Sunday, March 16, 2008

Superior Thermal Conductivity of Single-Layer Graphene


Superior Thermal Conductivity of Single-Layer Graphene

Alexander A. Balandin, Suchismita Ghosh, Wenzhong Bao, Irene Calizo, Desalegne Teweldebrhan, Feng Miao, and Chun Ning Lau

Nano Lett., 8 (3), 902907, 2008

DOI:
10.1021/nl0731872 (EDIT: Free access to this paper on arXiv, so now you don't have an excuse not to read it).

When I read the title, I thought, wonderful! An easy to read, one topic paper that tests a predicted property of graphenes. One of the many predicted properties of graphenes is their high thermal conductivity, higher even than last decade's (or last year's) wonder material, carbon nanotubes. This paper suspends a graphene layer over a silicon dioxide gap and then measures it's thermal conductivity with Raman spectroscopy.

Usual techniques for measuring thermal conductivity don't work because they depend on measuring the temperature change through the thickness of the material; unfortunately, graphene is only one atom thick. This means that the temperature change will have to be measured across the lateral dimension of the graphene, and it also means that the authors will have to keep the graphene from transferring it's heat to anything under (or over) it; any heat sink will have to be at the edges of the graphene.

The first problem, measuring temperature across the width of the sample, is solved by using confocal micro-Raman spectroscopy (a Raman scattering instrument on a microscope). The authors had recently discovered that the G peak in the Raman spectrum of graphene is temperature dependent (an earlier post centered around the D' band), which gave them a convenient handle on measuring thermal conductivity.

The second problem was a bit more interesting. If you're looking for an insulator that won't fool with your spectroscopy, air (or vacuum) is your best bet. How do you get, then measure, a layer of graphene with only air under it? Here's a handy homemade guide:
1. Take a SiO2 surface.
2. Create a trench in the middle of it.
3. Coat the surface with "Scotch tape method" exfoliated graphene.
4. Shine some light (probably a laser) in the middle to heat it up.
5. Check out that G band on the Raman spectrum.
Here's the way the authors depicted it:


After all that, the authors do a whole bunch of math, and I'm pretty much taking their word for it. They give a thermal conductivity value of 4840-5300 W/mK; as a comparison, diamond has a conductivity of about 0.2 W/mK, individual carbon nanotubes have a conductivity of 3500 W/mK, and carbon nanotube bundles have thermal conductivities ranging from 1750-5800 W/mK.
In conclusion, these guys did some really neat engineering to get a result that was really boring. Graphenes, as expected, have a high thermal conductivity.



Balandin, A.A., Ghosh, S., Bao, W., Calizo, I., Teweldebrhan, D., Miao, F., Lau, C.N. (2008). Superior Thermal Conductivity of Single-Layer Graphene. Nano Letters, 8(3), 902-907. DOI: 10.1021/nl0731872

8 comments:

Excimer said...

that was an awesome graphical representation.

Rob W said...

Thanks- I'm getting pretty high-tech.

georgio said...

I work with graphene, and I would have never thought to do anything like that ... congrats to authors

Alec said...

Dear Commenter:

Balandin work is cool indeed. This is a true discovery. But I would like to point your errors. First of all, you got wrong the thermal conductivity of diamond. It is ~2000 W/mK (NOT 0.2 W/mK). Most likely, you mixed up the units. Second of all, this dicovery is NOT borings. It is exciting and great. In fact, it may save the computer technology progress. The number one hard-ware problem now is heat removal. The discovery of extraordinary heat conduction of graphene can help to solve this problem. See other papers on-line on this.

Rob W said...

Alec-
Thanks for your input. I did have the conductivity for diamond wrong- later in the paper, the authors discuss a thermal conductivity of 0.2 W/mK for "diamond-like carbons", which is what I had lazily put down.

I also agree that this is important work with important implications. I'm working on getting excited about some of the more physics and device aspects of graphene, instead of what I'm narrowly focusing on.

preeti said...

graphene has various usage.
Graphene electronics,Conductive coatings,Aerospace industry,Support for metalic catalysts,Microactuators,MEMS and NEMS,Chemical and bio sensors,Multifunctional Materials Based on Graphene,Graphene Research

Single Layer Graphene

Best Essays said...

Simply wanted to inform you that you have people like me who appreciate your work. Definitely a great post.
superior paper

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