A new way of producing electron vortex probes for STEM

摘要

A spiral holographic aperture is used in the condensor plane of a scanningtransmission electron microscope to produce a focussed electron vortex probecarrying a topological charge of either $-1,0$ or $+1$. The spiral aperturedesign has a major advantage over the previously used forked aperture in thatthe three beams with topological charge $m=-1,0,1$ are not side by side in thespecimen plane, but rather on top of each other, focussed at different height.This allows us to have only one selected beam in focus on the sample while theothers contribute only to a background signal. In this paper we describe theworking principle as well as first experimental results demonstrating atomicresolution HAADF STEM images obtained with electron vortex probes. Theseresults pave the way for atomic resolution magnetic information when combinedwith electron energy loss spectroscopy.