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Thermo Fisher Scientific

EELS energy resolution 0.26eV for 1 sec @ 300kV

Issue

EELS energy resolution 0.26eV for 1 sec@300kV;Mono Beam Shape is abnormal in filtered mode. Cannot be improved by using Monostig or Focus.

Environment

Titan 80-300

Resolution

These are possible resolutions for the issue:

  • Exchange ACC

Cause

These are possible causes for the issue:

  • Mono hardware was defective

Details

  1. Previously it was reported that ZLP width in fast exposure became worse to around 0.33eV since last September when ZLP was not really stable but the resolution was less than 0.2eV in fast exposure in GIF CCD. It was found that mono beam center is off because it swings while changing mono focus. As the excitation gets bigger, the mono shift value becomes larger than usual. Mono beam with excitation will spread toward one direction with focusing changing and the beam looks very abnormal from usual.
  2. Calculated HT instability = 0.25 -0.3eV, so this means that GIF/ HT stability is OK.
  3. Checked AC stability 250mVp-p with and without low pass filter. DC stability is less than 1.6V/min p-p with and without low pass filter. – All in spec
  4. Performed mono gun alignment again but it did not fix the issue
  5. Replaced the tip then rechecked the EELS resolution two months later, it was 0.25eV for 1 second. the mono beam was not improved when adjusting monoStig Y at 0.7. If adjust MonoStig Y more than 0.7, it will automatically changed back to 0. Also the beam shape is not oval at 1.0 excitation. When focusing, it is not focusing at one point.
  6. Followed 100493, found I+ and I- is not OL. There was no reading on the insulation meter. And the resistance is 9.7Ohm.
  7. Followed 102961 5.1 to 5.4 passed.
  8. Followed 100493 and test capacitance and it failed, so mono is defective
  9. Exchanged a gun and this behavior is solved

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