Electron Microscopes

Electron Microscopes are split into two types: Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM). An Electron Microscope involves using a beam of Electrons rather than light. This beam has a much smaller wavelength (0.004nm) than light, so the resolution is much greater than when using a Light Microscope. Magnets are used rather than lenses. Electrons are not visible to humans, so the image produced is projected onto a screen (no colour) as an Electron Micrograph. Colour is sometimes added for visual aid. Staining is still used, but metal particles/salts are used instead.

Transmission Electron Microscopes, or TEM:
The TEM is when electrons pass through a very thin sample there is contrast in the denser parts, because the electrons don't pass through as easily. A 2D image is produced. The largest magnification possible with the TEM is x500,000.

 
The Scanning Electron Micrscope, or SEM:

The electron beam is fired at the sample, but doesn't pass through - they're reflected away to give a 3D image. The highest magnification with the SEM is around x100,000.

Summary:
The Electron Microscope has a much higher resolution than a ligh microscope (0.1nm!). We can also use the TEM to view the organelles inside cells, rather than the top layer of the specimen. The SEM can provide a unique 3D image when required. Some of the troubles involved in using an Electron Microscope are that the microscope is a difficult piece of equipment to master, and that the microscope must have a vaccuum (so the Electrons don't rebound off air particles etc) - greatly increasing the cost of the microscope.