Improvement of Raman enhancement factor due to the use of silver nanoparticles coated obliquely aligned silicon nanowire arrays in SERS measurements (original) (raw)
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Nanomaterials, 2021
In this study, we developed highly sensitive substrates for Surface-Enhanced-Raman-Scattering (SERS) spectroscopy, consisting of silicon nanowires (SiNWs) decorated by silver nanostructures using single-step Metal Assisted Chemical Etching (MACE). One-step MACE was performed on p-type Si substrates by immersion in AgNO3/HF aqueous solutions resulting in the formation of SiNWs decorated by either silver aggregates or dendrites. Specifically, dendrites were formed during SiNWs’ growth in the etchant solution, whereas aggregates were grown after the removal of the dendrites from the SiNWs in HNO3 aqueous solution and subsequent re-immersion of the specimens in a AgNO3/HF aqueous solution by adjusting the growth time to achieve the desired density of silver nanostructures. The dendrites had much larger height than the aggregates. R6G was used as analyte to test the SERS activity of the substrates prepared by the two fabrication processes. The silver aggregates showed a considerably lowe...
ACS Applied Materials & Interfaces, 2009
Silver nanoparticles (Ag NPs) were chemically deposited on silicon nanowires (SiNWs), prepared using the vapor-liquid-solid (VLS) growth mechanism, using an in situ electroless metal deposition technique. The resulting SiNWs/Ag NPs composite interfaces showed large Raman scattering enhancement for rhodamine 6G (R6G) with a detection limit of 10 -14 M and an enhancement factor of 2.3 × 10 8 . This large enhancement factor was attributed to the presence of "hot" spots on the SiNWs/Ag NPs substrate.
In this study, a new method was developed in which an oxidation layer is used to regulate the morphology of silver nanoparticles (AgNPs) formed on Si crystals during galvanic displacement (GD). Using an oxidation layer yielded reproducible and stable AgNPs@Si substrates for sensitive surface-enhanced Raman scattering (SERS) measurements. The estimated SERS enhancement was at least an order of magnitude greater than for substrates prepared using a conventional GD method. The formation of Si–O − on the Si surface increased the adsorption of the AgNPs. Highly reproducible results were obtained, with a relative standard deviation of approximately 5%. To investigate the role of the oxidation layer and to optimize the reaction conditions, the oxidation layer thickness and chemical composition of the reaction solution were adjusted. The degree of aggregation in AgNP formation was mainly controlled by the thickness of the oxidation layer, whereas the size of the AgNPs was affected by both the concentration of AgNO 3 and hydrofluoric acid in the reaction solution and the GD reaction time. When the optimized reaction conditions were used, the AgNPs@Si substrate had an enhancement factor of >10 7 .
Silicon Nanowires as Sensory Material for Surface-Enhanced Raman Spectroscopy
Silicon, 2018
This paper shows steps for silicon nanowires substrates synthesis in detail. The research is focused on experimental techniques optimization while the targeted application was a fabrication of highly sensitive substrates for surface-enhanced Raman spectroscopy (SERS). Horizontal silicon nanowires on top of two-inch wafers were obtained by vapour-liquid-solid growth inside the low-pressure chemical vapour deposition reaction tube. The silicon nanowires morphology was monitored by scanning electron microscope after a short and long growth period which defined an adequate deposition time for SERS applications. Surface-enhanced Raman spectroscopy features were tested on silver nanoparticles decorated substrates and the detection concentration limit of 10 −9 M of rhodamine 6G molecules was reached. Raman spectroscopy showed that the 532 nm laser excitation powers of less than 4 mW (∼0.57 kW/cm 2) do not widen the phonon peak or shift its frequency and the nanostructure distribution parameter of 3.7 nm was calculated. The horizontally placed Ag decorated nanowires are proved to be sensitive substrates for surface-enhanced Raman spectroscopy only if the silicon nanowires thickness, length, volume density as well as metal nanoparticle size and distribution are carefully designed.
MATERIALS TRANSACTIONS, 2014
Metal nanoparticles with nanoscale spacing are promising materials for the detection of single molecules through surface-enhanced Raman scattering. To increase the sensitivity of nanoparticles through the use of a nanoscale substrate, we fabricated various Ag NPdecorated silicon nanowalls for the Raman spectroscopic detection of rhodamine 6G (R6G). The sensitivity of detection was affected by the nanowall depth and was influenced by several parameters: the AgNO 3 concentration for metal-assisted etching, the HF/H 2 O 2 etching time for nanowall formation, and the Ag evaporation time for nanoparticle growth. For an approximately 400-nm-deep nanowall substrate having the optimal surface filling ratio and etching depth, we obtained an ultrahigh enhancement factor of 1.1 © 10 9 for the detection of R6G at a concentration of 10 ¹11 M.
Croatica Chemica Acta, 2017
The silicon based substrates for surface enhanced Raman spectroscopy (SERS) have been synthesized and tested. The silver-assisted electroless wet chemical etching method has been utilized for silicon nanowires production which has been proved as the promising SERS substrate. The morphology of the silicon nanowires coated with silver nanoparticles has been examined by scanning electron microscopy. The SERS measurements tested on rhodamine 6G molecules indicated the optimal silicon nanowire substrate production obtained for 5 M hydrofluoric acid and 30 mM silver nitrate etching solution. The results show SERS detection limit of 10-8 M rhodamine in aqueous solution.
ACS Applied Materials & Interfaces, 2017
This paper reports on a simple and cost-effective process of developing a stable surface enhanced Raman scattering (SERS) substrate based on silver (Ag) nanoparticles deposited on silicon (Si) surface. Durability is an important issue for preparing SERS active substrate as silver nanostructures are prone to rapid surface oxidation when exposed to ambient conditions, which may result in the loss of the enhancement capabilities in a short period of time. Here, we employ galvanic displacement method to produce Ag nanoparticles on Si(100) substrate pre-patterned with arrays of micro-pyramids by chemical etching and subsequently
Silicon Nanowire Arrays Coated with Ag and Au Dendrites for Surface-Enhanced Raman Scattering
MRS Advances, 2020
Silicon nanowires (SiNWs) were comprehensively characterized in dependence on conditions of their formation via metal (Ag)-assisted chemical etching (MACE) of monocrystalline Si. The Ag structures remained on/between SiNWs based on both n-and p-Si were found to promote surface enhancement of Raman scattering (SERS) from organic molecules adsorbed on their surface. The Ag structures on/between the SiNWs/p-Si facilitated two times higher SERS-signal from 10-6 M rhodamine 6G than those in the SiNWs/n-Si. The activity of the SERS-substrates based on p-Si was improved by modification with small Au dendrites, which provided rich family of hot spots and prevented degradation of the SERS-activity observed for pure Ag dendrites due to formation of Ag2S during one week of storage in air. The SERS-substrates based on the Au/Ag dendrites on SiNWs/p-Si allowed to achieve nanomolar detection limit of rhodamine 6G and 5,5′-dithiobis (2-nitrobenzoic acid).
Surface Enhanced Raman Scattering Enhancements from Silver Atomic Layer Deposition Coated Nanowire
2011
In this study, gold nanostructures (AuNSs) and silver nanoparticles (AgNPs) were integrated with a silver microflower-like structure deposited on a screen-printed carbon electrode (AgMF-SPCE) for enhancing surface-enhanced Raman scattering (SERS) by using 4-mercaptobenzoic acid (4-MBA) as a Raman reporter. SERS was enhanced by approximately 3.6-52.1-fold, depending on the frequency of the incident laser, the localized surface plasmon resonance frequency of metallic NPs, and particle-particle aggregation effects. Compared with AgNP/ SPCE and AgMF-SPCE substrates, the AgNP/AgMF-SPCE substrate showed high temperature tolerance and long-term durability. Furthermore, the proposed substrates easily obtained hot spots for other Raman reporters such as 4-aminothiophenol, 5,5′-dithiobis-2-nitrobenzoic acid, and 4-chlorothiophenol. A linear relationship was found between the Raman signal and the concentration of Raman reporters in the range 10 nM-100 μM, with the limit of detection in the range of 6.19-77.2 nM at a signal-to-noise ratio of 3.0. These results suggest that the AgNP/AgMF-SPCE substrate will be well suited for quantitative analysis.