Powder XRD of all as-prepared samples was performed on a Philips X’pert Multi-Purpose Diffractometer (MPD) (PANAlytical) equipped with Cu Kα radiation operating at 50 kV and 40 mA within the 2θ range from 5° to 75°. SEM imaging was conducted on the FEI Helios NanoLab 600i dual-beam focused ion beam precision manufacturing instrument operating at 5 kV. Before SEM imaging, a thin carbon layer (about 5 nm) was deposited on the particle surface by using a carbon coater (208C; Ted Pella, Inc.) to improve the electronic conductivity of the samples.
The sample water suspensions were dusted on the holey carbon-coated copper grids (Lacey Carbon, 300 mesh; Ted Pella, Inc.) for subsequent microanalysis. The TEM investigation was performed in the FEI Titan 80-300 Environmental TEM microscope with an objective lens corrector and the FEI Titan 80-300 S/TEM microscope at 300 kV. The S/TEM microscope was equipped with a probe spherical aberration corrector that enabled subangstrom imaging using STEM-HAADF detectors and a Bruker energy dispersive X-ray spectrometer for element analysis. For STEM-HAADF imaging, the inner and outer collection angles of the annular dark-field detector were set at 55 and 220 mrad, respectively. The STEM-HAADF images for 3D tomography were collected every 2° from −70° to +70°. The 3D reconstruction was performed using TomViz.
The sample water suspensions were dusted on the holey carbon-coated copper grids (Lacey Carbon, 300 mesh; Ted Pella, Inc.) for subsequent microanalysis. The TEM investigation was performed in the FEI Titan 80-300 Environmental TEM microscope with an objective lens corrector and the FEI Titan 80-300 S/TEM microscope at 300 kV. The S/TEM microscope was equipped with a probe spherical aberration corrector that enabled subangstrom imaging using STEM-HAADF detectors and a Bruker energy dispersive X-ray spectrometer for element analysis. For STEM-HAADF imaging, the inner and outer collection angles of the annular dark-field detector were set at 55 and 220 mrad, respectively. The STEM-HAADF images for 3D tomography were collected every 2° from −70° to +70°. The 3D reconstruction was performed using TomViz.