Surface-enhanced Raman scattering of silver-gold bimetallic nanostructures with hollow interiors

Surface-enhanced Raman scattering (SERS) activity of silver-gold bimetallic nanostructures (a mean diameter of ∼100nm) with hollow interiors was checked using p-aminothiophenol (p-ATP) as a probe molecule at both visible light (514.5 nm) and near-infrared (1064 nm) excitation. Evident Raman peaks of p-ATP were clearly observed, indicating the enhancement Raman scattering activity of the hollow nanostructure to p-ATP. The enhancement factors (EF) at the hollow nanostructures were obtained to be as large as (0.8±0.3) × 10⁶ and (2.7±0.5) × 10⁸ for 7a and 19b (b₂) vibration mode, respectively, which was 30-40 times larger than that at silver nanoparticles with solid interiors at 514.5 nm excitation. EF values were also obtained at 1064 nm excitation for 7a and b ₂-tyPe vibration mode, which were estimated to be as large as (1.0±0.3) × 10⁶ and (0.9±0.2) × 10 ⁷, respectively. The additional EF values by a factor of ∼10 for b₂-type, band were assumed to be due to the chemical effect. Large electromagnetic EF values were presumed to derive from a strong localized plasmas electromagnetic field existed at the hollow nanostructures. SERS activity of hollow nanostructures with another size (a mean diameter of ∼80 nm) was also investigated and large EF for 7a and b₂-type band are obtained to be (0.6±0.3) × 10⁶ and (1.7±0.7) × 10⁸, respectively, at 514.5 nm excitation and (0.2±0.1) × 10⁶ and (0.6±0.2) × 10 ⁷, respectively, at 1064 nm excitation. Although the optical properties of the hollow nanostructures have not yet been well studied, high SERS activities of the nanostructures with hollow interiors have been exhibited in our report.