Electronic microscope

November 2, 2021

The microscope is one of the most important scientific inventions in history, since thanks to it a large number of discoveries were made that allowed scientific advances to reach what we know today. In this we will thoroughly analyze the electron microscope , explaining what it is, what its parts are, how it works and the different types that exist.

What is the electron microscope?

The electron microscope is an instrument that has a great power of magnification . This is extremely important in scientific research because they have a great power of magnification, allowing a better view of the composition of a matter.

Through the use of this type of instrument, images can be increased to levels much higher than those obtained with optical microscopes, so it should be clear that electron microscopes are much more powerful and allow the image to be brought closer together.

How do they work?

Before explaining how these instruments work, it is important to have certain physical concepts well defined, starting with the concept of wavelength , which is the distance between two consecutive cycles. For example, in visible light each wave of a color has a certain unique wavelength.

The reason why it is important to understand the concept of wavelength is because within the field of optical microscopy it is directly related to the maximum magnification that these instruments can achieve. That is, the maximum magnification of an electron microscope depends on the wavelength of the microscope. The shorter the wavelength, the higher the resolution.

That is why the maximum magnification that an optical microscope can reach does not usually exceed 1,500 times, whereas the electronic microscope does.

In this way, the operation of an electron microscope is based on the use of electrons instead of visible light . This is because the wavelength of the electrons is proportional to their speed, which means that if the electrons are accelerated, much shorter wavelengths can be obtained .

Electron microscopes use this to be able to view samples at a much higher magnification. In a few words and simplifying we can say that its operation consists of a source of electrons that are accelerated at great speed, which impact against the sample in a way equivalent to light . Some electrons are reflected by the sample and others simply pass through. By detecting these electrons, an image of the sample can be created .

In the case of optical microscopes, these are usually classified between those of reflected light and those of transmitted light. As for electron microscopes, these can be distinguished between scanning electron microscopes and transmission electron microscopes . We will go into more detail on each of these two later.

The parts of an electron microscope

Now we will detail what are the main elements found inside electron microscopes, which are used to generate electrons and accelerate them towards the sample.

Electromagnetic lenses

The procedure that optical microscopes use to direct light rays towards the sample and magnify the image cannot be used in an electron microscope to be able to deflect the electrons.

That is why this type of equipment instead of using glass uses electromagnetic lenses, which generate magnetic and electric fields to be able to interact with the electrons and thus make them converge in the sample giving them their trajectory.

Electron source

As we specified earlier, electrons are the equivalent of light rays from an optical microscope, so it is necessary for microscopes to have an emitter or source of electrons.

This source is usually a tungsten filament that is heated so that the energy of its atoms and electrons can increase. From a point of energy level the electrons have enough energy to be able to leave their atoms, and once they are free, they are directed towards the sample so that the instrument can recreate an image of the sample.

Vacuum chamber

The procedures that started with the two parts explained above are carried out inside a vacuum chamber . This chamber is necessary, since otherwise the electrons would interact with the molecules that are in the air and their trajectory could not be determined correctly.

The sample to be observed has to be placed inside said vacuum chamber. This makes it impossible to observe living samples inside an electron microscope .

Fluorescent screen or detector

When the released electrons are directed towards the sample and impact or bounce against it, the information that allows the sample to be reconstructed has to be measured and received.

It can be done by means of a fluorescent screen , which reacts differently depending on the number of electrons that manage to hit it. Thus, the areas in which more or fewer electrons have impacted can be detected, allowing the sample to be reconstructed.

Currently there are other alternatives to the fluorescent screen, such as CCD sensors, which are also quite effective.

The information that the fluorescent screen is responsible for capturing is transmitted to a computer to be able to assign colors to the image that was obtained. This procedure is completely different from that used in optical microscopes, since in these it is the same light that is responsible for providing the sample to the eye. However, in electronic instruments such as our eyes are not prepared to detect electrons, it is necessary for the information to be recreated in a computer.

Different types of electron microscopes

At present you can find two types of electron microscopes: scanning and transmission.

Scanning electron microscope (SEM)

Scanning electron microscopes use the impact of electrons in the sample to be able to recreate an image. But in this specific type of instrument, the electrons are not responsible for illuminating the entire sample at the same time, but rather a “sweep” is made through the different parts of the sample .

Once the electrons begin to impact the sample, they lose part of their energy due to the interaction with the sample. The initial energy is transported in X-ray or heat emissions , and electrons are also produced that are released from the sample. These electrons are considered secondary electrons .

These instruments measure all the information to be able to extract an image of the sample that has been observed. Secondary electrons that are emitted by the sample when scanning are measured. Scanning electron microscopes are especially useful for being able to observe the surface of microorganisms .

Generally, a preparation is carried out on the sample by depositing a metal layer on it. This so that more secondary electrons are present when the sample is impacted by the main electrons.

The magnification achieved by this type of microscope is less than that of transmission microscopes, but they provide information in three dimensions that makes them a really useful instrument.

Transmission electron microscope (MET)

Electrons are also used in transmission electron microscopes to impact and pass through the sample.

These electronics are conducted to the sample by means of the electromagnetic lenses explained above, and once they manage to hit the sample, some electrons pass through it and others bounce off it. The electrons that managed to cross it are captured by the detector, which processes the information and generates an image .

Depending on the sample to be analyzed, the number of electrons that manage to cross it would vary. That is, some parts of the sample may have greater transparency than others, which makes it possible to see lighter parts in the image (parts that are easy to pass through) and dark parts (which are the parts that less electrons were able to pass through).

Normally the sample has to be prepared to be as thin as possible, having a thickness of less than 2000 angstroms , since if this is not done it will be very difficult for the sample to be penetrated by electrons.

This makes this type of microscopes widely used to be able to know internal details about the sample. The greatest weakness of these is that it does not allow information on the characteristics on the surface of the sample, such as its roughness or shape, unlike scanning microscopes that do provide this information.

In summary, electron microscopes are very useful laboratory instruments that allow more information about the samples, in addition to achieving a much higher magnification than optical microscopes.

Dr. Loony Davis5
 | Website

Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

Leave a Reply

Your email address will not be published. Required fields are marked *