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Goldstein (2003,) p22
Where it all begins...
Where it all begins...
Most SEMs look something like this diagram. The control console and viewing screens have been modernized, but all microscope columns share these core features.
The electron begins at the source (sometimes a filament) and travels through a series of electromagnetic lenses that focus the beam before it is emitted to interact with the sample, where it generates other signals to be collected by detectors.
What settings do we control?
What settings do we control?
At the source, we can change the accelerating voltage and the emission current.
Accelerating voltage affects probe sharpness and penetration depth (interaction volume.)
Emission current changes the electron flux.
Why would I choose a low accelerating voltage?
Why would I choose a low accelerating voltage?
With a higher voltage, and therefore higher penetration depth and larger interaction volume, surface features may be hidden by signal generated deeper in the sample.
Try a low voltage for surface features or less conductive samples.
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