Deposition of vertical carbon nanosheets by MPECVD at atmospheric pressure

Abstract

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.