  Density functional calculations were performed to systematically study a
series of finite and infinite cluster-assembled silicon nanotubes (SiNTs).
One-dimensional SiNTs can be prepared by proper assembly of hydrogenated
cage-like silicon clusters to form semiconductors with a large band gap, and
their electronic properties can be accurately tuned by transition metal doping
in the center of the tubes. Specifically, doping with Fe made the SiNTs
metallic and magnetic materials. More interestingly, a metal to half-metal
transition was observed with increasing tube radius in Fe-doped SiNTs, which
demonstrates that SiNTs doped with magnetic elements may find important
applications in spintronics.
