Characteristics of single metallic nanowire growth via a field-emission induced process

Abstract

The growth and characteristics of metallic nanowires formed by field emission in the presence of organometallic precursors are studied. At low growth currents, single nanowires can be formed, which allows a systematic study of the growth characteristics, and wire morphology, structure, and composition. The major role of metal ion deposition in forming the metallic core is demonstrated experimentally, while the formation of the carbonaceous overcoat results from the deposition of neutral atoms from the precursor dissociation process. Transmission electron microscope analysis of tungsten nanowires shows that the core is polycrystalline, with columnar grains dominating the microstructure for thin wires, while larger diameter nanowires are straddled by multiple grains with a wider range of sizes. The axial and radial growth rates of tungsten nanowires as a function of growth current were studied and can be accounted for by assuming a situation in which the rate of ion formation just ahead of the growing tip is supply-rate limited. At higher growth currents, forking and branching phenomena were found to be increasingly probable, and hence, a key to the growth of single, well-defined nanowires is to keep the growth current low. Thermal decomposition of the precursor can also contribute to nanowire growth, and evidence for this mechanism was found in the cases of precursors where autocatalytic decomposition is known to result in metal deposition at relatively low temperatures. © 2006 American Institute of Physics.