INFLUENCE OF ROUGHNESS AND INTERDIFFUSION IN ZONE-PLATE STRUCTURES ONTHE DIFFRACTION EFFICIENCY DESCRIBED BY COUPLED-WAVE THEORY

Diffractive transmission x-ray optics, e.g., zone plates and gratings, are well suited for x-ray microscopy and spectroscopy. X-ray optics f or use at short wavelengths require high zone aspect ratios which can be obtained by alternately depositing two materials with different x-r ay scattering properties on a microwire. The roughness and the diffusi on inherent to this process influence the diffraction efficiency of th ese optics. Using coupled wave theory, it is shown that roughness and interdiffusion increase the structure height required for optimal diff raction efficiency compared to ideally smooth structure profiles. In a ddition, the maximum obtainable diffraction efficiency decreases with increasing root-mean-square roughness and interdiffusion. (C) 1998 Ame rican Institute of Physics.