# Carbon Microstructures Synthesis in Low Temperature Plasma Generated by Microdischarges
## 2 Materials and Methods  
A schematic of the experimental set-up is shown in Figure 1. The experiments were carried out in an atmosphere of argon and cyclohexane as the carbon feedstock, at normal pressure, in a reactor chamber of 0.1 dm\({}^{3}\), made of PMMA. The hydrocarbon vapors were fed to the reactor from a bubbling flask, with argon as the carrier gas. The concentration of hydrocarbon in argon was controlled via mixing the cyclohexane vapors with additional argon. The flow rates of argon flowing directly to the reactor and throughout the flask were measured using flow meters. The temperature of liquid cyclohexane in the flask was stabilized at 21 \(\pm\) 1 \({}^{\circ}\)C and was slightly lower than the room temperature to avoid vapor condensation on the pipe's walls. The concentration of cyclohexane vapors was calculated from the flow rates of the vapor of cyclohexane and argon. The total flow rate of the mixture was kept constant at a level of 0.051 dm\({}^{3}\)/min. The concentration of cyclohexane was changed in the range of 1 to 5%. Cyclohexane of purity of 99.5% was supplied by Chempur (Poland) and argon of purity 99.999% by Linde gas. Before starting the experiment and plasma ignition, the reactor was rinsed with the gas mixture for 10 min to remove the air from the volume. Then, the voltage was switched on to the assumed magnitude set before. The voltage was switched off after a required time period.  
The electrical discharge was generated between a stainless-steel needle (composition in wt.%: Fe, 70; Cr, 18; Ni, 10; Si, 1) and a plate made of a nickel alloy (composition in wt.%: Ni, 75; Fe, 17; Mo, 5; Mn, 1.5). The diameter of the needle was 1 mm, the tip radius of the needle was about 30 \(\upmu\)m. The dimensions of the plate were 35 \(\times\) 20 mm. The distance between the electrodes was changed in the range of 1 mm to 15 mm.  
The electrodes were supplied from high voltage power supply SPELLMAN HV SL 600 W/40 kV/PN (Spellman, Pulborough, UK) of a positive polarity. The discharge current was stabilized by a series resistance with a value of 5 M\(\Omega\). The discharge current was changed from 0.4 mA up to 3 mA. The voltage between the electrodes was measured with high voltage probe TEktronix P6015A (Tektronix, Beaverton, OR, USA). The current pulses were measured by means of Rogowski type current monitor PEARSON 6600 (Pearson Electronics, Palo Alto, CA, USA) and Differential Preamplifier Tektronix ADA400A as amplifier of current signals. Both of the signals gained by these probes were recorded using digital storage oscilloscope TEktronix TDS 3032.  
Figure 1: Experimental setup.  
The as-made carbon deposit grown on the needle tip or plate was carefully removed from the reactor, placed at the microscopic stage covered with carbon tape, and examined under a scanning electron microscope (Zeiss EVO 40, Carl Zeiss, Germany) equipped with an energy dispersive spectroscope (EDS, Quantax 200, Bruker, UK). Renishaw inVia Raman Microscope (Renishaw, UK) with a 100\(\times\) objective lens and a laser with a power of 1.5 mW at a wavelength of 514 nm was used in order to analyze the Raman spectra of obtained carbon structures. The concentration of nanoparticles generated in microdischarge and leaving the reactor was measured using GRIMM Condensation Particle Counter 5416 (GRIMM Aerosol Technik Ainring GmbH & Co. KG, Ainring, Germany). The size distribution of aerosol particles was determined using Aerosol Particle Size Spectrometer LAP 322 (Topas GmbH, Dresden, Germany).