Burst-Mode Femtosecond Pulsed Laser Deposition for Control of Thin Film Morphology and Material Ablation

We introduce an alternative approach of pulsed laser deposition (PLD) using groups of closely time spaced (20 ns) ferntosecond laser pulses, namely burst-mode fs-PLD. This approach enables a broad and continuous tunability over the material morphologies ranging from nanoparticle aggregates to epitaxial thin films with completely droplet-free and atomically smooth surfaces. The tunability of materials is realized by simply tuning laser parameters. An unusual phenomenon of laser-matter interaction is revealed in terms of the breakdown of nanoparticles, the enhancement of plasma ionization, and the decrease of ablation threshold during the burst-mode fs-ablation. A TiO2 film, a wide band gap semiconductor, was deposited with as low as 50 nJ of pulse energy. This approach and the phenomenon are applicable to many other materials. (C) 2009 The Japan Society of Applied Physics