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I agree that classically, the potential generated by two surface
layers of dipoles oriented perpendicular to the surface is in the
first approximation directly proportional to the distance between
the layers, that is to the thickness, which argues against the
thickness-independent phase shift. Perhaps that is the reason for
Wanner et al 2006 (the paper recommended by Ben) to propose that
dipoles perpendicular to the beam should be considered:<br>
<br>
"Although only dipole moments with a component perpendicular to the
electron beam would contribute to a phase shift the irregular and
corrugated a-C surface will provide attachment sites for H<sub>2</sub>O
molecules to fulfill this condition."<br>
<br>
Interestingly, Hettler et al 2018, Charging of carbon thin films in
scanning and phase-plate transmission electron microscopy (
<a class="moz-txt-link-freetext" href="https://doi.org/10.1016/j.ultramic.2017.09.009">https://doi.org/10.1016/j.ultramic.2017.09.009</a> ) argue that the high
surface roughness of the Volta phase plate is needed to generate the
phase shift (at a high temperature). Furthermore, in their picture,
surface dipoles are absent from the region of the direct beam, which
causes lateral (perpendicular to the beam) redistribution of
electrons. Both of these could provide the "perpendicular dipoles"
proposed by Wanner et al 2006.<br>
<br>
Vladan<br>
<br>
<div class="moz-cite-prefix">On 6/18/19 9:26 AM, Philip Köck wrote:<br>
</div>
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<p style="margin-top:0;margin-bottom:0">Thanks for the
reference.</p>
<p style="margin-top:0;margin-bottom:0"><br>
</p>
<p style="margin-top:0;margin-bottom:0">I can't make sense of a
thickness-independent contribution to the phase shift either.
The way I see it even a surface layer of dipoles would lead to
a constant MIP and a phase shift proportional to the
thickness.</p>
<p style="margin-top:0;margin-bottom:0">One can think of a
simple model: A slab of completely neutral material (made of
neutrons) covered in a layer of positive charge and outside
that a layer of negative charge that balances the positive
charge. The potential inside this slab will be constant and
independent of the thickness of the slab.</p>
<p style="margin-top:0;margin-bottom:0"><br>
</p>
<p style="margin-top:0;margin-bottom:0">I wonder if we can get a
comment from someone who knows more.</p>
<p style="margin-top:0;margin-bottom:0"><br>
</p>
<p style="margin-top:0;margin-bottom:0">All the best,</p>
<p style="margin-top:0;margin-bottom:0"><br>
</p>
<p style="margin-top:0;margin-bottom:0">Philip</p>
</div>
<hr style="display:inline-block;width:98%" tabindex="-1">
<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt"
face="Calibri, sans-serif" color="#000000"><b>From:</b> 3dem
<a class="moz-txt-link-rfc2396E" href="mailto:3dem-bounces@ncmir.ucsd.edu"><3dem-bounces@ncmir.ucsd.edu></a> on behalf of Benjamin
Himes <a class="moz-txt-link-rfc2396E" href="mailto:himes.benjamin@gmail.com"><himes.benjamin@gmail.com></a><br>
<b>Sent:</b> Monday, 17 June 2019 20:45:48<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:3dem@ncmir.ucsd.edu">3dem@ncmir.ucsd.edu</a><br>
<b>Subject:</b> [3dem] (mean Inner potential) Re: 3dem Digest,
Vol 142, Issue 38</font>
<div> </div>
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<div>
<div dir="ltr">
<div dir="ltr">
<div class="x_gmail_default" style="font-size:small">Hi
Philip,</div>
<div class="x_gmail_default" style="font-size:small"><br>
</div>
<div class="x_gmail_default" style="font-size:small">The
mean inner potential (MIP) refers to a total "interaction"
potential that is considered a material property. It
consists of all the sources contributing to the potential
well seen by an imaging electron, including those you
suggest (nuclear and electronic contributions.)</div>
<div class="x_gmail_default" style="font-size:small"><br>
</div>
<div class="x_gmail_default" style="font-size:small">Yes,
physical changes to the surface via adsorbed matter will
directly affect the MIP. I believe the working hypothesis
for the source of the "Volta" potential is through
heat/exposure related modification of surface adsorbates.</div>
<div class="x_gmail_default" style="font-size:small"><br>
</div>
<div class="x_gmail_default" style="font-size:small">It is
also interesting to note that in addition to the
electronic character of the object, the surface
contributions of adsorbates and heating, there is another
thickness independent phase shift (at least for carbon)
the source of which I am not clear on. Happy to hear an
explanation from anyone in the know : )</div>
<div class="x_gmail_default" style="font-size:small"><br>
</div>
<div class="x_gmail_default" style="font-size:small">Please
have a look at this paper where all of the non-Volta
contributions are discussed and also measured.</div>
<div class="x_gmail_default" style="font-size:small"><br>
</div>
<div class="x_gmail_default" style="font-size:small"><b>"Electron
holography of thin amorphous carbon films: Measurement
of the mean inner potential and a thickness-independent
phase shift"</b></div>
<div class="x_gmail_default" style="font-size:small"><b><br>
</b></div>
<div class="x_gmail_default" style="font-size:small"><b>doi:
j.ultramic.2005.10.004</b></div>
<div class="x_gmail_default" style="font-size:small"><b><br>
</b></div>
<div class="x_gmail_default" style="font-size:small">HTH</div>
<div class="x_gmail_default" style="font-size:small"><br>
</div>
<div class="x_gmail_default" style="font-size:small">Ben</div>
<div class="x_gmail_default" style="font-size:small"><br
clear="all">
</div>
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<font size="2" face="Tahoma"
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style="font-size:13px"><font
face="Arial">Benjamin Himes</font><font
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cryoEM methods development </font><font
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target="_blank"
moz-do-not-send="true"><font
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lab</font></a><font
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Research Campus</font><font
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cryoSTAC development @ </font><a
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<br>
<div class="x_gmail_quote">
<div dir="ltr" class="x_gmail_attr">On Mon, Jun 17, 2019 at
12:17 PM <<a href="mailto:3dem-request@ncmir.ucsd.edu"
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1. mean inner potential of a solid (Philip K?ck)<br>
2. NYC Computational Cryo-EM Summer Workshop<br>
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3. side entry holder for autogrids? (Michael Elbaum)<br>
4. Re: side entry holder for autogrids? (Wim Hagen)<br>
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Message: 1<br>
Date: Mon, 17 Jun 2019 08:27:35 +0000<br>
From: Philip K?ck <<a href="mailto:philip.koeck@ki.se"
target="_blank" moz-do-not-send="true">philip.koeck@ki.se</a>><br>
To: "<a href="mailto:3dem@ncmir.ucsd.edu" target="_blank"
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Subject: [3dem] mean inner potential of a solid<br>
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<br>
Hi all.<br>
<br>
I've been wondering what the mean inner electrostatic
potential of a solid (for example the 10 V of carbon) is
actually due to.<br>
Is it purely caused by the distribution of nuclei and
electrons in the solid itself or could there be a
contribution from adsorbed surface charges?<br>
<br>
All the best,<br>
<br>
Philip<br>
<br>
<br>
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