it has been theoretically argued that atomic-size electron probes with customized phase distributions can detect electron magnetic circular dichroism (EMCD) . Based on this prediction we have recently shown that deliberately aberrated electron probes in scanning transmission electron microscopy (STEM) can be utilized to obtain chiral dichroic signals in materials via electron energy-loss spectroscopy (EELS) with high spatial resolution .
The experiments were performed in an aberration-corrected Nion UltraSTEMTM 100, equipped with a cold field emission electron source and a corrector of third and fifth order aberrations, operating at an accelerating voltage of 100kV . EEL spectra were collected using a Gatan Enfina spectrometer, with 0.3 eV/channel dispersion, giving an energy resolution of 0.9 eV. The convergence semi-angle for the incident probe and the EELS collection semi-angle were 30 mrad and 48 mrad, respectively.
Figure 1 shows two examples of drift (affine)-corrected Z-contrast images and denoised EEL spectra that were acquired simultaneously from the room temperature C-type antiferromagnet LaMnAsO. The data were acquired with the beam along the c-axis using a corrected electron probe (Fig. 1a to 1c) and the C34 = 15 μm aberrated probe (Figs. 1d to 1f) .
A clear EMCD signature in the EEL spectra, defined as (Mn↑ – Mn↓) presenting a change of sign in its integrated intensity between the L3 and L2 peaks, is only visible for the Mn L-edge acquired using the C34 aberrated probe. In Figs. 1e and 1f, this signal, shown in green, is positive at the L3 peak and negative at the L2 peak. For comparison, the Mn signal in 1b and 1c, shown in grey, does not display this distinctive signature, with both positive and negative components on both peaks.
We will discuss the experimental conditions necessary to reveal the magnetic ordering of individual atomic columns and atomic-size defects in materials .
 J. Rusz, J. C. Idrobo, and S. Bhowmick, Phys. Rev. Lett. 113, (2014) p. 145501.
 J.C. Idrobo et al., submitted (2016).
 O. L. Krivanek, et al.,Ultramicroscopy 108, (2008). p. 179-195.
 Research supported by Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy (DOE), Office of Science User Facility (JCI), by the Swedish Research Council and Swedish National Infrastructure for Computing (NSC center) (JR), and by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. DOE (MAM, CC, ARL), and by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy (CTS, RRV).
To cite this abstract:Juan Carlos Idrobo, Ján Rusz, Jakob Spiegelberg, Michael A. McGuire, Christopher T. Symons, Ranga Raju Vatsavai, Claudia Cantoni, Andrew R Lupini; Novel spectroscopy with atomic-size aberrated electron probes in stem. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/novel-spectroscopy-with-atomic-size-aberrated-electron-probes-in-stem/. Accessed: September 18, 2020
EMC Abstracts - https://emc-proceedings.com/abstract/novel-spectroscopy-with-atomic-size-aberrated-electron-probes-in-stem/