Elemental composition from ToF-ERDA (Fig. ) of a thicker film on Si from the same CVD process gives 81 at. % B, 18 at. % C, 0.5 at. % O and 0.2 at. % H, i.e., a B4C stoichiometry of the film, corresponding to the low temperature phases of B13C2 or B12C3. . XPS on this B4C reference film shows an agreement with the XPS spectra of the CNTs after CVD. The C 1s spectrum of the reference film (Fig. ) can be fitted with the same components corresponding to C-B and C-B-C bonds as the C 1s spectrum of the CNTs after CVD. The fitting curve corresponding to amorphous carbon in the reference film aligns with the higher intensity peak from the C-C bonds in the membrane. Presence of some amorphous carbon phase is typical in boron carbide CVD deposition from metalorganic precursors. The B 1s XPS spectrum of the reference film (Fig. ) show a similar B-B to B-C signal intensity ratio as in the B 1s spectrum of the CNTs after CVD. In addition, the C-B to C-B-C intensity ratio is similar in the CNTs after CVD and in the reference film, suggesting that the process rendered a similar material deposition on Si and the CNT membrane.