Surface enhanced Raman scattering due to interstitial gold nanoparticles into SiO2 spheres array

Abstract

Films of SiO2 spheres in a periodic array infiltrated with Au nanoparticles (NPs), were obtained by the co-assembly method. Samples with low (M1), medium (M2) and high (M3) concentrations of Au NPs were characterized by SEM, TEM and UV-Vis and Raman Spectroscopies. The images from the microscope show that the average size is 275 nm and 22 nm for SiO2 sphere and Au NP, respectively. Also, with the infiltration procedure the NPs form clusters and reside in the interstitial sites of the FCC array without modifying significantly the distance between the centers of the SiO2 spheres. However, the photonic band gap is shifted to larger wavelengths compared to the bare SiO2 Film. These samples are proposed as SERS substrates, and to evidence their sensitivity, Methylene Blue was used as the molecular probe at different concentrations. An Enhancement Factor, EF, of ∼105 is reached when the M3 film is used as SERS substrate. To have an insight about the Au NPs concentration effect in the SERS EF, discrete dipole approximation was employed to calculate the near electric field intensity of a system of SiO2 spheres and Au NPs, observing that the near field is more intense in the region between the SiO2 sphere surface and the Au NPs close to it.