A Model for Local Generation of Nanoparticles in Photoinduced Nanocomposites by the Focused Laser Light

Metal or semiconductor nanoparticles (NPs) can be instantly generated in polymers under the irradiation by light, thus converting them into the photoinduced nanocomposites. The light causes the photodestruction of the precursor molecules dissolved in the polymer matrix. As a result, some kind of elementary species (such as atoms of metal) are released and then precipitate into the NPs right within the bulk of the material. This paper considers theoretically the kinetics of the localized NP generation under the prolonged irradiation by the focused continuous-wave or pulsed laser light. It is shown that the maximal rate at which the elementary species can be generated by the laser beam is determined by the balance between the depletion rate of the precursor within the irradiated spot and its diffusion flux from the surrounding volume. The optimal beam power that yields the maximal species generation rate at the focus is calculated. At that and smaller beam power, the maximum material modification is located at the maximum of the laser intensity. With the higher beam power, the material modification can be performed within the hollow volume, leaving the focus untouched. The possibility of the local generation of NPs is studied within the framework of the simplest homogenous nucleation model. The locally generated elementary species tend to leave the irradiated zone due to the diffusion. However, if the initial precursor concentration is high enough, the growing NPs act as traps for elementary species thus impeding this delocalization effect.