Synthesis, structure, and multiply enhanced field-emission properties of branched ZnS nanotube-in nanowire core-shell heterostructures.

We report on the synthesis of a novel core-shell metal-semiconductor heterostructure where In forms the core nanowire and wurtzite ZnS forms the shell nanotube. In addition, controlled reaction conditions result in the growth of secondary quasi-aligned ZnS nanowires as numerous branches on the shell nanotubes. These hierarchical architectures are attractive for two reasons: (i) the sharp and quasi-aligned ZnS tips of the nanostructures are potential field-emitters and (ii) since In in bulk form is superconducting the synthesis of core In nanowires should now pave the way for further investigations on magnetic versus transport behavior in type-1 superconductors at the nanoscale. The synthesis could be achieved by employing a rapidly heating carbothermal chemical vapor deposition technique and a high reaction temperature. Transmission electron microscopy reveals that the core In nanowires are single crystals, whereas, within a hierarchical shell, the stem and the branches are separated with a crystalline interface. Field-emission measurements demonstrate remarkably large field enhancement which is explained on the basis of a sequential stepwise enhancement mechanism involving the consecutive stem and branch contributions. The present new nanoarchitectures are envisaged to be an important candidate for potential nanoelectronic devices.