Surface-enhanced Raman scattering characteristics of nanogaps formed by a flat Ag substrate and spherical Pt nanoparticles.
We estimated the apparent size of the 'hot site' for surface-enhanced Raman scattering (SERS) located within the gaps between Pt nanoparticles and a flat Ag substrate. Initially, no Raman peaks were detected for 4-aminobenzenethiol (4-ABT) on a flat Ag substrate. Upon attaching 68 nm-sized Pt nanoparticles onto the amine group of 4-ABT (thus denoted as Pt-4-ABT/Ag(flat)), Raman peaks were distinctly observed, not only with the excitation at 488 nm but also with the excitation at 632.8 nm. This means that electromagnetic 'hot site' had formed at the gaps between Pt nanoparticles and a flat Ag substrate. When 4-ABT molecules were adsorbed additionally onto the vacant sites of Pt nanoparticles in Pt-4-ABT/Ag(flat), the Raman signal did not increase further, suggesting that the SERS 'hot site' was very limited and located mostly at the gaps between Pt nanoparticles and a flat Ag substrate, in agreement with the finite-difference time-domain (FDTD) calculation. To a rough estimate, about 1000 molecules residing only within a ~15 nm diameter area of the center of the gap must have contributed most of the measured Raman signal of 4-ABT.
Department of Chemistry, Seoul National University, Seoul 151-742, Republic of Korea. kwankim@snu.ac.kr
Kwan
K
Kim
Hyang Bong
HB
Lee
Kuan Soo
KS
Shin
D004560:Electricity; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D010984:Platinum / Q000737:chemistry; D012834:Silver / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D013425:Sulfanilic Acids / Q000737:chemistry; D013997:Time Factors
D013425:Sulfanilic Acids; D012834:Silver; C100016:4-sulfanilic acid; D010984:Platinum; D006046:Gold