Although most of the research conducted on multiwall and singlewall carbon nanotubes since their discovery has been of a fundamental nature, a keen interest is shown for their potential applications. Apart from applications that may be realized in a distant future only, carbon nanotubes have shown great potential in some domains. For example, they have proven to be extremely stiff and resistant to bending and they also rank among the best electron field emitters that are now available. We present here some recent experimental results on these two topics.
We determined the Young's moduli of single wall nanotube bundles and multiwalled nanotubes, prepared by a number of methods, using atomic force microscopy (AFM). These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. Our research to date illustrates a qualitative relationship between the Young's modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced.
We also studied the field emission behavior of singlewall, closed and opened arc-discharge multiwall, and catalytically grown multiwall nanotubes, as single emitters and in film form. The nanotube field emitters show excellent field emission properties, but significant differences were observed between the different types of nanotubes. To obtain good performances as well as long emitter lifetimes, the nanotubes should be multiwalled and have closed, well-ordered tips. Complementary results such as energy distribution and luminescence induced by the field emission give furthermore precious indications on the field emission mechanism. The large field amplification factor, arising from the small radius of curvature of the nanotube tips, is partly responsible for the good emission characteristics. Additional evidence however shows that the density of states at the tip is non-metallic, appearing in the form of localized states with well-defined energy levels.
Departement de Physique, Ecole Polytechnique Federale de Lausanne
CH-1015 Lausanne, Switzerland
Phone: +41 21 6934410; Fax: +41 21 6933604