Double-Pulse Laser Ablation Applied to Reactive PLD Method for Synthesis of Carbon Nitride Film:A Second Laser Shot Delays

摘要

Carbon nitride films were deposited using ablation of graphite target by second harmonic radiation of Nd:YAG laser in nitrogen atmosphere. To produce high hardness films, the deposited particles should have sufficient kinetic energy to provide their efficient diffusion on a substrate surface for formation of crystal structure. However, a shock wave is arisen in ambient gas as a consequence of laser plasma explosive formation. This shock wave reflected from the substrate interacts with plume particles produced by the first laser pulse and decreases their kinetic energy. This results in decrease of film crystallinity. To improve film quality, two successive laser pulses was proposed to be used. At adjusting time delay, the particles induced by the second pulse wilt serve as a piston, which will push forward both stopped particles ablated by the first pulse and arisen from chemical reactions in ambient gas. An X-ray photoelectron spectroscopy (XPS) analysis of deposited films has shown an increase of content of sp~3 carbon atoms corresponding to crystalline phase, if double-pulse configuration is employed. The luminescence of excited C_2 and CN molecules in laser plume at different distances from the target was studied to optimize the delay between laser pulses.