Transport properties of functionalized carbon nanotubes: Density-functional Green’s function calculations

Transport properties of sidewall functionalized (fluorinated) single walled carbon nanotubes (SWCNTs) have been evaluated. We did the theoretical investigations using the density-functional theory coupled with the Green’s function approach. We show that a particular pattern of fluorination can change the electronic properties of the SWCNTs in an interesting way. We show the existence of one-dimensional carbon atom chains on the surface of SWCNT. When isolated from one another, each of these chains gives a conductance of $G_0$, leading to a many-fold increase in the conductance of metallic CNT. Even semiconducting CNT can change to zero band gap semiconductor.

Figure 1

(Color online) Graphene sheets with trans-polyacetylene (left) and cis-polyacetylene (right) like chainlike fluorination. Fluorine atoms (shown in white) are covalently bonded to the respective fluorinated carbon atoms. The direction of arrow represents the direction of rolling for armchair $(n,n)$ or zig-zag $(n,0)$ tubes, respectively.

Figure 2

(Color online) Cross sections along the tube direction of fluorinated CNT: (10,10) tube (a), (10-0) tube (b), (10,0) tube with three channels (c), (10,0) tube with two channels (d), (10,0) tube with one channel (e). The polyacetylenelike chains (channels) are indicated by arrows. Structures (c,d,e) are derived from the structure (b) without further optimization.

Figure 3

Transmission for (10,10) fluorinated CNT along with the corresponding band structure ($\Gamma \text{−}X$ direction). Dotted line shows the Fermi energy. The corresponding structure is shown in Fig. 2a.

Figure 4

(Color online) (b–e) shows the transmission for the nanotube fluorinated in a different pattern. The corresponding fluorinated structures are shown in Figs. 2b, 2c, 2d, 2e. The transmission for the ideal (10,0) CNT is also shown for comparison.

Figure 5

Band structure for the nanotubes fluorinated in different patterns. (b–e) are the band diagram for the structures shown in Figs. 2b, 2c, 2d, 2e, respectively. The corresponding transmission curves are shown in Figs. 4b, 4c, 4d, 4e. The band structure for the ideal (10-0) nanotube is also shown for comparision (a).