Scanning electron microscope (SEM) is an analytical instrument that uses focused electron beam to scan the surface of the sample, and obtains the surface morphology and composition information of the sample by exciting and collecting secondary electrons, characteristic X-ray and other signals. In the process of SEM imaging, accelerating voltage is a key parameter, which has an important influence on the imaging effect. In this paper, the effect of accelerating voltage on SEM imaging will be discussed in detail to help researchers optimize experimental conditions and improve imaging quality.

I. Effect of accelerating voltage on the range of influence of incident electrons

the higher the acceleration voltage, the greater the energy of the incident electron, and the greater its penetration and scattering range in the sample. This results in an expansion of the range over which secondary electrons can be generated from the point of incidence to hundreds of nanometers. Therefore, when observing a thicker sample or acquiring information in a larger range, Appropriately increasing the acceleration voltage helps to improve the imaging quality.

Second, the effect of accelerating voltage on the resolution of sample surface details.

With the increase of the acceleration voltage, the scattering range of the incident electrons increases, which makes the secondary electron region expand and the resolution of the sample surface details decreases. Therefore, in the pursuit of nanoscale surface detail resolution, the choice of low voltage is more appropriate. For example, the attachment of carbon nanotubes to the particle surface is more pronounced at 1kV than at 5kV.

Effects of Accelerating Voltage on Radiation Damage

some samples are susceptible to radiation damage, such as organic polymers, metal-organic frameworks, biological tissues, etc. The higher the accelerating voltage, the higher the carrying energy, the bombardment damage and thermal damage will increase. Therefore, for samples susceptible to radiation damage, lower voltages are recommended. For example, at an accelerating voltage of 1kV, the surface of the PMMA sphere is rounded and plump, while at 2kV the sphere appears a contracted depression.

Fourth, the effect of accelerating voltage on the charge of non-conductive samples.

In order to avoid the effect of charging on the imaging effect of non-conductive samples, a conductive film with a thickness of several nanometers is usually sputtered on the surface. However, for some samples, this method has limited effect. When the acceleration voltage is low, the number of electronic input and escape is relatively balanced, and the imaging brightness is more uniform. When the acceleration voltage is higher, the charging phenomenon is more obvious, which leads to the imbalance of imaging brightness or stripes.

Fifth, the effect of accelerating voltage on the signal-to-noise ratio of imaging.

The higher the accelerating voltage, the higher the energy carried by the incident electrons, the more secondary electrons produced by bombarding the sample, the stronger the signal, and the signal-to-noise ratio is improved. Therefore, when observing larger particles in the micron level and not pursuing surface details, increasing the acceleration voltage is beneficial to improve the signal-to-noise ratio and obtain a clearer imaging effect.

VI. Conclusions

accelerating voltage is one of the key parameters affecting the imaging of scanning electron microscope. By adjusting the acceleration voltage, the imaging effect can be optimized to a certain extent. In practical applications, researchers should reasonably select the accelerating voltage according to the sample characteristics, required resolution and signal-to-noise ratio, in order to obtain high-quality SEM imaging results.

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