Chapter 15 - Photoacoustic and optical spectroscopy of dye-coated plasmonic thin films of silver and gold

Abstract

Plasmonic nanomaterials and their composites with dyes have important applications in many fields of science and technology. The optical properties of plasmonic nanostructures in the thin films and their composite with dyes are discussed in this chapter. Photoacoustic spectroscopy of silver island films and optical properties of gold thin films as well as their composites with RhB and Rh6G dyes have been studied in detail. The spectra exhibit localized surface plasmon resonance (LSPR) peaks corresponding to the thickness of films. Dye coating on the silver film modifies the silver LSPR peak by splitting and enhanced absorption. Composite films on thick metal films show an increase in the transmission toward the longer wavelengths, where dye coatings act as an antireflection coating due to the changes in the dispersion and absorption of the films. The thin films of gold were found to have nanorods of noncylindrical shape (triangular base) and the size of the nanorods increased with film thickness. A linear relation is found between the wavelength of LSPR peak and the aspect ratio of the nanoparticles in gold thin films. The absorption spectra of plasmonic nanoparticles in thin films (≤6nm) as well as in the composite film with dyes can be explained by the Maxwell Garnett theory for nanoparticles having nearly spherical shape. The refractive index sensitivity of gold films is found to range between 250 and 305 nm/RIU for the film thickness ranging from 3 to 10nm, respectively. Applications of plasmonic films have also been discussed in the material science, photoacoustic imaging as well as in enhancing the efficiency of solar cells.