Scanning Electron Microscopy

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Interaction Volume •The ‘interaction volume’ is the area of the sample excited by the electron beam to produce a signal. •The penetration of the electron beam into the sample is affected by the accelerating voltage used, the higher the kV the greater the penetration. •The effective interaction volume can be calculated using the electron range, R:- 1.67 0.0276 A E0 R = ( µ m) 0.89 ρ Z Where A is the atomic weight (g/mole), Z is the atomic number, ρ is the density (in g/cm 3 ) and E o is the energy of the primary electron beam (in kV). Take the example of iron: A=55.85, Z=26, r=7.87 g/cm 3 Accelerating voltage (kV) Primary Electron Range (µm) 30 3.1 15 0.99 5 0.16 1 0.01 (10nm!) Signals generated in the interaction volume Analytical Workshop 2012
Signal Detection • The Everhard – Thornley Detector (ETD) is the most common detector used to detect secondary electrons to image surface topography. • Electrons are attracted to a +ve charge on a grid in front of the detector. The captured electrons are then amplified by a photo-multiplier before being digitised and sent to a screen. • The signal detected is transferred to a viewing screen as the beam is scanned building up the image. Everhard Thornley Detector Scanning to produce an image Analytical Workshop 2012
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 and 8: Thermionic Gun Filament Wehnelt cyl
Page 9 and 10: Comparison of Sources •W filament
Page 11: Scanning the Beam\Beam Interactions
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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