update on cryostation

Yasuhiro Oshima yoshima at stanford.edu
Fri Jun 6 16:33:43 PDT 2008


Hi Arash,
  I checked all the tips' continuity before cool it down and found 3& 4 were
strange. So it happened without oil condensation.

  As for oil back diffusion... The design of this vacuum system, including
automatic pump down/vent sequence is not good. There are no isolation valves
and this sequence supply the vent nitrogen from downstream of TMP into the
chamber right after stopping pump. Once these back diffused oil accumulate
in the chamber, it is very difficult to remove, just increase gradually. My
another suggestion is that to put valves between chamber/TMP and TMP/rotary
pump, and nitrogen line directly into the chamber, though it may make the
procedure complicated.
  Actually, we have seen hazy surface on our sample every time. But I did
not realized that this may behave as insulator.

Thanks,
  Yasuhiro
2008/6/6 Arash Hazeghi <ahazeghi at stanford.edu>:

>  Yasuhiro,
>
> Thanks for reporting the issues.
>
>  Regarding the back diffusion I will look at the pump and contact Varian,
> this shouldn't be a problem if the pump is operating correctly since we
> never had this issue before. There should not be back diffusion to the
> extent that you can detect oil in the chamber, if this is the case the pump
> has aged and gone bad, not that we need a dry pump.
>
> I checked the continuity between all probes at room T and they were OK, it
> is very strange that you are not getting good contact my guess is you are
> not touching the pads or as you mention there is a thin layer of something
> on your sample and at low voltages this may be an issue since the tips are
> really soft. Per your request, I will check this again.
>
> Now regarding the probe tips,* All four probe tips* were brand new and in
> *perfect* shape when I replaced them just last week. I will look in the
> logbook to see who used them. This is becoming a major issue, I cannot
> replace the probe tips every week and our group will not pay for it.  Per
> prof. Wong's suggestion from now on, whoever breaks the tips and don't
> report it will not only have to buy new tips but will also be suspended from
> the system for two weeks. No exceptions.
>
> Please be considerate when lowering and raising the tips. Never keep the
> tips contacted to the sample or in close proximity before pumping down or
> cooling. As the chamber goes to high vacuum the bellows  are stressed and
> bow a little bit, as a result tips that are close to surface will crush or
> may even run into each other. Position and lower the tips only when pressure
> and temperature have been stabilized. Never lean on the table, yank the
> cables or subject the system to mechanical shock when tips are in contact.
> If users operate the probes according to the training these tips should last
> for months.
>
>
>
> Thank you all for your cooperation ,
>
> Arash
>
>
>
>
>
>
> ----------------------------------------------------------------------------------
>
> Arash Hazeghi
>
>
>
> PhD Candidate
>
> Stanford Center for Integrated Systems
>
> CIS-X 300, 420 Via Palou Mall,
>
> Stanford, CA 94305
>
>
>
> phone: +1-650-725-0418
>
> web: http://www.stanford.edu/~ahazeghi
>
>
>
>
>
>
>
>
>
>
>
> *From:* yoshima73 at gmail.com [mailto:yoshima73 at gmail.com] *On Behalf Of *Yasuhiro
> Oshima
> *Sent:* Friday, June 06, 2008 3:13 PM
> *To:* Arash Hazeghi; Duygu Kuzum; shanbin at stanford.edu
> *Subject:* update on cryostation
>
>
>
> Hi all,
>
>   Now the cyostation working at 77K very well. As Shanbin pointed out, it
> seems that we had a contact issue between needle and metal pad due to very
> hard condensed liquid (maybe vacuum oil back diffused into chamber). I just
> replaced old vacuum oil of rotary pump. It turn into yellowish color
> gradually. It seems to be important to replace it like once in 3 months.
> Thanks for good suggestion, Arash! Another information are bellow.
>
>
>
> - new oil and container for old oil are near the cryostation. (Arash, could
> you move to good position?)
>
> - I still see some liquid (solid. maybe oil) on my samples. They look hazy.
>
> - if you'd like to solve this problem permanently, I would recommend to
> replace oil pump with diaphragm pump (this is dry).
>
> - probe tips 3 & 4 are not working (it seems completely isolated). Arash,
> please take a look at it!
>
> - probe tips 1 & 2 are bent and not comfortable.(It is not me...)
>
>
>
> Best,
>
>   Yasuhiro
>
>
> --
> Yasuhiro Oshima
> 408-398-4753 (cell)
>



-- 
Yasuhiro Oshima
Visiting Scholar
Prof. McIntyre Gr.
Materials Science and Engineering
Stanford University
650-725-3458
408-398-4753 (cell)
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