[3dem] dirty condenser apertures

[Wim Hagen]

Hi Heather,

I could be that the microscope was used too soon after the aperture exchange. Apertures get dirty from bad vacuum and beam interaction. When the apertures have been replaced in the morning and they have been imaged at the end of the day, the vacuum might not have been that good inside the scope. The vacuum readout might have been ok, but this reading comes from inside the ion getter pump so it  is the local vacuum in the pump that is measured.

I would clean/replace the apertures on a friday afternoon, let it pump for the weekend (don't cool it down immediately), use everything on monday again. Every day the scope is used,  regardless of the sample used, cool it down in the morning and run a cryo-cycle at the end of the day.
Cooling down the scope improves the column vacuum. During cryo cycle, the ion getter pumps are switched off, the turbo pump is started, the cold trap warms up and releases trapped water molecules which are removed by the turbo pump.

This keeps vacuum and apertures clean, regardless of the type of sample used.

Best regards,

Wim Hagen
EMBL Heidelberg

On Sep 28, 2012, at 4:53 PM, Heather Holdaway wrote:

> We have an FEI TF20 with a FEG.  We just changed out all the C2 apertures yesterday and they were looking very clean and nice at the end of the day.  We ran a cryo cycle overnight and now this morning all 4 apertures are very dirty.  Has anyone else ever had this happen?  Any ideas as to why the apertures became dirty so quickly?
> 
> Thanks!
> Heather
> -- 
> Heather Holdaway
> Electron Microscope Manager
> Cleveland Center for Membrane and Structural Biology
> 
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