**5.1 Experimental equipment**

The main part of the experimental setup, shown in Figure 8, is composed of the generation and deposition chamber. The laser beam is introduced into the generation chamber. The laser plume is confined by the ellipsoidal cell and uniform-sized nanoparticles are generated. An ambient gas is supplied into the ellipsoidal cell and the cell is filled with the gas. The deposition chamber is connected to the generation chamber through a skimmer, where the nanoparticles are extracted by the ambient gas flow. A substrate is placed in a vertical position for the deposition of the nanoparticles.

Fig. 8. Schematic diagram of the apparatus for the nanoparticle formation using Pulsed Laser Ablation

When the high-power pulsed laser is directed onto a solid sample in the ellipsoidal cell filled with the ambient gas, the plume is ejected perpendicular to the sample surface. At that time, a shock wave is also generated, driven by the plume expansion, and then propagates in the ambient gas. By placing the sample surface on the focal point of the ellipsoidal cell, the shock wave is reflected on the inner wall of the cell and focused onto the other focal point.

Thermodynamics of Nanoparticle Formation in Laser Ablation 139

Fig. 10. Histograms showing the diameters and the logarithmic normal distributions of the

Fig. 11. TEM images and corresponding the electron diffraction patterns of Cu

As already stated, in order to produce monodispersed nanoparticles, it is important to confine the plume within the converging shock waves. To confirm the importance of

nanoparticles.

nanoparticles.

**5.3 Confinement effects** 

The plume then collides with the ambient gas, which is considerably denser because of the shock wave focusing in the vicinity of this focal point. A mixture region, where the thermodynamic states are uniform, is formed in the boundary between the ambient gas of high density and the plume front and where the mono-disperse nanoparticles are formed.
