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 approximately 100 nm) 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)x10(6) and (2.7+/-0.5)x10(8) for 7a and 19b (b(2)) 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)x10(6) and (0.9+/-0.2)x10(7), respectively. The additional EF values by a factor of approximately 10 for b(2)-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 approximately 80 nm) was also investigated and large EF for 7a and b(2)-type band are obtained to be (0.6+/-0.3)x10(6) and (1.7+/-0.7)x10(8), respectively, at 514.5 nm excitation and (0.2+/-0.1)x10(6) and (0.6+/-0.2)x10(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.