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Warming my sample holder

  1. Dec 22, 2008 #1
    Hi all,

    I have a quite easy question, but I have no experience with this. At our lab we do a lot of experiments on low temperatures (<4K). For example we use helium-3 to obtain 500mK. To obtain this temperature we use Zeranin-wires in our setup. But now our sample (graphene) should be annealed on high temperature (~250 C) before the experiment starts. The question is: will the coating on my wires burn on this temperature or is there maybe a better wire to use at top of the insert? (since only of the insert is in the oven during warming)

    Thanks for your answers!
  2. jcsd
  3. Dec 22, 2008 #2
    I think that the answer is yes, the coating will be degraded.
    But I wonder why do you have to warm all your insert at that high temperature? I don't know what kind of system are you using, but He3 cryostats use to be delicated, warming them at such a temperature could damage it permanetly. For example the cryopump, the He3 valves or even the pressure inside the He3 volumen could be too high and explode.
    If you can explain a bit more of your idea...
    hope this helps
  4. Dec 22, 2008 #3
    Maybe I was indeed a bit short about the details. Our experimental setup is in principle apart from the HE3-system, we can insert it in the He3-cryostat. So during the heating the sample is in a pumped tube with inside an insert (at top the sample). I have over here poorly no pictures, but you can see it as follows:

    --(stick)+++++++++++++++++++++++++++++++++++++++++===| (Sample)|

    So you pump inside and flush 3 to 4 times with helium to get rid of air and oxygen. Maybe the last part is most important to prevent burning of the wires.

    But why heating my sample-holder? My sample is made of graphene, a single layer of graphite. Due to different effects the sample can be doped, more electrons or holes are on the surface of the sample. By heating and pumping on my tube, I can get rid of these charges and make the sample "neutral charged". (we can shift the so-called charge neutrality point (CNP))

    So far I have used a top sample-holder made of high sol, but this melts above 120 C. This temperature is not enough too anneal fast (I have now a heavily doped sample and already annealing for 3 weeks). So the new top-part is made of vespel, a high quality polymer that melts around 300 C. But as I remember from the past it can be risky too warm up the coating of my wires.

    Maybe best idea is too try this by trial and error with some test wires.
  5. Dec 23, 2008 #4
    Well at least, you won't break your insert :). But I think that your wires will be completely cooked, even if you evacuate the oxygen the coating will be burnt, at least it happened to me with manganine wires trying to do something similar.
    I advice to try to rewire the sample holder, with something better for this high temperature, but I guess that it won't be valid for a He3 cryostat. Anyway why you don't anneal the substrate and the you glue it into a sample holder?
    hope this help.
  6. Dec 23, 2008 #5
    I don't do the last step, because it will be recharged by water after removing it from he-atmosphere. So that's not an option.

    I think I have to rewire the part that is in oven.
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