Scanning Electron Microscopy

Improving Resolution
• Firstly, the wavelength of the imaging source is important.
In an optical microscope white light is used (λ – 380-700-nm)
• In an Electron Microscope the imaging source is a beam of electrons which has a
shorter wavelength (λ ~0.0025nm at 200kV) .
• This is approximately five times smaller than visible light and twice as small as a
typical atom – this is why electrons can ‘see’ atoms but white light can’t :-
Analytical
Workshop 2012
‘the analysis probe must be smaller than the feature being analysed’
• The wavelength of electrons is dependent on the accelerating voltage, i.e.:-
kV
Wavelength λ (pm)
20 8.588
100 3.702
200 2.508
300 1.968
• The higher the accelerating voltage the shorter the wavelength.