Electron Microscopes

Question 1

Electron Microscope

Answer 1

Stream of electrons accelerated to a positive potential, they are emitted via thermionic emission.

Stream is focussed on a thin beam using a magnetic lens.

Question 2

How to obtain useful resolution?

Answer 2

Electron wavelength needs to be approximately equal to the diameter of an atom (1x10^-10).

Question 3

Scanning Tunnelling Microscope (STM)

Answer 3

Uses principle of quantum mechanics.

A fine probe is moved off the surface of a sample and a voltage is applied. The electrons have to overcome the Coulomb Potential.

There is a possibility that some electrons will cross the sample from the sample to the tip (which needs to be 1mm above surface).

If probe moves over a higher layer of electrons, the current increases.