Fine tuning the charge transfer in carbon nanotubes via the interconversion of encapsulated molecules

Tweaking the properties of carbon nanotubes is a prerequisite for their practical applications. Here, we demonstrate fine tuning the electronic properties of single-wall carbon nanotubes via filling with ferrocene molecules. The evolution of the bonding and charge transfer within the tube is demonstrated via chemical reaction of the ferrocene filler ending up as secondary inner tube. The charge transfer nature is interpreted well within density functional theory. This work gives a direct observation of a fine-tuned continuous amphoteric doping of single-wall carbon nanotubes.

Figure 1

(Color online) $\mathrm{C}1s$ photoemission spectra for samples (A) SWCNT, (B) $\mathrm{Fe}{\mathrm{Cp}}_2@\mathrm{NT}$, (C) Fe doped DWCNT ($600°\mathrm{C}$ for $2\mathrm{h}$), and (D) Fe doped DWCNT ($600°\mathrm{C}$ for $22\mathrm{h}$). Gray (G) is a Doniach-Sunjic profile convoluted with Gaussian, reproducing well the $\mathrm{C}1s$ peak of the SWCNT. Inset: $\mathrm{Fe}2p$ absorption spectrum for samples B, C, and D.

Figure 2

(Color online) (a) $\mathrm{C}1s$ absorption spectra for the samples (A) SWCNT, (B) $\mathrm{Fe}{\mathrm{Cp}}_2@\mathrm{NT}$, (C) Fe doped DWCNT ($600°\mathrm{C}$ for $2\mathrm{h}$), and (D) Fe doped DWCNT ($600°\mathrm{C}$ for $22\mathrm{h}$). (b) Van Hove singularity peaks at ${\pi }^{\star }$ resonance edge on an expanded scale. Gray (G) shows the result of line shape analysis for the SWCNT (Ref. 19).

Figure 3

(Color online) $\mathrm{He}\mathrm{I}$ photoemission spectra for (A) pristine SWCNT, (B) $\mathrm{Fe}{\mathrm{Cp}}_2@\mathrm{NT}$, [(C)–(F)] Fe doped DWCNT or $\mathrm{Fe}{\mathrm{Cp}}_2@\mathrm{NT}$ annealed at $600°\mathrm{C}$ for 2, 8, 54, and $212\mathrm{h}$, respectively, and (G) $\mathrm{Fe}{\mathrm{Cp}}_2@\mathrm{NT}$ annealed at $1150°\mathrm{C}$ for $1\mathrm{h}$. Inset: annealing time dependence of charge transfer density (CT) for the outer tube in units of $e∕\mathrm{\AA }$.