Metallic behaviour of boron-containing carbon nanotubes by Hsu, W, Chu, S, Munoz-Picone, E, Boldu, J, Firth, S, Franchi, P, Roberts, B, Schilder, A, Terrones, H, Grobert, N, Zhu, Y, Terrones, M, McHenry, M, Kroto, H, Walton, D