Electron microscopy and photoelectron spectromicroscopy study of catalyst-free transformation of carbon nanoparticles into nanotubes

The reorganization of the morphologically complex amorphous carbon nanoparticle layers deposited on a Si substrate into ordered sp2 entities was investigated by means of two complementary techniques, synchrotron radiation x-ray photoelectron microscopy and scanning electron microscopy, which provided the necessary chemical and structural information at submicrometer length scales. The studies were focused on the effect of the local thickness of the carbon nanoparticle layer on the extent of the restructuring process. The lateral distribution of the phases formed on the surface and their local chemical configuration were revealed by measuring C 1s and the Si 2p core level spectra with photoelectron spectromicroscopy. The results showed that an effective graphitization, which on the basis of complementary characterization techniques was associated to the formation of single-wall nanotubes, occurs only in areas with a high density of nanoparticles. These findings indicate that tube self-assembling is promoted by the interaction between neighboring nanoparticles.