High-resolution lenses for sub-100 nm x-ray fluorescence microscopy

We report on the design, fabrication, and testing of Fresnel zone plates for high-resolution x-ray fluorescence microscopy using the scanning x-ray microscope at the European Synchrotron Radiation Source. The germanium lenses were optimized for operation near the sulphur absorption edge at 2472 eV photon energy. The high measured diffraction efficiencies of up to 9.6% and the good match to the spatial coherence of the undulator beam resulted in a photon flux of about ${\text{4×10}}^8$ photons per second within the bandwidth of a silicon $\text{〈111〉}$ monochromator. Using a test object consisting of zinc sulphide nanostructures, we were able to image features in sulphur x-ray fluorescence mode with lateral dimensions down to below 100 nm.