**Abstract**

Pulsed Laser Ablation (PLA) in background gas is a good technique to acquire specific nanoparticles under strong non-equilibrium states. Here, after a history of PLA is mentioned, the application of nanoparticles and its deposition films to the several fields will be described. On the target surface heated with PLA, a Knudsen layer is formed around the adjacent region of the surface, and high-pressure and high-temperature vapor atoms are generated. The plume formed by evaporated atoms blasts off with very high-speed and expands rapidly with a shock wave. A supercooling phenomenon occurs during this process, and number of nucleus of nanoparticle forms in vapor-phase. The nuclei grow by the condensation of vapor atoms and deposit on a substrate as nanoparticle film. If the radius of nanoparticle is uniformized, a self-ordering formation can be shown as a result of interactive process between each nanoparticle of the same size on the substrate. In this chapter, the related technology to realize a series of these processes will be expounded.

**Keywords:** PLA, PLD, nanoparticle, deposition, non-equilibrium, evaporation, laser plume, shock wave

## **1. Introduction**

Pulsed Laser Deposition (PLD), which is a film-forming technique by using PLA, has been experimented since the 1960s after the invention of the laser oscillator. Afterwards, in the wake of the realization of Q-switch Nd: YAG laser in 1970s and the electric discharge pumping high-speed repeatable excimer laser in 1980s, PLD has become a powerful tool to fabricate high-performance films such as semiconductors, heterostructure and superlattices. The success of high-temperature superconducting films in the mid-1980s led to the flourishing of laser ablation research.

In the early 1990s, the research on PLD application has made several developments such as heteroepitaxial films, perovskite oxide films, nitride films and diamond-like carbon films. Although the research on nanoparticles derived from the laser ablation had already been conducted as part of these developments, the discovery of Buckminster fullerene [1] was undoubtedly an important milestone in the following development of nanoparticle applications. In the 21st century, effect which shock waves have on the formation way of nanoparticle during laser ablation has been investigated [2, 3]. Several researches [4–6] in which the shock waves are positively used to form monodispersed nanoparticles and composite

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*Practical Applications of Laser Ablation*

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nanoparticles like core-shell type have been conducted. The laser ablation in nanoparticle research is regarded as the promising method at present which is possible to fabricate a novel function device in the area of electricity, semiconductor, energy and so on.

We have known PLD as a process during which a solid target is vaporized with laser irradiation, and then the nanoparticle formation in the gas phase is occurred, followed by its soft-landing on a substrate. But each process remains unclear to us. In order to apply the laser ablation method for the fabrication of functional materials, it is important to understand each step of the process so that we can put them to practical use. In this chapter, we divide the formation process of nanoparticle films as following steps for further studies: (1) temperature increase of solid surface by laser irradiation, (2) evaporation of the surface and its conversion to kinetic energy, (3) plume expansion with shock wave propagation, (4) supercooling of evaporated gas, (5) uniform sized nanoparticle formation, and (6) nanoparticle deposition and self-ordering on the substrate.
