Slide 3 of 25
Notes:
1. Intro - what is TEM? What is the resolution of TEM?
TEM - instrument that employs an electron beam that projects through the specimen and produces a two-dimensional image on the phosphorescent screen.
TEM was created in the 30-s of this century, after the discovery of the dual nature of the electrons and possibility to focus electron beam in the magnetic field. Its construction reminds the optical microscope - and you can see in what sense: both use the source of smth that will create an image:
light source and electrons
when heat (the applied voltage is 40000 and higher) the cathode starts to emit electrons that move towards the anode and some of them -through the aperture - in the column.
The speed they accelerate depends on the amount of the accelerating voltage present. In our case - TEM scope Philips CM200 can provide a voltage up to 200KV. The higher the speed of the electron - the shorter its wave length, thus the higher the resolution.
Electromagnets placed in the column focus the electrons, mimicking the glass lenses on the light microscope.
The column contains a very high vacuum - up to 10-5 - 10-8 Torr - to prevent the electrons from scattering and to help them reach the specimen.
