Theoretical study of $\mathrm{Ga}$-based nanowires and the interaction of $\mathrm{Ga}$ with single-wall carbon nanotubes

Gallium displays physical properties which can make it a potential element to produce metallic nanowires and high-conducting interconnects in nanoelectronics. Using first-principles pseudopotential plane method we showed that $\mathrm{Ga}$ can form stable metallic linear and zigzag monatomic chain structures. The interaction between individual $\mathrm{Ga}$ atom and single-wall carbon nanotube (SWNT) leads to a chemisorption bond involving charge transfer. Doping of SWNT with $\mathrm{Ga}$ atom gives rise to donor states. Owing to a significant interaction between individual $\mathrm{Ga}$ atom and SWNT, continuous $\mathrm{Ga}$ coverage of the tube can be achieved. $\mathrm{Ga}$ nanowires produced by the coating of carbon nanotube templates are found to be stable and high conducting.

Figure 1

Variation of binding energy $E_b$ of monatomic chain structures as a function of lattice parameter $c$. Various chain structures, linear chain (LC), planar wide angle zigzag (WZ), and narrow angle zigzag (NZ) structures are described by insets.

Figure 2

Left panels: Calculated energy-band structures of $\mathrm{Ga}$ LC, NZ, and WZ monatomic chain structures. Zero of the energy is set at the Fermi level and shown by dash-dotted line. Right panels: Counter plots of the band charge density $\left({\rho }_{\sigma },{\rho }_{\pi }\right)$ of LC structure and total charge density $\left({\rho }_T\right)$ of all three chain structures on a plane passing through the $\mathrm{Ga}\text{−}\mathrm{Ga}$ bonds.

Figure 3

A schematic description of different binding sites of individual atoms adsorbed on a zigzag $(8,0)$ tube. $H$, hollow; $B$, bridge; $Z$, zigzag; $T$, top site.

Figure 4

Energy-band structures are calculated for $\mathrm{Ga}$ adsorbed at the $H$ site of the $(8,0)$ tube with periodicity $c\sim 2c_{SWNT}$ and local density of states, LDOS, calculated at SWNT and at the adsorbed $\mathrm{Ga}$ atom. Upper panels are for exo adsorption of $\mathrm{Ga}$; lower ones are for endo adsorption. Zero of the energy is set at the Fermi level and shown by dash-dotted lines.

Figure 5

Counter plots of the total charge density ${\rho }_T\left(\mathbf{r}\right)$ of exo adsorbed $\mathrm{Ga}$ and endo adsorbed $\mathrm{Ga}$ on the $H$ site of the SWNT surface. The chemical bonding and charge transfer from $\mathrm{Ga}$ to SWNT are revealed from counter plots. The axis of the SWNT is shown by dashed lines.

Figure 6

Calculated energy band structure, total density of states (TDOS), and local density of states (LDOS) at the SWNT and at the $\mathrm{Ga}$ atoms of the $\mathrm{Ga}$-zigzag chain adsorbed on the $(8,0)$ tube. Zero of the energy is set at the Fermi level and is shown by dash-dotted line. The adsorption geometry is described by inset, where dark and light balls indicate $\mathrm{Ga}$ and $\mathrm{C}$ atoms, respectively.

Figure 7

Intermediate coating obtained by 16 $\mathrm{Ga}$ atoms located above each hexagon on the surface of SWNT. Distribution of $\mathrm{Ga}\text{−}\mathrm{Ga}$, $\mathrm{Ga}\text{−}\mathrm{C}$, and $\mathrm{C}\text{−}\mathrm{C}$ distances are illustrated by gray, dotted, and dark histograms, respectively, in the plot. $\mathrm{Ga}$ stripes and SWNT template are shown by dark and light balls.

Figure 8

Top and side views of fully $\mathrm{Ga}$ covered $(8,0)$ SWNT. The supercell incorporates 32 $\mathrm{C}$ [one unitcell of $(8,0)$ SWNT] and 22 $\mathrm{Ga}$ atoms. Distributions of first and second nearest-neighbor $\mathrm{Ga}\text{−}\mathrm{Ga}$, $\mathrm{Ga}\text{−}\mathrm{C}$, and $\mathrm{C}\text{−}\mathrm{C}$ distances are presented by gray, dotted, and dark histograms, respectively. Total density of states (TDOS) and local density of states (LDOS) calculated at the SWNT and at the $\mathrm{Ga}$ coating are shown in the lower panels.