A novel sample preparation method on CeO₂ nanoparticles with TEM grid embedded liquid CO₂ displacement and supercritical CO₂ drying for microscopic analysis

The structural information of nanomaterials obtained from the microscopy is essential to interpret the crystal morphology, growth, and reaction kinetics. Transmission electron microscopy (TEM) is one of the most popular tools for the characterization of nanomaterials. This study reveals that conventional preparation methods for the TEM analysis largely influence the morphology and size of the synthesized nanoparticles even when they are cautiously controlled. A rigorous image analysis on the TEM images in conjunction with the selected area electron diffraction analysis of the pherical aberration corrected TEM images substantiates that small non-faceted particles grow on the large faceted particles during the conventional sample preparation for microscopic analysis. This result shows that a proper sample preparation method must be used to observe the nanomaterial as synthesized. We propose a preparation method to preserve the morphology and size of the synthesized nanoparticles by TEM grid embedded liquid CO₂ displacement followed by supercritical drying.