Optical emission spectroscopy in cathodic arc deposition

Titanium and chromium arc discharges in nitrogen and argon in the pressure range between 10^-3 and 1 Pa have been studied using optical emission spectroscopy and electric probes. The pressure dependence of normalized line intensities could be explained in terms of the metal vapor generation at the cathode as well as ion-molecule collisions in the arc plasma far from the cathode. Obviously, inelastic electron collisions do not play a decisive role. The excited levels of metal species were found to be populated according to a Boltzmann distribution. An excitation temperature of about 0.3 eV was calculated for the neutrals, whereas the excitation temperature of ions was somewhat higher. The degree of vibrational excitation of various electronic states of the N₂ molecule was found to be nearly the same in Cr and Ti are discharges, respectively. The main result of the present study was that the excitation degree of chromium and titanium are discharges in argon and nitrogen, respectively, is similar