A STUDY OF MOLECULE FORMATION DURING LASER-ABLATION OF GRAPHITE IN LOW-PRESSURE NITROGEN

Plasma diagnostics were performed during excimer laser ablation of gra phite in a low-pressure Np atmosphere using time-and space-resolved op tical emission spectroscopy. The laser fluence and nitrogen pressure w ere set to values typically applied to pulsed laser deposition of thin films. Under these conditions, optical emission spectra were dominate d by continuum emission and spectral lines from carbon ions during the early plasma phase (t less than or equal to 200 ns), when the carbon vapour is located in the vicinity of the target surface, whereas molec ular bands of CP molecules and CN radicals were essentially observed a t later times when the vapour expands through the ambient gas. Emissio n spectra of C-2, CN and N-2(+) were recorded as functions of time for various distances from the target. From computer simulations of molec ular spectra, we deduced rotational and vibrational temperatures. The acquired information about the kinetics of excited plasma species and gas phase reactions contributes to a better understanding of pulsed la ser deposition of carbon nitride thin films.