134
G. Compagnini et al.
structural modifications induced by the LIL process are fundamentals to strongly
increase the photocatalytic performance.
4.1 Introduction
Research related to the production of nanoparticles and nanostructures of different
size, shape, structure, and composition is on the rise due to their large applications in
the different fields of science and technology [1–6]. Due to such an increasing request,
the production of different types of nanoparticles stimulated the development of new
strategies for their production by using different methodologies.
Many homemade vacuum machines have been built in various laboratories to
produce clusters of different materials having a nanometric size. However, vacuum
technologies require very good maintenance to obtain objects of high quality. For
instance, impurities present in the fly zone between the source and the deposition
plate may pollute the produced materials. Therefore, high vacuum conditions are
strictly required.
On the other hand, classical wet chemistry has been by far used with a large
number of different bottom-up approaches for nanomaterials fabrication involving
fundamental building blocks of matter: atoms and molecules [7, 8].
An intriguing alternative is to work directly in the liquid phase to grow and/or
modify nanosized materials using pulsed laser beams. In these cases, laser energy
can be used to ablate solid targets in the so-called Pulsed Laser Ablation in Liquids
technique (PLAL) or to modify previously synthesized colloidal dispersions, thus
changing the shape, size, and composition of the nano-entities or activate reactive
path for the formation of stable or metastable materials [9–14].
Regarding PLAL techniques, they involve a focused, high-power laser beam onto
the surface of a solid target that is submerged beneath a liquid. The interaction of
the laser with the target causes the surface to vaporize in the form of an ablation
plume. This contains species such as atoms, ions, and clusters, traveling with high
kinetic energy. The species in the plume collide and react with the molecules of
the surrounding liquid, producing new compounds that contain atoms from both
the original target and the liquid. Because of the intensity of the laser and the
nanosecond timescales, the instantaneous temperature and pressure within the reaction volume can be extremely high (many thousands of Kelvin and tens of GPa).
Such high-temperature, high-pressure, and high-density conditions provide a “brute
force” method of synthesizing novel materials that have hitherto been inaccessible
using milder, more conventional techniques. The mechanisms involved in the nucleation and phase transition of nanocrystals upon PLAL are not well understood. A
recent review [15] gave an overview of nucleation thermodynamics, the phase transition, and the growth kinetics in the case of nanocrystals obtained by laser ablation
of liquids.
Pulsed lasers have been also used to irradiate nanoparticles in liquid environments at fluences well below the ablation threshold (usually 0.1–0.5 J/cm
2 ). This has
G. Compagnini et al.
structural modifications induced by the LIL process are fundamentals to strongly
increase the photocatalytic performance.
4.1 Introduction
Research related to the production of nanoparticles and nanostructures of different
size, shape, structure, and composition is on the rise due to their large applications in
the different fields of science and technology [1–6]. Due to such an increasing request,
the production of different types of nanoparticles stimulated the development of new
strategies for their production by using different methodologies.
Many homemade vacuum machines have been built in various laboratories to
produce clusters of different materials having a nanometric size. However, vacuum
technologies require very good maintenance to obtain objects of high quality. For
instance, impurities present in the fly zone between the source and the deposition
plate may pollute the produced materials. Therefore, high vacuum conditions are
strictly required.
On the other hand, classical wet chemistry has been by far used with a large
number of different bottom-up approaches for nanomaterials fabrication involving
fundamental building blocks of matter: atoms and molecules [7, 8].
An intriguing alternative is to work directly in the liquid phase to grow and/or
modify nanosized materials using pulsed laser beams. In these cases, laser energy
can be used to ablate solid targets in the so-called Pulsed Laser Ablation in Liquids
technique (PLAL) or to modify previously synthesized colloidal dispersions, thus
changing the shape, size, and composition of the nano-entities or activate reactive
path for the formation of stable or metastable materials [9–14].
Regarding PLAL techniques, they involve a focused, high-power laser beam onto
the surface of a solid target that is submerged beneath a liquid. The interaction of
the laser with the target causes the surface to vaporize in the form of an ablation
plume. This contains species such as atoms, ions, and clusters, traveling with high
kinetic energy. The species in the plume collide and react with the molecules of
the surrounding liquid, producing new compounds that contain atoms from both
the original target and the liquid. Because of the intensity of the laser and the
nanosecond timescales, the instantaneous temperature and pressure within the reaction volume can be extremely high (many thousands of Kelvin and tens of GPa).
Such high-temperature, high-pressure, and high-density conditions provide a “brute
force” method of synthesizing novel materials that have hitherto been inaccessible
using milder, more conventional techniques. The mechanisms involved in the nucleation and phase transition of nanocrystals upon PLAL are not well understood. A
recent review [15] gave an overview of nucleation thermodynamics, the phase transition, and the growth kinetics in the case of nanocrystals obtained by laser ablation
of liquids.
Pulsed lasers have been also used to irradiate nanoparticles in liquid environments at fluences well below the ablation threshold (usually 0.1–0.5 J/cm
2 ). This has