High-yield synthesis of carbon coils on tungsten substrates and their behavior in the presence of an electric field
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Josie Prado Department of Chemical Engineering, Oregon State University, Corvallis, Oregon 97331
George M. Coia Department of Chemistry, Portland State University, Portland, Oregon 97207 (Received 13 March 2003; accepted 23 July 2003)
We report an effective procedure for fabricating carbon microcoils and nanocoils with three-dimensional spiral structures in high yield by nickel (Ni)-catalyzed thermal decomposition of acetylene. The Ni catalyst particles used in this preparation were electrochemically deposited onto tungsten substrates. Springlike coils having low pitch and micrometer-scale diameters and ropelike coils having higher pitch and nanometer-scale diameters were observed. Electrical and optical properties were investigated by employing a field-emission probe system equipped with an optical spectrometer. In an applied field above 1.5 V/m, significant electron emission was observed from individual ropelike nanocoils. The approximately linear slope of the corresponding Fowler–Nordheim plot denotes predominately field-emission behavior. During measurement, individual carbon coils aligned themselves along the electric field, exhibiting a natural resonance on some occasions. As the field strength increased above 2.5 V/m, the emission-current density for a single nanocoil was measured to be on the order of 104 A/cm2. This high-current density caused Joule heating, resulting in strong photon emission by incandescence.
I. INTRODUCTION
Carbon coils are considered to be potential candidates for such applications as microsprings, effective fillers in electromagnetic shielding materials, and elastic packing materials resistant to high temperatures and corrosive environments.1,2 An earlier report by Baker et al.3 in the 1970s demonstrated the formation of spiraled carbon filaments by catalytic nickel (Ni) and Sn/Fe decomposition of acetylene. However, the formation of these coiled carbon filaments was rather random, and the yield of the coils was very low. A method introduced by Motojima and colleagues4,5 resulted in the high-yield growth of carbon microcoils with coil diameters in the range of 3–6 m. The production of carbon coils from various substrate–catalyst combinations has been reported elsewhere.1–7 In this paper, we introduce a procedure for the consistent production of carbon coils in high yield on tungsten substrates using electrochemically deposited Ni catalyst particles, as well as a discussion of the growth mechanism of these coils with respect to preparation parameters. Our motivation for using tungsten as a substrate is due to its high melting point and good conductivity, which make tungsten a potentially useful substrate in nanodevices. We also investigate the electrical and 2580
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J. Mater. Res., Vol. 18, No. 11, Nov 2003 Downloaded: 14 Mar 2015
optical behavior of these coils in the presence of an electric field. To our knowledge, these findings have not been reported elsewhere. In this paper, we use the inclusive term “carbon coils” to refer to both microcoils a
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