Silver-filled single-walled carbon nanotubes: Atomic and electronic structures from first-principles calculations

We have studied the atomic and electronic structures of silver-filled $(n,0)$ single-walled carbon nanotubes (Ag@SWCNTs) for $n=6$, 7, 8, and 10 by using first-principles calculations. We find that silver atoms encapsulated in SWCNTs self-aggregate to form ultrathin nanowires, of which the atomic arrangement depends on the diameter of the SWCNTs as well as the silver content. The electronic structures of the Ag@SWCNTs can be tuned from semiconducting to metallic by controlling the silver content. The hybridization of electronic states and the charge transfer between the encapsulated silver nanowires (AgNWs) and the SWCNTs are also addressed by performing Milliken population analysis combined with the projected density of states.

Figure 1

(Color online) The top view and the side view of the stable configurations of the Ag@(n,0)SWCNTs with different silver contents. (a), (b), and (c) for the Ag@(6,0)SWCNTs; (d), (e), and (f) for the Ag@(7,0)SWCNTs; (g), (h), and (i) for the Ag@(8,0)SWCNTs; and (j) for the Ag@(10,0)SWCNT. The size of the supercell and the silver content are denoted by $C_{8\times n(n=6,7,8,10)}{\mathrm{Ag}}_{m(m=1,2,4,12)}$.

Figure 2

(Color online) The potential energy profiles of a single silver atom in the $(n,0)$ SWCNTs, with $n=6$, 7, and 8. (a) the schematic representation to show stable sites ($A$ and $B)$ of a silver atom in SWCNTs; (b) the potential energy distribution along the axial direction; (c) the potential energy distribution along the radial direction, the position of the tube walls is indicated by the dashed lines; (d) the potential energy profile of a single silver atom moving into an open-ended (7,0) SWCNT along the axial direction, the dashed line indicates the position of the tube edge.

Figure 3

The band structures of pristine (p-) and silver-filled (Ag@)SWCNTs with different silver contents, (a) for a p-(6,0) SWCNT; (b), (c), and (d) for the Ag@(6,0)SWCNTs; (e) for a p-(7,0) SWCNTs; (f), (g), and (h) for the Ag@(7,0)SWCNTs; (i) for a p-(8,0) SWCNT; (j), (k), and (l) for the Ag@(8,0)SWCNTs.

Figure 4

(Color online) The electron density of states (PDOS) projected on the atomic orbitals of carbon (top panel) and silver (bottom panel) for the configurations, as shown in Fig. 1. The PDOSs of different silver atoms are represented by different colors in Fig. 4i. The dashed lines indicate the Fermi levels.

Figure 5

(Color online) The electron projected density of states (PDOS) of carbon (top panel) and silver (bottom panel) atoms for the ${\mathrm{C}}_{64}{\mathrm{Ag}}_2$ configuration. The red and blue lines stand for spin up (majority) and spin down (minority), respectively. The dashed line indicates the Fermi level $\left(E_F\right)$.