Far Field Optical Properties of a Monolayer of SiO 2 Spheres and Small Au Nanoparticles
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.128
Far Field Optical Properties of a Monolayer of SiO2 Spheres and Small Au Nanoparticles A. Santos Gómez and A. L. González Instituto de Física, Benemérita Universidad Autónoma de Puebla. Apdo. Post. J-48, Puebla, Pue., 72570, México.
ABSTRACT
Here, we present a numerical study of the far field optical response of a monolayer composed by an hexagonal closed packed array of SiO2 spheres with a single Au NP at each interstitial position. The Optical Efficiencies, Reflection, Transmission and Absorption at normal incidence, were calculated using Discrete Dipole Approximation model extended to periodic targets. In order to consider different amounts of loads of Au NPs per unit of area in the monolayer, we have fixed the diameter of Au NPs (9 nm) and varied the diameter of the SiO2 spheres. The numerical calculations indicate that Au-SiO2 composite monolayers can absorb and scatter the incident electromagnetic wave, as the load of Au NPs increases the monolayer becomes less transparent to light and the spectra are red-shifted. The profile of the absorption spectrum of the Au-SiO2 composite monolayer is very similar to that of a Au NPs monolayer (composite monolayer without the Silica spheres) but less intense, presumably because the Silica spheres screen the coupling of the Localized Surface Plasmons of Au NPs.
INTRODUCTION The incorporation of metal nanoparticles (NPs) into ordered dielectric structures has extensively been investigated for applications in catalysis, optical devices, sensors, solar cells and other [1, 2, 3]. The photonic band gap, position and intensity of the Bragg peak, reflectance, transmittance and absorption of these composite materials can be tuned mainly through variation of the load of metal NPs, size of NPs or periodicity of the structure [4]. Recently, M. Toledo and colleagues reported the deposit of films composed by an hexagonal closed packed array of SiO 2 spheres with small Au nanoparticles (NPs) located at the intersites [5]. They obtained films using different volume concentration of Au NPs and, notably, the reflectance spectra presented a shift to larger wavelengths as more content of Au NPs. Those films have been shown to be
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useful as Surface Enhanced Raman Scattering (SERS) substrates for detecting organic molecules. Here we present a numerical study of the far field optical response of a monolayer composed by an hexagonal closed packed array of SiO2 spheres with a single Au NP at each interstitial site. The diameter of Au NP is equal to 9 nm and the diameter of the SiO2 sphere has been considered as a variable, that is equivalent to vary the separation distance among Au NPs and, as a consequence, the amount of NPs per unit of area. The Optical Efficiencies, Reflecti
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