title: Efficient focusing of 8 keV X-rays with multilayer Fresnel zone plates fabricated by atomic layer deposition and focused ion beam milling.
abstract: Fresnel zone plates (FZPs) recently showed significant improvement by focusing soft X-rays down to ~10 nm. In contrast to soft X-rays, generally a very high aspect ratio FZP is needed for efficient focusing of hard X-rays. Therefore, FZPs had limited success in the hard X-ray range owing to difficulties of manufacturing high-aspect-ratio zone plates using conventional techniques. Here, employing a method of fabrication based on atomic layer deposition (ALD) and focused ion beam (FIB) milling, FZPs with very high aspect ratios were prepared. Such multilayer FZPs with outermost zone widths of 10 and 35 nm and aspect ratios of up to 243 were tested for their focusing properties at 8 keV and shown to focus hard X-rays efficiently. This success was enabled by the outstanding layer quality thanks to ALD. Via the use of FIB for slicing the multilayer structures, desired aspect ratios could be obtained by precisely controlling the thickness. Experimental diffraction efficiencies of multilayer FZPs fabricated via this combination reached up to 15.58% at 8 keV. In addition, scanning transmission X-ray microscopy experiments at 1.5 keV were carried out using one of the multilayer FZPs and resolved a 60 nm feature size. Finally, the prospective of different material combinations with various outermost zone widths at 8 and 17 keV is discussed in the light of the coupled wave theory and the thin-grating approximation. Al2O3/Ir is outlined as a promising future material candidate for extremely high resolution with a theoretical efficiency of more than 20% for as small an outermost zone width as 10 nm at 17 keV.
authors.affiliation: Modern Magnetic Systems, Max Planck Institute for Intelligent Systems, Heisenbergstrasse 3, Stuttgart, Germany.
authors.forename: Marcel
authors.initials: M
authors.lastname: Mayer
authors.forename: Kahraman
authors.initials: K
authors.lastname: Keskinbora
authors.forename: Corinne
authors.initials: C
authors.lastname: Grévent
authors.forename: Adriana
authors.initials: A
authors.lastname: Szeghalmi
authors.forename: Mato
authors.initials: M
authors.lastname: Knez
authors.forename: Markus
authors.initials: M
authors.lastname: Weigand
authors.forename: Anatoly
authors.initials: A
authors.lastname: Snigirev
authors.forename: Irina
authors.initials: I
authors.lastname: Snigireva
authors.forename: Gisela
authors.initials: G
authors.lastname: Schütz
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D020450:Heavy Ions; D007909:Lenses; D011856:Radiographic Image Enhancement / Q000295:instrumentation*; D011859:Radiography / Q000295:instrumentation*; D012542:Scattering, Radiation; D014961:X-Ray Diffraction / Q000295:instrumentation*; D014965:X-Rays
keywords: ALD; FIB; Fresnel zone plate; hard X-ray; multilayer; sputtered-sliced