Local thermal equilibrium plasma modeling for analyses of gas-phase reactions during reactive-laser ablation

Number densities of atoms, ions, and molecules in plasmas composed of two-element vapor-gas mixtures have been computed assuming local thermal equilibrium. The calculations include the formation of diatomic molecules by chemical reactions between both elements. Temperature range and total number densities of elements have been set to values characteristic for plasmas generated by pulsed-laser ablation of solid targets under low-pressure atmospheres. Mixtures of aluminum, carbon, and titanium vapors with either oxygen or nitrogen have been considered. The model predicts strong oxidation for all materials in O2. Contrarily, only very small quantities of nitride radicals are formed when mixing metal vapor with N2 whereas carbon nitridation leads to CN formation of a few percent. The results contribute to a better understanding of gas-phase reactions during thin film deposition by reactive laser ablation.