Encapsulation of Floating Carbon Nanotubes in ${\mathrm{SiO}}_2$

In many applications of carbon nanotubes (CNT), it is desirable to have them embedded in a dielectric such as ${\mathrm{SiO}}_2$, without significantly impacting their electronic properties. Here we investigate the CNT-${\mathrm{SiO}}_2$ interface of an embedded CNT using first-principles calculations. We show that strong Si-O-C bonds form, suggesting the feasibility of ${\mathrm{SiO}}_2$ deposition on CNTs. We further show that subsequent hydrogenation eliminates all the Si-O-C bonds, leading to floating CNTs with electronic properties very close to those of pristine CNTs in vacuum.

Figure 1

Initial configuration (no relaxation allowed) for a $(9,0)$ carbon nanotube in a hollow tube of quartz. (Si: gray, C: light gray, O: dark gray spheres).

Figure 2

Configuration of Fig. 1 after relaxation. A $(9,0)$ carbon nanotube is embedded in ${\mathrm{SiO}}_2$ with large distortions present. (Si: gray, C: light gray, O: dark gray spheres).

Figure 3

Same as Fig. 2, but after partial hydrogenation that leads to the elimination of many of the Si-O-C bridges and a decrease in CNT and ${\mathrm{SiO}}_2$ distortions. (Si: gray, C: light gray, O: dark gray, H: white spheres).

Figure 4

A $(9,0)$ carbon nanotube floating in ${\mathrm{SiO}}_2$ obtained after saturated hydrogenation of the initial configuration of Fig. 2. (Si: gray, C: light gray, O: dark gray, H: white spheres).

Figure 5

Detail of the band structure of (a) a $(9,0)$, and (b) a $(7,0)$ carbon nanotube floating in vacuum (solid lines) and in ${\mathrm{SiO}}_2$ (dashed lines). Zero of energy is set at the vacuum valence band maximum. $\Gamma X^{\prime }$ is one fifth of the $\Gamma X$ segment.