Spectroscopic diagnostics of a pulsed arc plasma in the presence of acetylene

Plasma fluxes for deposition of diamond-like carbon films were generated by the four-electrode device with graphite cathode in vacuum as well as in acetylene atmosphere at pressure of 0.2–2 Pa. Optical emission spectra of the cathodic-arc carbon plasma in a wavelength range of 400–1000 nm were studied. For observation along the plasma flow at acetylene pressures of 0.2, 0.5 and 1.0 Pa the intensity of the C2 molecular band at 563.55 nm increases by a factor of 6, 8 and 11, respectively, in comparison with values for a vacuum discharge. When displacing the observation line from the discharge axis a sharp decrease of carbon ion emission is detected while radiation of C2 molecules remains approximately the same. For observation across the plasma flux the emission of C2 molecular bands predominates over carbon ions both for the vacuum discharge and the discharge in acetylene. However on acetylene addition the intensities of carbon ions and hydrogen spectral lines increase by 1.5–3 times. It was found that the gas-kinetic temperature of the plasma is about 0.1 eV.