Performance Test of Fresnel Zone Plate with 50 nm Outermost Zone Width in Hard X-ray Region

A microfocusing experiment for hard X-rays has been performed to evaluate the performance of Fresnel zone plate optics. A tantalum Fresnel zone plate with an outermost zone width of 50 nm and a thickness of 0.5 µm has been fabricated by electron-beam lithography. The focused beam size measured by a knife-edge scan is 58 nm in full-width at half-maximum for the first-order diffraction at an X-ray energy of 8 keV. It can be concluded that this zone plate has nearly diffraction-limited resolution in the hard X-ray region. The measured diffraction efficiency is 5% at 8 keV. The spot size using the third-order focus of the zone plate is measured to be approximately 30 nm.