The C1s spectrum from the pyrolyzed carbon structure only has a single peak at 283.7 eV. In the O1s spectral region, the pyrolyzed carbon features a peak at 531.8 eV significantly reduced in intensity from the corresponding peak of the SU-8 polymer before pyrolysis. The difference in O/C ratios between the SU-8 polymer structure before (23.2%) and that after pyrolysis (3.1%), confirms a low level of oxygen in the pyrolyzed carbon. This result is in agreement with that obtained on other pyrolyzed carbon structures [27]. Figure 5 XPS spectra
in (a) C1s and (b) O1s regions. XPS spectra were obtained from a bare SU-8 structure before pyrolysis and a pyrolyzed bulk carbon structure. The electrical properties of the suspended carbon nanowires were evaluated using a two-probe check details I-V technique using
the posts as contact pads instead of using a four-point probe method. A two-probe approach could be used in this case because the effects of contact resistance and spreading resistance, which are the main sources of electric measurement errors, could be neglected here since the nanowire is connected to the post monolithically and the carbon nanowire has a much greater resistance compared to the carbon posts due to their large size difference. Carbon nanowires with a width and thickness of approximately 190 nm showed excellent ohmic contact, and the wire resistance decreased as the temperature increased (Figure 6a). The MK-8776 manufacturer inverse proportionality of temperature and resistance is indicative of the semiconductor-like behavior of the suspended carbon nanowire. The electrical conduction mechanism in disordered carbon is explained by a hopping-based mechanism at low temperatures (<250 K) [28] and a thermally
activated mechanism at higher temperatures (>250 K) [13]. As we made measurements at temperatures Avelestat (AZD9668) above room temperature, the following relationship of conductivity vs. temperature applies [13]. (1) where σ 0 is a constant, k B is the Boltzmann constant, and ϵ act is the activation energy. The activation energy ϵ act is defined as ϵ act = ϵ C − ϵ F , where ϵ C is the conduction band edge and ϵ F is the Fermi level. The activation energy obtained by fitting a plot of ln(σ) versus T -1 from the resistance measurement results was approximately 0.146 eV. This small activation energy of the carbon nanowire is also found in predominantly sp2 carbonaceous materials such as pyrolyzed polyfurfuryl alcohol nanowires [13] and confirms that the composition of the suspended carbon nanowire is mainly non-graphitizing sp2 bonded Selleck SIS3 carbons. Figure 6 Conductivity-temperature relationship of a suspended carbon nanowire (size approximately 190 nm). (a) Voltage versus current curves in various temperature conditions. (b) Conductivity to temperature curve in a logarithmic scale. The suspended carbon nanowire was characterized electrochemically by cyclic voltammetry in a 10-mM K3Fe(CN)6 solution with 0.5 M KCl (Figure 7a).
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