Scanning electron microscope (SEM)

Function: Lets users look at the surface of objects at high resolution.

Maximum magnification: Approximately 500,000x.

Best for:

• Looking at surfaces of objects.

• Looking at objects in 3D.

Disadvantages:

• Resolution often not as high as the transmission electron microscope.

• Can’t be used to look at living things (samples need to be dried and coated in metal before visualising).

• Costly to run.

Video: Liz Girvan is a SEM expert with Otago Micro and Nanoscale Imaging. She explains how a scanning electron microscope (SEM) works by knocking electrons off the surface of a sample.

Understand more about SEM microscopy in Why we use SEM, Artefacts in the SEM and Sputter coating.

Transcript

Liz Girvan

This is a scanning electron microscope or SEM. The action starts at the top of the column, which is this piece here, which is where the electron gun is. Inside here we have got different electromagnetic lenses, which focus that, all those electrons into a nice little beam. At the bottom down in here we’ve got a final lens, which is where the electrons are focused again and then pop out and hit the sample, which is sitting just below it.

That beam, instead of just coming straight down, it actually moves quite rapidly backwards and forwards across the sample. You get electrons being knocked off the surface of the sample and then picked up by a detector, and they’re called secondary electrons. They show you most of the information.

Acknowledgements
Liz Girvan, University of Otago