Chemists Show Mega Interest in Nanotechnology

Chemists Show Mega Interest in Nanotechnology

by Dr. John Emsley

WHAT'S HOT IN CHEMISTRY...

Rank	Paper	Citations This Period Nov- Dec 98	Rank Last Period Sep- Oct 98
1	G.N. Murshudov, A.A. Vagin, E.J. Dodson, "Refinement of macromolecular structures by the maximum-likelihood method," Acta Cryst., D53:240-55, May 1997. [U. York, England; Free U. Brussels, Belgium] *XB256	18	5
2	S.J. Tans, et al., "Individual single-wall carbon nanotubes as quantum wires," Nature, 386(6624):474-7, 3 April 1997. [Delft U. Technol., Netherlands; Rice U., Houston, TX] *WR256	15	2
3	C. Journet, et al., "Large-scale production of single-walled carbon nanotubes by the electric-arc technique," Nature, 388(6644):756-8, 21 August 1997. [U. Montpellier, France; LPS, Chatillon, France; U. Nantes, France; U. Pennsylvania, Philadelphia] *XR667	15	†
4	A.M. Rao, et al., "Diameter-selective raman scattering from vibrational modes in carbon nanotubes," Science, 275(5297):187-91, 10 January 1997. [5 U.S. institutions] *WC022	14	10
5	L.A. Curtiss, et al., "Assessment of Gaussian-2 and density functional theories for the computation of enthalpies of formation," J. Chem. Phys., 106(3):1063-79, 15 January 1997. [Argonne Natl. Lab., IL; Bell Labs, Lucent Technol., Murray Hill, NJ; Northwestern U., Evanston, IL] *WD070	12	8
6	Z. Yang, et al., "Total synthesis of epothiline A: the olefin metathesis approach," Angew. Chem., 36(1-2):166-8, February 1997. [Scripps Res. Inst., La Jolla, CA; U. Calif., San Diego] *WH998	11	†
7	K. Matyjaszewski, T.E. Patten, J. Xia, "Controlled/"living" radical polymerization. Kinetics of the homogeneous atom transfer radical polymerization of styrene," J. Amer. Chem. Soc., 119(4):674-80, 29 January 1997. [Carnegie Mellon U., Pittsburgh, PA] *WE826	10	6
8	C. Granel, et al., "Controlled radical polymerization of methacrylic monomers in the presence of a Bis(ortho-chelated) arylnickel (II) complex and different activated alklyl halides," Macromolecules, 29(27):8576-82, 30 December 1996. [U. Liege, Belgium] *WB741	9	7
9	S. Beuermann, et al., "Critically evaluated rate coefficients for free-radical polymerization, 2^a): Propagation rate coefficient for methyl methacrylate," Macromol. Chem. Phys., 198(5):1545-60, May 1997. [8 institutions worldwide] *XA606	8	†
10	J.R. Heath, C.M. Knobler, D.V. Leff, "Pressure/temperature phase diagrams and superlattices of organically functionalized metal nanocrystal monolayers: the influence of particle size, size distribution, and surface passivant," J. Phys. Chem. B, 101(2):189-97, 9 January 1997. [U. Calif., Los Angeles] *WL103	8	†

SOURCE: ISI's Hot Papers Database. the full legend.

Nanochemistry is fast becoming one of the major areas of chemistry. Its appeal lies in the long-dreamt-of ability to investigate and manipulate matter at the level of individual atoms and molecules. And while it is scientific curiosity that is currently driving research forward in this area, there is the tempting thought that discoveries could play a key role in a future world of nano devices and nano computers. Most interest in this area, at least in terms of cited papers, has been in carbon nanotubes, and the current Hot Ten list contains three such papers (#2, #3, and #4).

Carbon nanotubes have the potential to conduct electricity, although this depends very much on the way the atoms of the tube walls are stacked. In the November/December 1998 edition of Science Watch there were five papers on carbon nanotubes, and that by Charles Lieber of Harvard University merited comment, since it reported the structure of single-walled nanotubes (SWNTs) with an accuracy hitherto unachievable. Lieber speculated whether SWNTs would ever become commercially important given the difficulty of producing them.

The paper currently at #3 shows a way in which this might be overcome, and is a joint effort by groups working at the universities of Nantes and Montpellier in France, and Pennsylvania in the United States. The project leader is Patrick Bernier, based at Montpellier, who is Research Director of CNRS, France’s national research center. The secret of making SWNTs in bulk lies in using a metallic catalyst, composed of yttrium and nickel powder in the ratio of 1:4.

This is mixed with powdered graphite and inserted into a hole drilled into a graphite rod, which is then used as the anode in an electric arc discharge. Without the catalyst, such an arc discharge gives high yields of fullerenes and multi-walled nanotubes, but with the catalyst present the sparking chamber fills with "rubbery" soot and filaments of carbon, whose analysis by resolution transmission electron microscopy (TEM) shows them to be well-defined SWNTs. Gram quantities of SWNTs can now be produced easily and cheaply.

Paper #10 is also about nanotechnology, in this case the creation of metal nano crystals, and shows a degree of sophistication that would have been unthinkable only a few years ago. It reports on the growing of special nano-crystals of silver and gold on the surface of water, and reveals the factors which govern the process. The research comes from James Heath of the Department of Chemistry and Biochemistry at UCLA, whose group has already incorporated them into electronic devices (Appl. Phys. Lett., 70: 3107, 1997).

Heath explores how pressure and temperature, and the chain-length of associated surfactant molecules, affect the formation of the nanocrystals that are only 2-7.5 nanometers in size. They deduced how the thermodynamic factors affected crystal formation, and how it also depended on the "excess conical volume" (V) of the surfactants which radiate from the crystal surface. When V is large, low-density structures are produced. They found that their nanocrystals showed an ability to self-assemble, which adds to their attraction.

Paper #10 also announces methods for making two-dimensional artificial solids from silver and gold quantum dots, which is the name given to nano-sized particles of diameter 5-50 nanometers. The paper reports evidence for quantum dots interacting strongly with one another. In a follow-up paper in Science (277:1978, 1997), Heath was able to demonstrate for the first time that it was possible to design a solid from quantum dots, and show its unique properties. Using techniques developed in #10 he demonstrated that a two-dimensional lattice of quantum dots could be reversibly switched between a metal and an insulator under ambient conditions. "This was the paper which I would have expected to produce most citations," comments Heath, basing his expectations of the fact that the research has implications not only for making optical switching networks, but possibly for quantum computing.

Dr. John Emsley is Science Writer in Residence
at the Department of Chemistry, University of Cambridge, U.K.