In situ and ex situ grazing incidence diffraction anomalous fine structure study of GaN/AlN quantum dots

5 pages, 2 figures, 1 table.-- PACS 61.10.Eq, 61.10.Ht, 61.10.Nz, 61.46.+ w, 68.65.Cd, 68.65.HbWe report on a general method that takes advantage of the full capability of anomalous diffraction and can be applied to the challenging case of small size embedded nanostructures. We study in situ and ex situ GaN Quantum Dots (QDs) grown by Plasma Assisted Molecular Beam Epitaxy (PAMBE), and encapsulated by an AlN epilayer. We investigate the QD strain and composition that are related to size, morphology, and cap layer thickness by means of anomalous diffraction in grazing incidence. The X-ray energy is tuned across the Ga K-edge where the Ga atoms scattering power is strongly modified and diffraction becomes chemically selective, giving direct information on composition. Quantitative analysis of the oscillatory extended region above the edge gives information on composition and out-of-plane strain of the dots.Peer reviewe