Laser Ablation-Deposited CN _x Thin Films

Abstract

Amorphous CN _x thin films were deposited at room temperature by pulsed laser ablation of graphite targets in a controlled atmosphere using both N₂ and N₂/Ar gas mixtures. The structural and electronic properties of the samples were investigated by means of X-ray photoelectron, reflection electron energy loss and Raman spectroscopy. Nitrogen contents as high as 32% have been estimated. The overall results show a progressive transformation of the C–C sp ³ bonds into sp ²–hybridized C–N ones with the development of sp ² carbon clusters upon increasing the gas pressure values. By means of fast photography measurements, different regimes of the laser-induced plasma expansion dynamics have been evidenced. The results indicate that the electronic and structural properties of the laser ablation-deposited CN _x films depend strongly on the regime under which the plasma expansion takes place, not simply on the overall nitrogen content. In this respect the role played by the gas composition and pressure are of fundamental importance.