The continuing development of low-energy electron microscopy for characterizing surfaces

Instrumental aspects of low-energy electron microscopy are reviewed with a view toward the future evolution of this reemergent technology. Both elastically scattered and inelastically excited electrons in the 0–1000-eV range may be used to form direct rather than scanned images of surfaces in the 3–10-nm resolution range. Different instrumental setups may be used to form images that selectively contain information about the topography, crystalline structure, chemical composition, or magnetic orientation of the first few monolayers. Frequently, parallel imaging allows observation of dynamic processes occurring during observation. Key electron optical elements and their systemic relationships are described in the context of a still hypothetical generalized instrument that would allow complementary exploitation of many contrast modes. Image quality issues such as resolution, sensitivity, statistics, and contrast selectivity are considered with a view toward their optimization, in many cases by drawing ideas and technologies from other fields of microscopy.