Wet-etched diffractive lenses for hard X-rays

A method for the fabrication of linear transmission Fresnel zone plates for X‐rays in the 8–15 keV photon energy range is presented. The diffractive elements are generated by electron‐beam lithography and chemical wet etching of 〈110〉‐oriented silicon membrane substrates. Diffractive structures with aspect ratios of more than 30 for 300 nm‐wide structures were obtained. The diffraction efficiency of such a lens was measured for 13.3 keV radiation to be 20%.