Laser-Generated Ag Nanoparticles in Mesoporous TiO₂ Films: Formation Processes and Modeling-Based Size Prediction

Abstract

Controlling the formation of nanoparticles (NPs) by direct laser writing ensures an efficient way of engineering the optical responses of nanocomposite materials through adjusting laser parameters such as power, focusing, and writing speed. The growth of NPs, photooxidation, and reduction affect the light absorption by an ensemble of laser-activated NPs. However, those self-consistent processes are not well understood. Previous studies explained the growth or shrinkage of silver NPs by neglecting heat diffusion. It remained unclear, however, how the NP size can be controlled by the laser writing speed. In this work, based on the coupled calculations of size variation, heat diffusion, and light absorption by an ensemble of NPs, we propose a two-dimensional model taking into account the spatial information of size and temperature. The spatial size distribution is revealed to be nonuniform, leading to the transmission inhomogeneity along the laser written lines. This fact is confirmed by the in situ transmission experiments. The performed study also depicts a novel view in which NPs grow ahead of the laser beam center because of the heat diffusion. The nonlinear growth never stops until it exhausts the majority of the free Ag 0 in the matrix, while the amount of Ag 0 by reduction cannot compensate the consumption. After that, the photo-oxidation dominates the process and finally controls the writing speed dependency of NP's size. The simulations also show that it is not the activation energy of Ag 0 diffusion, but the ionization efficiency affects the final NP size, which helps to understand how to improve the laser processing of differently prepared samples.

Effective medium-based optical real-time control over plasmon tuning in laser-induced nanocomposites

“…For the experiment, mesoporous thin films are firstly preparation by using either sol-gel or a complex and multistage procedure, and the obtained films are impregnated with silver ions by soaking in salts as described elsewere 6,7,8 . As a result, SiO2 and TiO2 matrices with embedded small (around 3 nm) Ag nanoclusters were obtained.…”

Electrochemical Properties of Silver Nanoparticles in Mesoporous Silica and Titania Films: Specific Behavior of Titania Composite

“…To build mesoporous silica and titania films, a sol−gel process and block copolymer self-assembly method has been used. 54,55 Among the numerous methods existing to form silver NPs in mesoporous films, 45,56,46,47 a reduction of silver ion solution by a coulometric method has been chosen to control the quantities of silver introduced. 57−60 Using these materials as electrodes, the influence of experimental parameters on voltamperometric CV curves such as the scanning speed and the starting potential are examined.…”

Insights into Ultrashort Laser-Driven Au:TiO2 Nanocomposite Formation

“…1−3 Many characteristics of such optical nanocomposites are attributed to size distribution and concentration of the embedded metal NPs and are often connected to the local field enhancement around them, as well as to their thermoplasmonic properties. Such effects, such as linear and nonlinear optical properties, [4][5][6]6,7 as well as chemical reactivity 8 of composite materials were investigated. Among a variety of such composite materials, titanium dioxide-based films attracted tremendous attention due to their high thermodynamic stability within a wide range of temperatures, relatively wide band gap, the difference in the surface layer semiconducting properties from those of the bulk phase, inertness, nontoxicity, as well as low price.…”

“…During the past decade, nanocomposite materials based on a transparent matrix with metal nanoparticles (NPs) have become particularly attractive in the growing fields of photonics, catalysis, and security research. − Many characteristics of such optical nanocomposites are attributed to size distribution and concentration of the embedded metal NPs and are often connected to the local field enhancement around them, as well as to their thermoplasmonic properties. Such effects, such as linear and nonlinear optical properties, − ,, as well as chemical reactivity of composite materials were investigated. Among a variety of such composite materials, titanium dioxide-based films attracted tremendous attention due to their high thermodynamic stability within a wide range of temperatures, relatively wide band gap, the difference in the surface layer semiconducting properties from those of the bulk phase, inertness, nontoxicity, as well as low price. − Moreover, an incorporation of plasmonic NPs considerably enhances light absorption and modifies its range as a result of plasmon resonances. , As a result, such materials can be effectively used to improve the photocatalytic performance of TiO 2 films due to electron transfer processes in such composites. , Therefore, semiconducting nanocomposites based on titanium dioxide are promising for the production of the next generation of solar cells, photocatalysts, gas sensors, or UV detectors. − …”

“…Numerous methods were proposed to introduce metal NPs into solid matrices, including chemical and thermal methods, photodeposition, sputtering, and core–shell nanostructure fabrication. ,− Among them, laser methods are fairly promising as they are able to provide a precise control over material properties ,, and local modification of the size and distribution of NPs, , as well as for structural modifications and phase changes of the matrix material. , In addition, laser methods are safer and cleaner than other methods, since commonly there is no need to use toxic substances.…”