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. 2021 Aug 27;11(9):2209.
doi: 10.3390/nano11092209.

Revealing the Hemispherical Shielding Effect of SiO2@Ag Composite Nanospheres to Improve the Surface Enhanced Raman Scattering Performance

Fengyan Wang  1 , Daxue Du  1 , Shan Liu  1 , Linna Wang  1 , Tifeng Jiao  1 , Zhaopeng Xu  2 , Haiyan Wang  1
Affiliations

Revealing the Hemispherical Shielding Effect of SiO2@Ag Composite Nanospheres to Improve the Surface Enhanced Raman Scattering Performance

Fengyan Wang et al. Nanomaterials (Basel). .

Abstract

Many studies widely used SiO2@Ag composite nanospheres for surface enhanced Raman scattering (SERS), which mainly contributes to electromagnetic enhancement. In addition to experiments, previous simulations mostly adopted a two-dimensional model in SERS research, resulting in the three-dimensional information being folded and masked. In this paper, we adopted the three-dimensional model to simulate the electric field distribution of SiO2@Ag composite nanospheres. It is found that when the Ag nanoparticles are distributed densely on the surface of SiO2 nanospheres, light cannot pass through the upper hemisphere due to the local surface plasmon resonance (LSPR) of the Ag nanoparticles, resulting in the upper hemisphere shielding effect; and if there are no Ag nanoparticles distributed densely on the surface of SiO2 nanospheres, the strong LSPR cannot be formed, so the incident light will be guided downward through the whispering gallery mode of the spherical structure. At the same time, we designed relevant experiments to synthesize SiO2@Ag composite nanosphere as SERS substrate and used Rhodamine 6G as a probe molecule to study its SERS performance. This design achieved a significant SERS effect, and is very consistent with our simulation results.

Keywords: LSPR; SERS; three-dimensional models; upper hemisphere shielding.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Three-dimensional electromagnetic enhancement distribution (stereoscopic view, top view and front view) of SiO2@Ag in S1, S2 and S3.
Figure 2
Figure 2
TEM images of SiO2 and SiO2@Ag nanospheres substrate with different samples: (a) S0, (b) S1, (c) S2, and (d) S3, scale bar 500 nm.
Figure 3
Figure 3
(a) XRD of SiO2 and SiO2@Ag composite nanospheres; (b–e) XPS analysis of SiO2@Ag core-shell NPs ((b) survey spectrum; (c) Ag 3d; (d) Si2p; (e) O 1s spectra); (f) UV-Vis absorption of SiO2(S0) and SiO2@Ag with different samples(S1–S3).
Figure 4
Figure 4
SEM images of SiO2@Ag nanosphere substrate with 3 different samples: (a) S1, (b) S2, and (c) S3; and the corresponding magnification enlarged by 6 times (d) S1, (e) S2, and (f) S3.
Figure 5
Figure 5
Wettability of the SiO2@Ag composite-nanospheres substrates: (a) S2, and (b) S3.
Figure 6
Figure 6
(a) SERS spectrum of different preparation conditions on SiO2@Ag substrate, (b) SERS spectrum of R6G with 102 M adsorbed on silicon substrate, (c) SERS spectrum of different concentrations (10−10–10−6 M) of R6G adsorbed on SiO2@Ag substrate, and (d) Intensity distribution of R6G molecules (1 × 10−6 M) at the peak of 611 cm−1 from 10 different batches of SiO2@Ag nanocomposite spheres substrates.
See this image and copyright information in PMC

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