Dynamical diffraction effects in STEM orbital angular momentum resolved electron energy-loss magnetic chiral dichroism

Abstract

In this paper, we explore the properties of dynamical diffraction coefficients in orbital angular momentum resolved electron energy-loss magnetic chiral dichroism spectra, in a scanning transmission electron microscopy setup. We demonstrate that for basic zone axis geometries with fourfold or threefold symmetry the coefficients are constrained to have simplified forms. By exploiting these properties, we show how a dichroism spectrum accessible using this technique is only weakly dependent on sample thickness and, more generally, on dynamical diffraction effects. Our results indicate that in such cases it is possible to determine the orbital and spin components of atomic magnetic moments approximately from experimental spectra without the need for additional dynamical diffraction calculations.

Theoretical and practical aspects of the design and production of synthetic holograms for transmission electron microscopy

“…It is possible to measure the full OAM spectrum of a beam in one acquisition. Applications include measurements of the magnetic moments of dipoles, 80 as well as in EMCD 81,82 and plasmon characterization. 83 S-CGH fabrication requires a knowledge of the functions that are to be encoded in the unwrapper S-CGH (Λ 1 ) and corrector S-CGH (Λ 2 ).…”

Alignment of electron optical beam shaping elements using a convolutional neural network

“…The main effect of this aberration is broadening of the beam in the radial direction (P r ), which depends on the sign of the defocus. The OAM resolution is preserved instead, meaning that a moderate amount of defocus f can be tolerated if only the OAM component is of interest [42,43,44,45,46]. A more prominent source of resolution loss is the size mismatch (SM) between the beam and element S2 (Fig.…”

First demonstration of angular-momentum-resolved electron energy-loss spectroscopy

“…The simultaneous analysis of electron energy-loss and OAM dispersion of inelastically scattered electrons, denoted OAM-EELS, has been predicted to enable innovative experiments in different scientific fields, encompassing plasmonic systems [23], biomolecular systems [24] and magnetic materials [25,26]. Here, we present the experimental realization of a combined OAM-EELS measurement by placing an OAM sorter in the post-specimen section of a TEM.…”