I am interested in the electronic structure and properties of molecules and materials, with particular emphasis on transport, magnetism, superconductivity, device fabrication and miniaturization and the discovery of new classes of electronic materials.

Neutral Radical Conductors

This approach to organic conductors is based on the normal metals, such as copper and sodium. These inorganic free radicals conduct electricity because they possess a closed shell of electrons together with one electron in an outer s orbital that becomes ionized in the solid state and leads to the familiar metallic properties.

In some case we are interested in making materials from molecules. In this work we have crystallized neutral carbon-based radicals and this has recently lead to the discovery of a neutral organic solid with the highest conductivity yet reported. Below are shown the molecular structure of this compound and a crystal wired up for conductivity measurements.

The radical shown above is non-planar; that is, it is spiroconjugated at the boron atom so that spin density is delocalized over orthogonal p-systems into two dimensions. In the perchlorophenalenyl radical shown below, we have an almost planar radical that is prevented from dimerizing by the bulk of the chlorine atoms but ends up in a propeller shape.

Carbon Nanotubes

In this project we are interested in taking a material (soot) to its molecular form and back again. Carbon nanotubes are produced in the form of soot in an electric arc furnace and it requires a great deal of chemistry and engineering to obtain them in pure form. A carbon nanotube can be envisaged as a piece of graphite rolled-up into a perfect cylinder with a fullerene cap. The figure shows a (5,5) single-walled carbon nanotube (SWNT) – this is the nanotube that would be nucleated by a hemisphere cut from C60 with growth along the C5-axis. This nanotube is of the armchair type (see the open end), and because the indices (n,m) are equal, this SWNT is predicted to be metallic. The other SWNT types – zigzag and chiral occur in both metallic and semiconducting forms depending on the particular values of the indices.

Single-walled carbon nanotubes (SWNTs) possess outstanding materials properties, such as their high aspect ratio, chemical and thermal stability, strength and thermal conductivity. However, their electrical conductivity properties cannot be fully realized because they occur as a mixture of semiconducting and metallic SWNTs. Clearly for nanoelectronic applications, it is essential to be able to produce SWNTs of a specific band electronic structure and this will require new preparation techniques and separation procedures. For application in the area of high strength composites, the ability to disperse the SWNTs, and to introduce cross-linking sites through wall chemistry will clearly be vital in realizing the full potential of these materials.

We are working on all aspects of the large scale synthesis, purification, dissolution, chemical functionalization, separation, chromatography, microscopy, spectroscopy and theory of SWNTs. For the most part, chemistry occurs in solution and we therefore intend to focus on the soluble single-walled carbon nanotubes that were invented by our group. We believe that most of the promising applications of SWNTs will ultimately depend on our ability to process these materials in (organic) solution.

Selected Publications

Chi, X.; Itkis, M. E.; Patrick, B. O.; Barclay, T. M.; Reed, R. W.; Oakley, R. T.; Cordes, A. W.; Haddon, R. C., The First Phenalenyl-Based Neutral Radical Molecular Conductor. J. Am. Chem. Soc. 1999, 121, 10395-10402.

Chen, J.; Hamon, M. A.; Hu, H.; Chen, Y. A.; Rao, M.; Eklund, P. C.; Haddon, R. C. “Solution Properties of Single-Walled Carbon Nanotubes,” Science 1998, 282, 95-98.