Hybrid Metal-Dielectric-Metal Sandwiches for SERS Applications

Abstract

The development of efficient plasmonic nanostructures with controlled and reproducible surface-enhanced Raman spectroscopy (SERS) signals is an important task for the evolution of ultrasensitive sensor-related methods. One of the methods to improving the characteristics of nanostructures is the development of hybrid structures that include several types of materials. Here, we experimentally investigate ultrathin gold films (3–9 nm) near the percolation threshold on Si/Au/SiO2 and Si/Au/SiO2/graphene multilayer structures. The occurring field enhanced (FE) effects were characterized by a recording of SERS signal from Crystal Violet dye. In this geometry, the overall FE principally benefits from the combination of two mechanisms. The first one is associated with plasmon excitation in Au clusters located closest to each other. The second is due to the gap plasmons’ excitation in a thin dielectric layer between the mirror and corrugated gold layers. Experimentally obtained SERS signals from sandwiched structures fabricated with Au film of 100 nm as a reflector, dielectric SiO2 spacer of 50 nm and ultrathin gold atop could reach SERS enhancements of up to around seven times relative to gold films near the percolation threshold deposited on a standard glass substrate. The close contiguity of the analyte to graphene and nanostructured Au efficiently quenches the fluorescent background of the model compound. The obtained result shows that the strategy of combining ultrathin nano-island gold films near the percolation threshold with gap plasmon resonances is promising for the design of highly efficient SERS substrates for potential applications in ultrasensitive Raman detection.

A New Approach to the Formation of Nanosized Gold and Beryllium Films by Ion-Beam Sputtering Deposition

“…A characteristic feature of the gold and beryllium films that were obtained is a higher reflection coefficient after the tenfold application of the nanoscale metal layer deposition–sputtering, in comparison with the direct single deposition. Thus, at a wavelength of 800 nm for gold films, it increases from 93.5 to 95% ( Figure 7 a curves 1 and 2), which is quite close to the reflection coefficient for the bulk material [ 36 ] that amounts to slightly more than 97% [ 27 ]. The reflection coefficient of the nanosized beryllium films has a lower value and increases from 51.7 to 55.3% at the same wavelength.…”

“…An increase in the reflection coefficient with a decrease in roughness ( Figure 7 a, curves 1 and 2 or curves 3 and 4) is associated with a decrease in the characteristic size of the surface irregularities. The maximum values of the reflection coefficient that is inherent to bulk materials [ 36 ] in the corresponding frequency range are explained by the weakening of the role of the surface in radiation scattering.…”

Model of the SARS-CoV-2 Virus for Development of a DNA-Modified, Surface-Enhanced Raman Spectroscopy Sensor with a Novel Hybrid Plasmonic Platform in Sandwich Mode

“…The surface of the sensor element is represented with a multilayered structure based on subsequently coated silver mirror film, dielectric film, and Ag nanoparticles, further referred to as film-Ag/SiO 2 /nano-Ag NPs ( Figure 3 a). As noted above, the amplification of the Raman signal for sandwiches in comparison with one-contained-layer nanostructured silver surface is associated with the excitation of both gap plasmons in the SiO 2 layer and local surface plasmon resonances in nano-Ag NPs [ 5 , 6 , 7 , 8 ]. Moreover, the back reflection from the bottom Au layer gives rise to a stronger absorbance and, therefore, the enhancement factor (EF) since the excitation beam passes through the top film twice.…”

“…Such a hybrid scaffold provides efficient work with high-molecule volumetric objects such as live cells and offers sufficient optical transparency for both fluorescence and SERS imaging. The novel hybrid metal-dielectric-metal sandwiched structures [ 5 , 6 ] demonstrate high sensitivity and reproducibility of the SERS signal [ 7 , 8 ]. In this geometry, the overall enhancement factor principally benefits from the combination of two main mechanisms.…”

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

“…The precise control of nanogaps between plasmonic nanoparticles (NPs) at a nanometer scale is crucial to produce a high density of strong and stable EM hot spots. To maintain the specific sub-nanometer gap, a dielectric layer can be considered as a nanogap spacer between two layered plasmonic metal nanostructures-namely, metal-dielectric-metal hybrid nano-architectures [27][28][29][30]. The dielectric spacer offers several benefits: protecting the plasmonic core from oxidation, tunning the LSPR properties, and maintaining a sub-nanometer gap between metal nanostructures to obtain a strong EM hotspot [31][32][33][34].…”