501 research outputs found
First principles determination of the Peierls stress of the shuffle screw dislocation in silicon
The Peierls stress of the a/2 screw dislocation belonging to the shuffle
set is calculated for silicon using density functional theory. We have checked
the effect of boundary conditions by using two models, the supercell method
where one considers a periodic array of dislocations, and the cluster method
where a single dislocation is embedded in a small cluster. The Peierls stress
is underestimated with the supercell and overestimated with the cluster. These
contributions have been calculated and the Peierls stress is determined in the
range between 2.4 x 10-2 and 2.8 x 10-2 eV {\AA}-3. When moving, the
dislocation follows the {111} plane going through a low energy metastable
configuration and never follows the 100 plane, which includes a higher energy
metastable core configuration
Ascoli's theorem for functions vanishing at infinity and selected applications
AbstractWe give a new form of the Ascoli theorem for functions on RN tending to some given closed subset Z of a complete metric space E at infinity. For instance, when E is a normed space and Z={0}, the usual uniform decay requirement is replaced by the assumption that the 0 function is the only continuous function produced by some limiting process. This formulation, which has significant practical value in concrete applications, is described in its general form, but with emphasis on the case when Z is totally disconnected. Variants in Sobolev spaces and the properness of nonlinear ordinary differential operators are discussed
Stability of undissociated screw dislocations in zinc-blende covalent materials from first principle simulations
The properties of perfect screw dislocations have been investigated for
several zinc-blende materials such as diamond, Si, -SiC, Ge and GaAs, by
performing first principles calculations. For almost all elements, a core
configuration belonging to shuffle set planes is favored, in agreement with low
temperature experiments. Only for diamond, a glide configuration has the lowest
defect energy, thanks to an sp hybridization in the core
Theoretical study of dislocation nucleation from simple surface defects in semiconductors
Large-scale atomistic calculations, using empirical potentials for modeling
semiconductors, have been performed on a stressed system with linear surface
defects like steps. Although the elastic limits of systems with surface defects
remain close to the theoretical strength, the results show that these defects
weaken the atomic structure, initializing plastic deformations, in particular
dislocations. The character of the dislocation nucleated can be predicted
considering both the resolved shear stress related to the applied stress
orientation and the Peierls stress. At low temperature, only glide events in
the shuffle set planes are observed. Then they progressively disappear and are
replaced by amorphization/melting zones at a temperature higher than 900 K
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