Effect of plasma treatment on electrical conductivity and Raman spectra of carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were treated with a radio-frequency discharge. We found that MWCNTs showed opposite trends in electrical conductivity when treated with oxygen and hydrogen plasmas. MWCNTs showed enhanced electrical conductivity when placed at cathode with oxygen plasma treatment, whereas MWCNTs treated at positive column did not show such a trend. In contrast, the conductivity of MWCNTs dropped sharply with hydrogen plasma treatment. The measured conductivity trends of MWCNTs are correlated with observed Raman spectral shift. The possible mechanisms of the change in electrical conductivity in plasma-treated MWCNTs are discussed.