Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 19/09/2012 05:30:04

Title: How do electron microscopes make electrons?
Post by: thedoc on 19/09/2012 05:30:04

Rebecca Arthur  asked the Naked Scientists:
   
Where do they get the electrons from for the electron microscope?
 
Secondarily, can you please explain how they work and what happens exactly when they're used?
 
Thanks again!
 
Rebecca Arthur
Breckenridge, CO

What do you think?

Title: Re: How do electron microscopes make electrons?
Post by: chris on 19/09/2012 20:07:27

The electron microscope uses an electron gun similar to the one found in a television set.

This comprises an electrically-heated source filament. Electrons "boiled off" from the filament and it glows are accelerated and focused by an electrical and magnetic field to produce an electron beam that is then concentrated on the target for visualisation. In transmission electron microscopy - the original form of the technique - the beam then strikes a phosphor-coated screen, casting a shadow of the imaged object. But because the electron beam is spreading out after hitting the target, the imaged object on the screen appears magnified.

Title: Re: How do electron microscopes make electrons?
Post by: wolfekeeper on 20/09/2012 20:21:26

The electrons go around the electric circuit that includes going through or onto the specimen.

They're not created or destroyed in an electron microscope; electrons are always present in any electrical conductor they're just fired off, impact onto the sample and then are collected back up and put back into the other end of the conductor again. As they flow through the circuit through the conductor they form a tiny electric current.

Title: Re: How do electron microscopes make electrons?
Post by: evan_au on 20/09/2012 21:47:20

Quote

can you please explain how they work

Just like light, electrons can be thought of as both a wave and a particle.
A light microscope can shine light through an object, or bounce light off an object to form an image.
An electron microscope can "shine" electrons onto an object, or bounce electrons off an object to form an image.

The difference is that electrons have a much smaller wavelength than visible light, so they can take pictures of much finer details than a light microscope. The wavelength of the electron is dependent on its energy, so by using a higher voltage in the electron microscope, you can see finer details (within limits).

Some pros & cons: Light passes through air and water, so we can see living and moving things in full natural colour. Most electron microscopes need a strong vacuum, so you only get to see dead things, and usually in black-and-white.
http://en.wikipedia.org/wiki/Electron_microscope

Title: Re: How do electron microscopes make electrons?
Post by: syhprum on 21/09/2012 19:59:17

I do not think Electron microscopes use a heated filament as the source of Electrons but rather a sharp Tungsten point as the cathode.