Carbon Solves a Problem, Gold Poses a Puzzle
What's Hot in Chemistry, November/December 2010
By Dr. John Emsley
In the previous extraction of Hot Papers, reports about graphene occupied eight of the ten positions; that has now increased to nine. Only paper #7 offers something different and in the form of gold "superatoms." More about this in a minute.
Some of the graphene papers are new to the list, and the one reaching the highest position is #5 and is about graphene ultracapacitors.
Kostya Novoselov (top) and Andre Geim (bottom) were
recently announced as winners of the 2010 Nobel Prize is Physics for their
graphene work
Another graphene paper, at #8, is also concerned with the electrical ability of this material and in fact it might well solve the problem of what to use as a transparent conducting film for liquid crystal devices when the current material, indium tin oxide (ITO) becomes prohibitively expensive as supplies of rare indium dwindle. This metal comes mainly as a by-product of zinc and lead mining whose ores contain 1–2% of indium. There are no indium mines, nor ever likely to be.
Clearly some alternative will have to be found this century, and graphene might take over from ITO. It is a mere one atom thick, optically transparent, chemically inert, mechanically strong, absorbs only 2% of the incident light (compared to 15% for ITO), and is an excellent conductor. The problem is one of depositing a film of graphene onto glass, and that is just what paper #8 is about.
The research comes from scientists at the University of Manchester, U.K., led by the now-celebrated duo of Kostya Novoselov [see also] and Andre Geim, [see also: 1 ¦ 2 ¦ 3] recently announced as winners of the 2010 Nobel Prize in Physics for their discovery of graphene. In the work reported in #8, they were able to deposit single-layer graphene flakes onto glass slides and then attach chromium/gold contacts.
The production of single-layer graphene film was done by exfoliating crystals of natural graphite using sonication in the presence of dimethylformamide (DMF), a solvent that solubilizes the graphite. After a few hours sonication, the DMF contained a large proportion of monolayer graphene. The suspension was then centrifuged at 13,000 rpm for ten minutes to remove the thicker flakes.
The resulting liquid was sprayed onto a preheated glass slide, and this created a film of graphene approximately 1.5 nm thick, consisting mainly of single-layer material, although some was two or three layers thick—not that this affected light absorption to any great extent.
Graphene Nano-Ribbons.
From an interview with
Zhihong Chen regarding the Special Topic of
Graphene.
The slides were finally annealed for two hours in an atmosphere of argon at 250° C. The resulting graphene-coated glass behaved just as required.
The researchers claim that scaling up from laboratory slides to a full-sized glass panel should not prove a problem. They believe that graphene really can become a substitute for ITO in all its applications. But will it really work—and when?
As Novoselov tells Science Watch, "It requires a critical mass of experiments for people to start to believe that such applications are actually realistic. Last year we saw dramatic progress in mass-production of graphene, and many applications have now become a reality." This, he says, explains the interest in paper #8 because it was so far-sighted.
Currently Novoselov is working to improve the quality of graphene samples and to understand the novel physics observed in such devices.
"The progress in improving the quality of graphene and in its mass production during the last year has been amazing," he says. "It exceeds all expectations. What one can be sure about is that the first applications of graphene will soon come, and that this most exciting material still has a lot to offer."
This may also be true of the material described in paper #7, which examines the mysterious ability of gold to cluster in what the report terms "superatom" complexes. The paper comes from a group led by Hannu Häkkinen of the University of Jyväskylä, Finland, and is the result of collaboration among groups in Germany, the U.S., and Sweden. It deals with superatoms Au102, Au39, Au13, and Au11, to which are attached phosphine and thiolate ligands.
The researchers have come up with a theory of inherent stability for these numbers, and if their theory is correct, then other superatom clusters of gold, such as Au25 and Au37, are waiting to be discovered.
Dr. John Emsley is based at the Department of Chemistry, Cambridge University, U.K.
What's Hot in Chemistry | |||
---|---|---|---|
Rank | Paper |
Cites This Period May-Jun 10 |
Rank Last Period Mar-Apr 10 |
1 | C. Lee, et al., "Measurement of the elastic properties and intrinsic strength of monolayer graphene," Science, 321(5887): 385-8, 18 July 2008. [Columbia U., New York, NY] *327FB | 46 | 1 |
2 | X.S. Li, et al., "Large-area synthesis of high-quality and uniform graphene films on copper foils," Science, 324(5932): 1312-4, 5 June 2009. [U. Texas, Austin] *453TF | 36 | 3 |
3 | D.C. Elias, et al., "Control of graphene’s properties by reversible hydrogenation: Evidence for graphane," Science, 323(5914): 610-3, 30 January 2009. [U. Manchester, U.K.; Inst. Microelectronics Tech., Chernogolovka, Russia; Cambridge U., U.K.; U. Nijmegen, Netherlands] *400JB | 35 | 4 |
4 | A. Reina, et al., "Large area, few-layer graphene films on arbitrary substrates by chemical vapor deposition," Nano Letters, 9(1): 30-5, January 2009. [MIT, Cambridge] *395IZ | 34 | 2 |
5 | M.D. Stoller, et al., "Graphene-based ultracapacitors," Nano Letters, 8(10): 3498-3502, October 2008. [U. Texas, Austin] *358HD | 31 | + |
6 | D.V. Kosynkin, et al., "Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons," Nature, 458(7240): 872-6, 16 April 2009. [Rice U., Houston, TX] *433CS | 26 | 7 |
7 | M. Walter, et al., "A unified view of ligand-protected gold clusters as superatom complexes," PNAS, 105(27): 9157-62, 8 July 2008. [6 institutions worldwide] *326GA | 24 | + |
8 | P. Blake, et al., "Graphene-based liquid crystal device," Nano Letters, 8(6): 1704-8, June 2008. [U. Manchester, U.K.; Inst. Microelectronics Tech., Chernogolovka, Russia] *313LL | 23 | + |
9 | Y.M. Lin, et al., "Operation of graphene transistors at gigahertz frequencies," Nano Letters, 9(1): 422-6, January 2009. [IBM T.J. Watson Res. Ctr., Yorktown Heights, NY] *395IZ | 23 | + |
10 | L.Y. Jiao, et al., "Narrow graphene nanoribbons from carbon nanotubes," Nature, 458(7240): 877-80, 16 April 2009. [Stanford U., CA] *433CS | 22 | 5 |
SOURCE: Thomson Reuters Hot Papers Database. Read the Legend. |
KEYWORDS: Graphene, Andre Geim, Kostya Novoselov, liquid crystal devices, sonication, single-layer graphene film.