X-ray multilevel zone plate fabrication by means of electron-beam lithography: Toward high-efficiency performances

X-ray microscopy is a research area in which enormous progress has been made in the last years. The advent of third-generation synchrotons, together with the progress made in the fabrication of new optical devices, such as zone plate, are the two main factors that have influenced the interest around microscopy science. The article will treat the fabrication, by means, exclusively, of electron-beam lithography, of high-efficiency zone plates for x rays in the energy range of hard x rays. We were able to fabricate four-level zone plates made of gold and nickel, whose total thickness is 2.1 μm for gold, and 4.0 μm for nickel. The resolution, of the last level, is equal to 0.5 μm. These zone plates have experimental efficiency of about 38% in the case of gold, and 55% in the case of nickel, at the first diffraction order and at 7 keV x-ray energy. To our knowledge, the nickel zone plates have the highest efficiency ever obtained at x-ray wavelengths.