Ultra-high resolution zone-doubled diffractive X-ray optics for the multi-keV regime

X-ray microscopy based on Fresnel zone plates is a powerful technique for sub-100 nm resolution imaging of biological and inorganic materials. Here, we report on the modeling, fabrication and characterization of zone-doubled Fresnel zone plates for the multi-keV regime (4-12 keV). We demonstrate unprecedented spatial resolution by resolving 15 nm lines and spaces in scanning transmission X-ray microscopy, and focusing diffraction efficiencies of 7.5% at 6.2 keV photon energy. These developments represent a significant step towards 10 nm spatial resolution for hard X-ray energies of up to 12 keV.