# Carbon Microstructures Synthesis in Low Temperature Plasma Generated by Microdischarges
## 3 Results
### Carbon Deposit
The SEM micrographs of the carbon deposits obtained for different discharge currents with an inter-electrode distance of 3.75 mm and a 5% cyclohexane concentration are shown in Figure 15:1 For a discharge current of 1.4 mA (Figure 20a), the carbon nanowalls were indistinct and barely visible. When the discharge current was increased to 1.6 mA (Figure 20b), the carbon nanowalls were large and densely packed. For a current of 1.8 mA (Figure 20c), carbon nanowalls are not produced and only the nanowalls' nuclei can be noticed on the surface of the deposit. For a discharge current of 2 mA (Figure 20d), carbon nanowalls did not grow. Figure 15:2 Fragments of carbon deposit obtained at the anode for cyclohexane concentrations of (**a**) 1%, (**b**) 5% for positive polarity and (**c**) 5% for negative polarity, with a discharge current of 1.8 mA. Figure 15:3 SEM pictures of carbon deposits obtained for different discharge currents: (**a**) 1.4 mA, (**b**) 1.6 mA, (**c**) 1.8 mA and (**d**) 2.0 mA with an inter-electrode distance of 3.75 mm and a 5% cyclohexane concentration. Left column: general view of carbon fiber, right column: close-up view of fiber’s surface. A comparison of the growth rate of the carbon deposit synthesized on the needle for different inter-electrode distances and various discharge currents is shown in Figure 15:4 The slowest growth rate was observed for the lowest inter-electrode distance. Generally, for an inter-electrode distance lower than 7 mm, the growth rate decreased, which could be an effect of the different radicals obtained during the decomposition of cyclohexane. The sticking probability of radicals such as CH\({}_{\text{x}}\), C\({}_{2}\)H\({}_{\text{x}}\), CH and C differ in value [47], which could be dependent on the temperature of the surface/substrate [48]. Figure 22 shows the current density flowing through the anode deposit determined from the discharge current divided by the average cross surface area of the carbon deposit at its tip. Increasing the current density results in the increasing temperature of the deposit surface due to Joule heating. The carbon deposits without carbon nanowalls had diameters in the range of 15-30 \(\upmu\)m, whereas the diameters of the deposits covered with carbon nanowalls were in the range of 32-50 \(\upmu\)m. The carbon deposits without carbon nanowalls and with carbon nanowalls were obtained for a current density higher than 395 A/cm\({}^{2}\) and lower than 320 A/cm\({}^{2}\), respectively. Figure 15:5 Growth rate of carbon deposit synthesized on the tip of needle electrode during electrical discharges of positive polarity versus discharge current, for a 5% cyclohexane concentration. Figure 15:6 Current density on the anodic deposit for deposit with and without carbon nanowalls obtained for various discharge currents. After deconvolution, the first-order Raman spectra of amorphous carbon material consist of two main peaks between 1200 and 1700 cm\({}^{-1}\). Similar results were obtained for the synthesized carbon structures and are shown in Figure 23a. The peak located near 1600 cm\({}^{-1}\) is called graphitic (G band) and is associated with an in-plane stretching of sp2-bonded carbon atoms. The peak around 1350 cm\({}^{-1}\) is called a disorder-induced or D band. For single-crystal perfect graphite D band is not observed [49]. Figure 15:7 Raman spectra analysis of obtained carbon deposits: (**a**) Raman spectrum, (**b**) Raman shift of G and D bands, (**c**) the ratio intensity of D band and G band vs. cyclohexane concentration, with a discharge current of 1.8 mA. Additionally, the obtained carbon fibers had both peaks, G and D band. For 1% cyclohexane, the G band was at about 1605 cm\({}^{-1}\) and did not change significantly with an increasing cyclohexane concentration from 1 to 5 wt.% (Figure 23b). The position of the D band changed in the range of 1350 to 1360 cm\({}^{-1}\), with the maximum shift at 1360 cm\({}^{-1}\) for 3% cyclohexane. In addition to the D and G bands, small peaks at 1200, 1510 and 1550 cm\({}^{-1}\) were also obtained.