4 Prakt. Met. Sonderband 47 (2015) 
[1,2]. The efficiency of the optical element for a given photon energy depends on the length of the 
zones along the optical axis whereas the resolution is limited by the width of the outermost zone. 
Using FZP, which consists of concentric rings of different widths (see Fig. 1), spatial resolutions Le 
down to several 10 nm are achievable. 
Zone Plate 
dan Focus ’ 
Mi 
ZZ % 
A Rn 
Fig. 1: Scheme of a Fresnel zone plate. 
Since the resolution of the state-of-the-art FZP is limited by the structural width of the outermost 
ring and since the manufacturing using a patterning process based on electron beam lithography and 
subsequent etching is technologically limited to several 10 nm thickness, it is expected that ap- if 
proaches like zone plate stacking will push the limits only slightly further. Multilayer Laue lenses Ea 
(MLL) are an emerging approach for new X-ray optics which are cut out of a multi-layer stack, iL 
manufactured by thin film deposition [3,4]. The thicknesses of those layers follow the zone plate 
law, and layer thicknesses down to 1 nm can be produced with high quality. Such a lens provides 
one-dimensional focusing of X-rays in case of parallel beam illumination. Hence, two crossed MLL 
have to be assembled for two-dimensional focusing or imaging (see Fig. 2) [5-8]. 
MLL-h 
MLL-v 
— Substrate 2) Coed 
b) 
Fig. 2: (a) MLL focusing of X-rays. (b) Crossed MLL after FIB preparation and assembly acting as a lens to image the 
object (OB) to the screen (SC) [6]. 
SC 
£30