Fig. 1. Comparison of half-period zone structure between (a) the normal PZPs and (b) the PNPZPs.

Fig. 2. Schematic diagram of PNPZPs. On the left are two different material ZPs; putting them together we have PNPZPs (right), each material being the negative phase shift material that is acceptable at the working energy.

Fig. 3. Energy dependence of the refractive-index contributions to some metals.

Fig. 4. Height of zone dependence of the first-order diffraction efficiency of the Ni PZPs at 511.9 eV.

Fig. 5. First-order diffraction efficiency as a function of the heights of the two metals at 511.9 eV.

Fig. 6. Theoretical first-order efficiency of ZPs as a function of the zone height at a working energy of 511.9 eV.