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Glossary terms about Spot size

Spot size
The size of the beam cross section at the surface of the sample. This affects 1) the resolution of the image and 2) the number of electrons generated from the sample.


12 pages mention Spot size

Beam Adjustment
It may be necessary to adjust the probe size (spot size) to match the magnification. 
Electromagnetic lenses, apertures and beam size
So the condenser lens current controls this initial spot size and is referred to as the spot size control. 
Magnification
The ability of the SEM to resolve fine structures is limited by the diameter of this spot size (probe size). 
Role of sample height
The "trade-off" for an increased WD is that the electron beam must travel a greater distance from the gun and therefore has a larger spot size on the specimen. 
Scan rate and signal to noise ratios
The image quality of the SEM is limited by the spot size and the ratio of the signal (S) produced by the electron beam to the noise (N) imparted by the electronics of the instrument in the displaying of this signal (S/N). 
Spot size
At low magnifications we use a larger spot size than at higher magnifications. 
Troubleshooting: edge effect, charging, sample damage
The number of electrons relates to a number of parameters including, beam current, the emission level of the gun, the spot size, and the apertures between the gun and the specimen. 
Virtual SEM - bone
Shows the affect of such settings as accelerating voltage, spot size, Z-depth, filament current, magnification, and astigmatism. 
Virtual SEM - rock
Shows the affect of such settings as accelerating voltage, spot size, Z-depth, filament current, magnification, and astigmatism. 
Virtual SEM - slag
Shows the affect of such settings as accelerating voltage, spot size, Z-depth, filament current, magnification, and astigmatism. 
Virtual SEM - sparkler
Shows the affect of such settings as accelerating voltage, spot size, Z-depth, filament current, magnification, and astigmatism. 
What is astigmatism?
At exact focus the streaking vanishes and focus can be correctly achieved if the spot size is suitable.