Surface analysis of a well-aligned carbon nanotube film by positron-annihilation induced Auger-electron spectroscopy

Positron-annihilation induced Auger-electron spectroscopy (PAES) was used to study the surface of a well-aligned carbon nanotube film grown on a Si substrate. Since the nanotubes are aligned perpendicular to the substrate, the surface analysis of the film provides information on the tip of the nanotube. We compared the Auger spectra obtained by PAES and 3 keV electron-induced AES (EAES) and found that PAES has an extremely high sensitivity to small quantities of impurities such as Cl, N, and O. The result can be explained by the fact that the positrons implanted at low energy (50 eV) have high probabilities of being trapped by the impurities adsorbed at the tip of the nanotubes. Depth-resolved positron lifetime spectroscopy and Doppler-broadening spectroscopy were also carried out to get information on the depth profiles of defects and impurities in the carbon nanotube (CNT) film.