High-efficiency multilevel zone plates for keV X-rays

The development of high brilliance X-ray sources coupled with advances in m anufacturing technologies has led to significant improvements in submicrome tre probes for spectroscopy, diffraction and imaging applications. The gene ration of a small beam spot size is commonly based on three principles(1) t otal reflection las used in optical elements involving mirrors or capillari es), refraction (such as in refractive lenses(2)) and diffraction. The latt er effect is employed in Bragg-Fresnel or Soret lenses, commonly known as F resnel zone plate lenses. These lenses currently give the best spatial reso lution, but are traditionally limited to rather soft X-rays-at high energie s, their use is still limited by their efficiency. Here we report the fabri cation of high-efficiency, high-contrast gold and nickel multistep (quatern ary) Fresnel zone plates using electron beam lithography. We achieve a maxi mum efficiency of 55% for the nickel plate at 7 keV. In addition to their h igh efficiency, the lenses offer the advantages of low background signal an d effective reduction of unwanted diffraction orders. We anticipate that th ese lenses should have a significant impact on techniques such as microscop y(3), micro-fluorescence(4) and micro-diffraction(5), which require medium resolution (500-100 nm) and high flux at fixed energies.