X-Ray Characterization of Nanostructured Materials

摘要

One of most general diffraction laws, Debye formula, allows to calculate X-Ray powder diffraction pattern of any cluster of atoms, with no additional assumptions about its structure. Nowadays computers enable a direct ('ab initio') calculations of diffraction profiles for clusters as large as several hundred A in diameter, fairly covering scale of nanomaterials. Population of atomic models of SiC, GaN and diamond nanocrystals used for calculations of the diffraction effects were built to examine the effects of average grain size, grain size distributions, presence of stacking faults, shape anisotropies, surface strains, bulk strains or a combination of above. Genetic Algorithm (GA) survives the fittest individual model, with compliance to experimental data as a fitness function. Here we give some examples of X-Ray-based analysis of nanocrystalline materials and we will concentrate on sensitivity of the method to some specific structural properties, in particular to determination of grain size distribution and presence of stacking faults in individual crystallites. In this work we will present the method of performance of 'ab initio' calculations of the diffraction profiles of nanocrystalline powders which we developed and we present here as rpnano package being a software tool for X-Ray characterization of nanostructured materials.