Temperature dependence of inner tube growth from ferrocene-filled single-walled carbon nanotubes

The growth of inner tubes from ferrocene-filled single-walled carbon nanotubes was studied with Raman spectroscopy. Special attention was paid to inner tubes formation based on the annealing temperature and the outer tube diameter. Besides the presence of inner tubes radial breathing mode, a new Raman feature appears around 1250 cm−1, which is always related to the appearance of the inner tube. The thermal stability of the inner tube strongly depends on the outer tube diameter. The inner tube formed inside outer tube with 1 nm diameter is destructed at 1000 °C, but it can survive more than 1300 °C with outer tube diameter of about 1.6 nm. Furthermore, the splitting of G line and the shift of 2D line were discussed regarding to the appearance of inner tubes.