How a scanning electron microscope (SEM) works?
A scanning electron microscope scans a beam of electrons over a specimen to produce a magnified image of an object. That’s completely different from a TEM, where the beam of electrons goes right through the specimen.
- Electrons are fired into the machine.
- The main part of the machine (where the object is scanned) is contained within a sealed vacuum chamber because precise electron beams can’t travel effectively through the air.
- A positively charged electrode (anode) attracts the electrons and accelerates them into an energetic beam.
- An electromagnetic coil brings the electron beam to a very precise focus, much like a lens.
- Another coil, lower down, steers the electron beam from side to side.
- The beam systematically scans across the object being viewed.
- Electrons from the beam hit the surface of the object and bounce off it.
- A detector registers these scattered electrons and turns them into a picture.
- A hugely magnified image of the object is displayed on a TV screen.