Fabrication of tungsten Fresnel zone plates for hard x-rays using wet etching

A novel and scalable method to fabricate tungsten Fresnel zone plate (FZP) structures with a high aspect ratio using the wet etching method is presented. FZPs with an outermost zone width of 370 nm and a height of 1.1 μm were fabricated in tungsten on a 35 μm polyimide film. They were designed for a focal length of 50 cm at 8 keV such that the radius is 100 μm for 142 zones, with an opaque center zone. The fabrication method presented is a simple single step resist process. The testing of FZP was carried out at the Indus-2 synchrotron source, where focusing was observed as per design parameters. The transmission characteristics of polyimide coupled with the phase shifting properties of tungsten make the FZP useful also at lower energies. An improvement in the zone plate structural parameters and hence its performance has also been discussed.

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