What is the charging effect?

Scanning electron microscopy is mainly used for observing the microstructure of sample surfaces. However, during the observation of samples, the image often becomes abnormally bright, distorted, and even blurred due to the charge effect, which seriously affects the imaging quality.

Figure 1 Electron emission characteristic curve of solid insulation material. The horizontal axis represents the energy of incident electrons, and the vertical axis represents the electron yield of the sample. The phenomenon of charging can be expressed by Kirchhoff's current law, which states that the sum of currents flowing towards a node at any given moment is equal to the sum of currents flowing out of the node. The following formula can be used to express:

Among them, I_pIt is the current of the incident electrons, δI_bIt is the sum of the currents of backscattered electrons and secondary electrons, I_scIt is the grounding current of the sample, and Q is the discharge charge within time t.