Scanning Electron Microscopy

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<strong>Electron</strong> Gun • There are two main types of gun – Thermionic and Field Emission (FEG). • Thermionic gun :- Simplistically, a material (often a piece of twisted tungsten) is heated to a high temperature so that it will emit electrons. • Can also use LaB 6 crystal grown to a tip – gives a brighter beam than W for same kV. Analytical Workshop 2012 Tungsten filament Tungsten filament assembly LaB 6 filament tip
Thermionic Gun Filament Wehnelt cylinder - 10-10000kV + Anode earth •Filament is heated and begins to produce electrons. •<strong>Electron</strong>s leave the filament tip with a negative potential so accelerate towards the earthed anode and into the microscope column. •A small negative bias on the Wehnelt then focuses the beam to a crossover which acts as the electron source. Analytical Workshop 2012
Page 1 and 2: Scanning Electron Microscopy Field
Page 3 and 4: Improving Resolution • Firstly, t
Page 5: Layout of a Generic SEM Gun 1 Apert
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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