[3dem] contamination...leopard?

[Wim Hagen]

Dear Tobias,

Many years ago we noticed something similar on our Polara after a sample being inside the column for just one night:

-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 31901 bytes
Desc: not available
URL: <http://mail.ncmir.ucsd.edu/pipermail/3dem/attachments/20220105/9315ad04/attachment-0002.jpg>
-------------- next part --------------


Some suggested a vacuum leak but I installed a mass spec for helium leak testing which showed no leak and the spectrum looked great for a cold microscope. Inspection of the cartridge showed that it was not clipped properly:

-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.jpg
Type: image/jpeg
Size: 33079 bytes
Desc: not available
URL: <http://mail.ncmir.ucsd.edu/pipermail/3dem/attachments/20220105/9315ad04/attachment-0003.jpg>
-------------- next part --------------


My first guess is that you might be suffering from a sample temperature problem, not a vacuum problem. Could also be caused/amplified by bad cryo-shielding around the sample (-> temperature problems). Since it is a Titan Halo, I would expect a cryo-box or cryo-shields: does that part cool down properly? During cooldown it should move when imaged at the lowest magnification, this small movie shows 30 minutes of a Tecnai 12 retractable cryo-box movement during cooldown:

-------------- next part --------------
A non-text attachment was scrubbed...
Name: cryoboxcooldown.m4v
Type: video/x-m4v
Size: 1030899 bytes
Desc: not available
URL: <http://mail.ncmir.ucsd.edu/pipermail/3dem/attachments/20220105/9315ad04/attachment-0001.bin>
-------------- next part --------------


On systems with side-entry cryo-holders, the pump-time for holder insertion is limited and pressure is not measured by the vacuum system. If a grid contains a lot of frozen ethane (from a fast transfer from ethane into liquid nitrogen on the plunge freezer), this ethane will sublimate in vacuum: too much ethane and/or short pump time -> column vacuum crashes as the ion getter pumps see a lot of ethane coming in when the holder is inserted. 

Best,

Wim Hagen
EMBL Heidelberg

> On 5. Jan 2022, at 10:23, Tobias Furstenhaupt <furstenh at mpi-cbg.de> wrote:
> 
> Dear colleagues,
> 
> although we dont get a high samplethroughput on our Titan Halo, we tested the Gatan ELSA holder and imaged 3 days and nights straight to get data for SPA.
> I heard that side-entry TEMs (like our Halo) are more prone to contamination build up over time but we could not see a clear increase in contamination over time.
> But our images suffered badly from contamination (see attached images). We see images with fuzzy contamination and also images with darker, more well defined blobs. Probably just two stages in the course of contamination buildup - or what do you think?
> We also sometimes see the contamination in in two phases (attachment liquid_border). 
> 
> Am I right in assuming that we see the notorious leopard ice that is humidity contamination from a bad vacuum or slow/suboptimal handling after plungefreezing? Indeed our vacuum crashed more often than not when inserting the holder (despite greasing the O-Ring in advance)...so this could explain it. What is your opinion when you see the images?
> 
> thanks alot in advance :)
> Tobias 
> 
> 
> ----------------------------------- 
> Tobias F?rstenhaupt, PhD 
> head of Electron Microscopy 
> Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) 
> Pfotenhauerstrasse 108 
> 01307 Dresden, Germany 
> 
> mail: furstenh at mpi-cbg.de 
> phone: (+49) (0)351 210-2690 
> cell: (+49) (0)176 / 44498706 (NEW!)
> <fuzzy_contamination.png><liquid_border.png><well_defined_contamination.png>_______________________________________________
> 3dem mailing list
> 3dem at ncmir.ucsd.edu
> https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem