Wednesday, March 26, 2008

Experimental evidence of a single nano-graphene

Experimental evidence of a single nano-graphene

A. M. Affounea, B. L. V. Prasada, Hirohiko Satoa, Toshiaki Enoki, Yutaka Kaburagib and Yoshihiro Hishiyama

Chemical Physics Letters, 2001, 348(1-2), 17-20.

Although the cornerstone paper in the graphene field came out in 2004, scientists and engineers have been trying to make graphene for a while. This 2001 paper summarizes a nifty trick to (possibly) make some low-quality graphene islands on top of graphite, but fails to measure any of the properties of graphene.

The authors begin by stating that by heating "nano-diamond powder" at 1600 C, one gets graphite. Knowing this, here's their approach:

1. Put a solution of colloidal diamond nano-particles onto a highly-oriented pyrolytic graphite (HOPG, fancy graphite) surface.
2. Apply an electrical charge to one side, pulling some of the particles down to the HOPG/fancy graphite surface and making a thin film of the diamond nano-particles. This is called electrophoretic deposition (here's another site that's a bit more helpful than the Wikipedia page).
3. Heat the heck out of the HOPG substrate.
4. Observe big spots on the surface of your HOPG using STM.
5. Claim that your spots must be single-layer graphene, since the height of particles is .35-.37 nm, as opposed to normal graphite inter-layer distance of .335 nm.

I'm not totally convinced here- they might have made graphene, but why would you want that to sit on top of graphite? The STM images (not worth seeing, believe me) in step 4 do show some very distinct islands, which I guess means they did something, but having a 0.02 nm (4.5%) difference in your step height doesn't inspire a lot of confidence. The authors try in vain to get scanning tunneling spectroscopy (STS) measurements to check out the electronic properties, but alas, they are unsuccessful.

At the end of the day, the authors use only STM and AFM images to show they made single-layer graphene by electrophoretic deposition and thermal decomposition. I've still got my doubts, and either way it ended up being another 3 years until someone could get graphene nice enough to probe the electronic properties.

Affoune, A. (2001). Experimental evidence of a single nano-graphene. Chemical Physics Letters, 348(1-2), 17-20. DOI: 10.1016/S0009-2614(01)01066-1