[3dem] 626 holder drift- reply to Benoit Zuber

[Kenneth Goldie]

Greetings Benoit,

does the drift show any circular motion? Slow straight drift then a sudden circular sweep? If so, I would suspect it is a clip ring problem where the grid is not being held firmly and moves after a while due to charging or possibly a warming affect. Replace the clip ring, and/or the spring that holds the clip ring in place when "clipped" into the holder. Be careful not to damage the tip. We do this at least once per year but use our holders daily, so depends how often the holder is used. A quick way to check if the grid is held well is to clip a grid (one you do not mind destroying!) into the holder at room temperature and then poke it with a sharp tweezer tip to see if it moves at all. It should hold tightly so that it does not slide at all and the grid bars will rip under the force of the tweezer before the grid moves. The 70 degree holders are more prone to clip ring problems as the rings have to be thinner so they do not have so much "bite". Try again with the holder cooled in the transfer station. The holder tip and "pit" where the grid goes into should also be meticulously clean (sonicate the tip in a suitable solvent). Vacuum problems can normally be excluded if you pump the Dewar on a pump stand for a while to high vac 1x10 -5 or better, close off the the holder Dewar valve for 3 minutes and open again. If the vacuum drops substantially then you have a vacuum problem but as you allude to, this normally shows as drift along the rod axis.
If all else fails send off to Gatan who will be very happy to fix it for a good fee.
Good luck

and best regards

Ken

Ken Goldie, PhD
Facility Manager, C-CINA, Biozentrum, University Basel
Mattenstrasse 26 | D-BSSE | WRO-1058 | CH-4058 Basel | Switzerland
http://c-cina.org<http://c-cina.org/> | Tel. +41-61-387 32 18| eMail. k.goldie at unibas.ch<https://mail.unibas.ch/owa/UrlBlockedError.aspx>




Today's Topics:

1. drift (benoit.zuber at ana.unibe.ch)


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Message: 1
Date: Wed, 22 Jan 2014 14:35:12 +0000
From: <benoit.zuber at ana.unibe.ch>
To: <3dem at ncmir.ucsd.edu>
Subject: [3dem] drift
Message-ID:
<ED52A0B89182E14795358F187A42231542878483 at aai-exch-mbx1.campus.unibe.ch>

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Dear colleagues

Our cryo-holder (Gatan 626 70 degrees) has recently started showing an interesting drift behavior under cryo conditions on our Tecnai F20 (imaging with SerialEM). After transfer and the usual temperature stabilization, the holder is quite stable for about one hour. Then the problem starts (see https://dl.dropboxusercontent.com/u/6743833/drift/drift.mp4 ). The sample starts drifting quite fast in one direction, slows down after drifting between roughly 500 and 1000 nm and then drifts in the opposite direction until it returns to its original position and stops. It then remains stable for a variable amount of time (typically 1 minute) and then starts a new cycle of drift. The stage position reading does not change during this time. The temperature reading of the holder is also stable. Interestingly, the drift direction is perpendicular to the tilt axis.
We suspect a tiny and discontinuous leak in the vacuum chamber of the cryo-holder dewar. Nonetheless, we would have expected the movement to be parallel tilt axis if it was due to thermal changes in the holder rod.
Has anyone faced (and fixed) this problem before? Any tip would be highly appreciated.

Best wishes
Beno?t

Beno?t Zuber
Institute of Anatomy
University of Bern
Baltzerstrasse 2
CH-3000 Bern 9
Switzerland
Tel. +41 31 631 84 40
benoit.zuber at ana.unibe.ch
http://www.ana.unibe.ch/~exmo/

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