1,996 research outputs found
Theoretical investigations of a highly mismatched interface: the case of SiC/Si(001)
Using first principles, classical potentials, and elasticity theory, we
investigated the structure of a semiconductor/semiconductor interface with a
high lattice mismatch, SiC/Si(001). Among several tested possible
configurations, a heterostructure with (i) a misfit dislocation network pinned
at the interface and (ii) reconstructed dislocation cores with a carbon
substoichiometry is found to be the most stable one. The importance of the slab
approximation in first-principles calculations is discussed and estimated by
combining classical potential techniques and elasticity theory. For the most
stable configuration, an estimate of the interface energy is given. Finally,
the electronic structure is investigated and discussed in relation with the
dislocation array structure. Interface states, localized in the heterostructure
gap and located on dislocation cores, are identified
Comparison between classical potentials and ab initio for silicon under large shear
The homogeneous shear of the {111} planes along the <110> direction of bulk
silicon has been investigated using ab initio techniques, to better understand
the strain properties of both shuffle and glide set planes. Similar
calculations have been done with three empirical potentials, Stillinger-Weber,
Tersoff and EDIP, in order to find the one giving the best results under large
shear strains. The generalized stacking fault energies have also been
calculated with these potentials to complement this study. It turns out that
the Stillinger-Weber potential better reproduces the ab initio results, for the
smoothness and the amplitude of the energy variation as well as the
localization of shear in the shuffle set
A shortest-path based clustering algorithm for joint human-machine analysis of complex datasets
Clustering is a technique for the analysis of datasets obtained by empirical
studies in several disciplines with a major application for biomedical
research. Essentially, clustering algorithms are executed by machines aiming at
finding groups of related points in a dataset. However, the result of grouping
depends on both metrics for point-to-point similarity and rules for
point-to-group association. Indeed, non-appropriate metrics and rules can lead
to undesirable clustering artifacts. This is especially relevant for datasets,
where groups with heterogeneous structures co-exist. In this work, we propose
an algorithm that achieves clustering by exploring the paths between points.
This allows both, to evaluate the properties of the path (such as gaps, density
variations, etc.), and expressing the preference for certain paths. Moreover,
our algorithm supports the integration of existing knowledge about admissible
and non-admissible clusters by training a path classifier. We demonstrate the
accuracy of the proposed method on challenging datasets including points from
synthetic shapes in publicly available benchmarks and microscopy data
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
Dislocation formation from a surface step in semiconductors: an ab initio study
The role of a simple surface defect, such as a step, for relaxing the stress
applied to a semiconductor, has been investigated by means of large scale first
principles calculations. Our results indicate that the step is the privileged
site for initiating plasticity, with the formation and glide of 60
dislocations for both tensile and compressive deformations. We have also
examined the effect of surface and step termination on the plastic mechanisms
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