Electronic structure of boron-nitride nanotubes (BNNTs) can be tuned in a wide range through covalent functionalization, as experimentally and theoretically evidenced. Various functional groups were covalently attached to BNNTs. The ultraviolet-visible absorption spectra indicate that the electronic structure of BNNTs drastically changes under functionalization. First-principle calculations reveal that the covalently functionalized BNNTs can be either $n$- or $p$-doped depending on the electronegativity of molecules attached, and their energy gap can be adjusted from ultraviolet to visible optical range by varying concentration of functionalized species.

• Received 7 April 2006
• Corrected 1 November 2006

DOI:https://doi.org/10.1103/PhysRevB.74.153413