[3dem] Newbie question - Thickness of the ice

[shixinwang at micron.com]

Two good ways for your sample: 
1) EELS. 
2) tomography. 
EELS is easy, it gives relative thickness in terms of mean free path.
You will need to get the mean free path value if you need the absolute
thickness. 

Tomography is the direct way. You will get good result if there is
enough surface features (particles, contaminations, etc). Even if you
don't do whole tomography, you may figure out the sample thickness if
there is enough features on both surfaces. 
If you do tomography, the tomogram will do everything for you. If you
don't do the whole tilt series, try this: tilt the sample over some
large range (say, 0 degree, 20 degree, 40 degree, -40 degree), compare
the particles (I guess there are virus) position to guess if they are on
both sides. If so, try tilt the sample to bring two virus overlap (one
on top surface, and one on bottom surface), Remember that tilt angle.
Then tilt away to some large angle. The combination of the distance of
the two virus and the tilt angle will give you the distance between the
two virus. From that and the tilt angle where the two overlap, you can
calculate the sample thickness, assuming the ice is flat at zero tilt.
Of course, if you can find two viruses overlap at zero tilt, the
calculation will be much easier. 

Shixin



-----Original Message-----
From: 3dem-bounces at ncmir.ucsd.edu [mailto:3dem-bounces at ncmir.ucsd.edu]
On Behalf Of Eduardo Sanz Garcia
Sent: Friday, October 24, 2008 6:30 PM
To: 3dem at ucsd.edu
Subject: [3dem] Newbie question - Thickness of the ice

Dear 3DEM users,

How do I asses the thickness of the ice for SPA?
Is there any qualitative method to determine the ice thickness?

Thank you very much.
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