Z contrast of platinum and palladium catalysts

Abstract The usefulness of Crewe's Z-contrast technique for the study of small catalyst particles in the scanning transmission electron microscope is investigated and discussed. By forming suitable combinations of the annular dark-field and energy-loss signals, structural details in platinum particles as small as 2 nm may be imaged, and clusters of image size approaching the probe dimensions (0·5 nm), not visible in the bright-field images, may be detected. In the case of crystalline supports, about 10% of the particles are obscured by strong diffraction contrast in the substrate, although it is found that contrast variations arising from thickness variations in the substrate are suppressed in the energy-loss signal. Particle sizes in the various signals employed are compared.