## 3 Results and Discussion  
Figure 1 shows electron microscope images of CNFs webs synthesized at 1000 \({}^{\circ}\)C (CNF 1000), 1200 \({}^{\circ}\)C (CNF 1200) and 1400 \({}^{\circ}\)C (CNF 1400). The CNFs have uniform diameter ranging from 350 nm to 450 nm regardless of the pyrolysis temperature. However, their morphologies were significantly influenced by the processing temperature. The CNFs become wavy from straight morphology as increasing pyrolysis temperature. (Figure 1a,e,i) High magnification scanning electron microscope (SEM) images clearly reveal morphological changes in the surface as well as the junction between CNFs. (Figure 1b,f,j) The CNF 1200 and CNF 1400 have smooth surface while the CNF 1000 shows a rough surface, which indicates the rearrangement of carbon atoms by the increase of pyrolysis temperature [28; 29]. The morphological change in the junction between CNFs is also significant. Physically touched interface changes to being merged as an increase of pyrolysis temperature. Figure 1j clearly shows fused cross junction for CNF 1400. The microstructure of CNF webs was further characterized using the transmission electron microscopy (TEM). Although the CNF 1000 shows a significant contrast in the brightness at the core and shell (Figure 1c), any noticeable difference in the brightness is not observed for both CNF 1200 and CNF 1400 (Figure 1g,k), which is associated with the rearrangement of carbon atoms at the surface. Figure 1d,h,i show the high resolution (HR) TEM images for CNF webs. An increase in pyrolysis temperature results in a transformation of the amorphous and disordered structure into the high ordered and large graphitic structure. These structural and morphological differences in the CNFs, such as graphitization degree and in junction interface, significantly affect the electrical property. The CNF 1000, 1200 and 1400 exhibit sheet resistances of 15.3, 9.6 and 5.0 ohm/sq (Figure S1). X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to investigate the physicochemical properties of CNF webs. XRD patterns of CNF webs are shown in Figure 2a. The diffraction peak around the 20 angle of 25\({}^{\circ}\)  
Figure 1: Electron microscope images of carbon nanofibers (CNF) 1000, CNF 1200 and CNF 1400. (**a,b**) SEM and TEM images of (**a–d**) CNF 1000, (**e–h**) CNF 1200, and (**i–l**) CNF 1400.  
the (002) crystallographic plane of graphite crystallite. The intensity and sharpness of this peak gradually increased with the pyrolysis temperature. Figure 2b shows the Raman spectra for CNF webs. Two dominant peaks are observed at the \(\sim\)1340 cm\({}^{-1}\) and \(\sim\)1580 cm\({}^{-1}\), which are assigned to D-band and G-band, respectively. The intensity ratio of D band to G band (I\({}_{\rm D}\)/I\({}_{\rm G}\)) of the CNF webs decreases with an increase of the pyrolysis temperature, which clearly implies an enhancement in the graphitization degree. The high-resolution C1s spectra of XPS for CNF webs are shown in Figure 2c. Although all CNF webs have the highest intensities at 284.6 eV, the full width at half maximum (FWHM) for C1s spectra depends on their pyrolysis temperature. The CNF 1000, 1200 and 1400 have the FWHM values of 1.5, 1.4 and 1.2 eV, respectively, which indicates CNF 1400 has the highest graphitization degree among CNF webs. In O1s spectra (Figure 2d), both CNF 1200 and CNF 1400 exhibit more symmetric and narrow spectra towards higher binding energy than those of CNF 1000, which implies a decrease in the relative proportion of C=O and C-OH groups. The CNF 1200 and 1400 do not show any noticeable N1s related peak while the obvious N1s related peak is observed in CNF 1000 (Figure S2). The N1s related peak in CNF 1000 reveals the presence of nitrogen atom from polyacrylamideonitrile (PAN). The N atoms might be related to the high I\({}_{\rm D}\)/I\({}_{\rm G}\) intensity in the Raman result and low electronic conductivity [30; 31].