Department of Chemistry, Seoul National University, Seoul 151-742, Republic of Korea.
Spectrochim Acta A Mol Biomol Spectrosc. 2013 Jan 1;100:10-4. doi: 10.1016/j.saa.2012.01.049. Epub 2012 Jan 27.
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.
我们估算了位于 Pt 纳米颗粒和平坦 Ag 基底之间间隙内的表面增强拉曼散射（SERS）“热点”的表观尺寸。最初，在平坦的 Ag 基底上，4-巯基苯胺（4-ABT）没有检测到拉曼峰。当将 68nm 大小的 Pt 纳米颗粒附着到 4-ABT 的氨基上（因此表示为 Pt-4-ABT/Ag（平坦））时，不仅在 488nm 激发下，而且在 632.8nm 激发下，都明显观察到拉曼峰。这意味着在 Pt 纳米颗粒和平坦 Ag 基底之间的间隙处形成了电磁“热点”。当额外将 4-ABT 分子吸附到 Pt-4-ABT/Ag（平坦）中的 Pt 纳米颗粒的空位上时，拉曼信号没有进一步增加，表明 SERS“热点”非常有限，主要位于 Pt 纳米颗粒和平坦 Ag 基底之间的间隙处，这与有限差分时间域（FDTD）计算结果一致。粗略估计，只有大约 1000 个分子位于间隙中心的~15nm 直径区域内，它们必须对 4-ABT 的大部分测量拉曼信号做出贡献。
