Coherent x-rays produced by synchrotrons have provided an invaluable tool for studying the static and dynamical structural properties of matter on the macroscopic scale. There is now a desire, in both biological and condensed-matter systems, to shift toward the probing of microscopic samples on the nanoscale. Although hard (short-wave-length) x-rays can be focused to approximately 100-nm spot sizes using reflection, refraction, or diffraction techniques, it is reflection from a high-quality surface that is expected to hone the focus down to the 20-nm level and thereby provide the capability of a true nanometer-scale structural probe. Using a combination of surface machining and surface interferometry, Mimura et al. have designed a platinum-coated, silicon-based elliptical mirror with a surface roughness better than 2 nm from peak to valley. After fabricating the mirror to match the optical requirements of their 1-km-long beamline, they demonstrate focusing of 15-keV hard x-rays to a beam width of ∼25 nm. By combining two such mirrors in orthogonal planes, they expect the x-rays to be focused to a spot size of ∼30 nm. — ISO
Appl. Phys. Lett. 90, 051903 (2007).