Energetics and Electronic Properties of Small Diameter Si and Ge Nanotubes

By using first-principles pseudopotential method, the energetics and electronic properties of a series of small diameter Si, Ge and SiGe nanotubes are intensively investigated. It is found that the gear-like nanotubes (g-NTs) are energetically more favorable than their hexagonal counterparts (h-NTs). The total energies of these tubes usually decrease as the diameters increase, while those of gear-like Ge tubes are relatively insensitive to the diameter and chirality. For the gear-like SiGe tubes with inner-diameters D <= 0.42 nm, there exists an interesting state which is energetically more favorable than the larger ones. Our calculations show that these g-NTs exhibit significantly different electronic properties from h-NTs. The possibility to using SiGe nanotubes as high performance thermoelectric materials is also discussed.