[3dem] beam blank versus beam shutter

[Wim Hagen]

Dear Tim,

As Robert already mentioned, Tecnai uses the gun coils to blank and on STEM systems these gun coils are filtered. On cryo systems, or for other applications where the blanking needs to be fast, the gun filter is removed and a dummy plug has to be placed on the lower slot. Backside of the TEM cabinet, upper left part, CGPF1 (between QDCR3 and 4). Somewhere in the junk that probably sits in some cabinet for many years, you should find such a dummy plug. I’m not sure anymore if the board is part of the interlock, so if you find the plug and want to swap it with the CGPF1 board, it’s safer to first switch off the system.

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Best,

Wim Hagen
EMBL Heidelberg

> On 17. May 2021, at 08:39, Tim Gruene <tim.gruene at univie.ac.at> wrote:
> 
> 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
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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
> 
> GPG Key ID = A46BEE1A
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