Details of the operating parameters of the arc discharge methane decomposition process are provided in Table 1. Table 1 Operating parameters of carbon strands Parameter Value Temperature At room environment Frequency 50 Hz High voltage 1 to 26 kV Flow rate 200 to 800 ppm Precursor DNA Synthesis inhibitor gas Pure methane (99.99%) Pressure Atmospheric Diagnostics of the carbon film Once the arc discharge is initiated, methane decomposition starts causing the resultant carbon atoms to deposit and stack up between the two electrodes creating a conductive bridge. The growth time was measured to be 11.6 s

at the voltage of 16.4 kV. The carbon film fabricated in this process is inspected using high-resolution optical microscopy, as shown in Figure 2. There are three configurations for installing the electrodes on the PCB board, namely, plane to plane (PTP), tip to plane (TTP), and tip to tip (TTT); however, in this study, we have only investigated the TTT structure.

Figure 2 TTT electrode configuration (a) before arc discharge decomposition, (b) carbon film obtained. Inspection by scan electron microscopy A scanning electron microscope (SEM) scans the samples with a focused beam of electrons. As the electrons collide with the atoms in the sample, they produce various signals which can be detected and measured [18]. These signals provide information about the surface topography and composition Wnt inhibitor of the sample. Microphotographic images from SEM have been provided in Figure 3a,b,c,d. Figure 3 SEM image of a sample. Imaging Non-specific serine/threonine protein kinase mode (a) × 370 at 15 kV, (b) × 1,500 at 10 kV, (c) × 4,000 at 15 kV, and (d) × 14,000 at 10 kV. Among all types of carbon allotropes, only graphene, graphite, and CNTs show electrical

conductivity. On the other hand, the carbon films also show conducting behavior. This implies that the grown carbonaceous materials belong to one of the above types of graphitized carbon. With reference to similar images from carbon materials published in the literature [19–21], it can be observed by comparison that the scanned material is composed of carbon. Results of optical emission spectroscopy The optical emission during arc discharge decomposition was captured in the wavelengths ranging from 385 to 750 nm through a spectrophotometer (StellarNet, Tampa, FL, USA), and the data of the recorded spectra was sketched using MATLAB software. Three evolved peaks of methane species were prominent which belong to CH, C2, and Hα as shown in Figures 4 and 5. As illustrated in Figure 4, the spectrum consists of the evolved phase of ionized species of methane which indicates peaks of CH at 397 and 431 nm, swan band C2 appearing at 516.75, and hydrogen Hα appearing at 657.33 nm.