[3dem] Charging & vpp

[Benjamin Himes]

For a detailed look at specimen charging see Chris Russo's paper (
doi.org/10.1016/j.ultramic.2018.01.009)

Charging as related to the VPP, see Rado's paper (
dx.doi.org/10.1073/pnas.1418377111)

"Beam irradiation produces positive charges on nonconducting surfaces (21,
22), which leads to phase retardation (22). The phase advance observed here
means that the irradiated area has a negative potential, which cannot be a
result of beam- induced electrostatic charging."

Happy reading,

Ben

On Sun, Mar 24, 2019, 3:00 PM <3dem-request at ncmir.ucsd.edu> wrote:

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>    1. Re: ctf-fitting with phase plate (Daniel Asarnow)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Sat, 23 Mar 2019 12:51:34 -0700
> From: Daniel Asarnow <asarnow at msg.ucsf.edu>
> To: Philip K?ck <Philip.Koeck at ki.se>
> Cc: "3dem at ncmir.ucsd.edu" <3dem at ncmir.ucsd.edu>
> Subject: Re: [3dem] ctf-fitting with phase plate
> Message-ID:
>         <CALiNCbY15w+-61iDOKXJbXTX5cYkMcMe8Sjb=
> HDBb5gqYFG+wQ at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hi Philip,
> It's just an additional phase added to the argument of the sine and cosine
> (amplitude contrast) functions in the CTF. See e.g. Eqn 2. in the CTFFIND4
> paper <http://www.sciencedirect.com/science/article/pii/S1047847715300460
> >.
> It is not dependent on spatial frequency - every frequency gets the same
> additional phase shift due to the plate. Here is a gist
> <https://gist.github.com/asarnow/b47c7f1c7aab1d292c10a8c03dd1b6b8> of a
> Python function for evaluating the CTF, which is much the same as those in
> Relion or cisTEM.
>
> I'm not sure if anyone knows the sign of the accumulated charge, but I
> imagine electrons are deposited and the charge is negative. Maybe someone
> else here has a better physically intuitive argument one way or the other.
>
> Best,
> -da
>
> On Sat, Mar 23, 2019 at 5:23 AM Philip K?ck <Philip.Koeck at ki.se> wrote:
>
> > Hi.
> >
> > I've been looking for information on the contribution of a self charging
> > phase plate (hole free or Volta)
> > to the argument of the CTF in weak amplitude and phase approximation for
> > homogenous specimens.
> >
> > What function is used to describe the phase shift as a function of
> spatial
> > frequency?
> >
> > Also, is the charge produced by the TEM-beam positive or negative (or
> > both)?
> >
> > All the best,
> >
> > Philip
> >
> >
> >
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