What is SEM? How does it work? Major application and impact of acceleration voltages? difference with TEM

  

Introduction: 

SEM stands for Scanning Electron Microscopy, which is a type of electron microscopy used to obtain high-resolution images of materials and biological specimens at the nanoscale.

The basic working principle of SEM involves the use of a beam of high-energy electrons that are focused onto a sample using electromagnetic lenses. The electrons interact with the sample, causing the emission of secondary electrons and backscattered electrons, which are detected and used to generate an image of the surface of the sample. SEM images can provide high-resolution details about surface topography, morphology, and elemental composition. Its function of it is in Figure 1.

Figure 1: SEM working arrangement.

One of the major applications of SEM is in materials science, where it is used to study the microstructure of materials and to characterize their properties. SEM is also widely used in the biological sciences to study the structure and function of cells and tissues.

The acceleration voltage is an important parameter in SEM, as it affects the interaction between the electron beam and the sample. Increasing the acceleration voltage can result in higher-resolution images, as higher-energy electrons can penetrate deeper into the sample and generate more secondary and backscattered electrons. However, higher acceleration voltages can also cause damage to the sample and may affect the results of the imaging. The choice of acceleration voltage, therefore, depends on the nature of the sample and the specific application.

In addition to imaging, SEM can also be used for various other analytical techniques, such as energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD), which can provide information about the elemental composition and crystallographic structure of the sample. The impact of acceleration voltage can also affect the performance of these analytical techniques.

 

What is TEM? What are the differences between SEM and TEM? How does sample preparation important?

TEM stands for Transmission Electron Microscopy, which is a type of electron microscopy used to obtain high-resolution images of the internal structure of materials and biological specimens at the nanoscale.

The basic working principle of TEM involves the transmission of a beam of high-energy electrons through a thin sample, which interacts with the sample, causing the electrons to scatter and diffract. The scattered electrons are then detected and used to generate an image of the internal structure of the sample. TEM images can provide detailed information about the crystal structure, morphology, and defects of materials and biological specimens.

The main difference between SEM and TEM is that SEM provides images of the surface of the sample, while TEM provides images of the internal structure of the sample. Another key difference is that SEM uses backscattered and secondary electrons to generate the image, while TEM uses transmitted electrons.

Sample preparation is extremely important in TEM, as the sample must be thin enough to allow the electrons to transmit through it. This typically involves cutting the sample into thin sections using a microtome, and then mounting the sections onto a thin support grid made of materials such as carbon or copper. The thickness of the sample section can vary depending on the application but is typically in the range of 50-200 nm.

In addition to thinning the sample, sample preparation for TEM can also involve additional steps such as staining, which is used to enhance the contrast between different components of the sample, and cryogenic freezing, which is used to preserve the sample in a near-native state.

Overall, both SEM and TEM are powerful tools for investigating the structure and properties of materials and biological specimens at the nanoscale, and the choice of which technique to use depends on the specific application and the type of information needed. However, sample preparation is crucial for obtaining high-quality images and accurate results in both techniques. Find more information here.