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Electron microscope

Transmitting electron microscopeTransmitting electron microscope Optical microscopes can only magnify objects up to 2000 times—greater magnifications do not reveal any more detail. Electron microscopes can magnify objects millions of times. The first electron microscope, which could magnify objects up to 400 times, was built in 1932 by German engineers Ernst Ruska and Max Knoll. In their instrument, the image was made not by light but by a beam of tiny subatomic particles called electrons. The images created by electron microscopes are called electron micrographs. They may be viewed on television screens using video cameras, or digitized and viewed on computer screens.

How it works

A diagram of a scanning electron microscopeA diagram of a scanning electron microscopeIn an electron microscope, a beam of tiny particles called electrons does the same job as light in an optical microscope. It is fired at the object and then focused by electromagnetic “lenses” on to a screen that emits light where the electrons hit it.

A scanning electron micrograph of a snowflakeA scanning electron micrograph of a snowflake

Types of electron microscope

There are two main types of electron microscope. In a transmitting electron microscope (TEM), the beam of electrons is fired through an extremely thin slice of the specimen. TEMs magnify objects up to 2 million times. In a scanning electron microscope (SEM), a very narrow beam of electrons is fired at the surface of the specimen. The beam scans across the surface and a sensor detects the electrons bouncing off. In this way, a three-dimensional image of the specimen is built up. SEMs magnify objects up to 500,000 times.

A scanning electron micrograph of a fruit fly's eyeA scanning electron micrograph of a fruit fly's eye

There are more than 40 different types of microscope, apart from optical microscopes, in use today.

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