[en] We address the question: what is the smallest spot size to which an x-ray beam can be focused? We show that confinement of the beam within a narrowly tapered waveguide leads to a theoretical minimum beam size of the order of 10 nm (FWHM), the exact value depending only on the electron density of the confining material. This limit appears to apply to all x-ray focusing devices. Mode mixing and interference can help to achieve this spot size without the need for ultrasmall apertures

[en] We present a way to fabricate high-aspect-ratio silicon microcavity arrays which can be used for the investigation of confinement-induced ordering phenomena within colloid solutions. In these studies, the microcavity arrays serve as containers for confinement of the colloid. X-ray diffraction measurements on empty gratings enable the characterization of the container shape, and the same method can be used to detect ordering phenomena in colloid-filled gratings. Simulations assuming a periodic density profile in the grating gaps show that a clear change in the scattered X-ray intensity can be expected