![]() ![]() In STEM mode, the beam is finely focused and scans the sample area (as SEM does), while the image is generated by the transmitted electrons (like in TEM). Most modern TEMs can be switched to “STEM mode”, and the user only needs to alter their alignment procedure. It can be applied to both systems, but its full capabilities are revealed when applied to a TEM tool. There is one more electron microscopy technique to mention, which is a combination of TEM and SEM, namely scanning transmission electron microscopy (STEM). ![]() Dedicated grids and holders are used to mount the TEM samples. Many methods have been developed, including electropolishing, mechanical polishing, and focused ion beam milling. The samples need to be very thin, as flat as possible, and the preparation technique should not introduce any artifacts (such as precipitates or amorphization) to the sample. In contrast, TEM sample preparation is a quite complex and tedious procedure that only trained and experienced users can follow successfully. SEM samples require little or no effort for sample preparation and can be directly imaged by mounting them on an aluminum stub. This reveals one more major difference between the two techniques: sample preparation. SEMs provide a 3D image of the surface of the sample, whereas TEM images are 2D projections of the sample, which in some cases makes the interpretation of the results more difficult for the operator.ĭue to the requirement for transmitted electrons, TEM samples must be very thin (generally less than 150 nm) and in cases that high-resolution imaging is required, even below 30 nm, whereas for SEM imaging, there is no such specific requirement. On the other hand, if you would like to know what the crystal structure of your sample is, or if you want to look for possible structural defects or impurities, then using a TEM is the only way to do so. For example, if you want to get information on the surface of your sample, like roughness or contamination detection, then you should choose a SEM. This all depends on what type of analysis you want to perform. Which electron microscopy technique is best for your analysis? SEM resolution is limited to ~0.5 nm, while with the recent development in aberration-corrected TEMs, images with spatial resolution of even less than 50 pm have been reported. Moreover, one of the most pronounced differences between the two methods is the optimal spatial resolution that they can achieve. As a result, TEM offers invaluable information on the inner structure of the sample, such as crystal structure, morphology, and stress state information, while SEM provides information on the sample’s surface and its composition. The transmission electron microscopy (TEM) principle, as the name suggests, is to use the transmitted electrons, the electrons that are passing through the sample before they are collected. SEMs use a specific set of coils to scan the beam in a raster-like pattern and collect the scattered electrons. A series of electromagnetic and electrostatic lenses to control the shape and trajectory of the electron beamĪll of these components are housed inside a chamber that is under high vacuum.For both techniques, electrons are used to acquire images of samples. Working principle of scanning electron microscopes and transmission electron microscopes The main difference between SEM and TEM is that SEM creates an image by detecting reflected or knocked-off electrons, while TEM uses transmitted electrons (electrons that are passing through the sample) to create an image. As a result, TEM offers valuable information on the inner structure of the sample, such as crystal structure, morphology and stress state information, while SEM provides information on the sample’s surface and its composition. Here, we briefly describe their similarities and differences. The two main types of electron microscopes are the transmission electron microscope (TEM) and the scanning electron microscope (SEM). Their versatility and extremely high spatial resolution render them a very valuable tool for many applications. Electron microscopes have emerged as a powerful tool for the characterization of a wide range of materials. ![]()
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