Zone plates for x-ray microscopy at 300-Å resolution

Abstract

Zone plates with outermost zone width ≥300 Å have been fabricated by high-resolution E-beam writing in carbon contamination resist. The replication of a range of such zone plates into gold has been successful. The zone plates have been tested in scanning x-ray microscopes using synchrotron radiation at both Brookhaven and Daresbury, U.K. The latter microscope is a new development with a scanning stage having a fine step size of 100 Å. The design and performance of the new scanning microscope are discussed, as are the practical problems of zone plate fabrication and scanning x-ray microscopy as the point-to-point resolution improves. The further development of soft x-ray imaging is considerably aided by theoretical considerations of the optical properties of diffracting elements incorporating the 3-D structure, i.e., including the effect of the zone plate thickness. An integral formulation we have developed for this thick slit problem makes use of the circular zone-plate symmetry and also provides a possible route toward the solution of the inverse problem in zone plate design.