[3dem] Objective Astigmatism Stability

[Farzad]

Dear Colleagues,

After receiving valuable comments from you, especially those from Sacha De
Carlo, Christos Savva, Richard Gursky and Bill Anderson we came to a
conclusion that contamination should be one of the most important causes of
"astigmatism drift". So we tried a cryocycle and the EM is "almost" stable
but not 100%. It may need more time to be completely cleaned or may need
extra cleaning procedures.

I learned that we have to pay more attention to the cleanness of the grids
and tweezers and also about the new tweezer an extra attention is needed
since they are grinded in the factory and there might be a loose stainless
steel particle/shavings which may enter with the sample into the column.
The stainless steel becomes magnetic in LN2 temperature. Also any
dielectric (insulating) particle such as staining materials or formvar may
cause electric charge and deflect the beam. So, I decided to always
sonicate the new tweezers from now on and to clean my grids and tweezers
and dry them with proper solutions before use.

Thank you guys for helping me in this matter.

Farzad Hamdi



On Tue, Aug 20, 2019 at 11:42 AM Farzad <farzaad at gmail.com> wrote:

> Dear All,
>
> Anybody has any experience in measuring the stability of objective
> astigmatism in FEI F20 FEG columns (Tecnai, Talos or Glacios)? How much let
> say "astigmatism drift" is normal if we do not change anything and come
> back to the instrument after 15 minutes. I mean just imagin after
> correcting it on a carbon film area and check it on a same region and same
> optical set-up after a certain time?
>
> the sample is normal carbon grid, no magnetic or loos particles there, and
> also there is no major sample drift.
>
> Regards
>
> Farzad
>
>
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