) of the loops that form during irradiation.