Argonne Researchers Create New Diamond-nanotube Composite Material

The technique is the firstsuccessful synthesis of a diamond-nanotube nanocomposite, which meansfor the first time this specialized material has been produced at thenanometer size – one-millionth of a millimeter, or thousands of timessmaller than the period at the end of this sentence.

The resultestablished for the first time a process for making these materials areality, setting the stage for several fundamental advances in thefield of nanostructured carbon materials.

The resulting materialhas potential for use in low-friction, wear-resistant coatings,catalyst supports for fuel cells, high-voltage electronics, low-power,high-bandwidth radio frequencymicroelectromechanical/nanoelectromechanical systems (MEMS/NEMS),thermionic energy generation, low-energy consumption flat paneldisplays and hydrogen storage.

Diamond is called the hardestmaterial because of its ability to resist pressure and permanentdeformation, and its resistance to being scratched. Carbon nanotubes,which consist of sheets of graphitic carbon wrapped to form tubes withdiameters only nanometers in size, are the strongest structures becausethey can withstand the highest tensile force per gram of any knownmaterial.

“Diamond is hard because of its dense atomic structureand the strength of the bonds between atoms,” said Argonne's JohnCarlisle, one of the developers of the new material. “The larger thedistance between atoms, the weaker the links binding them together.Carbon's bond strength and small size enable it to form a denser,stronger mesh of atomic bonds than any other material.”

Diamondhas its drawbacks, however. Diamond is a brittle material and isnormally not electrically conducting. Nanotubes, on the other hand, areincredibly strong and are also great electrical conductors, butharnessing these attributes into real materials has proved elusive.

Byintegrating these two novel forms of carbon together at the nanoscale anew material is produced that combines the material properties of bothdiamond and nanotubes.

The new hybrid material was created usingUltrananocrystalline™ diamond (UNCD™ ), a novel form of carbondeveloped at Argonne. The researchers made the two materials –ultrananocrystalline diamond and carbon nanotubes – grow simultaneouslyinto dense thin films.

This was accomplished by exposing asurface covered with a mixture of diamond nanoparticles and ironnanoparticle “seeds” to an argon-rich, hydrogen-poor plasma normallyused to make UNCD. The diamond and iron “seeds” catalyze the UNCD andcarbon nanotube growth, respectively, and the plasma temperature anddeposition time are regulated to control the speed at which thecomposite material grows, since carbon nanotubes normally grow muchfaster than ultrananocrystalline diamond.

“Experimenting withthese variables led us to the right combination,” said Argonne'sJeffrey Elam, one of the developers. Added another of the developers,Xingcheng Xiao, “It is possible that the plasma environment causeslocal charging effects that cause attractive forces to arise betweenthe ultrananocrystalline diamond supergrains and the carbon nanotubes.If so, such hybrid structures could have interesting electronic andphotonic transport properties.”

The next step is to developpatterning techniques to control the relative position and orientationof the ultrananocrystalline diamond and carbon nanotubes within thematerial.

“In addition, we hope to understand the structure andproperties of these materials, particularly the mechanical,tribological and transport properties,” developer Orlando Auciello said.

The research was featured in the June on the cover of the peer-reviewed journal, Advanced Materials.

Thenation's first national laboratory, Argonne National Laboratoryconducts basic and applied scientific research across a wide spectrumof disciplines, ranging from high-energy physics to climatology andbiotechnology. Since 1990, Argonne has worked with more than 600companies and numerous federal agencies and other organizations to helpadvance America's scientific leadership and prepare the nation for thefuture. Argonne is managed by the University of Chicago for the U.S.Department of Energy's Office of Science.