We demonstrate sub-100 nm resolution water-window soft X-ray full-field transmission microscopy with a compact system. The microscope operates at lambda = 3.37 nm and is based on a 100 Hz table-top regenerative debris-free droplet-target laser-plasma X-ray source in combination with normal-incidence multilayer condenser optics for sample illumination. High-spatial-resolution imaging is performed with a 7.3% efficiency nickel zone plate and a 1024 x 1024 pixel CCD detector. Images of dry test samples are recorded with exposure times of a few minutes and show features smaller than 60 nm.
High-resolution x-ray microscopy makes use of nanostructured diffractive optics such as Fresnel zone plates made of nickel. These micro zone plates are manufactured using microscopic galvanoforms and electrodeposition techniques. Copolymer galvanoforms for nickel micro zone plates were irradiated with high doses of x-ray radiation to increase the degree of cross-linking of the copolymer network; in this way, exact pattern replication in the galvanoform was obtained for zone aspect ratios of up to 8:1. Using these galvanoforms, nickel micro zone plates were produced for the soft x-ray wavelength λ=2.4 nm, with smallest zone widths of 30 nm and 40 nm, achieving first-order diffraction efficiencies of up to 13% and 20%, respectively.
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