ge 116 module 1: scanning electron microscopy part 1: electron optics, beam- specimen interactions...
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Ge 116 Module 1: Scanning Electron Microscopy
Part 1: Electron optics, beam-specimen interactions & imaging
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What is an SEM?Parts of an SEM:
• Vacuum chamber and pumps
• Electron source
• Electron column:
• High Voltage
• Optics
• Scan coils
• Stage
• Detectors
• Analog or digital display
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Electron sources: Filament
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Electron sources: Filament
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Electron sources: Field Emission
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Electron sources: Field Emission
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Electron sources: Comparison
Source Brightness (A/cm2sr)
Lifetime Source Size
Beam Stability
W filament 105 <100 h >30 m 1%
LaB6 106 <1000 h >5 m 1%
Field Emission
108 >1000 h < 30 nm 2%
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Electron optics• Condenser Lenses
• Apertures
• Stigmators
• Scan Coils
• Objective Lens
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Electron Beam Limits
Minimum beam diameter ~1
Spherical Aberration Coefficient, ~2 cm
Electon DeBroglie wavelength, ~9 pm
Probe current
Source Brightness
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Electron Beam Limits
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Beam-Specimen Interactions• Elastic
– Back-scattered electrons
• Inelastic– Secondary electrons– Bremsstrahlung X-rays– Characteristic X-rays– Auger electrons
• Other– Cathodoluminescence– Specimen current
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Beam-Specimen Interaction Volume
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Beam-Specimen Interaction Volume
Increased backscatter yield for inclined specimen surface
Horizontal spread of backscatter emission for normal and inclined specimens
Locations of secondary electron emission
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Backscattered Electrons
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Backscattered Electrons
(b is specimen current image)
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Secondary Electrons
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Secondary Electrons