Secondary electron imaging in transmission electron microscopy: technique and application in nanocatalysis

The determination of the smallest structures and surface morphologies of nanoparticles using Transmission Electron Microscopy (TEM) is widely regarded as one of the most essential techniques for modern researchers. Despite its proven scientific effectiveness, TEM has certain limitations, the main one of which is that the analysis of nanoparticles or their agglomerates - in fact three-dimensional structures - results in two-dimensional images, which may not fully reflect their complex geometries. A promising solution to this problem lies in the integrated on modern TEM devices secondary electron (SE) detectors. These detectors, optimized for capturing low-energy secondary electrons, function similarly to those in Scanning Electron Microscopy. Complementing high-resolution TEM or STEM images, the SE detector provides three-dimensional images with a resolution close to or equal to atomic, while allowing avoidance of the labor-intensive and time-consuming processes associated with TEM-based 3D tomography, for example. With current advancements in detector technology, secondary electron imaging holds significant potential as a primary tool for investigating the morphology of a wide spectrum of nanomaterials, including nanoparticles and powders, paving the way for broader applications in nanoscience and materials research. In this review, we will briefly cover the features of the method and its main physical principles, and recent advances in its application in nanocatalysis with platinum group metals-based catalysts, where the application of this method could be revolutionary. The distribution of metal nanoparticles on the carbon or other support is a critical factor directly affecting the performance of these materials. And, as practice shows, traditional TEM often fails to provide comprehensive information on their morphology.