Plasma chemistry of an expanding Ar/C2H2 plasma used for fast deposition of a-C:H

Mass spectrometric measurements in combination with Langmuir probe measurements reveal that the plasma chemistry of an expanding Ar/C₂H₂ is dominated by argon-ion-induced dissociation of the precursor gas. Under high arc current conditions complete depletion of acetylene is observed, indicating an efficient consumption of the injected acetylene. A clear correlation between the ion fluence emanating from the arc determined from modeling the mass spectrometry results and Langmuir probe measurements is observed. First measurements by means of cavity ring down and optical emission spectroscopy of the products of the dissociation of acetylene indicate that the dominant dissociation channel is C₂H and H.