A compound microscope may be useful for school applications and light research, but if you want a tool that is capable of showing you any sample you wish to examine in extreme detail, what you should get is an electron microscope. The latter functions on certain principles, as you will see right away.
The main differences between a compound and an electron microscope
If we’re talking numbers, let us tell you just this: an electron microscope can magnify any object up to 10 million times, which is 5,000 times more than what a compound model can do. It is easy to gather from this that electron models are used in cutting edge research and they will not be found in the school lab.
Another big difference you should know between the two types of microscopes is what they use to induce the magnification process. Compound microscopes use a beam of light, whereas electron microscopes use the magnetic properties of electrons. More will be explained as follows.
The wavelength of electrons
Louis de Broglie was the first scientist to create the hypothesis according to which electrons have wave properties. When compared to the wavelength of light, electrons have a value of 100,000 smaller. As you can see, there is a considerable difference, hence the superior performance of an electron microscope when compared to a compound model.
But how does the length of the magnetic wave influence the outcome of what you can see through a microscope? The answer is quite simple. Magnetic waves with shorter lengths manage to penetrate better through the surface of an object, thus allowing you to view what lies beneath.
It would not be possible to use a microscope for extensive research without this quality. If you ever have the chance to see pictures of the same sample seen through a regular microscope and an electron model, you will notice the vast differences between what they can do.
The electrons create, therefore, a sharper image. You will be able to notice details that are not only impossible to see with the naked eye but are also invisible to a compound microscope.
How do the electrons convert their magnetic properties into magnification?
Since that is the topic we want to discuss here, let’s see what electrons do and how they do it. Inside such a microscope, the electrons are emitted by a so-called electron gun made of tungsten. The generated electrons are sent into the column as soon as the gun is supplied with electrical energy. This part of the microscope should be completely free of any impurities, as they can hinder the action of the electrons.
All these electrons are nothing but small magnets that, inside the column, will start to converge. It is the same process that happens inside a regular microscope where the beam of light emitted converges to create the magnification effect.
Once the electrons converge, their magnetic waves penetrate the surface of the object placed under the microscope. The image they create is projected on a fluorescent screen that comes coated with phosphorus to enhance the clarity of what you see.
This is how an electron microscope works. The image the electrons create is further projected on a computer screen when you can observe it better.
What are the types of electron microscopes available?
There are two types of such microscopes in use right now: TEMs or Transmission Electron Microscopes, and SEMs or Scanning Electron Microscopes. They both have correspondents in light microscopes. We will tell you right away how the two work to magnify the samples observed through their eyepieces.
TEMs are, in many ways, like compound microscopes, which are their light counterpart. A TEM can magnify an object up to five million times, which is superior in every way to a compound model. Even if there are, let’s say, two atoms that are incredibly close to one another, such a microscope will be able to tell them apart.
For this reason, TEMs are used for observing what happens inside a cell and for studying structures that are deep inside a material, tissue, or anything else that goes under scrutiny.
This type of microscope will project a two-dimensional image that comes in either black and white or grey-scale. As the electrons bombarding the samples are absorbed or go through, a picture of shadow and light is created. The darker the parts of the image, the denser the object the electrons encounter.
While TEMs are very powerful, they have their fair share of downsides. You can only examine one aspect of your sample, and you won’t get a field of view that is large enough for observing various details. Unless you use very thin samples, you won’t be able to see all that you want to observe. Also, misaligning the sample will cause severe distortions.
If you don’t want to deal with the unpleasant limitations of a TEM, you can try an SEM. This type of microscope can deal with thicker samples, and you won’t experience the same troubles with misalignments as you would when using a TEM.
Furthermore, SEMs are capable of creating three-dimensional images, which means that the researcher can observe more details. You will also get a larger field of view, another aspect that contributes to the superiority of SEMs over TEMs.
One thing you should know about SEMs is that they work with more than just electrons. They also use X-rays and photons, and when a surface is bombarded with all these emissions, a tri-dimensional image is formed.
You may wonder if there are any drawbacks of using SEMs. First of all, you won’t get the same magnification you would when using a TEM. SEMs offer a magnification of 100,000, which is considerably less when compared to what TEMs can do, as shown earlier.
What electron microscope is better?
It would not be correct to say that SEMs are better than TEMs, or the other way around. The truth is that they are used for different applications, so both types have their uses.