Thermal reactions at the interface between Si and C nanoparticles: nanotube self-assembling and transformation into SiC.

The thermal reactions induced in C nanoparticles films deposited on Si substrates were followed by high resolution C1s and Si 2p core level spectroscopy. These particles, when annealed at _1300 K transform into single wall carbon nanotubes [Appl. Phys. Lett. 80 (2002) 1441; Chem. Phys. Lett. 355 (2002) 395]. With increasing temperature a progressive re-hybridization of the sp3 into the sp2 carbon phase was observed. At 1270 K the C1s core level showed a major component at 284.29 eV related to the graphitic tubes, and minor one at 283.75 eV, attributed to CASi bonds at the interface, which however do not seem to participate in the nanotube self-assembling. A strong reaction between Si atoms evaporated from the substrate and nanotube walls was observed at 1400 K, which led to the formation of stoichiometric SiC, occurring as a site-confined reaction.