# Carbon Microstructures Synthesis in Low Temperature Plasma Generated by Microdischarges
## 1 Introduction  
Methods of production and functionalization of different carbon structures has been the subject of intense investigations in recent years. It has passed less than 30 years since [PERSON] published his results of experimental investigations on the production of carbon nanotubes in a high-current arc discharge. Since that time, many papers have been published in the field of the synthesis of carbon nanotubes, carbon onions, diamond-like carbon using various types of electrical discharges, chemical vapor deposition or laser ablation. Plasma generated by electrical discharges is used in various industrial processes, for example, for thin film deposition, surface properties modification, sterilization, noxious compound decomposition, particulate matter precipitation, micro- and nanostructures synthesis, etching or electric-discharge-machining. These processes, operating at pressures ranging from the atmospheric to the elevated to below one pascal, are generated by a high voltage of various frequencies, such as direct-current (DC), alternating-current (AC), radio-frequency (RF), microwaves (\(\mu\)W) or by pulsed discharges (PD). These discharges can be generated between the following electrodes of different geometries: needle-plate, two parallel plates, rod-plate, etc., with or without dielectric barrier between them. Nowadays, a high-current arc discharge is one of the most effective methods used to obtain single- and multi-walled carbon nanotubes [1]. The synthesis of carbon structures or thin film deposition in low-power electrical discharges is rarely met in the literature. High voltage, low current discharges, such as corona discharge, generate non-equilibrium plasma, but can produce electrons of high kinetic energy, advantageous for such processes as ionization, excitation, molecules decomposition or polymerization. Usually, microplasma is generated in a gas at or near atmospheric pressure (0.1 MPa) between electrodes spaced at small distances, ranging from a fraction of a millimeter to 10 mm. The word \"microplasma\" was probably used for the first time by [PERSON] in 2003 [2], but \"microdischarge\" was found in a paper by [PERSON] and [PERSON] [3] (see [4]). The main advantage of using microplasma-based processes is that the physical processes and chemical reactions can occur in high-pressure gas flowing continuously through a plasma reactor, contrary to low pressure plasma sources, which require vacuum installation. In materials processing science, microplasma is used to synthesize nanoscale structures such as, for example, SiO\({}_{2}\) thin films [5], Si nanocones [6], carbon dendrites [7], or carbon amorphous deposits [8]. Generally, the most popular discharge types for microplasma generation are plasma-jet discharge and dielectric barrier discharge. The investigations of carbon fiber synthesis between a needle and plate electrodes were presented by [PERSON] and [PERSON] [9], but in n-heptane vapors, and nitrogen as a carrier gas. The source of plasma was a corona glow discharge of negative polarity (a needle was used as the cathode). Carbon fibers of grained and irregular morphology were obtained as a result of discharge in that gas mixture. Similar structures, named carbon dendrites, were obtained by [PERSON] et al. using a glow discharge generated in ethanol as the carbon feedstock [7]. Raman spectra indicated that the synthesized dendrites have glassy carbon- and pyrocarbon-like structures. A negative corona discharge was also used to deposit carbon dendrites from the products obtained by the de-polymerization of polystyrene [10]. In recent years, low-current electrical discharges have also been tested as a method of carbon nanostructures synthesis. For example, [PERSON] et al. [11] synthesized carbon nanotubes in a corona discharge at atmospheric pressure. During electrical discharge in a methane/hydrogen mixture using an anodic aluminum oxide template on a stainless-steel plate and cobalt as a catalyst, multi-walled carbon nanotubes with a diameter of about 40 nm were obtained.