FEG microscope problems

[Henning Stahlberg]

Dear colleagues,

We once had a similar problem that also originated from the Ethernet 
cable.
However, it did not affect the beam deflection, but rather the beam 
energy spread, as detected by a spectrum from a GIF.

The shielded Ethernet cable was connecting the ground of the Gatan Mac 
to the ground of the hub, which was connected to the ground of the 
building, which was connected to the ground of the microscope, which 
was connected to the ground of the Gatan Mac. All these groundings 
formed a loop, which is then a strong antenna for magnetic AC fields.

We simply replaced the one Ethernet cable by two shorter Ethernet 
cables in series. These two shorter cables were connected via a little 
PLASTIC connector-box. This way, the plastic connector interrupted the 
grounding, transforming the loop configuration into a star-like 
configuration. (This hint was from Bernd Kraus from Gatan, Germany.)

Henning.



On Thursday, May 15, 2003, at 12:09  PM, Pacific GridTech wrote:

> Dear colleagues,
>
> A similar experience may help Terje to shoot his
> multiple beams problem. I would like to share it with
> everyone.
>
> Few years ago, while we were adjusting a new installed
> CM200FEG scope which equiped with a Gatan Imaging
> Filter CCD, we found a similar problem of multiple
> beams. Since the scope was installled inside a room
> which is with iron walls arround, the outside
> electromaganetic fields were mostly blocked and the
> intensity of fields were reduced to a very low level.
> Therefore, in our case, the multiple beams problem is
> un-likely due to the outside fields.
>
> Eventually, we found the problem is due to an
> un-capped port on the ethernet coaxial cable
> connector. The CCD camera on the scape is controlled
> by a Mac computer and the Mac is connected to local
> area network over a coaxial cable. However, the Mac
> was connected to a multiple coaxial cable connector
> firstly, then the connector connected to ethernet Hub.
> One of the port in the multiple coaxial cable
> connector is un-covered with a port cap, therefore, it
> exposed in air. By capped or un-capped the port, the
> multiple beams problem can be removed or appeared
> respectively. We still don't know the reason.
>
> I hope Terje could gain enlightenment from it for
> shooting his problem.
>
> Wendy Zhang
> Pacific GridTech
> A high quality Cryo-EM grid provider
> 3505 Caminito Carmel Landing
> San Diego, CA 92130, USA
> Tel: (858) 336 8938; Fax: (858) 259 5511
> Email: info at grid-tech.com
> Web: http://www.Grid-Tech.com/
>
>
>
> --- hainfeld at bnl.gov wrote:
>> this may not be the right ans, but:
>> field emitters have electrons coming off of low work
>> function crystal
>> surfaces.  the tip is usually 111 oriented W.  But
>> emission comes from the
>> other surrounding planes, and if not blocked will
>> focus to multiple beams.
>> J. Hainfeld
>>
>> At 02:52 PM 5/8/2003 +0800, Terje Dokland wrote:
>>
>>> We recently had a new JEOL 2010FEG microscope
>> installed. However, after
>>> installation, we find that there is not one, but
>> four to six beam spots!
>>>
>>> The technician says it is due to magnetic
>> interference. He also claims
>>> that it has no effect on resolution, and that may
>> be true with respect to
>>> gold or graphite, but I'm sure it can't be very
>> good for coherence and
>>> phase contrast, and hence the whole purpose for
>> having an FEG is lost!
>>>
>>> Has anybody else had such experience with an FEG
>> microscope? Was it due to
>>> magnetic interference, and was there a way to fix
>> it? We will try a
>>> magnetic field canceler in a few weeks time. Is
>> this likely to work?
>>> Suggestions are welcome, as I am not too happy to
>> pay for the microscope
>>> until this problem has been solved!
>>>
>>> terje
>>>
>>> --
>>> ------------------------------------
>>> Dr. Terje Dokland
>>> Senior Scientist
>>> Institute of Molecular and Cell Biology  <--- NOTE
>> NEW ADDRESS !
>>> 1 Research Link, A*STAR Building
>>> Singapore 117604
>>> Phone: 65-6872 7405  Fax: 65-6872 7007
>>> E-mail: dokland at imcb.nus.edu.sg
>>>
>>> "Convictions are greater enemies of truth than
>> lies"
>>>                                 F. Nietzsche
>>
>> -----------------------------------------------------
>>
>> Dr. James F. Hainfeld  *  hainfeld at bnl.gov
>> Brookhaven National Laboratory  *  Biology Dept.  *
>> Bldg. 463  *  Upton,
>> NY  11973   USA
>> Tel.  631-344-3372  *  Fax. 631-344-3407
>> website:
>> http://bnlstb.bio.bnl.gov/biodocs/stem/stem.html
>>
>
--------------------------------------------------------------------
Henning Stahlberg
M.E. Mueller Institute for Structural Biology; Biozentrum
University of Basel; Klingelbergstr. 70; CH-4056 Basel; Switzerland
Tel: +41-61-267 22 54		Fax: +41-61-267 21 09	
mailto:Henning.Stahlberg at unibas.ch
http://www.mih.unibas.ch/Homepages/stahlberg
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