What is electron microscope?
An electron microscope is used to examine objects that are smaller than about 0.2 µm, like viruses or the insides of cells. Instead of light, electrons are used in electron microscopy. Free electrons move in waves, just like light.
The electron microscope can see much more detail than any of the other microscopes. Because electrons have shorter wavelengths than visible light, therefore electron microscopes can see more detail.
The wavelengths of electrons are about 100,000 times shorter than the wavelengths of visible light. So, electron microscopes are used to look at things that are too small for light microscopes to see. Images made by electron microscopes are always in black and white, but some details can be brought out by adding color.
The electron microscope uses electromagnetic lenses, instead of glass lenses to focus a beam of electrons on a specimen.
Principle of electron microscope
Electron microscopes use the signals created when an electron beam hits a sample to make its structure, shape, and chemical makeup.
- The electron gun produces electrons.
- Two sets of condenser lenses concentrate the electron beam on the specimen and subsequently into a thin tight beam.
- An accelerating voltage (usually between 100 kV and 1000 kV) is supplied between the tungsten filament and anode to transport electrons down the column.
- The specimen under examination is made exceedingly thin, at least 200 times thinner than those used in optical microscopes. The sample is already on the specimen holder, and 20-100 nm-thick pieces are cut from it.
- The electronic beam goes through the specimen, and the fast moving electrons scatter in different directions. Depending on the thickness of different parts of the specimen.
- The denser (having more density) parts of the specimen scatter more electrons, so that part of the image looks darker because fewer electrons hit that part of the screen. On the other hand, areas that are clear are brighter.
- The electron beam that comes out of the sample goes to the high-powered objective lens, which forms the intermediate magnified image.
- Finally, the ocular lenses produce the final magnified image.
Types of electron microscope
What is a Transmission electron microscope?
In a transmission electron microscope (TEM), an electron beam from an electron gun passes through a prepared ultrathin specimen segment. The electron beam is concentrated on a small region of the specimen using an electromagnetic condenser lens that serves the same function as the condenser of a light microscope.
How it works
Specimens are placed on a grid made of copper mesh. Electrons flow through the specimen and amplify the picture via an electromagnetic objective lens. After that, an electromagnetic projector lens focuses the electrons onto a photographic plate. The final picture is called a transmission electron micrograph. It consists of many light and dark areas that show how many electrons different parts of the specimen absorbed.
Scanning electron microscope
The scanning electron microscope (SEM) is better than a transmission electron microscope (TEM) because it doesn’t need to cut specimens into thin pieces.
How it works
it shows specimens in a very interesting three-dimensional way. In scanning electron microscopy, an electron gun makes the primary electron beam, which is a narrow stream of electrons. These primary electron beam emits electrons to the surface of the specimen and is scattered after hitting the surface of the specimen. the scattered electron is known as the secondary electron. These secondary electrons are then sent to an electron collector, amplified, and used to make a picture photographic plate. A scanning electron micrograph is a name for this picture.
Advantages and Disadvantages of electron microscope
Advantages
- Electron microscopy can be used in many different areas of research, such as technology, industry, biomedical science, and chemistry. Some examples of uses are the inspection of semiconductors, quality control and assurance, the study of atomic structures, and the development of new drugs.
- With the right training, an electron microscope operator can use the system to make images of structures that are very clear and full of detail. These images can show complex and delicate structures that may be hard to see with other methods.
- It is used in biomedical research to find out the structure of tissues, cells, organelles, and macromolecular complexes are put together.
Disadvantages
- It is not possible to study living things. Because electrons are easily scattered by other molecules in the air, samples have to be studied in a vacuum. This means that this method can’t be used to study living things. This makes it hard to see how living things interact, which limits how electron microscopy can be used in biological research.
- An electron microscope can only make images in black and white. Images must be given fake colors.
- These might be in the picture that is made. Artifacts are leftovers from preparing samples, and to avoid them, you need to know a lot about how to prepare samples.
- Electron microscopes are very specialized pieces of equipment that are very expensive. Since most projects have limited budgets, using an electron microscope for research may not be a good idea. But running costs can be the same as other options like confocal light microscopes, so investing in a basic electron microscope is still something to think about, even if money is a big reason why the technology isn’t used.
- Even though technology has improved over the years, electron microscopes are still big, heavy pieces of equipment that take up a lot of room in a lab. Also, because electron microscopes are so sensitive, magnetic fields and vibrations from other lab equipment can make it hard for them to work. If the researcher wants to put an electron microscope in their lab, this is something they should think about.
- Electron microscopes need to be run by experts, and it can take them years to learn how to use this technology correctly.
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