Why is graphene placed in a cryostat in research?

[fisher468]

I have been told when making transport measurements of graphene it is usually placed in a cryostat and cooled to ~ 4K. However I cannot find any sources that back this up and don't fully understand why it is done in the first place.

My thoughts are that it is to measure the carrier mobility with minimal the scattering effects. But is it not more beneficial to measure this at room temperature as this is the most likely situation for graphene based devices.

Also, is there another situation when it is suitable to cool graphene to cryogenic temperatures?

 

[ZapperZ]

I have been told when making transport measurements of graphene it is usually placed in a cryostat and cooled to ~ 4K. However I cannot find any sources that back this up and don't fully understand why it is done in the first place.

My thoughts are that it is to measure the carrier mobility with minimal the scattering effects. But is it not more beneficial to measure this at room temperature as this is the most likely situation for graphene based devices.

Also, is there another situation when it is suitable to cool graphene to cryogenic temperatures?

Unfortunately, without providing any kind of citation to illustrate what you are referring to, it is very difficult to address the specific reason why things are done that way.

Note that if one is trying to study the intrinsic property of the material, one really does not want the properties and the intricate details to be washed out by thermal effects. That is why many studies are done at very low temperatures. Band structure mapping using ARPES, for example, are often done at low temperatures so that the bands can be seen very clearly, especially if they are deeper bands that tend to be broader. If you are also trying to study scattering effects, such as electron-electron scattering, etc, you definiltely want to minimize thermal effects so that you can pick out these weak, subtle phoenomenon.

So without really knowing what specific measurment it is ("transport measurement" doesn't say much), it is impossible to explain why such a thing is done at low temperatures.

Zz.

 

[TeethWhitener]

"transport measurement" doesn't say much

I think "transport measurement" in this case refers to drain current vs. gate voltage in a FET configuration (transfer curve). It's a pretty standard measurement in graphene research.

But is it not more beneficial to measure this at room temperature as this is the most likely situation for graphene based devices.

Sure, you can do these measurements at room temperature. We do this all the time in the lab I work in. The advantage of lower temperatures is that the Dirac point is really well resolved and sharp (because the electrons are less "smeared out" across the Fermi level). This makes it easier to do things like measuring precisely how much various adsorbed species dope the graphene. But you still see a conductivity minimum in the transfer curve of a graphene FET even at room temperature.