Beam current affects signal to noise, charging, and resolving power. Find out how and why.
Optimizing Beam Current - SEM
What is beam current? Beam current is a measurement of the number of electrons in the electron beam. In an SEM, beam current has three major impacts on your image: signal to noise (S/N), charging, and resolving power. No two samples are the same, so no single beam current is good for all samples! Below is a guideline to help you optimize beam current for your sample.
Low Signal to Noise (S/N)
- Signal is low because there are not many electrons hitting the sample.
- Compensate for low S/N by using longer pixel dwell times during image collection.
- There are not many electrons hitting the sample, which reduces charging.
- Allows you to resolve smaller features because the size of the beam is smaller.
High Signal to Noise (S/N)
- Many electrons hit the sample, producing a large amount of signal.
- The amount of noise does not change, so the S/N ratio improves.
- There are a large number of electrons hitting the sample surface, which take longer to be grounded, especially by a non-conductive material.
- Resolution decreases when the size of the beam becomes larger than the features of interest.
Sufficient Signal to Noise (S/N)
- An optimal beam current produces sufficient S/N to produce quality images.
- While optimizing beam current, also experiment with pixel dwell times. Dwell time has a large impact on S/N too.
- An optimal beam current produces little to no charging.
- Coating samples with a conductive material can help reduce charging too.
- An optimal beam current allows you to resolve features of interest.
- Resolving smaller features requires the use of a lower beam current.
Low Signal to Noise (S/N)
- Signal is low because there are not many electrons hitting the sample.
- Compensate for low S/N by using longer pixel dwell times during image collection.
- There are not many electrons hitting the sample, which reduces charging.
- Allows you to resolve smaller features because the size of the beam is smaller.
High Signal to Noise (S/N)
- Many electrons hit the sample, producing a large amount of signal.
- The amount of noise does not change, so the S/N ratio improves.
- There are a large number of electrons hitting the sample surface, which take longer to be grounded, especially by a non-conductive material.
- Resolution decreases when the size of the beam becomes larger than the features of interest.
Sufficient Signal to Noise (S/N)
- An optimal beam current produces sufficient S/N to produce quality images.
- While optimizing beam current, also experiment with pixel dwell times. Dwell time has a large impact on S/N too.
- An optimal beam current produces little to no charging.
- Coating samples with a conductive material can help reduce charging too.
- An optimal beam current allows you to resolve features of interest.
- Resolving smaller features requires the use of a lower beam current.
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On to Pixel Dwell Time!Click the button to the right to keep on learning!
On to Pixel Dwell Time!