[3dem] 914 Synopsis

[Cindi Schwartz]

Dear 3DEMers,

I got a lot of response about the 914 holder and thought I would try  
and give a synopsis of what's been said:

1. Try and leave the cryo-shield in place at least 20min after  
inserting the holder into the scope. We're not sure on this one, but  
in general, I would say that almost all of us open the shield as soon  
as the column vacuum recovers (less than 5-10 min).  However, we do  
the same thing with the 626 and have no cauliflower at all.

2. Try to look at a grid in the 626 first, then transfer to the 914.  
We haven't done this, although it was on my list to try.

3. Other labs (3) reported similar issues and after tomography see  
that this cauliflower (or cobblestone) appearance is only on one  
surface. This suggests that maybe the cryo-shield is the culprit as  
there is a small gap between the cryo-shield and the tip.

4. One suggestion was to open the cryo-shield quickly, check to make  
sure there was something worth looking at, then close the cryo-shield  
and wait 30min.

5. Others who wait at least 20min before opening the cryo-shield also  
have cauliflower ice when using the 914.

6. A similar phenomenon happened with the old CT3500 design (1996). It  
was solved by cooling the holder down, letting it frost up, put into  
the Gatan cryo-pumping station to maintain vacuum, and then after  
opening the cryo-shield, noting that frost was building up on the  
edges of the specimen. We don't have a way to do this in our lab, so  
someone else should volunteer for this :)

7. At least one person has reported to Gatan this issue, but no one  
else has complained until now. I think that we now have enough  
anecdotal evidence at least for Gatan to take this as a serious issue  
and look at their design.

Thanks for your input!

Cindi


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Cindi L. Schwartz
University of Colorado, Boulder
Dept. MCDB
BL3DEMC
O: 303-492-7980
F: 303-735-0770
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