Metallic nanoparticles play an important role in heterogeneous catalysis; these nanoparticles are usually finely dispersed onto high-surface-area supports and act as active centers during a catalytic reaction. The performance of a supported metal catalyst is often directly related to the size and spatial distribution of the nanoparticles. Traditionally, TEM/STEM techniques have to be used to visualize highly dispersed nanoparticles. A major limitation of TEM/STEM techniques is, however, the stringent requirements of samples that can be examined: Useful information can be extracted from only very thin areas of a sample. The preparation of samples suitable for TEM/STEM observation can also pose a challenging problem for examining certain types of catalyst samples such as catalyst beads, pellets, powders, cylinders, or other forms that are often used in industrial applications. These and other limitations preclude the application of TEM/STEM techniques to extracting useful information about the surface or subsurface properties of thick or bulk catalyst samples.