Recent advances in the improvement of secondary electron image resolution to the subnanometer level demand further knowledge of the origin of secondary electron emission to interpret the experimental results. The generally accepted estimation of the non-localized range of the inelastic scattering of incident electrons and the subsequent generation of secondary electrons in a solid cannot explain the 0.7 nm resolution of secondary electron images obtained in a scanning transmission electron microscope operated at 100 kV. Resolution and contrast of secondary electron images are interrelated. High contrast as well as high resolution can be obtained at the same time. Contrast mechanisms are also complicated due to the origin of the generation of secondary electrons by incident electrons or by other energetic secondary electrons. Surface adsorption and thin layer contamination will change the collected secondary electron signal dramatically which makes the image interpretation difficult. Surface defects might give observable secondary electron image contrast due to the change of total secondary electron yield caused by the defects or by the adsorbed species at the defect. Ultra-high resolution secondary electron imaging provides important information in the study of surface reactions and related surface problems in a scanning transmission electron microscopy instrument.
Liu, J. and Cowley, J. M.
"Contrast and Resolution of Secondary Electron Images in a Scanning Transmission Electron Microscope,"
Scanning Microscopy: Vol. 2
, Article 12.
Available at: https://digitalcommons.usu.edu/microscopy/vol2/iss4/12