Densities of a-and aþc-type threading dislocations for a series of GaN films grown in different modes by metalorganic vapor phase epitaxy are determined from the x-ray diffraction profiles in skew geometry. The reciprocal space maps are also studied. Theory of x-ray scattering from crystals with dislocations is extended in order to take into account contribution from both threading and misfit dislocations. The broadening of the reciprocal space maps along the surface normal and the rotation of the intensity distribution ellipse is attributed to misfit dislocations at the interface. We find that the presence of a sharp AlN/GaN interface leads to an ordering of misfit dislocations and reduces strain inhomogeneity in GaN films. V

""We report on the experimental and theoretical investigation of the relaxation in Ge-rich SiGe\\\/Ge\\\/Si heterostructures. The experimental x-ray diffraction data are interpreted with the help of a model including both edge and 60 degrees misfit dislocations in the calculated x-ray scattering intensity. Our results show that highly positionally correlated edge dislocations dominate in the relaxation of the compressive strain at the Ge\\\/Si interface, while a smaller tensile strain at the SiGe\\\/Ge interfaces released by uncorrelated\\\/little correlated 60 degrees dislocations."

We report on the atomic architecture of metastable precipitates in a model Mg-0.5 at. %Nd system. High resolution Z-contrast observations in scanning transmission electron microscopy demonstrate that a common elementary structure, made of Nd atomic pillars, is shared by precipitates involved in the early decomposition of the system. A combination of Z-contrast projections has been used to establish the accurate location of Nd atoms in the atomic pillars, therefore allowing the determination of structure and composition of precipitates. Other precipitates compositions are extrapolated by means of a quantitative analysis.