Large Variety of Behaviors for the Raman G′ Mode of Single Walled Carbon Nanotubes upon Electrochemical Gating Arising from Different (n,m) of Individual Nanotubes

The dependence of the second-order Raman G' mode of individual single walled carbon nanotubes (SWCNTs) as a function of electrochemical gating has been studied using in situ Raman spectroelectrochemistry. We show that the change of the frequency of the G' mode with electrode potential (delta(omega(G)')/delta(V)) is specific for different (n,m) of individual SWCNTs. The study of the G' mode at the single nanotube level allowed us to observe many effects that get averaged in observations for the SWCNT bundles. These effects included an unusual dependence of the G' mode frequency on electrode potential (V) for particular individual tubes, namely a decrease of the G' mode frequency with increasing magnitude of electrode potential. This occurs for both increasing and decreasing V relative to V = 0. It is demonstrated that there is no simple dependence of delta(omega(G'))/delta(V) on tube diameter or excitation laser energy. Furthermore, the G' mode intensity drops with an increase or decrease of the electrode potential relative to V = 0 and this decrease in the G' mode intensity was found to be gradual and not abrupt, which suggests a more complicated mechanism than the simple bleaching of electronic transitions. These observations give guidance to future theoretical work on this topic.