By transmission electron microscopy with extended Burgers vector analyses, we demonstrate the edge and screw character of vertical dislocations (VDs) in novel SiGe heterostructures. The investigated pillar-shaped Ge epilayers on prepatterned Si(001) substrates are an attempt to avoid the high defect densities of lattice mismatched heteroepitaxy. The Ge pillars are almost completely strain-relaxed and essentially defect-free, except for the rather unexpected VDs. We investigated both pillar-shaped and unstructured Ge epilayers grown either by molecular beam epitaxy or by chemical vapor deposition to derive a general picture of the underlying dislocation mechanisms. For the Burgers vector analysis we used a combination of dark field imaging and large-angle convergent beam electron diffraction (LACBED). With LACBED simulations we identify ideally suited zeroth and second order Laue zone Bragg lines for an unambiguous determination of the three-dimensional Burgers vectors. By analyzing dislocation reactions we confirm the origin of the observed types of VDs, which can be efficiently distinguished by LACBED. The screw type VDs are formed by a reaction of perfect 60° dislocations, whereas the edge types are sessile dislocations that can be formed by cross-slips and climbing processes. The understanding of these origins allows us to suggest strategies to avoid VDs.

We discuss the rather scattered measurements of the lattice parameters for C49 TiSi2, which are reported in literature, along with new and accurate X-ray diffraction measurements and ab-initio calculations. Both agree in indicating that the density of the metastable C49 structure cannot be much smaller than the one for the polymorphic C54 phase, as it is commonly reported. We conclude by demonstrating that only in the case of such a smaller difference in density between the two phases, the elastic strain contribution to the nucleation energy of the C54 structure in the C49 matrix can be neglected. The estimation of the critical radius strongly depends on this issue.

We point out that the predictive power of tight binding potentials is not limited to obtaining fairly accurate total energy calculations and very satisfactory structural evolutions by molecular dynamics simulations. They also allow for a nice physical picture of the links between bonding and stability in different structures, which is particularly helpful in the case of binary suicides

In this paper we report a molecular dynamics simulation at constant pressure and constant temperature of the structural phase transition occurring in epitaxial FeSi2 from the fluorite phase (metallic and pseudomorphic) to orthorhombic one (semiconductor and bulk stable). The evolution of the electronic density of states is carefully monitored during the transformation and we can show that the Jahn-Teller coupling between the density of states at the Fermi level and the lattice deformation drives the metal-semiconductor transition.

In this paper we report the cohesion energy curves for different CoSi2 structures calculated by a semiempirical tight binding scheme. We set up a stability hierarchy among them and provide a kinetic model which could explain very recent and apparently contradictory Molecular Beam Epitaxy findings concerning the stability of a new pseudomorphic phase, i.e. the defected CsCl.

We report the vibrational spectra of β-FeSi2 calculated by molecular dynamics simulations with a tight binding potential and provide a quantitative confirmation of the anisotropic behaviour found by new Infrared (IR) measurements for small monocrystals This analysis allows for the interpretation of more complex IR results previously found for epitaxial samples.

By fitting orthogonal tight binding parameters to the ab inlio bands of Calciumfluorite FeSi2 (γ-phase) and Cesiumcloride FeSi, we calculate the electronic structure (bands and density of states) and the total-energy of the semiconductive, orthorombic β-phase and the disordered, cubic one. The latter, the γ and the β nfigurations, have been recently observed at different annealing temperatures in thin films grown on Si (111) by Molecular Beam Epitaxy. The transferability of our method among different phases allows for a comparison of the cohesive energy curves which, in turn, supplies an interpretation of the relative stability and the growth kinetics.