Peels 666 spectrometer

STEM imaging was performed using a Nion UltraSTEM100 operated at a 60 kV accelerating voltage in UHV (~10⁻⁹ mbar). The collection angles of the high-angle annular dark-field (HAADF) and medium-angle annular dark-field (MAADF) detectors were 80–300 mrad and 60–80 mrad, respectively. The probe convergence angle was 30 mrad. A Gatan PEELS 666 spectrometer, retrofitted with an Andor iXon 897 electron-multiplying charge-coupled device camera, was used for the EELS experiments^{55 (link)}. During measurements, the energy dispersion, the beam current and the EELS collection semi-angle were 1 eV per channel, 30 pA, and 35 mrad, respectively. The direct transfer of samples without ambient exposure was enabled using a STEM with a customized sample loading and transfer system^{41 (link),42 (link),56 (link)}.

High angle annular dark-field (HAADF) and EELS spectrum imaging were performed on a Nion UltraSTEM 100 operated at 100 kV with a 30 mrad convergence semi-angle and a fifth-order aberration corrector. Spectra were acquired with a Gatan PEELS 666 spectrometer retrofitted with an Andor iXon 897 electron-multiplying charge-coupled device (EMCCD) camera. A dispersion of 1.2 eV per channel and an exposure time of 50 ms per spectra were used to record the oxygen K-edge, Mn and Ni L_2,3 edges and La M_4,5 edge in a 32 by 128 pixel spatial grid.