update on cryostation

Duygu Kuzum duygu at stanford.edu
Fri Jun 6 16:41:09 PDT 2008


I also observed that last year too.Probing at low temperature was very  
difficult.Sometimes I got bad contact causing a lot of noise.Sometimes  
I couldnt get contact.

Thanks Yasuhiro,

Duygu

Quoting Yasuhiro Oshima <yoshima at stanford.edu>:

> 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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