Narrow Results

The possible transition states, minimum energy paths (MEPs) and migration mechanisms of defect clusters and xenon-vacancy defect clusters in uranium dioxide (UO₂) have been investigated using the dimer and the nudged elastic-band (NEB) methods. The nearby O atom can easily hop into the oxygen vacancy position by overcoming a small energy barrier, which is much lower than that for the migration of a uranium vacancy. A simulation for a vacancy cluster consisting of two oxygen vacancies reveals that the energy barrier of the divacancy migration tends to decrease with increasing the separation distance of divacancy. For an oxygen interstitial, the migration barrier for the hopping mechanism is almost three times larger than that for the exchange mechanism. Xe moving between two interstitial sites is unlikely a dominant migration mechanism considering the higher energy barrier. A net migration process of a Xe-vacancy pair containing an oxygen vacancy and a xenon interstitial is identified by the NEB method. We expect the oxygen vacancy-assisted migration mechanism to possibly lead to a long distance migration of the Xe interstitials in UO₂. The migration of defect clusters involving Xe substitution indicates that Xe atom migrating away from the uranium vacancy site is difficult.

Nitrogen is an important impurity in Czochralski grown silicon (Cz–Si) as it enhances oxygen precipitation through the formation of vacancy–nitrogen–oxygen clusters and in particular the ${\mathrm{\text{V}}}_m{\mathrm{\text{N}}}_2{\mathrm{\text{O}}}_n$ complexes. Here, we employ density functional theory (DFT) to predict the structure of ${\mathrm{\text{V}}}_m{\mathrm{\text{N}}}_2{\mathrm{\text{O}}}_n$ ($m,n=1,2$). We report that the lowest energy ${\mathrm{\text{V}}}_m{\mathrm{\text{N}}}_2{\mathrm{\text{O}}}_n$ ($m,n=1,2$) defects are very strongly bound. These results are consistent, and support the previously reported theoretical and experimental conclusions that ${\mathrm{\text{V}}}_m{\mathrm{\text{N}}}_2{\mathrm{\text{O}}}_n$ structures could form.

In this paper, formation of defects/defect clusters in nickel nanowires (Ni-NWs) due to interaction of a 60 kilo-electron-volt (keV) beam of proton (H${}^{+})$ ions is studied. Ni-NWs are exposed to various fluencies of H${}^{+}$ ions ranging between $1.5\times 10^{15}$ and $1.5\times 10^{17}$ions/cm². The analysis of pristine and H${}^{+}$ ion-irradiated Ni-NWs samples is mainly done using transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. Stopping range of ions in matter (SRIM) simulation software is employed to verify the production of defect clusters in Ni-NWs theoretically. Furthermore, insight of creation of defects in Ni-NWs due to interaction of low energy H${}^{+}$ ions in keV range is made using the theory of collision cascade effect. The study of defect clusters induced in Ni-NWs under H${}^{+}$ ions beam irradiation is essential for application of Ni-NW-based nanodevices in harsh environment containing plenty of H${}^{+}$ ions such as for use in spacecraft equipped for space missions.