First-principles study of a hybrid carbon material: Imperfect fullerenes covalently bonded to defective single-walled carbon nanotubes

The electronic properties of a novel hybrid carbon material, the NanoBud, is investigated by using a first-principles method. Our results suggest that NanoBuds of zigzag carbon nanotubes are semiconductors, no matter whether the zigzag nanotubes are metallic or semiconducting. Local states appear in the band gap of the NanoBuds near the Fermi level. NanoBuds of armchair carbon nanotubes remain metallic. These properties may have great potential applications in future nanodevice design.

Figure 1

Optimized geometries of NanoBuds of zigzag (12,0) SWCNTs with different bud heights: (a) Bud 1, (b) Bud 2, and (c) Bud 3. Contact atoms of Bud 2 that make major contributions to the local states in the band gap above the Fermi level are denoted by gray balls.

Figure 2

Band structures of pure (12,0) SWCNT (a) and NanoBuds of (12,0) SWCNT with different bud heights, (b) Bud 1, (c) Bud 2, and (d) Bud 3. The distance between the nearest fullerenes is about $17\mathrm{\AA }$. (e) Band structure of Bud 2 of (12,0) SWCNTs with the distance between the nearest fullerenes being about $26\mathrm{\AA }$. The Fermi level is set to zero.

Figure 3

Band structures of (a) pure (14,0) SWCNT and (b) Bud 2 of (14,0) SWCNT with the distance between the nearest fullerenes being about $17\mathrm{\AA }$. The Fermi level is set to zero.

Figure 4

Band structures of pure (8,8) SWCNT (a) and NanoBuds of (8,8) SWCNT with different bud heights, (b) Bud 1, (c) Bud 2, and (d) Bud 3. The distance between the nearest fullerenes is about $17\mathrm{\AA }$. (e) Band structure of Bud 2 of (8,8) SWCNTs with the distance between the nearest fullerenes being about $26\mathrm{\AA }$. The Fermi level is set to zero.