Electron Microscopes Flashcards

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1
Q

Electron Microscope

A

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.

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2
Q

How to obtain useful resolution?

A

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

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3
Q

Scanning Tunnelling Microscope (STM)

A

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.

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