1 research outputs found
Understanding the Growth Mechanisms of Ag Nanoparticles Controlled by Plasmon-Induced Charge Transfers in Ag-TiO<sub>2</sub> Films
Mesoporous thin films of TiO<sub>2</sub> doped with silver can
undergo spectacular microstructural modifications upon laser scanning
at visible wavelengths through the excitation of a localized surface
plasmon resonance in Ag nanoparticles (NPs). The latter can result
in competitive physicochemical mechanisms, leading either to the shrinkage
or to the growth of NPs depending on the exposure conditions. Contrary
to intuition, we provide evidence that the speed of the laser scan
controls the size of NPs as follows: low speeds lead to silver oxidation
and a decrease in the NP size, whereas high speeds induce rapid temperature
rises and a spectacular growth of NPs. Both regimes are separated
by a speed threshold that depends on extrinsic and intrinsic parameters
such as laser power, beam diameter, and initial size of Ag NPs. We
propose here a comprehensive model based on a set of coupled differential
equations describing the transformations of silver under laser excitation
between the Ag<sup>0</sup>, Ag<sup>+</sup>, and metallic NP states,
which provides a convincing physicochemical explanation of the experimental
findings. This study constitutes a significant advance in the understanding
of oxidation–reduction processes involved during laser exposure
of metallic NPs and opens new directions to control their growth rate
and their final size