Core–Shell Plasmonic Nanostructures on Au Films as SERS Substrates: Thickness of Film and Quality Factor of Nanoparticle Matter

Abstract

Assembling plasmonic nanoparticles on metal films is an elegant method for the design of SERS platforms with dense hot spots and amplified electric fields. Interaction between the localized surface plasmons of metal nanoparticles within assemblies induces collective plasmonic modes which can further couple with the propagating surface plasmons prevailing on the metal films. Herein, we report on the electric field effects as well as Raman signal enhancements arising due to the sandwiching of Au and Ag core−shell nanoparticle assemblies on Au films with varying thicknesses of the underlying metal film. The sandwich plasmonic platforms are prepared by linking Ag@SiO 2 as well as Au@SiO 2 nanoparticles on Au films using (3-mercaptopropyl)trimethoxysilane (3-MPTS). The interaction between the SiO 2 shell on the Ag/Au nanoparticles and free silanol groups on 3-MPTS provides a monolayer of core−shell systems on the Au films, as corroborated by SEM images. Finite-difference time-domain simulations with heptamer models of Ag@SiO 2 and Au@SiO 2 particles on Au films confirm an enhancement in the electric field upon sandwiching the nanoparticle aggregates on the Au films. The Raman signal enhancement factors for the dye Rhodamine 6G are estimated, and the enhancement in the Raman signal intensities on Ag@SiO 2 over Au@SiO 2 assembled on a 20 nm Au film is attributed to the higher Q-factor of Ag. The largest measured Raman signal intensity on Ag@SiO 2 on a 60 nm thick Au film, ∼10 7 , is reasoned based on the variation of the electric field intensity of the Au film as a function of its thickness.

Solid-State Dewetting of Thin Silver Films into Spherical Nanoparticles under High-Current Pulsed Ion Beam Irradiation

“…Figure 2b−e shows the SEM images of Ag NP arrays formed from Ag coatings irradiated with an IPIB of 10 A/cm 2 ion beam current densities and number of pulses ranging from 1 to 4. Figure 2f−j corresponds to a single pulse IPIB irradiation with current densities increasing from 10 to 60 A/cm 2 .…”

Tunable Near-Field Enhancement in Structure-Adjustable Au Nanodumbbells for Improved SERS and Double-Resonantly Enhanced SHG

“…The tunable end size of Au NDs offers more freedom to manipulate the plasmonic nanocavity in the particle-on-film system. Normally, the size of the nanocavity in the particle-on-film system is controlled by tuning the thickness of the spacer, such as the surfactant, molecule, 2D materials, and SiO 2 . ,− Metal nanostructures including spheres, cubes, and rods were put on the film to generate strong plasmon coupling and fascinating plasmon modes . For the Au ND-involved particle-on-film system, the surfactant (CTAB) can be regarded as the first ultrasmall gap when putting it on a Au film.…”

Hierarchically Assembled Plasmonic Metal-Dielectric-Metal Hybrid Nano-Architectures for High-Sensitivity SERS Detection

“…The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/nano12030401/s1. Figure S1: Histogram of Au NPs arrays on Si/SiO 2 substrate by the annealing of 10 nm Au at 800 C for 120 s; Figure S2: Raman spectra of R6G molecules (10−6 M) measured at 30 different locations on PMDM hybrid nanostructures to test the SERS reproducibility; Table S1: Raman band assignments of R6G molecules; Table S2: Comparison of SERS performance of current work and previously reported plasmonic NP-based SERS substrates (references [45][46][47][48][49][50][51][52][53] are cited in Table S2).…”