Scan speed

To improve the quality of the image we need to reduce the scan speed. This is equivalent to increasing dwell time, which may be used on some SEM instruments. Slowing the scan speed down gives the detector and the image processing electronics more chance to "count" the signal being detected (i.e. electrons) and therefore improves your signal to noise ratio.

Reducing your scan speed will:

  • Reduce noise in your image
  • Increase visible details on your surface
  • Improve the accuracy of measurements you make with your image
  • Increase the time needed to acquire an image

Quick Guide to Scan Speed

  • Used primarily for navigation around a sample to find regions of interest, and for setting your field of view.

    • ~80 ms per frame
    • Very high noise ratio
    • Better used with SE detector

  • Used to help precisely navigate around on a specimen, or to set field of view, when higher quality is needed to see features.

    • ~1-4 s per frame
    • Better quality image, but can be noisy with low signal
    • Slow 1 most useful for navigation with BSE detector

  • For capturing images of higher quality after regions of interest found, field of view set, and image is focussed.

    • ~20-160 s per frame
    • Best quality for capturing images

  • Most used for focussing and stigmation adjustment but can be useful for finding features of interest and navigation.

    • Improved image quality over fast scan
    • Increased frame rate due to reduced scan area

Next - Stigmatism Correction

Back to MCFP Learning Home