[3dem] Pre-Specimen Shutter (Yu, Xiaodi [JRDUS])

[Tim Gruene]

Dear Wim,

thanks a lot for the detailed explanation!

Are there reasons for not having a mechanical shutter in a TEM? I would
think a metal lid at, e.g. the Condenser 2 aperture would be very small
and the removal should be fast enough to not disturb most
applications.


Best,
Tim



On Wed, 24 Jun 2020 13:05:37 +0200
Wim Hagen <hagen at embl.de> wrote:

> Tecnai and CM microscopes did not have a dedicated coil to blank the
> beam pre-specimen, so the gun deflector coils where used to blank the
> beam, hence "Gun Deflector (beam blanker)". Since deflector
> electronics were noisy at the time, they were filtered and thus slow,
> which could be seen when opening the column valves on a e.g. normal
> Tecnai: the beam would slowly move in from the side of the screen.
> On cryo-systems the gun deflector electronics filter was removed so
> it was fast enough for blanking purposes, but you didn’t want to do
> STEM on those systems as the noise on the gun coils would ruin
> things. On Titan systems a true dedicated blanker coil was
> introduced, hence "Gun blanker (pre-specimen shutter)", but some
> parts in software still use the gun deflection coils, hence a
> confusing mix of things, depending on which software one uses to
> control the camera. Talos/Glacios does not have a dedicated blanker
> ("Gun blanker (pre-specimen shutter)”), everything is still done
> through the gun deflection coils ("Gun Deflector (beam blanker)”).
> All the newer scopes have better deflection electronics, so no
> filtering needed, so shuttering is fast enough, so far…. Best, Wim
> 
> > On 24. Jun 2020, at 03:19, Matthews-Palmer, Teige
> > <t.matthews-palmer14 at imperial.ac.uk> wrote:
> > 
> > Can anyone explain the difference between Gun Deflector (beam
> > blanker) and Gun Blanker (pre-specimen shutter)? Gun Blanker sounds
> > either like a mechanical shutter hardware option not installed; or
> > part of the Gun Deflector - but then why is it a separate device in
> > the microscope control software?
> > 
> > Grateful for any explanations!
> > Teige
> >   
> >> On 24 Jun 2020, at 02:02, Jason Kaelber <jason.kaelber at rutgers.edu
> >> <mailto:jason.kaelber at rutgers.edu>> wrote:
> >> 
> >> This email from jason.kaelber at rutgers.edu
> >> <mailto:jason.kaelber at rutgers.edu> originates from outside
> >> Imperial. Do not click on links and attachments unless you
> >> recognise the sender. If you trust the sender, add them to your
> >> safe senders list
> >> <https://urldefense.com/v3/__https://spam.ic.ac.uk/SpamConsole/Senders.aspx__;!!Mih3wA!VFParMj59ZHBcjRq4bZfapb6-MrwsKanClm_O9bCr_8yFnjrCicS3CNQKZ0L4R0o_Q$>
> >> to disable email stamping for this address. Hello Xiaodi, The
> >> Blanker/Shutter Monitor window is showing what you would expect it
> >> to show if everything is working. When the deflector coil
> >> (pre-specimen shutter) is displayed as orange (N/A), the
> >> Blanker/Shutter Monitor window does not know the instantaneous
> >> state because it is controlled by the camera. Unfortunately you
> >> would also see the orange if it's almost working but the camera is
> >> not controlling the blanking correctly (very rare). Cheers, Jason
> >> 
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-- 
--
Tim Gruene
Head of the Centre for X-ray Structure Analysis
Faculty of Chemistry
University of Vienna

Phone: +43-1-4277-70202

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