Plasma-Induced Formation of Ag Nanodots for Ultra-High-Enhancement Surface-Enhanced Raman Scattering Substrates

Quantum Science Research, Hewlett-Packard Laboratories, 1501 Page Mill Road, Palo Alto, California 94304, USA.
Langmuir (Impact Factor: 4.46). 05/2007; 23(9):5135-8. DOI: 10.1021/la063688n
Source: PubMed


We report here plasma-induced formation of Ag nanostructures for surface-enhanced Raman scattering (SERS) applications. An array of uniform Ag patterned structures of 150 nm diameter was first fabricated on a silicon substrate with imprint lithography; then the substrate was further treated with an oxygen plasma to fracture the patterned structures into clusters of smaller, interconnected, closely packed Ag nanoparticles (20-60 nm) and redeposited Ag nanodots ( approximately 10 nm) between the clusters. The substrate thus formed had a uniform ultrahigh SERS enhancement factor (1010) over the entire substrate for 4-mercaptophenol molecules. By comparison, Au patterned structures fabricated with the same method did not undergo such a morphological change after the plasma treatment and showed no enhancement of Raman scattering.

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    • "The characteristic of LSPR depends on the composition, size, array structure, and shape of silver nanostructures and the dielectric environment [4] [5]. Ag nanostructures have been formed by various lithographic techniques [5] [6]. Ag nanostructure has led to many important applications pertaining to a sensor. "
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    • "Theoretical analysis and experimental data suggest that a separation of less than 5 nm between aggregated nanoparticles is necessary for strong SERS enhancement[22]. However, this scale of controlled separation is still beyond the resolution of any scalable top-down fabrication approach[23]. An alternate approach is to utilize self-assembled nanostructures that are uniform enough on a macro scale so that a reasonably enhanced and reproducible SERS signal can be obtained. "
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    ABSTRACT: Metallic nanorods synthesized by oblique angle deposition on glass substrate are utilized as nano-scale structures that can be coated with SERS active metal to allow for excitation of surface plasmons. The synthesized nanorods have an average length of ~500-600 nm and are randomly distributed on the substrate. The SERS studies with Near-IR excitation at 785 nm show significant enhancement with good uniformity to detect sub-monolayer concentrations of 4-methylbenzenethiol and 1,2-benzendithiol probe molecules. The simple synthesis and the reproducibility of SERS measurement make these substrates a promising candidate for trace level detection of biological and chemical species.
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