Breaking surface states causes transformation from metallic to semi-conducting behavior in carbon foam nanowires

Abstract

Carbon foam nanowires (CFNWs), which are mixed sp2/sp3 hybridized microporous one-dimensional structures, have received much attention in the past two decades. In the present work, first-principle and molecular dynamics (MD) calculations revealed that the surface states causes the metallicity of CFNWs with small size, which demonstrates a Dirac cone-like dispersion near Γ in the Brillouin zone, while the metallicity of large size CFNWs are caused by the bulk states. However, hydrogenation of the CFNWs turns the metallicity into semiconducting with an expansion of the band gap by 0.15–1.5 eV. Interestingly, the metallicity is enhanced when hydrogenation on the top of the CFNWs. Atomic cohesive energy analysis suggests that the CFNWs are energetically favorable up to its melting point at 2200 K. When heating above the melting point, CFNWs transit into multi-walled carbon nanotubes (MWCNTs), agreeing with experimental observations. These findings indicate the feasibility of metallic-semiconductive transition, which have potential applications in nanoscale devices, hydrogen storage and the preparation of MWCNTs.