Growth Mechanisms and Kinetics of Photoinduced Silver Nanoparticles in Mesostructured Hybrid Silica Films under UV and Visible Illumination

Abstract

The growth of silver nanoparticles in mesostructured hybrid silica films under laser illumination is investigated by optical absorption spectroscopy and transmission electron microscopy. At low laser doses in the UV range, a blue-shift of the plasmon resonance is observed for increasing particle size. This size dependence is interpreted on the basis of the Mie theory assuming a two-layer core-shell model resulting from the localization of the nanoparticles in the block copolymer part of the film. At higher laser doses, the observed red-shift of the resonance wavelength and decrease of the absorbance level at resonance are attributed to the formation of a high refractive index shell around the nanoparticles that thickens slowly with the dose. The growth kinetics of silver nanoparticles is also studied for different illumination wavelengths in the UV and visible ranges. Surprisingly, the nanoparticles also grow under visible illumination. This is partly attributed to the release of electrons by the degrading copolymer under illumination. The decrease of the photoreduction process rate with the incident wavelength increase has been evaluated quantitatively. We propose an autocatalytic model that fits well with the experimental data and suggest that the absorption of some incident wavelengths by the generated small silver clusters boosts their own growth.

Self-organized growth of metallic nanoparticles in a thin film under homogeneous and continuous-wave light excitation

“…Its refractive index was deduced from the Maxwell-Garnett theory using for the refractive index of small Ag nanoparticles the expression of the dielectric function of bulk silver, corrected in size taking into account the classical free path effect. 36 The overall TiO 2 thickness was 155 nm. A constant absorption coefficient was also applied to TiO 2 to take into account losses caused by scattering by the nanocrystals.…”

Law of Mass Action Type Chemical Mechanisms for Modeling Autocatalysis and Hypercycles: Their Role in the Evolutionary Race

“…[17] It is, however, interesting to note that although the term 'mechanism' was consistently mentioned in that paper, in kinetic sense a 'mechanism' has to consist of elementary or quasi-elementary steps exclusively, where law of mass action type kinetics is uniquely fulfilled for each and every step. Misuse of term 'mechanism' and 'kinetic model' is not restricted to self-replication studies it may as well be found in other fields [18][19][20] thus the problem seems to be more general than one would otherwise expect. Recently, Virgo et al showed that in case of a polymerization model not only first-order autocatalysis but even more complex overall positive feedback processes may appear resulting in a superexponential growth.…”

Towards a metallic top contact electrode in molecular electronic devices exhibiting a large surface coverage by photoreduction of silver cations

“…Subsequent photoreduction of the coordinated silver cations in 1Ag + LB films results in the formation of disklike metallic silver nanoparticles, which cover a significant portion of the film surface, and this system is denoted here as 1AgNP. The photoreduction mechanism of silver cations 16 as well as the subsequent nucleation and growth mechanism of the silver nanoparticles 17,18 have been studied in detail before. Fig.…”