Publications by authors named "Pizzagalli L"

It is now well established that materials are stronger when their dimensions are reduced to the submicron scale. However, what happens at dimensions such as a few tens of nanometers or lower remains largely unknown, with conflicting reports on strength or plasticity mechanisms. Here, we combined first-principles molecular dynamics and classical force fields to investigate the mechanical properties of 1-2 nm Si and SiC nanoparticles.

View Article and Find Full Text PDF

Brittle topologically close-packed precipitates form in many advanced alloys. Due to their complex structures, little is known about their plasticity. Here, a strategy is presented to understand and tailor the deformability of these complex phases by considering the Nb-Co µ-phase as an archetypal material.

View Article and Find Full Text PDF

The mechanical properties of endofullerenes have been investigated by performing compression tests using finite temperature first principles molecular dynamics calculations. We considered various X@C systems, with X a single noble gas atom (He, Ne, Ar, Kr, or Xe), small molecules (HO, CH), or small helium clusters. In the absence of compression, it is observed that there is no or at best a negligible effect of X on the properties of C.

View Article and Find Full Text PDF

First principles calculations, based on density functional theory, have been carried out to investigate the role of screw dislocations in the bulk n-type conductivity which is usually observed in indium nitride. Energetics, atomic and electronic structures of different core configurations of dislocations, running along the [0001] polar or along the [112[combining macron]0] non-polar direction, have been determined and compared. This enabled inspection of the modifications in the properties of screw dislocations when the growth direction is changed.

View Article and Find Full Text PDF

Understanding how edge misfit dislocations (MDs) form in a GeSi/Si(001) film has been a long standing issue. The challenge is to find a mechanism accounting for the presence of these dislocations at the interface since they are not mobile and cannot nucleate at the surface and glide towards the interface. Furthermore, experiments can hardly detect the nucleation and early stages of growth because of the short time scale involved.

View Article and Find Full Text PDF

We propose an original method for the determination of the physical properties of nanometer sized helium bubbles using spectrum imaging in an energy-filtered transmission electron microscope. Helium bubbles synthesized by high fluence implantation and thermal annealing in silicon are investigated. The acquisition parameters are determined to optimize both signal/noise ratio and time.

View Article and Find Full Text PDF

A new parametrization of the widely used Stillinger-Weber potential is proposed for silicon, allowing for an improved modelling of defects and plasticity-related properties. The performance of the new potential is compared to the original version, as well as to another parametrization (Vink et al 2001 J. Non-Cryst.

View Article and Find Full Text PDF

Combining density functional theory, the nudged elastic band technique, and the ultradense fluid model, we investigated the desorption process of He and Ne in silicon. Our results show that the internal surfaces of gas-filled bubbles are not a limiting factor during desorption experiments, since the surface reconstruction opens diffusion paths easier than in the bulk. We show that the vibrational contribution to the energy of helium in the bulk has to be considered in order to determine realistic pressures in the bubbles, when comparing experiments and simulations.

View Article and Find Full Text PDF

The stability of atomic and molecular hydrogen in the vicinity of a screw dislocation in silicon has been investigated using first-principles calculations. The lowest energy configurations are obtained for H atoms located in the dislocation core, suggesting that the segregation of hydrogen is favoured in the dislocation core. It is found that a spontaneous dissociation of H(2) could occur in the dislocation core.

View Article and Find Full Text PDF

An interatomic potential has been developed to describe interactions in silicon, carbon and silicon carbide, based on the environment-dependent interatomic potential (EDIP) (Bazant et al 1997 Phys. Rev. B 56 8542).

View Article and Find Full Text PDF

We report an unexpected characteristic of dislocation cores in silicon. Using first-principles calculations, we show that all of the stable core configurations for a nondissociated 60 degrees dislocation are sessile. The only glissile configuration, previously obtained by nucleation from surfaces, surprisingly corresponds to an unstable core.

View Article and Find Full Text PDF

An accurate characterization of the structure of hydrogen-induced platelets is a prerequisite for investigating both hydrogen aggregation and formation of larger defects. On the basis of quantitative high resolution transmission electron microscopy experiments combined with extensive first principles calculations, we present a model for the atomic structure of (001) hydrogen-induced platelets in germanium. It involves broken Ge-Ge bonds in the [001] direction that are dihydride passivated, vacancies, and trapped H(2) molecules, showing that the species involved in platelet formation depend on the habit plane.

View Article and Find Full Text PDF

We demonstrate how a saddle point search method can be used to study dislocation mobility in a covalent material-a non-trivial transition mechanism in a complex system. Repeated saddle point searches have been carried out by using the minimum mode following algorithm and dimer method in combination with several empirical potential functions for silicon in order to determine the mechanisms for the creation and migration of kinks on a non-dissociated screw dislocation in a silicon crystal. For the environment-dependent interatomic potential, three possible kink migration processes have been identified with activation energies of 0.

View Article and Find Full Text PDF

The high lattice mismatched SiC/Si(001) interface was investigated by means of combined classical and ab initio molecular dynamics. Among the several configurations analyzed, a dislocation network pinned at the interface was found to be the most efficient mechanism for strain relief. A detailed description of the dislocation core is given, and the related electronic properties are discussed for the most stable geometry: we found interface states localized in the gap that may be a source of failure of electronic devices.

View Article and Find Full Text PDF