Abstract
Metal nanoparticles (MNPs) embedded dielectric thin films are very crucial for many optoelectronic applications. This report investigates various ways of tuning the plasmonic properties of such nanocomposite thin films. For this, the well-known plasmon resonance condition was first generalized to include the shape and volume fraction of MNPs. This was followed by deriving an empirical formula for the resonance position (λR) which was worked out to be the positive root of a quadratic equation. The coefficients of the deduced quadratic relation involve the parameters obtained from the empirical fit to some of the experimental dielectric functions of MNPs available in literature. The derived working formula enables research community to tune the LSPR of nanocomposites in the whole range of visible wavelengths. The derived formula also concluded that with known lower volume fractions, shape of MNPs affects λR the most, compared to the other parameters. The derived formula was validated by calculating the full extinction spectra. It was shown for the first time that there exists an optimum value of oblate shape to give maximum resonance for a given nanocomposite.
Highlights
Noble metal nanoparticles (MNPs) have appealed researchers a lot with respect to the fundamental as well as emerging applied research because of their fascinating optical properties [1,2,3]
The present work revisits the resonance condition for nanocomposite thin films so as to include the shape and volume fraction, and for the first time (ii) derives a working formula that helps in tuning the plasmonic position and (ii) demonstrates the existence of an optimum shape for maximum optical density for a given pair of metal nanoparticle-dielectric film combination
Deviations may appear if (i) the desired localized surface plasmon resonance (LSPR) position is beyond 900 nm, (ii) proper value of εd is not known/used, (iii) the size is so small that quantum size effect starts appearing in the optical properties, in case of AgNPs [30], and (iv) Volume fraction of the metal nanoparticle is high enough to defy the basic assumption of no interparticle coupling
Summary
Noble metal nanoparticles (MNPs) have appealed researchers a lot with respect to the fundamental as well as emerging applied research because of their fascinating optical properties [1,2,3]. The LSPR positions can become tunable in the visible-near infrared region of electromagnetic spectrum if the shape, size, structure and environment of the particles can be controlled. Among the mentioned variations for tunability, controlling environment becomes an easy when the nanoparticles are embedded inside another dielectric matrix It is even more advantageous for several applications, if the surrounding matrix is transparent the region of LSPR occurrence. The present work revisits the resonance condition for nanocomposite thin films so as to include the shape and volume fraction, and for the first time (ii) derives a working formula that helps in tuning the plasmonic position and (ii) demonstrates the existence of an optimum shape for maximum optical density for a given pair of metal nanoparticle-dielectric film combination
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