[3dem] (mean Inner potential) Re: 3dem Digest, Vol 142, Issue 38

Wed Jun 26 08:57:58 PDT 2019

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:

"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_2 O molecules 
to fulfill this condition."

Interestingly, Hettler et al 2018, Charging of carbon thin films in 
scanning and phase-plate transmission electron microscopy ( 
https://doi.org/10.1016/j.ultramic.2017.09.009 ) 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.

Vladan

On 6/18/19 9:26 AM, Philip Köck wrote:
>
> Thanks for the reference.
>
>
> 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.
>
> 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.
>
>
> I wonder if we can get a comment from someone who knows more.
>
>
> All the best,
>
>
> Philip
>
> ------------------------------------------------------------------------
> *From:* 3dem <3dem-bounces at ncmir.ucsd.edu> on behalf of Benjamin Himes 
> <himes.benjamin at gmail.com>
> *Sent:* Monday, 17 June 2019 20:45:48
> *To:* 3dem at ncmir.ucsd.edu
> *Subject:* [3dem] (mean Inner potential) Re: 3dem Digest, Vol 142, 
> Issue 38
> Hi Philip,
>
> 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.)
>
> 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.
>
> 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 : )
>
> Please have a look at this paper where all of the non-Volta 
> contributions are discussed and also measured.
>
> *"Electron holography of thin amorphous carbon films: Measurement of 
> the mean inner potential and a thickness-independent phase shift"*
> *
> *
> *doi: j.ultramic.2005.10.004*
> *
> *
> HTH
>
> Ben
>
> ------------------------
> Benjamin Himes
>
> cryoEM methods development
> Grigorieff lab 
> <https://mail.hhmi.org/owa/redir.aspx?C=SbsCefkcbOt75jDyr05lpd3OifVN_utmfvnhZrtXS7Bl2i2eOXXVCA..&URL=http%3a%2f%2fgrigoriefflab.janelia.org%2f>, 
> HHMI Janelia Research Campus
>
> cryoSTAC development @ emClarity 
> <https://mail.hhmi.org/owa/redir.aspx?C=8yDzXj54yTidMevTB7q5m3liEVwqAZ9LxuXQ4iYOVvtl2i2eOXXVCA..&URL=https%3a%2f%2fgithub.com%2fbHimes%2femClarity%2fwiki>
>
> -------------------------
>
>
> On Mon, Jun 17, 2019 at 12:17 PM <3dem-request at ncmir.ucsd.edu 
> <mailto:3dem-request at ncmir.ucsd.edu>> wrote:
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>        1. mean inner potential of a solid (Philip K?ck)
>        2. NYC Computational Cryo-EM Summer Workshop
>           (Cindy Rampersad-Phillips)
>        3. side entry holder for autogrids? (Michael Elbaum)
>        4. Re: side entry holder for autogrids? (Wim Hagen)
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>     ----------------------------------------------------------------------
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>     Message: 1
>     Date: Mon, 17 Jun 2019 08:27:35 +0000
>     From: Philip K?ck <philip.koeck at ki.se <mailto:philip.koeck at ki.se>>
>     To: "3dem at ncmir.ucsd.edu <mailto:3dem at ncmir.ucsd.edu>"
>     <3dem at ncmir.ucsd.edu <mailto:3dem at ncmir.ucsd.edu>>,
>             "microscopy at microscopy.com
>     <mailto:microscopy at microscopy.com>" <microscopy at microscopy.com
>     <mailto:microscopy at microscopy.com>>
>     Subject: [3dem] mean inner potential of a solid
>     Message-ID:
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>
>      Hi all.
>
>     I've been wondering what the mean inner electrostatic potential of
>     a solid (for example the 10 V of carbon) is actually due to.
>     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?
>
>     All the best,
>
>     Philip
>
>
>
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