Scanning Electron Microscope vs.Optical Microscope

Advantages

• Continuously variable magnification
• High resolution
• Depth of focus
• Elemental analysis attachments

Disadvantages

• Cost
• More knobs
• Vacuum
• Sample limitations

Scanning Electron Microscope(simplified drawing)

Signal Generation

In (Probe)

• Focused mono-energetic electron beam

Out (Signal)

• Imaging

Backscattered electrons

Secondary electrons

• Analysis

X-rays

Characteristic x-rays

Bremsstrahlung x-rays (background “noise”)

Auger electrons

Topographic contrast

SEM general info

SEM general info

• Mount the sample on the holder
• “Paint” the conductive path

SEM general info

• Load the sample into the SEM

SEM general info

• Vacuum pump 4 minutes
• Turn on filament current & accelerating voltage
• Fiddle with the knobs

Sample Prep

• Low C steel
• High C steel
• Unknown C steel
• Quenched from 1700 degF
• Anneal to 900 degF
• Furnace cooled from 1700 degF

High C (optical 600x)

High C (SEM 400x)

High C (SEM 3000x)

Low C vs High C (SEM 200x)

Low C(3000x vs 10000x)

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