Instructions for Use of the Scanning Electron Microscope (SEM)

Saturating the Filament

To maximize resolution (SEM) and xray counts (EDS), the electron beam must be saturated at the second peak. The more energy that is put into the filament, the more saturated it becomes. Note: over-saturating the filament will significantly decrease filament life. Read this procedure carefully to avoid over-saturating it.

  1. Align the gun before saturating the filament the first time you turn the beam on for the day. Use the same set up parameters for saturating the filament.
    • Detectors: Auto BC = BC
    • Gun: Spot = 400
    • Gun: EHT Target = 20kV
    • Scanning: Scan speed = 2
    Saturation may need to be adjusted more frequently than alignment, particularly when the filament is new. Saturate approximately every 30 minutes for the first few hours after replacing the filament. After that, check saturation every few hours of SEM use.
  2. In Gun Align window, select Emission image. (Or from main menu, go to Beam > Emission.)
  3. The beam pattern should be a solid elipse, centered on the green crosshairs. Check or adjust the saturation by doing the following.
    • If the beam pattern IS NOT solid:

    • Slowly increase the Fil I Target to the point where it becomes solid. When there is no longer a change in the beam shape or brightness, the filament is saturated. Back off of the fully saturated target and then bring it up again to the point where the beam pattern just stops changing.

    • If the beam pattern IS solid:

    • Slowly decrease the Fil I Target until the beam pattern is halo-like, with a bright ring around the outside and a darker center. Then follow the procedure above.


  • Fil I Target for new filaments is high initially, until excess material burns off the filament. Once the material burns off, the energy level that was needed to saturate it initially is now too high. This is why you must check saturation frequently when you put in a new filament.
  • Fil I Target is more stable and lower on older filaments than new filaments (requiring less frequent saturation).
  • Fil I Target is approximately 3.400 on new filaments
  • Fil I Target is approximately 3.200 on older filaments