The combination of grazing-incidence small-angle x-ray scattering with tomographic and phase retrieval methods is presented for the reconstruction of the three-dimensional (3D) electron density of nanometer sized objects. The measured 3D intensity distribution in reciprocal space is used for the phase retrieval and reconstruction of the shape and electron density of epitaxial SiGe islands with the shape of truncated pyramids with a 200 nm square base. A spatial resolution below 20 nm demonstrated in this work cannot be achieved by traditional tomographic methods.

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