Surface-enhanced Raman scattering of amorphous silica gel adsorbed on gold substrates for optical fiber sensors

Abstract

Two kinds of gold substrates are used to produce surface-enhanced Raman scattering (SERS) of amorphous silica obtained via the sol-gel route using tetraethoxysilane Si(OC2H5)4 (TEOS) solution. The first substrate consists of a gold nanometric film elaborated on a glass slide by sputter deposition, controlling the desired gold thickness and sputtering current intensity. The second substrate consists of an array of micrometer-sized gold inverted pyramidal pits able to confine surface plasmon (SP) enhancing electric field, which results in a distribution of electromagnetic energy inside the cavities. These substrates are optically characterized to observe SPR with, respectively, extinction and reflectance spectrometries. Once coated with thin layers of amorphous silica (SiO2) gel, these samples show Raman amplification of amorphous SiO2 bands. This enhancement can occur in SERS sensors using amorphous SiO2 gel as shells, spacers, protective coatings, or waveguides, and represents particularly a potential interest in the field of Raman distributed sensors, which use the amorphous SiO2 core of optical fibers as a transducer to make temperature measurements.

Thermally Stable TiO2‐ and SiO2‐Shell‐Isolated Au Nanoparticles for In Situ Plasmon‐Enhanced Raman Spectroscopy of Hydrogenation Catalysts

“…However, these thin coatings proved to be unstable above 300 °C, whereas 2.2 nm coatings remain stable up to 400 °C (Figure , Figures S22 and S23 in the Supporting Information). The amorphous SiO 2 coating also densifies with temperatures above 300 °C, as can be observed by the growth of D 1 , D 2 , and Si−OH stretching vibrations in the Raman spectra of SiO 2 @Au after heat treatments (Figure S18 in the Supporting Information) . Starting from 500 °C, all substrates are completely changed in structure as is observed in the extremely low Rh6G signal and the strongly improved pyridine/Rh6G ratio (Figure right).…”

“…The amorphous SiO 2 coating also densifies with temperatures above 300 8C, as can be observed by the growth of D 1 ,D 2 ,a nd SiÀOH stretchingv ibrations in the Ramans pectra of SiO 2 @Au after heat treatments ( Figure S18 in the SupportingI nformation). [47,48] Starting from 500 8C, all substrates are completely changed in structure as is observed in the extremely low Rh6G signal and the strongly improved pyridine/Rh6G ratio (Figure 4right). Owing to the densification of the coatings, it is recommended to stay below 400 8Cwhen using SiO 2 -a nd TiO 2 -SHINS.…”

Structural analysis of sputtered amorphous silica thin films: A Raman spectroscopy investigation

“…For instance, this technique is frequently used to investigate amorphous thin films with high-intensity Raman answer, in particular silicon, carbon [40]- [41]- [42]- [43] and chalcogenides [44]- [45]. For thin films (<1 µm), specific substrates (fluorides) with a low Raman background signal can be used [46]- [47] and, in some specific cases, surface-enhanced Raman scattering has a beneficial influence on the thin film signal intensity [48]- [49]. However, some practical applications require to deposit an amorphous silica thin film onto a silicate glass substrate.…”

Development and Comparison of Surface-Enhanced Raman Scattering Gold Substrates for In Situ Characterization of ‘Model’ Analytes in Organic and Aqueous Media

“…The sputtering current intensity has been set at 80 mA for all experiments. Substrate denoted by AuS1 was developed by depositing a nanometric gold film of 25 nm on a glass slide, as described by Degioanni et al [14] to produce SERS of amorphous silica. SERS substrate denoted by AuS2 consisted of a gold nanometric film of 25 nm deposited on a glass slide covered by a flat TEOS/3-MPS (1/1) sol film.…”

“…In the case of top-down approaches, the oldest used electrochemical roughening technique [6][7][8] leading to the poor control of the shape and size of the nanostructure [9] and thus to low signal reproducibility, substrates based on lithographic techniques (e.g. E-beam lithography [10], nanosphere lithography [11,12], soft-lithography [13]) or sputtering deposition have earned interest [14][15][16]. Indeed, these techniques allow to provide a large-scale uniformity of the structures with various shapes ensuring high SERS signal reproducibility.…”