Peeling off effects in vertically aligned Fe₃C filled carbon nanotubes films grown by pyrolysis of ferrocene

We report the observation of an unusual self-peeling effect which allows the synthesis of free standing vertically aligned carbon nanotube films filled with large quantities of Fe₃C and small quantities of γ-Fe crystals. We demonstrate that this effect depends on the interplay of three main factors: (1) the physical interactions between the chosen substrate surface and grown carbon nanotubes (CNTs), which is fixed by the composition of the used substrate (111 SiO₂/Si or quartz), (2) the CNT-CNT Van der Waals interactions, and (3) the differential thermal contraction between the grown CNT film and the used substrate, which is fixed by the cooling rate differences between the grown film and the used quartz or Si/SiO₂ substrates. The width and stability of these films are then further increased to cm-scale by addition of small quantities of toluene to the ferrocene precursor.