Affiliation:
1. Institute of Applied Physics, Eberhard Karls University of Tuebingen 1 , Auf der Morgenstelle 10, D-72076 Tuebingen, Germany
2. NMI Natural and Medical Sciences Institute at the University of Tuebingen 2 , Markwiesenstr. 55, D-72770 Reutlingen, Germany
Abstract
The generation of small electron probes is the basis for various techniques in which such a probe is scanned across a sample, and special probe shapes like vortices can be desirable, e.g., to gain insight into magnetic properties. Micron-scale phase plates or holographic masks, in combination with demagnifying optics, are usually used for creating such special probe wave functions. Here, we present the fabrication of nanometer-sized phase plates based on thickness-selected and stacked graphite layers as well as an analysis of their performance. First, a spiral phase plate is demonstrated that creates a vortex beam with an orbital angular momentum of 1 and an outer radius of 2.5 nm. Second, a three-level Fresnel lens built from two nanopatterned graphite membranes is presented, which achieves a focal spot with a full width at half maximum of 5.5 nm. Third, an array of electron sieves is demonstrated, each of which creates a focal spot with a radius of 2 nm, and the array is applied as a Shack–Hartmann wavefront detector. These elements allow the generation of few-nanometer sized focused probes or vortices without the need for additional optical elements.
Funder
Deutsche Forschungsgemeinschaft
Ministerium für Wissenschaft, Forschung und Kunst Baden-Württemberg
European Union