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.