Shaping and Shelling Pt and Pd Nanoparticles for Ultraviolet Laser Excited Surface-Enhanced Raman Scattering

Ultraviolet laser excited surface-enhanced Raman scattering (UV−SERS) was obtained on platinum and palladium surfaces using adenine and SCN − as the probe molecules. Diverse Pt and Pd nanoparticles, i.e., Pt nanospheres, Pt nanocubes, and Au core Pt or Pd shell nanoparticles with different shell thicknesses, were synthesized, and their UV−SERS enhancements were compared. The dependence of the UV−SERS activity on the crystalline structure was investigated. The result indicates that a high-quality crystalline structure is favorable for a higher enhancement, while nanoparticles with a low-quality crystalline (e.g., chaotic and loose grain) structure could be poor SERS active. UV−vis absorption spectra of core−shell nanoparticles were also recorded, and the plasmon band in the UV region which shifts with the shell thickness is regarded to account for the UV−SERS enhancement of Au@Pd and Au@Pt nanoparticles. For the Au@Pd nanoparticle system, the enhancements excited with the UV and visible lasers show an opposite dependency on the shell thickness. The Au core plays an important role in the enhancement in the visible region, while the Pd shell itself produces an effective enhancement in the UV region.