How Does SEM Compute Sample Structure?

[Dario56]

In SEM, secondary electrons are emitted from the surface of the sample computing surface structure when they reach detector while backscattered electrons give information about structure and chemical composition of internal parts of the sample.

However, what I don't understand is what does emission of secondary electrons and backscattered electrons have to do with structure? I can't connect how does detector construct image of the sample based only on received electrons.

 

[Valerie Park]

The way that the scanning electron microscope (SEM) works is by using electrons to scan the surface of a sample. The primary electrons emitted from the electron gun interact with the surface of the sample, causing secondary electrons and backscattered electrons to be emitted. These secondary and backscattered electrons are detected by the detector. The detector then creates an image of the sample based on the intensity of the electrons it receives. The image created shows not only the topography of the sample but also the chemical composition of its different parts. The combination of these two types of data provides a detailed view of the structure and composition of the sample.