Electron microscopes

The microscope described on the What is a microscope? page uses light to magnify the image of the object we are looking at. With light microscopes we can see things such as cells, parasites and some bacteria. To see much smaller things, including viruses and structures inside cells, such as DNA, we need a more powerful type of microscope.

Electron microscopes use subatomic particles called electrons to magnify objects. The electrons are fired at the sample very fast. When electrons travel at speed they behave a bit like light, so we can use them to make an image. But because electrons have a smaller wavelength than visible light they can reveal very tiny details.

This makes electron microscopes more powerful than light microscopes. A light microscope can magnify things up to 2000x, but an electron microscope can magnify between 1 and 50 million times depending on which type you use! To see the results, look at the image below.



Scanning Electron Microscopes

Scanning Electron Microscopes (SEMs) can magnify a 3-dimensional objects - perhaps a bed bug or a fruit seed! The outside surface of the object is scanned, which is how the Scanning Electron Microscope gets its name.

Electrons are fired towards the sample. The electrons move very fast, and when they hit the sample they bounce off its outside surface. The bounced-back electrons are detected by a screen, which then makes an image we can see on a computer.

An SEM can magnify a sample by about one million times (1,000,000x) at the most. Because a sample can be used in its natural state, the SEM is the easiest electron microscope to use. The final image looks 3D and shows you the outside of your sample.



SEM Quiz

Now you know how an SEM works, see if you can identify some samples the SEM has magnified in the quiz below.



Transmission electron microscopes

Transmission Electron Microscopes (TEMs) are a bit different to SEMs. To look at something using a TEM the sample must be sliced into a very thin section and prepared specially. The electrons pass, or transmit, through the thin section of the sample, which is how the Transmission Electron Microscope gets its name.

Electrons are fired very fast towards the sample, just like in an SEM. Because the sample is so thin, when the electrons hit the sample, they pass through it! After passing through the sample, the electrons reach a screen where the image appears. The image can be seen on the screen itself, or on a computer screen.

A TEM can magnify a sample up to 50 million times (50,000,000x). This is far more than the SEM! However, it takes a long time to prepare a sample for TEM, which makes TEMs harder to use. The final image you see from a TEM looks 2D – it shows a thin section through your sample.



Return to the Microscopes homepage, discover how a microscope works, or investigate the tiny things in our microworld using microworld ID!