Section: New Results

Atomistic modelling of diamond-type Si${}_x$Ge${}_y$C${}_z$Sn${}_{1-x-y-z}$ crystals for realistic transmission electron microscopy image simulations

Participants: Leonard Jaillet and Cyril Guedj.

The realistic simulations of transmission electron microscopy (TEM) images requires an accurate definition of the positions of all atoms, which are linked to the mechanical properties of the material. We are working on an approach to build optimized models to represent the lattice parameters and elastic properties of Si, Ge, diamond, alpha-tin and related diamond alloys.

In order to compute precisely the complex Si${}_x$Ge${}_y$C${}_z$Sn${}_{1-x-y-z}$ diamond crystals, a dedicated parametrization of the Keating force field has been proposed. An original periodic boundary strategy has also been provided. Our tool can be used to interpret experimental TEM with a speed several orders of magnitude higher than for ab-initio methods. The method predicts the correct lattice parameters and elastic constants for published experimental results with low deviation. Finally, we have shown that subsequent Monte Carlo simulations predict original self-ordering effects in C in good agreement with the theory. A publication is in preparation on this topic.

Figure 4. Crystal of Si${}_{40}$Ge${}_{60}$ where two carbon atoms (circled in red) have been inserted. The properties of the crystal such as its lattice parameter can be characterized in function of the position of the carbon atoms.