32,864 research outputs found
Clustering of vacancy defects in high-purity semi-insulating SiC
Positron lifetime spectroscopy was used to study native vacancy defects in
semi-insulating silicon carbide. The material is shown to contain (i) vacancy
clusters consisting of 4--5 missing atoms and (ii) Si vacancy related
negatively charged defects. The total open volume bound to the clusters
anticorrelates with the electrical resistivity both in as-grown and annealed
material. Our results suggest that Si vacancy related complexes compensate
electrically the as-grown material, but migrate to increase the size of the
clusters during annealing, leading to loss of resistivity.Comment: 8 pages, 5 figure
Vacancy-Impurity Nanoclusters in Solid Solutions
The existence of vacancy--impurity clusters due to quantum properties of
vacancies in phase separated solid solutions of 4He in 3He is analyzed and
discussed. Additional mechanism called vacancy assisted nucleation is proposed.
According to this assumption the vacancy-impurity clusters should have b.c.c.
structure.Comment: 5 pages, 1 figure, Late
Hydrogen and vacancy clustering in zirconium
The effect of solute hydrogen on the stability of vacancy clusters in
hexagonal closed packed zirconium is investigated with an ab initio approach,
including contributions of H vibrations. Atomistic simulations within the
density functional theory evidence a strong binding of H to small vacancy
clusters. The hydrogen effect on large vacancy loops is modeled through its
interaction with the stacking faults. A thermodynamic modeling of H segregation
on the various faults, relying on ab initio binding energies, shows that these
faults are enriched in H, leading to a decrease of the stacking fault energies.
This is consistent with the trapping of H by vacancy loops observed
experimentally. The stronger trapping, and thus the stronger stabilization, is
obtained for vacancy loops lying in the basal planes, i.e. the loops
responsible for the breakaway growth observed under high irradiation dose.Comment: submitte
Plentiful magnetic moments in oxygen deficient SrTiO3
Correlated band theory is employed to investigate the magnetic and electronic
properties of different arrangements of oxygen di- and tri-vacancy clusters in
SrTiO. Hole and electron doping of oxygen deficient SrTiO yields
various degrees of magnetization as a result of the interaction between
localized magnetic moments at the defected sites. Different kinds of Ti atomic
orbital hybridization are described as a function of the doping level and
defect geometry. We find that magnetism in SrTiO is sensitive to
the arrangement of neighbouring vacancy sites, charge carrier density, and
vacancy-vacancy interaction. Permanent magnetic moments in the absence of
vacancy doping electrons are observed. Our description of the charged clusters
of oxygen vacancies widens the previous descriptions of mono and
multi-vacancies and points out the importance of the controled formation at the
atomic level of defects for the realization of transition metal oxide based
devices with a desirable magnetic performance.Comment: 6 pages, 5 figures, continuation of arXiv:1408.310
Vacancy clustering and diffusion in silicon: Kinetic lattice Monte Carlo simulations
Diffusion and clustering of lattice vacancies in silicon as a function of
temperature, concentration, and interaction range are investigated by Kinetic
Lattice Monte Carlo simulations. It is found that higher temperatures lead to
larger clusters with shorter lifetimes on average, which grow by attracting
free vacancies, while clusters at lower temperatures grow by aggregation of
smaller clusters. Long interaction ranges produce enhanced diffusivity and
fewer clusters. Greater vacancy concentrations lead to more clusters, with
fewer free vacancies, but the size of the clusters is largely independent of
concentration. Vacancy diffusivity is shown to obey power law behavior over
time, and the exponent of this law is shown to increase with concentration, at
fixed temperature, and decrease with temperature, at fixed concentration.Comment: 14 pages, 12 figures. To appear in Physical Review
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