Section 3

Silver Nanostructures for SERS and Photoelectrochemical Applications

**Chapter 10**

Films

**Abstract**

*and Enrique Sánchez Mora*

SiO2 sphere, the EF is as high as 1 103

**1. Introduction**

**171**

Theoretical and Experimental

Factor of SiO2-Ag Composite

*Paulina De León Portilla, Ana Lilia González Ronquillo*

Herein we addressed a study to determine the enhancement factor (EF) of the

nanoparticles and SiO2 spheres. The study involves the synthesis, structural composition and optical response by using experimental techniques and theoretical-numerical modeling. A colloid with single NPs and agglomerates of them, with a tannic acid layer on its surface, was produced. Separately, porous SiO2 spheres were obtained. A mixture of both, Ag NPs and SiO2 particles was used to produce the films by solvent evaporation method. It is shown that single or agglomerated Ag NPs are preferentially located at the interstices of the SiO2 spheres. Using discrete dipole approximation, the SERS EF has been estimated considering the agglomeration and tannic acid layer. Both, the dielectric spheres and tannic acid layer diminish the electric field intensity and therefore the SERS EF. When a Ag NP with/without a dielectric shell is touching a

, the zones where this value is reached are

Raman signal reached by composite films with two main components, Ag

smaller when the dielectric layer is present. With a cluster of 3 nude Ag NPs

**Keywords:** SiO2 spheres, silver nanoparticles, composite film, tannic acid, functionalization, near field intensity, discrete dipole approximation

Research around the optical properties of Ag nanoparticles (NPs) has been a topic of

high importance for diverse applications as coating, plasmonic antennas, for drug delivery, as components of molecular detectors, among others [1–6]. The convenience of using Ag NPs lies in their intense plasmonic response with a surface plasmon resonance (SPR) in the visible optical range. The SPR is a phenomenon that occurs when a metal NP is excited by an electromagnetic wave, the conduction electrons respond to the electromagnetic field in such a way that oscillations of the electron charge distribution occur in the vicinity or on the surface of the particle. Ag NPs have their SPR in the

range from 350 to 600 nm, depending on their size and morphology [7, 8].

surrounded by SiO2 spheres an EF of 2.4 103 is obtained.

Study on the Functionalization

Effect on the SERS Enhancement
