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Nano fabrication of high efficiency stacked crystal zone plate for x-ray optics

The development of nanotechnology gives new possibilities for fabrication of high efficiency X-ray optical elements. The stacked multilevel crystal Zone Plate (ZP) is fabricated by means of high resolution negative tone inorganic HSQ (Hydrogen Silsesquioxane or XR-1541) electron-beam resist. About 80% of the HSQ resist became SiO2 after electron beam lithography. This is a simple method to fabricate ZPs with SiO2 masks. Stacked multilevel silicon ZPs consisting of bi-level zone profiles have been investigated. The composed multilevel ZP consists of two separate ZPs which have different structures. The distance between ZPs varied from 0mm up to 2mm. We recorded the maximal efficiency when the distance between ZPs varied from 0μm up to 150μm (about same efficiency). The efficiency of stacked multilevel crystal ZP has decreased when the distance between ZPs has varied from 0μm up to 2mm. The efficiency of the phase ZP is 40.5%. The maximum efficiency for bi-level ZP without absorption is 68.4%. We obtain theoretically 54.6% and experimentally 47% efficiency for the stacked bi-level ZP when the distance between ZPs was 0μm. The experimentally and theoretically investigations were done for x-ray energy at the 8 KeV and 12.4 KeV. The radial distribution of intensity is determined as a convolution of the zone plate transmission function and the Kirchhoff propagator in par-axial approximation. The algorithm is based on the FFT procedure and studied by means of computer programming simulation.