TEM vs SEM
Both SEM (scanning electron microscope/microscopy) and TEM (transmission electron microscope/microscopy) refer both to the instrument and the method used in electron microscopy.
There are a variety of similarities between the two. Both are types of electron microscopes and give the possibility of seeing, studying, and examining small, subatomic particles or compositions of a sample. Both also use electrons (specifically, electron beams), the negative charge of an atom. Also, both samples in use are required to be “stained” or mixed with a particular element in order to produce images. Images produced from these instruments are highly magnified and have a high resolution.
However, an SEM and TEM also share some differences. The method used in SEM is based on scattered electrons while TEM is based on transmitted electrons. The scattered electrons in SEM are classified as backscattered or secondary electrons. However, there is no other classification of electrons in TEM.
The scattered electrons in SEM produced the image of the sample after the microscope collects and counts the scattered electrons. In TEM, electrons are directly pointed toward the sample. The electrons that pass through the sample are the parts that are illuminated in the image.
The focus of analysis is also different. SEM focuses on the sample’s surface and its composition. On the other hand, TEM seeks to see what is inside or beyond the surface. SEM also shows the sample bit by bit while TEM shows the sample as a whole. SEM also provides a three-dimensional image while TEM delivers a two-dimensional picture.
In terms of magnification and resolution, TEM has an advantage compared to SEM. TEM has up to a 50 million magnification level while SEM only offers 2 million as a maximum level of magnification. The resolution of TEM is 0.5 angstroms while SEM has 0.4 nanometers. However, SEM images have a better depth of field compared to TEM produced images.
Another point of difference is the sample thickness, “staining,” and preparations. The sample in TEM is cut thinner in contrast to a SEM sample. In addition, an SEM sample is “stained” by an element that captures the scattered electrons.
In SEM, the sample is prepared on specialized aluminium stubs and placed on the bottom of the chamber of the instrument. The image of the sample is projected onto the CRT or television-like screen.
On the other hand, TEM requires the sample to be prepared in a TEM grid and placed in the middle of the specialized chamber of the microscope. The image is produced by the microscope via fluorescent screens.
Another feature of SEM is that the area where the sample is placed can be rotated in different angles.
TEM was developed earlier than SEM. TEM was invented by Max Knoll and Ernst Ruska in 1931. Meanwhile, SEM was created in 1942. It was developed at a later time due to the complexity of the machine’s scanning process.
Summary:
1.Both SEM and TEM are two types of electron microscopes and are tools to view and examine small samples. Both instruments use electrons or electron beams. The images produced in both tools are highly magnified and offer high resolution.
2.How each microscope works is very different from another. SEM scans the surface of the sample by releasing electrons and making the electrons bounce or scatter upon impact. The machine collects the scattered electrons and produces an image. The image is visualized on a television-like screen. On the other hand, TEM processes the sample by directing an electron beam through the sample. The result is seen using a fluorescent screen.
3.Images are also a point of difference between two tools. SEM images are three-dimensional and are accurate representations while TEM pictures are two-dimensional and might require a little bit of interpretation. In terms of resolution and magnification, TEM gains more advantages compared to SEM.