DyScO3 Sample Preparation¶

Cross-sectional TEM specimens were prepared on the DyScO3 substrate, using a Thermo Fisher Helios G4 UX focused ion beam with a Ga+ ion beam of 30 and 5 keV, and followed by a final milling step of 2 keV to reduce damage. To protect the surface from ion beam damage, we deposited carbon and platinum layers before milling. The specimen thickness was ~15 nm estimated by convergent beam electron diffraction analysis.

DyScO3 Electron Microscopy Acquisition¶

STEM X-EDS mapping was acquired with a Thermo Fisher Scientific Spectra 200 operated at 200 kV equipped with Dual-X X-EDS detectors with a collection solid angle of 1.76 sr. The STEM X-EDS maps were acquired with a probe current of 120 pA and a semi-convergence angle of 25 mrad, continuously raster-scanned with drift correction with a dwell time of 5 μs and over a total acquisition time of ~30 minutes. The elemental maps were first obtained by fitting the peak intensities above the background with the Cliff-Lorimer method.

Core-Shell Co₃O₄-Mn₃O₄ Sample Preparation¶

An organic/aqueous suspension was prepared by adding 0.080 g of Co₃O₄ nanocubes into a mixture of oleylamine (5 mmol), oleic acid (0.5 mmol), formic acid (3.15 mmol, Aldrich), and 15 mL of xylenes (Aldrich). The as-prepared suspension was heated to 40 °C under air and aged for 3 h with magnetic stirring. And then, 0.7 mL of 0.7 M aqueous solution of manganese (II) chloride tetrahydrate was rapidly injected into the suspension at 90 °C and aged for 1.5 h under air. After the reaction, the nanocrystals were washed with hexane/ethanol and retrieved by centrifugation. The final product was prepared with three iterations of this process.

Core-Shell Co₃O₄-Mn₃O₄ Electron Microscopy Acquisition¶

Simultaneously acquired HAADF and EELS tilt series for the Co₃O₄-Mn₃O₄ specimen were collected on a double aberration-corrected modified FEI Titan 80–300 microscope (the TEAM I instrument at the National Center for Electron Microscopy within Lawrence Berkeley National Laboratory) operated at 300 keV with a probe current of 115 pA and semi-angle of roughly 10 mrad. This microscope is equipped with a Gatan K3 detector and Continuum spectrometer. The simultaneously acquired HAADF and EELS spectrums were acquired with a dwell time of 0.677 ms receiving a total electron dose of $8.37 \times e/\AA^2$ ($1.16 \times e/\AA^2$, $7.21 \times e/\AA^2$ for the HAADF and EELS modalities, respectively).