Electron microscopy uses signals generated by the interaction of an electron beam with a sample to obtain information about structure, morphology and composition.
Electron guns produce electrons.
Two sets of condensers focus the electron beam onto the sample, where it is focused into a thin beam.
To move the electrons down the column, an accelerating voltage (usually between 100 kV-1000 kV) is applied between the tungsten filament and the anode.
The samples to be examined are very thin, at least 200 times thinner than a light microscope. Cut ultrathin sections of 20-100 nm that have been placed on the sample holder.
An electron beam passes through the sample and the electrons are scattered depending on the thickness or refractive index of different parts of the sample.
Dense areas in the sample scatter more electrons and therefore appear darker in the image because fewer electrons hit that area of the screen. Conversely, transparent areas are brighter.
The electron beam emerging from the sample reaches the objective lens, which has high power and forms an intermediate magnified image.
The eyepiece then produces a final, further magnified image.
