Scanning Electron Microscopy

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Why use an SEM? Analytical Workshop 2012 Fig 1. Examples of features resolvable using different imaging techniques
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 <strong>Electron</strong> 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.
Page 1: Scanning Electron Microscopy Field
Page 5 and 6: Layout of a Generic SEM Gun 1 Apert
Page 7 and 8: Thermionic Gun Filament Wehnelt cyl
Page 9 and 10: Comparison of Sources •W filament
Page 11 and 12: Scanning the Beam\Beam Interactions
Page 13 and 14: Signal Detection • The Everhard -
Page 15 and 16: Variable Pressure SEM •Localised
Page 17 and 18: Compositional Analysis - Back Scatt
Page 19 and 20: BackScattered Imaging • Back scat
Page 21 and 22: Examples Images Imaged using ET Det
Page 23: Conclusions •Scanning Electron Mi

Scanning Electron Microscopy

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