[3dem] Re: [Microscopy] Ice contamination

P Wang P.Wang at sheffield.ac.uk
Wed Nov 7 08:34:35 PST 2007

Dear David and Angel,

Many thanks for the reply. I might not state very clearly for the proposed of
this test. The suggestion of this method is to be used to find out whether
there is ice contamination during the cold transfer or not. On other word is
that can we know where the ice contamination came from if there is any when we
just open the gun valves by this method without knowing previous condition of
the carbon film.



Quoting Angel Paredes <Angel.Paredes at uth.tmc.edu>:

> Hi Peiyi,
> Better yet, if you have a gatan holder.  Put the grid in the holder at 
> room temperature.  Put it in the scope and then cool the holder down while 
> it is in the scope.  When it is cold, let it sit in the scope for a while. 
> When its been there for a while, go to a higher mag and put the beam on 
> the carbon with the beam expanded to just the size of the viewing screen. 
> Let it sit for a while, then go down in mag.  If there is contamination, 
> you will see a round foot print of the beam used at the higher mag on the 
> lower mag image you see on the screen.  The suggestion you have below 
> would also work but if contamination is slow or very little, the 
> contamination would be gone fast after the beam exposes the area before 
> you see burning.
> angel
> On Wed, 7 Nov 2007 P.Wang at sheffield.ac.uk wrote:
> >
> >
> >
> >
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> > Dear all,
> >
> > May I have your guys options about the test method of ice contamination. I
> have
> > been suggested to use following way to test whether there is an ice
> > contamination or not during the cryoTEM session:
> >
> > Cooling down a plain carbon film grid in LN2. Cold transfer it into
> microscope
> > and focus the beam at lower magnification (5000X). It shall be able to see
> a
> > burning area on the carbon film and then brings the temperature up. This
> area
> > would disappear during the temperature up so this is suggestion that there
> is
> > an ice contamination.
> >
> > Your options are highly appreciated.
> >
> > Peiyi
> >

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