Nanofabrication of Zone Plates for X-Ray Microscopy

Abstract

High resolution electron beam lithography (EBL) has been developed to make zone plates on Si₃N₄ membranes. The highest resolution zone plates to date use gold as the absorber and have nominal outer zone widths as small as 30 nm for use in imaging x-ray microscopy. Their characteristics have been measured in collaboration with the Göttingen x-ray microscopy group at BESSY [1]; small features (≈ 30 nm) in test patterns were resolved. For scanning instruments both gold and nickel zone plates have been made; the latter show improved efficiency due to their phase shift and attenuation characteristics. Nickel zone plates for the water window with nominal outer zone widths as small as 40 nm have been made; an efficiency >10% at λ = 3.6 nm was measured at the SUNY/NSLS microscope. In addition, high efficiency (≈ 15% at 2.5 nm) zone plates for photoelectron microscopy have been made with 100 nm finest zone widths using 300 nm of electroplated nickel.