Real-Time Monitoring of Plasmonic Evolution in Thick Ag:SiO₂ Films: Nanocomposite Optical Tuning

Abstract

An in situ optical microspectroscopy study of the surface plasmon resonance (SPR) evolution of Ag nanoparticles (NPs) embedded in thick SiO(2) films deposited on soda-lime glass has been conducted during thermal processing in air. The temperature and time dependences of the SPR were analyzed in the context of Mie extinction and crystal growth theories and were discussed along with consideration of oxidation processes and film/substrate physicochemical interactions. At relatively high temperatures, Ag NPs were indicated to grow first through a diffusion-based process and subsequently via Ostwald ripening. At lower temperatures, an initial decrease in Ag particle size was indicated due to oxidation, followed by NP diffusion-based growth. The growth and oxidation stages appeared temperature and time dependent, allowing for the tuning of material properties. The product of Ag NP oxidation was revealed by photoluminescence spectroscopy performed ex situ as single Ag(+) ions. The oxidative effect of the air atmosphere on Ag NPs was shown to be ultimately circumvented by the thick nanocomposite film. The phenomenon was explained on the basis of the displacement of the Ag/Ag(+) redox equilibrium toward Ag NP stability after ion migration toward the substrate being self-constrained. In addition, the current spectroscopic approach has been proposed for estimating the activation energy for silver diffusion in the SiO(2) matrix.

Silicon as Reducing Agent for Controlled Production of Plasmonic Copper Nanocomposite Glasses: A Spectroscopic Study

“…Under such circumstances, diffusion-based particle growth takes place at elevated temperatures in order for the supersaturation degree to be decreased, leading to an increase in particle size. 18 During this process, the average particle diameter d varies in proportion to the square root of the holding time t as…”

“…18 In this context, the data for particle sizes derived from Eq. 4 are plotted as a function of the square root of holding time in the inset of Fig.…”

Kinetics of Ag nanoparticle growth in thick SiO2 films: An in situ optical assessment of Ostwald ripening

“…In such context, we have recently proposed in situ optical microspectroscopy for studying the time evolution of the optical properties of metal nanocomposites during thermal processing, in an effort to advance current understanding of physico-chemical properties of these systems [9,10]. The temperature and time dependencies of the growth and oxidation of Ag NPs in SiO 2 films relevant to optoelectronics have been a subject of further investigation via the technique [11,12]. Namely, in Refs.…”

“…Namely, in Refs. [11] and [12], films of varying thicknesses deposited on soda-lime glass substrates were studied spectroscopically in real time during heat treatment (HT) in air atmosphere. Subsequently, data analysis was carried out in the framework of Mie extinction and crystal growth theories, together with consideration to the kinetics and thermodynamic properties intrinsic to metal particles' oxidation.…”

“…Subsequently, data analysis was carried out in the framework of Mie extinction and crystal growth theories, together with consideration to the kinetics and thermodynamic properties intrinsic to metal particles' oxidation. A quantitative assessment of NP growth via Ag diffusion in air atmosphere was reported merely for relatively thick films (800 nm thick) [11], for which the activation energy for the process was estimated at 2.6 eV. On the other hand, a quantitative determination of the activation energy for Ag NP growth in the Ostwald ripening regime has not been reported for the films under in situ thermal processing in air [11,12].…”