Scanning Electron Microscopy

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Field Emission Gun (FEG) FEG source – W tip • A very strong magnetic field (~10 9 Vm -1 ) draws electrons from a very fine metallic tip (usually W). •An extraction voltage of around 2kV is applied to the first anode to create an intense electric field to allow electrons to escape from the tip. •The second anode is then used to accelerate the electrons into the microscope at the required energy. •Combination of the two anodes focuses the beam into a crossover creating a fine beam source.
Comparison of Sources •W filaments are very simple and inexpensive. •LaB 6 filaments give greater brightness than W (approximately X10), but cost more. •FEG’s give much more brightness than thermionic systems. •FEG’s give a more monochromatic electron source and finer probe (i.e. better resolution). •Temperatures used are much lower than for thermionic sources (particularly cold cathode FEG’s). •FEG’s require better vacuum systems and are more expensive. Analytical Workshop 2012 Comparison of the three types of source operating at 100kV
Page 1 and 2: Scanning Electron Microscopy Field
Page 3 and 4: Improving Resolution • Firstly, t
Page 5 and 6: Layout of a Generic SEM Gun 1 Apert
Page 7: Thermionic Gun Filament Wehnelt cyl
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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