Synthesis of Self-aligned Tungsten Nanowires on Single Crystalline Tungsten Substrates
W. Wu, Q. Yu, S-S Pei
University of Houston, US
Keywords: Tunsten, nanowire, array, field emission
Abstract:Metallic nanowires have attracted much attention due to their unique mechanical, magnetic, optical and electronic properties, and their function as well-defined building blocks for nanodevices.1-3 Tungsten (W), in particular, is of great interest, being promising in applications such as emitters for field emission and field ionization, interconnection lines, and gate electrodes for integrated circuits.4-7 To realize these applications, considerable effort has been devoted to the synthesis, and the precise control of the position and orientation of W nanowires on substrates. However, only a few results have been reported.5,6,8-10 In this work, we report the growth of self-aligned W nanowires directly from single crystalline W substrates. The sample was prepared by heating a Ni-coated W substrate with W oxide power upstream as source at 850°C in the gas flow of N2 for bubbling DI water and H2 in a conventional horizontal tube furnace. The as-prepared sample was examined by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS) investigations were also conducted during the TEM experiments. The diameter of the resulting nanowires is in the range of 10-100 nm, and the lengths can be up to several microns. Both the SAED pattern and the high resolution TEM results demonstrate that the synthesized aligned nanowires are W with a bcc crystal structure growing along the  direction. Since the synthesis temperature 850°C is significantly lower than the eutectic point 1495°C of the bulk Ni-W binary system, the vapor-solid-solid mechanism is likely responsible for the growth of Ni-catalyzed W nanowires in our experiment. Currently, we are testing the field electron emission properties of these aligned W nanowires, results from our studies will be presented.