Silver-gold nano-composites for photo-catalytic and sensing applications

xperimental results of photo-catalytic activity of Ag-Au nano-composites on different
type of titania are compared with numerical simulations. The action spectra
of photo-catalyzed oxidation and the extinction (absorption together with scattering)
spectra are compared for similar shape and size nanoparticles. Different shell-core
composites using Ag and Au are numerically modeled for qualitative understanding
of the light enhancement and its localization on the nanoparticle-titania substrate.
We show that the electrical field component perpendicular to the interface between
nanoparticle and substrate contributes the major field enhancement portion.
Light enhancement at hot-spots and its scaling with gap size are revealed by surface
enhanced Raman spectroscopy (SERS). Alloying of Ag and Au on nanoscale is
demonstrated. The sp-to-d band transition of electrons in the plasmonic Ag and Au is
proposed as a model of photo-catalysis at the wavelengths longer that the fundamental
optical transition in titania (approximately 3.1 eV or 400 nm).
Surface-enhanced infrared absorption (SEIRA) spectroscopy, is applied to highlyselective
metal hole arrays (MHA), enhancing specific molecular vibrations for
molecule fingerprinting, with up to 10 times enhancement of the absorption peaks
within the 200-2000 cm−1 band. Selective IR band enhancement can be used for identification
of specific molecules within complex mixtures and can be extended to longer
wavelengths to probe the THz molecular bands.
Discussed systems can bemodeled with a high fidelity using finite-difference timedomain
(FDTD) methods. Sensing applications with microparticles can also be modeled
providing insight in applications in far-IR (10-50 μm) and towards THz spectral
range. The very same principles are applicable for broadband light energy harvesting.