Titan themis 300

TEM images were taken using a FEI Tecnai T12 Spirit microscope operated at an acceleration voltage of 120 kV. FFT analysis was performed using ImageJ software. Each TEM sample was prepared after CTAB removal by evaporating 10 µL of suspension on TEM grid in dry air. Cryo-TEM images were collected under low-dose conditions using a customized FEI Titan Themis 300 operating at 300 kV equipped with a cryo-box and FEI Ceta 16 M camera. More details can be found in the Supplementary Methods.
SAXS patterns were obtained at the G1 station at the Cornell High Energy Synchrotron Source (CHESS) using a 10 keV beam and a sample-to-detector distance of 40 cm. All samples were powders prepared by vacuum drying MSN suspensions after CTAB removal and were imaged soon after drying.
Nitrogen sorption measurements were performed using a Micromeritics ASAP2020 instrument. For each measurement, approximately 10 mg of freshly vacuum-dried powder sample was degassed at room temperature under vacuum overnight prior to the analysis.

In-situ 4D-STEM was performed on FEI Titan Themis 300 (80 keV, 0.55 mrad convergence semi-angle) with electron microscope pixel array detector (EMPAD) and DENS Wildfire heating holder. For 4D-STEM, a convergent beam electron diffraction (CBED) pattern was recorded at each beam position using the EMPAD detector. EMPAD’s high dynamic range (1,000,000:1) and single electron sensitivity^{39 (link)} allows simultaneous recording of intense Bragg beams alongside weak superlattice reflections. Virtual satellite dark field images were formed by integrating intensities from all satellite peaks at each scan position.
In-situ TEM revealed layer-by-layer polytypic transition. The polytype difference is indiscernible in low-magnification with HAADF-STEM, as two polytypes have equal density. However, the change in bond coordination at polytype boundaries provide visible coherent contrast in TEM. The in-situ movie and SAED patterns were taken with JEOL 2010F (operated at 200 keV) with Gatan Heater Holder and Gatan OneView Camera.
Cross-sectional HAADF-STEM images were taken on JEOL 3100R05 (300 keV, 22 mrad) with samples prepared on FEI Nova Nanolab DualBeam FIB/SEM.

For the structural characterization, X-ray diffraction (XRD) was performed on a D/max2500pc diffractometer with a Cu Kα radiation. X-ray photoelectron spectroscopy (XPS) detection was through an ESCALAB 250Xi spectrometer with a monochromatic Al-K source. The morphology characterization was conducted using a JEM-2100F transmission electron microscope (TEM) for TEM images, high-resolution TEM (HRTEM) images and selected area electron diffraction (SAED) patterns. The high angle annular dark field (HAADF) images were obtained through a double-corrected FEI Titan Themis 300 electron microscope. The component analysis was confirmed using an inductively coupled plasma optical emission spectroscopy (ICP-OES).