Selective modification of aligned carbon nanotubes by N2 plasma and their diode behavior.

Aligned carbon nanotubes made by pyrolysis of ferrocene are selectively treated with N2 plasma at various durations. Raman spectra reveal that polar bonds form at treated regions and result in increased Raman breathing mode. XPS support Raman and verify the C-O/C-N formations in carbon lattices. Electrical measurements show an unipolar p-type character as probes are placed in contact with untreated regions of nanotubes. Reposition of probes at untreated and treated regions respectively produces a current-voltage profile that resembles a p-n junction diode with forward current reaching a value as high as 100 mA at 3 V. Ab initio calculations confirm the on-tube junction and creation of a donor state is owing to C-N formations.