Electronic transport properties of fullerene functionalized carbon nanotubes: Ab initio and tight-binding calculations

Fullerene functionalized carbon nanotubes—NanoBuds—form a novel class of hybrid carbon materials, which possesses many advantageous properties as compared to the pristine components. Here, we report a theoretical study of the electronic transport properties of these compounds. We use both ab initio techniques and tight-binding calculations to illustrate these materials’ transmission properties and give physical arguments to interpret the numerical results. Specifically, above the Fermi energy we find a strong reduction in electron transmission due to localized states in certain regions of the structure while below the Fermi energy all considered structures exhibit a high-transmission energy band with a geometry-dependent width.

Figure 1

(Color online) Typical CNB structures studied in this work. The CNB consists of an imperfect C60 attached to an armchair (8,8) SWNT via a neck region, made of a (6,0) SWNT. The number of unit cells in the neck region can vary; panel (a) shows a zero-unit-cell neck (CNB0) while (b) shows a two-unit-cell neck (CNB2).

Figure 2

Transmission as a function of energy for nanobuds CNB0, CNB1, CNB2, and a passivated six-vacancy CNBV. Results for a pristine (8,8) SWNT are shown for comparison (dotted line). For all neck sizes the transmission is strongly reduced except for a plateau region below $E_F$. With increasing neck length this region shifts upward in energy and more dips appear at low energies. The CNBV has a strongly reduced transmission in the plateau region and high transmission at $E_F$.

Figure 3

(Color online) Top: PDOS for the bud and neck parts of the CNB3 system. There is a strong correlation between PDOS and the transmission. Bottom: the probability of the eigenchannel scattering states at the dip in transmission indicated by an arrow in the top panel. Comparing left $\left(T=0.74\right)$ and right panel $\left(T=0.26\right)$ shows that stronger reduction in transmission is related to stronger localization of states in the bud and neck.

Figure 4

(Color online) The transmission for SWNT, CNB3, and CNB15 calculated with a tight-binding model. The trends from first-principles calculations are well captured for the smaller CNB3 system. Significantly increasing the system size results in a large number of dips which below $E_F$ display some degree of periodicity.