[3dem] beam blank versus beam shutter

[Tim Gruene]

Dear Robert,

thanks a lot for the numbers, they are very helpful!

The link to Appl. Phys. Lett. seems interesting. I had a mechanic
shutter for the C2-aperture in mind. I will look into the other options.

Best wishes,
Tim


On Fri, 14 May 2021 13:44:15 +0000 "Buecker, Robert"
<robert.buecker at mpsd.mpg.de> wrote:

> Dear Tim,
> 
> the speed of the blanker varies a lot between TEMs and their
> configuration. On our TF20 STEM, where blanking is achieved by
> mis-adjusting the beam tilt, it was in the few seconds range (hence
> unusable for our ED experiments) originally. However, this was
> remedied by replacing a specific electronics board (with what is
> essentially a dummy plug) that filters the gun deflector currents, at
> the expense of somewhat reduced STEM resolution due to jitter. It is
> now of the order of 10 ms, so would be acceptable for your ED
> collection. We actually can trigger our Medipix detector from the
> shutter signal then, though mostly we go vice versa. Titans, on the
> other hand, have a dedicated beam blanker which is ms-range without
> influencing beam jitter or drift. In our JEOL 2100 we get 10 ms or so
> by default, but pushed it to sub-µs using a custom electro-static
> blanker (which might be overkill for most use cases). There is also
> beautiful work by the Antwerp group on a fast magnetic blanker that
> sits on the C2 aperture (Appl. Phys. Lett. 108, 093103). That said, I
> see no real reason against well-engineered (that is, no magnetic
> stray fields, charging, long-term reliability…) mechanical shutters,
> even though I’d rather stick to magnetic or electric.
> 
> Cheers,
> Robert
> 
> --
> Dr. Robert Bücker
> Centre for Structural Systems Biology // University of Hamburg
> Notkestraße 85 // 22607 Hamburg // Germany
> robert.buecker at cssb-hamburg.de<mailto:robert.buecker at cssb-hamburg.de>
> +49 157 70210628
> 
> 
> Am 14.05.2021 um 13:50 schrieb Tim Gruene
> <tim.gruene at univie.ac.at<mailto:tim.gruene at univie.ac.at>>:
> 
> Dear all,
> 
> In 1975, Unwin and Henderson used a beam shutter instead of the beam
> blank (JMB 1975, 94, 425-440) to avoid specimen drifts.
> 
> When I collected ED data with the EIGER detector, i.e. at 100Hz
> (10.1002/anie.201811318), we used a beam blank. I had to inspect each
> data set individually, because the beam was creeping towards its final
> stable position, which took 50-75images, i.e. 0.5-0.75s. This seems a
> lot to me. Those data were measured with a Tecnai F30, which
> is less than 46 years old, but not the latest model either.
> 
> Personally, I would prefer a mechanical shutter over a beam blank.
> What is the current situation with modern TEMs? Does the beam find its
> position within a ms when using the beam blank? Are there reasons NOT
> to use a mechanical shutter? For crystallographic purposes, the
> opening of the shutter to trigger the detector for data recording
> seems quite plausible.
> 
> I look forward to your experience and opinions.
> 
> Best regards,
> Tim
> 
> --
> --
> Tim Gruene
> Head of the Centre for X-ray Structure Analysis
> Faculty of Chemistry
> University of Vienna
> 
> Phone: +43-1-4277-70202
> 
> GPG Key ID = A46BEE1A
> <OpenPGP digital
> signature>_______________________________________________ 3dem
> signature>mailing list
> 3dem at ncmir.ucsd.edu<mailto:3dem at ncmir.ucsd.edu>
> https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem
> 



-- 
--
Tim Gruene
Head of the Centre for X-ray Structure Analysis
Faculty of Chemistry
University of Vienna

Phone: +43-1-4277-70202

GPG Key ID = A46BEE1A
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 195 bytes
Desc: OpenPGP digital signature
URL: <http://mail.ncmir.ucsd.edu/pipermail/3dem/attachments/20210517/3cf02a3d/attachment.sig>