The scanning electron microscope

What is freeze-etching?

Making a replica of the exposed surface by coating in a thin layer of carbon. The cell is then etched away using acid. The carbon replica faithfully reproduces the surface and is viewed by the SEM.

Does the SEM contain a vacuum?

Yes

Does it contain a condenser lens?

Yes, its an electomagent

Resolution of SEM?

5 nm

Magnification of SEM?

x200-300

How do you see structures inside the cell?

Freeze-fracturing

What are around the specimen?

Electron detectors which are stimulated by the electrons. Electron signals are sent from the detector to a computer, which creates the image on a computer screen.

What happens to the electron beam?

Instead of passing through the specimen, they bounce off. The specimen is usually coated in a very thin layer of heavy metal to help with reflection.

How does it work?

It uses an electron gun, but the electron beam sweeps across the specimen.

Does it involve sections?

No

Is there an objective or projector lens?

No

Is the specimen a section?

No, the electrons do not pass through it, they reflect off it.

What determines the pattern of reflected electrons?

The surface contours

What does the SEM give an image of?

The surface of a structure

What is freeze fracturing?

Tissue is frozen using liquid nitrogen and hit with a tiny metal blade. It breaks or fractures, usually along lines of weakness. The surface revealed is then viewed by the SEM.