Ge 116 Module 1: Scanning Electron Microscopy

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Ge 116 Module 1 Scanning Electron Microscopy

• Part 1 Electron optics, beam-specimen
  interactions imaging

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(No Transcript)
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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 lt100 h gt30 ?m 1
LaB6 106 lt1000 h gt5 ?m 1
Field Emission 108 gt1000 h lt 30 nm 2
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Electron optics

• Condenser Lenses
• Apertures
• Stigmators
• Scan Coils
• Objective Lens

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Electron Beam Limits
Probe current
Minimum beam diameter
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Source Brightness
Electon DeBroglie wavelength, 9 pm
Spherical Aberration Coefficient, 2 cm
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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
Locations of secondary electron emission
Horizontal spread of backscatter emission for
normal and inclined specimens
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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