jp3127847_si_001.pdf (1.32 MB)
Optical Properties of Au Nanoparticles Included in Mesoporous TiO2 Thin Films: A Dual Experimental and Modeling Study
journal contribution
posted on 2013-04-11, 00:00 authored by V. M. Sánchez, E. D. Martínez, M. L. Martínez
Ricci, H. Troiani, G. J. A. A. Soler-IlliaGold
nanoparticles (NP) were synthesized inside ordered mesoporous
TiO2 thin films (MTTF) by stepwise reduction of AuCl4– with NaBH4. This leads to an
optical material (Au@TiO2) of interest for plasmonic applications.
The films (pure titania or gold-titania nanocomposites) were thoroughly
characterized by UV–visible and ellipsometry spectroscopies.
The dielectric function of the MTTF, considered as the dielectric
environment in which the NP are embedded, was acquired by ellipsometry
and rationalized by the asymmetric Bruggeman model as an effective
medium formed by the mixture of dense TiO2 and air. Nanocomposite
Au@TiO2 systems present an isotropic dispersion of Au NP
in the 5–8 nm range. The UV–visible spectra obtained
with a low nanoparticle filling fraction of the pore volume (fNP < 2%) are accurately reproduced by both
Maxwell–Garnett (MG) and Mie theories. Accurate and coincident
values of fNP and NP size are obtained
by this method. The dielectric function of Au NP used in this work
was studied in detail; in particular, the interface damping parameter
related to the NP/MTTF interface was determined by comparison with
TEM microscopy. The potential of the ellipsometry technique to determine
the material plasmonic response, and its correspondence with the UV–visible
spectra, are discussed. This spectroscopy technique opens the possibility
to study the plasmon response of the material to changes in the environment
due to the presence of vapors, and other in situ experiments, as well
as to provide nanostructural information of metallic nanoparticles
(NP size, interparticle distance, number of NP) with well-defined
spatial localization in a multilayered system.