Production of SERS Substrates Using Ablated Copper Surfaces and Gold/Silver Nanoparticles Prepared by Laser Ablation in
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https://doi.org/10.1007/s11664-020-08373-7 Ó 2020 The Minerals, Metals & Materials Society
Production of SERS Substrates Using Ablated Copper Surfaces and Gold/Silver Nanoparticles Prepared by Laser Ablation in Liquids THE BINH NGUYEN
,1,2 NHU ANH NGUYEN,1 and TRONG DUC TRAN1
1.—Department of Physics, VNU University of Science, Hanoi, Vietnam. 2.—e-mail: [email protected]
Our study aimed to produce SERS substrates using nanostructured copper (Cu) surfaces prepared by laser ablation in water. A laser ablation schema was designed for this purpose. The laser power and laser irradiation time for creating a nanostructured surface suitable for SERS were determined. To increase the enhancement factor (EF) of the SERS substrates, gold (Au) and silver (Ag) nanoparticles were deposited on the ablated Cu surfaces to produce AuNP/aCu and AgNP/aCu substrates. The Au (and Ag) nanoparticles were also prepared by laser ablation of a Au (and Ag) piece in ethanol. The EFs for SERS of the AuNP/aCu and AgNP/aCu substrates are 1.2 9 106 and 6 9 106, respectively. The SERS spectra of malachite green with low concentrations of 0.1 ppm can be detected with high quality by using these SERS substrates. Key words: Surface-enhanced Raman scattering (SERS), nanostructured surface, localized surface plasmon resonances (LSPRs), SERS substrate, laser ablation
INTRODUCTION Surface-enhanced Raman scattering (SERS) was first discovered in the 1970s.1–3 Over the past five decades, SERS and its applications have seen continuous development. SERS enhancement was explained by two mechanisms, namely, a chemical (CHEM) enhancement and an electromagnetic (EM) enhancement.3–5 The CHEM enhancement is commonly ascribed to a charge-transfer resonance involving the transfer of electrons between the molecule and the conduction band of the metal. The EM enhancement results from the amplification of the incoming and scattered radiation via the excitation of localized surface plasmon resonances (LSPRs) involving plasmonic nanostructures.5–8 Gold (Au), silver (Ag) and copper (Cu) are often used as plasmonic materials because they have
(Received February 11, 2020; accepted July 29, 2020; published online August 13, 2020)
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LSPRs that cover most of the visible and nearinfrared wavelength range where most Raman measurements occur.8,9 Because the largest portion of the overall SERS enhancement is typically due to the EM enhancement, a great number of different plasmonic nanostructures for SERS (SERS substrates) have been proposed and developed. Metallic nanoparticles are of major importance in plasmonic nanostructures. As a result of their simple and cost-efficient production, metallic nanoparticles are among the most commonly used SERS substrates.10 Because the enhanced electromagnetic field decreases rapidly with distance from the metallic surface, close contact between the analyte molecule and the metallic nanoparticles is required to obtain a large EF for SERS.3,11,12 In addition, the field enhancement is increased in nanostructured gaps between two o
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