Microstructures and Linear/Nonlinear Optical Properties of Monolayered Silver Nanoparticles

Abstract

We investigated the microstuctural properties, as well as the linear and the nonlinear optical properties of silver nanoparticles embedded within a polymer matrix. The monolayered silver nanoparticles were fabricated by using a thermal treatment of thin silver films sandwiched between two polyimide (PI) precursor films. From the transmission electron microscopy images of the PI-matrix-embedded silver nanoparticles, we found that silver nanoparticles arranged in a monolayer were formed within the polymer matrix. The average diameter (D) and the volume fraction (f) of silver nanoparticles depended on the silver film thickness (t) before undergoing thermal treatment: D = 5.0 nm (f = 14 %) and D = 11.8 nm (32 %) for sample A (t = 2.5 nm) and sample B (t = 10 nm), respectively. The monolayered silver nanoparticles exhibited a surface plasmon effect with tunable resonance wavelengths: lambda(SPR) = 464 nm (D = 5.0 nm, f = 14 %) and lambda(SPR) = 523 nm (D = 11.8 nm, f = 32 %). The variation in the surface plasmon resonance wavelengths (lambda(SPR)) for the two different silver nanoparticles could be described by applying the Maxwell-Garnett effective-medium approximation to the composite material. From the Z-scan experiment, we obtained the two-photon-absorption coefficients (beta) of the two different samples: beta = 2.4 x 10(-7) cm/W (D = 5.0 nm, f = 14 %, lambda(SPR) = 464 nm) and)3 = 1.0 x 10(-7) cm/W (D = 11.8 nm, f = 32 %, lambda(SPR) = 523 nm). The optical nonlinearity of silver nanoparticles is thought to be attributed to a two-photon-absorption-induced plasmonic resonance.