science/technology
Carbon nanoparticle film is hard, elastic
"The matrix between the graphitic nanoparticles seems to be tetrahedral amorphous carbon," Amaratunga tells C&EN. "This gives a thin film with excepResearchers in England have created tional mechanical properties." He points tough, flexible thin films of pure carbon out that thefilmis not only very hard, like by depositing carbon nanoparticles onto "amorphous diamond," but also elastic as a substrate at high velocity. The hardness a result of the nanoscale surface deformaand elasticity of the films suggest that a tion allowed by the carbon nanoparticles. "qualitatively new form of carbon thin "The linkage of carbon nanoparticles film is obtained," according to the group by 5p3 bonds is something that could [Nature, 383, 321 (1996)]. help make macroscopic materials from The work was carried out by a team of these nanoparticles, such as sheets of fielectrical engineers and materials scientists bers of exceptional mechanical stabiliat the University of Liverpool, led by elec- ty," comments Florian Banhart, research trical engineering professor Gehan Amara- scientist at the Max Planck Institute for tunga, in collaboration with industrial part- Metal Research in Stuttgart, Germany. "Until now, the weak van der Waals atner Multi-Arc Inc., Rockaway, N.J. 2 The 500-nm-thick films consist of frag- traction between sp -bonded graphitic ments of carbon nanotubes and carbon nanoparticles has prevented making me"onions" linked together by strong dia- chanically stable composites." Pulickel M. Ajayan, a visiting research mond-like tetrahedral sp* bonds. Carbon nanotubes are nanometer-wide needle- fellow at the Stuttgart institute, adds: "It like cylindrical tubes of concentric gra- shows a useful way of tailoring mechaniphitic carbon capped by fullerene-like cal properties, such as hardness and elashemispheres, whereas carbon onions are tic behavior, of carbon-based materials spherical particles consisting of concen- by incorporating nanoparticles of carbon as building blocks. The results suggest tric shells of graphitic carbon.
the possibility of linking carbon nanoclusters to fabricate nanostructured bulk carbon composites." The Liverpool researchers prepared the thin films by adapting the vacuum carbon arc process used to condense carbon plasma as thin films of tetrahedral amorphous carbon onto substrates. "We create a local high-pressure region near the arc spot which is successful in forming onions, nanotubes, and fullerenes, together with carbon plasma," explains Amaratunga. "All the products are then carried by the expanding supersonic gas plume into a low-pressure chamber where the substrates are placed. Because they impact on the substrate at high velocity, they fragment. In this way we get carbon thin films with nanotube and onion fragments." Although insight into the detailed structure of carbon nanoparticlefilmsrequires further study, the group writes, "their relative ease of deposition makes them particularly suitable for evaluation as protective coatings in applications ranging from computer memory disks to surgical implants." Michael Freemantle
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