SEM Topography Source

In Scanning Electron Microscope (SEM) imaging, the topography of a sample's surface is primarily determined by detecting secondary electrons (SE). These low-energy electrons are emitted from the very near-surface region of the sample when interacted with the primary electron beam. Differences in the number of SE collected from different surface locations directly correlate to the surface's height variations, providing detailed topographical contrast.

SEM Atomic Contrast Source

Atomic contrast in SEM, also known as Z-contrast, depends on the atomic number of the elements within the sample. This contrast is mainly obtained from back-scattered electrons (BSE). BSEs are high-energy electrons from the primary beam that are reflected (scattered) back out of the sample due to elastic collisions with atomic nuclei. Regions with higher atomic number elements scatter more electrons, appearing brighter in BSE images, thus providing atomic contrast.

Electron Signal Summary

• Topography: Primarily sourced from Secondary Electrons (SE).
• Atomic Contrast: Primarily sourced from Back-scattered Electrons (BSE).
• Auger Electrons are typically used for elemental composition analysis, not primary topographical or atomic contrast imaging in standard SEM.

Therefore, information about topography and atomic contrast in a typical SEM image is obtained from secondary electrons and back-scattered electrons, respectively.