The deposition process is studied of vertical carbon nanosheets by microwave (MW) plasma-enhanced chemical vapor deposition (PECVD) at atmospheric pressure. A coaxial MW plasma source with a surface-wave discharge at 2.45 GHz produces plasma in a gas mixture (Ar/H2/CH4) in the processing chamber. The emissive spectra of the plasma column in pulsed regime of the source are registered by an iHR550 spectrometer. The light from the plasma column is collected by a lens system connected to the spectrometer by an optical fiber. The dependence of the gas temperature in the plasma column on the absorbed MW power is obtained from the recorded OH-band and CN-band spectra by using the LIFBASE program. The plasma density is estimated from the Stark broadening of the Hβ-line, while the electron temperature is estimated by the line-ratio method using argon lines. The composition of the outlet gases from the chamber is measured and analyzed by an Agilent Micro gas chromatograph. The results obtained demonstrate the high efficiency of the methane decomposition process in the hot region of the plasma column (T g ~ 3000 K). The deposition of vertical carbon nanosheets is carried out at fixed plasma parameters and controlled substrate temperature. Cu plate and Ni-foam are used as substrates. The carbon nanostructures formed on the metallic substrates are studied by SEM; the dependence is thus obtained of their morphology on the plasma parameters, gas temperature and substrate temperature. The structures are confirmed as graphene sheets via Raman spectroscopy. The results demonstrate the viability of our system for deposition of vertical carbon sheets at atmospheric pressure.

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Deposition of carbon nanostructures from ethanol precursor at atmospheric pressure can be enhanced via the use of a double-discharge system - a microwave and a DC discharge. We used a surface-wave discharge at a frequency of 2.45 GHz in a gas mixture of Ar, H2 and C2H5OH to create a plasma column in a small-diameter ceramic tube and a plasma plume above it. The plume spectra in the UV/Vis range were measured by an optical system with an iHR550 spectrometer; the gas temperature and the electron temperature and density were calculated from the emission lines. The high gas temperature T g ∼3000 K and electron density (∼6×1020 m3) in the microwave plasma plume cause an effective dissociation of the ethanol even at low levels of absorbed power (10 W) and a strong carbon Swan band is registered in the spectrum. Transporting the created neutral and charged particles to the substrate at atmospheric pressure is difficult due to their short mean-free-path; we, therefore, applied an additional DC discharge. This two-discharge system allows more reactive species and ions from the ethanol decomposition to reach the substrate, thus speeding up the deposition of carbon nanostructures. Such structures were deposited on Ni foil and Ni foam substrates under fixed plasma parameters and controlled substrate temperature. The morphology of the produced graphene structures was studied using SEM and Raman spectroscopy.

Carbon nanostructures, such as carbon nanowires, nanotubes, nanosheets, have found applications in many areas – from electronics to medicine. Recently, they attracted particular attention as materials for energy storage due to their large aspect ratios, specific surface areas, and electrical conductivity. An efficient method for their deposition on metallic surfaces at atmospheric pressure is microwave plasma-enhanced chemical vapor deposition (MPECVD). In this study, metallic surfaces with deposited carbon nanostructures were used for preparation of capacitor electrodes. The capacitance of an electrolytic capacitor with metal electrodes without and with deposited carbon nanostructures was measured by an electronic system. The resulting high value of the capacitance of a capacitor with electrodes with deposited carbon nanostructures is discussed on the basis of these structures morphology as studied by SEM.

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