Transport suppression in polymer-doped zigzag carbon nanotubes

The conductance of zigzag carbon nanotubes in the presence of grafted polymers attached to their walls is investigated. A theoretical study of the dependence of the transport on the nature of the molecule and on the concentration of attached structures is presented. The attached structures are shown to lead to the formation of resonant states trapping the electronic carriers and suppressing the conductance. An exponential decay of the conductance with increasing concentration of attached molecules marks the ballistic regime while a weaker decay dependence highlights a crossover to a diffusivelike electronic behavior.

Figure 1

(Color online) Conductance of a (6,0) CN with molecules (finite chains with five atoms) attached to its walls, as a function of the Fermi energy. The two solid curves correspond to the cases of one and five attached molecules, whereas the dotted line is for a closed ring configuration and the dashed one for a pure CN. Solid circles at the energy axis mark the electronic eigenvalues of the attached chain. Energies are given in units of the hopping energy $({\gamma }_0=1)$ and the molecule parameters are chosen as ${ϵ}_m=0.1$ and ${\gamma }_m=0.8$; ${\gamma }_c=1$.

Figure 2

(Color online) Conductances as functions of energy for a (6,0) CN grafted with 24-atom linear chain molecules. Solid circles represent the electronic eigenenergies of the isolated chains. Results are for 1% (solid curve) and 10% (dashed line) molecular concentrations; ${\gamma }_c=0.3$, ${ϵ}_m=0.1$, and ${\gamma }_m=0.8$. Dotted line is for ${\gamma }_c=0.9$ and molecular concentration 10%.

Figure 3

(Color online) (a) Conductance decay as a function of the concentration of molecules (24- and 115-atom chains) attached to a (9,0) CN, at one of the eigenvalues of the chains. Inset shows the exponential decay for low concentrations. (b) Conductance distribution for a (9,0) CN with 0.14%, 5%, 27%, and 70% of the CN sites covered by polymers (${\gamma }_c=0.3$, ${ϵ}_m=0.1$, and ${\gamma }_m=0.8$).

Figure 4

(Color online) Gray-scale maps of the conductance as functions of the coverage percentage of attached molecules and the Fermi level, written in terms of the tube hopping ${\gamma }_0$. The results are for molecules described by finite 24-atom chains with ${ϵ}_m=0.1$ and ${\gamma }_m=0.8$. Results are for (3,0) and (9,0) tubes at the left and right parts of the figure, respectively.

Figure 5

(Color online) Conductance of a (6,0) CN with a fixed molecular concentration of 1% as a function of the coupling energy between the CN and the chain and at a Fermi energy coincident with the central eigenvalue of the attached chain. Distinct lengths are considered for the attached molecules (${ϵ}_m=0.1$, ${\gamma }_m=0.8$, and ${\gamma }_c=0.3$).