[3dem] icing with Gatan ELSA 698

[Reinhard Rachel]

Hi Tim, 

getting back to this from the PC. 

> our Gatan ELSA 698 holder produces ice such that we see the ice rings
> in the ED diffraction pattern. 

suspicious .... at which nominal temp. (indicated on the controller) do you
start to see the ice ring (= crystallinity)?

> The ice evaporates at -130C, but returns
> as soon as we reduce the temperature again below about -140C.

these temp. readings are even more suspicious. How do you know how good the
vacuum is  in the sample holder area? hmm. The vacuum meter is not in this
area, but pretty far away from the tip of the holder;  meaning you do not
exactly know.   In a typical, good vacuum of a TEM, water will only "go away" =
sublimate in a measurable rate at higher temperature. I would have to check my
old tables, but -120 or -110 C? (this is equivalent to freeze-etching in the
old Balzers machines! at -130 C, water usually does not sublimate, not at
10(-6) mbar; but, this depends on the real absolute temperature and the UHV
status exactly in this area; no machine has a physical vacuum meter sitting on
the sample. Thus, the behaviour of the sample is an indicator for (a) temp, (b)
vacuum).  --  I am not convinced that the temperature indicated is correct, if
the water 'evaporates' = sublimates.
And yes, you are likely to have a lot of water inside the column. A really
good reason to go for a 3-4 days bakeout. Easily done, and more than worth
doing.  And have the leak rate checked on your TEM. 

> This also occurs when we insert the holder at room temperature and only
> cool it once fully inserted into the TEM (JEOL JEM2100Plus)

as already said: how good is the vacuum of this TEM? Bakeout recently done?
are the vacuum meters ok and checked, recently? 

> Would there be any ideas for the cause of this icing, and maybe even a
cure?

first thing: vacuum is bad. Second, have the Elsa checked (Temp. indicated is
odd  ...) 
kind regards,
Reinhard

-- 
Prof. Dr. Reinhard Rachel
University of Regensburg
Centre for EM / Anatomy
Faculty of Biology & Preclin. Med.
Universitaetsstrasse 31
D-93053 Regensburg - Germany
tel +49 941 943 -2837, -1666
mail reinhard.rachel at biologie.uni-regensburg.de
office: VKL 3.1.29 
member of the IFSM board

Next microscopy conferences:
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