Abstract
It is desirable to extend the surface-enhanced Raman scattering (SERS) from the conventionally used visible range into the infrared region, because the fluorescence background is lower in the long-wavelength regime. To do this, it is important to have a SERS substrate suitable for infrared operation. In this work, we report the near infrared SERS operation based on the substrates employing star-shaped gold/silver nanoparticles and hyperbolic metamaterial (HMM) structure. We first fabricate the SERS substrate in which nanoparticles are separated from a silver film by a thin dielectric layer. Performance of the SERS substrate is investigated with a 1064-nm excitation source. Compared with similar silver film-based substrates employing respectively gold and silver spherical nanoparticles, it is found that, Raman intensity scattered by the substrate with star-shaped nanoparticles is 7.4 times stronger than that with gold nanoparticles, and 3.4 times stronger than that with silver nanoparticles. Following this, we fabricate the SERS substrate where the star-shaped nanoparticles are deposited over a HMM structure. The HMM structure comprises three pairs of germanium-silver multilayers. Further experimental result shows that, with the star-shaped nanoparticles, the HMM-based substrate yields 30% higher Raman intensity for near infrared SERS operation than the silver film-based substrate does.
Highlights
The substrate based on star-shaped gold/silver nanoparticles and hyperbolic metamaterial (HMM) structure is highly promising for surface-enhanced Raman scattering (SERS) study in the near infrared region
We have investigated the feasibility of employing star-shaped gold/silver nanoparticles and HMM structure for SERS study in the infrared region
Compared with gold and silver spherical nanoparticles, experimental results with a 1064 nm excitation source indicate that the SERS substrate employing star-shaped gold/ silver nanoparticles has the strongest Raman intensity, which is 7.4 times higher than that employing gold spherical nanoparticles and 3.4 times higher than that employing silver spherical nanoparticles
Summary
Surface-enhanced Raman scattering (SERS) is an efficient spectroscopy technique[1,2,3,4,5], which finds wide applications in biosensing[6,7,8,9,10,11,12,13,14,15], material science[16,17,18], and electrochemistry[19]. The star-shaped gold/silver nanoparticles are used to fabricate two types of substrates for infrared SERS operation. The star-shaped nanoparticles are separated from a silver film by a thin layer of aluminium oxide (Al2O3) Such a nanoparticle-on-mirror structure[45,46,47,48] has been shown to be an effective structure for SERS substrate. For the HMM-based substrates, the one employing star-shaped gold/silver nanoparticles still exhibits stronger Raman scattering than the ones employing gold and silver nanoparticles do under the excitation wavelength of 1064 nm. The substrate based on star-shaped gold/silver nanoparticles and HMM structure is highly promising for SERS study in the near infrared region
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