[3dem] Gatan Cryo-Holder
DocDave50 at aol.com
DocDave50 at aol.com
Wed Sep 22 07:02:11 PDT 2010
Hi Heater,
At Yale, we have the 626 which is very stable in terms of temperature,
vacuum, etc. In our runs, we constantly were able to achieve well less than
0.5A/sec drift throughout an entire session.
One issue that we did experience and, in talking with others found this to
be true, is that there is a slight tilt in the holder off of a=0. I
noticed this because with a set to 0, the dewar did not hang parallel with the
microscope center line. I measured the tilt angle using an unused thin holey
carbon grid at room temperature. The angular deviation was something
approximately 5.5o when the holder is set to a=0. This was determined by
setting focus at one side of the grid orthogonal to the tilt axis and then
refocusing on the other side the grid using Da. The same measurement was made
along the tilt axis and yielded little to no significant Da. This was done
a number of times because it was clear that the dewar was not hanging
parallel with the center line of the microscope and it is possible that either a
grid was partially bent or the clip ring not set correctly. In many
applications, this slight angular deviation may not represent a problem. On the
other hand, I do find it to be of concern since a=0 should be better
controlled.
Another issue that we had with our holders was the clip ring assembly. In
the older 60o Gatan Cryo-holders, the clip ring had a slight screw thread
to insure that it was tightly onto the grid at -192C. In the 70o holder,
on the other hand, there is a tension clip in the tip of the holder which
gets loose over time. While at room temperature you can hear and feel the
clip ring insert, at -192C, it was very difficult to ensure that the clip
ring was in place such that it wouldn't be lost in the microscope. Other than
the obvious issue of having to retrieve a dropped clip ring from
compustage assembly, a loose clip ring will contribute to significant drift rates.
As a testimony to this issue, during one repair to our compustage on the
Tecnai 20, 6 clip rings were found inside the Cryo Box. Unfortunately, lost
clip rings are something that user's seem to fail to report to the facility
manager until there are no clip rings remaining in inventory.
Just a thought.
David W. Chester, Ph.D.
currently unemployed due to funding losses
Visiting Research Faculty
Department of Cellular and Molecular Physiology
Yale University School of Medicine
333 Cedar Street
New Haven, CT. 06520
_docdave50 at aol.com_ (mailto:docdave50 at aol.com)
(203) 213-4167
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