Spectroscopic studies on self-supporting multi-wall carbon nanotube based composite films for sensor applications

Self-supporting composite buckypapers containing 50 wt% multi-wall carbon nanotubes (MWCNTs) and SnOx or VOx were prepared by filtration using two different methods. Either the metal-oxides were pre-prepared and mixed with the nanotubes only before filtration (co-filtration method), or the MWCNTs were placed into the synthesis autoclaves of the oxides (single-step method) and the buckypaper was filtered from the product of this synthesis. The resulting composites were characterized by high resolution scanning electron microscopy, XPS, IR and Raman spectroscopy. Whereas the co-filtered samples are simple mechanical mixtures of their individual components, in case of the single-step composites we have found evidence for the existence of an interfacial region between the carbon nanotubes and the metal oxides. This is verified by the appearance of Sn and V in lower oxidation state from the metal-oxide side as well as by the presence of a low-frequency shoulder of the Raman G-band from the carbon nanotube side. The latter feature resembles a Breit–Wigner–Fano type line which is characteristic for phonon coupling to an electronic continuum.