[3dem] Seeking advice on Lab6 filament life time

[Farzad]

Dear Mufeeda,

The lifespan of a LaB6 gun depends on several critical factors, including
(1) vacuum level, (2) oversaturation, and (3) mechanical stresses. In a
conventional TEM setup where a nearly parallel electron beam is employed
(not STEM), it is recommended to operate with a filament current level
that's one or two steps below the saturation limit. Exceeding this
saturation point can lead to adverse consequences as the tip begins to
deplete its lanthanum content, subsequently causing an increase in work
function. To counteract this increase, users may raise the filament
current, further accelerating tip depletion. Moreover, maintaining a low
vacuum level can introduce contamination, and in severe cases, trigger
arcing, both of which can harm the tip.

Earöy determination of the end of the LaB6 gun's operational life can be
somewhat complex. If the gun is correctly installed and perfectly aligned,
any abnormal emission patterns, such as deviations from the classic
four-fold emission shape with a central peak or significantly reduced beam
current, can be indicative of an approaching end. It's essential to note
that blinking, in itself, doesn't necessarily signal the end of the gun's
life; it could be attributed to issues in the high-tension tank, gun head,
cable, or even suboptimal vacuum conditions. Contaminants in the wehnelt
cup, objective pole piece or within other parts of the column can also
induce such effects. While arcing is less likely to occur at 120 kV, it's
still crucial to verify the vacuum level and monitor emission current
fluctuations. If issues persist, it's advisable to consult your service
contract provider.

Please be aware that my direct experience with LaB6 TEMs is limited to an
older Philips CM200, and I haven't worked with a Talos 120 kV. However, as
a general guideline, the typical lifespan of a LaB6 gun under continuous
operation is approximately six months. Factors like suboptimal vacuum
levels, arcing, frequent thermal cycling (number of turning on and off),
and oversaturation (excessive filament current) can shorten this lifespan
due to thermal stresses and contamination buildup.

Best Regards,

Farzad Hamdi
Kastritis Laboratory for Biomolecular Research
Institute of Biochemistry and Biotechnology, Biocenter,
Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
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On Wed, Oct 11, 2023 at 8:19 AM Mufeeda C M <mufeeda.01 at gmail.com> wrote:

> Dear 3D EM members,
>
> We have Talos L120C, recently we noticed that the beam is quite unstable
> (it kind of started flickering). Filament readout shows 830+ hrs. Should
> we replace the filament sooner?
>
> Is there any disadvantage if we set the filament heating upto 50?
>
> [image: image.png]
>
> --
>
> Thanks & Regards
> Mufeeda Madathummal
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> 3dem at ncmir.ucsd.edu
> https://mail.ncmir.ucsd.edu/mailman/listinfo/3dem
>
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