ATOMIC IMAGING OF PARTICLE SURFACES.

Over the last twenty years, small metal particle specimens have been extensively studied by electron microscopy. The interest has been to characterize their chemical and structural nature, with the intention of understanding the nucleation and growth of small clusters as well as heterogeneous catalysis. In the process, numerous electron microscope imaging techniques have been used. However, these methods all suffer from one serious shortcoming - the resolution is relatively poor (approximately 10 A) and information about the catalytically interesting surface of the particle is not available. Following technical improvements to the Cambridge High Resolution Electron Microscope, the authors have recently resolved the atomic structure of surfaces on small particles and thin films. This has included direct observation of surface reconstruction effects due to elastic and plastic deformations at surfaces and surface steps and facetting. This paper describes the principle of the technique, reviews the results and considers their implications with respect to catalysis.