Friday, February 20, 2009

Highly conducting graphene sheets and Langmuir–Blodgett films

Xiaolin Li, Guangyu Zhang, Xuedong Bai, Xiaoming Sun, Xinran Wang, Enge Wang, Hongjie Dai (2008). Highly conducting graphene sheets and Langmuir–Blodgett films Nature Nanotechnology, 3 (9), 538-542 DOI: 10.1038/nnano.2008.210

Sequel to Hongjie Dai's nanoribbons article. The researchers make "expandable graphite" (basically graphite oxide, GO) by pumping in sulfuric and nitric acid. They expand/partially reduce it by heating to 1000 C, then throw in more sulfuric acid (oleum) and tetrabutyl ammonium hydroxide (TBA) in DMF to further intercalate stuff into the layers. Apparently, the graphite oxide approach works because the oxygen functionalities allow all kinds of stuff to sneak in between the layers.

Dai and friends then make films of their GO-esque material before and after annealing/reducing at 800 C in H2 gas. The films are compared to GO made with a more traditional Hummer's method by AFM, TEM, electron diffraction (ED), IR, and X-ray photoelectron spectroscopy (XPS). They find that their pre-annealed films had less oxygen functionalities, higher conductivity, and were more hydrophobic than the traditional GO. Post-annealing films of graphene (which they could deposit with organic solvents onto surfaces) were shown to have a lower incidence of defects (basically holes) than traditional reduced graphite oxide. Essentially, these authors found a more gentle way to make graphene from the graphene oxide approach.