The Extended X-Ray Absorption Fine Structure (EXAFS) allows to probe the short-range order in crystalline and non-crystalline materials with chemical selectivity. In the conventional methodology of analysis, structural parameters such as coordination numbers, mean value and standard deviation of the distributions of interatomic distances are obtained by means of a non-linear fit of the EXAFS equation to the experimental data. Except in the case of highly symmetrical crystal structures, the modeling of the signal can be quite complex. In the Reverse Monte Carlo (RMC) method, the structure is optimized through various modifications of the atomic positions, driven by a Metropolis-like algorithm, in which the probability of acceptance of each movement depends on the difference between the measured and calculated EXAFS signals. At the end of the simulation, the final state of the system is a list of atomic positions consistent with the experimental data. This method allows to obtain several properties that are not directly obtained from the conventional analysis, including the partial distribution function (PDF) for several coordination spheres, correlations of atomic displacements and bond angle distributions. In this project, we will study samples of the GeSi system containing various degrees and types of disorder (thermal, structural and chemical), which includes polycrystalline, nanocrystalline, amorphous and liquid samples. Structures obtained by Classical Molecular Dynamics will be used as initial state in the analysis of liquid and amorphous samples.
News published in Agência FAPESP Newsletter about the scholarship: