Characteristics of Nanogaps Formed by Planar Au and Pt Nanoparticles Revealed by Raman Spectroscopy
Characteristics of Nanogaps Formed by Planar Au and Pt Nanoparticles Revealed by Raman Spectroscopy
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DOI：
10.1021/jp207247v
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发表时间：
2011-11-03
影响因子：
3.7
通讯作者：
Shin, Kuan Soo
中科院分区：
文献类型：
--
作者：
Kim, Kwan;Lee, Hyang Bong;Shin, Kuan Soo
拉曼峰对于存在于宏观上光滑的金属基底上的分子几乎检测不到。然而，通过使Ag或Au纳米颗粒覆盖在吸附物分子上，可以观察到拉曼峰。例如，在平坦的Au衬底上没有检测到4-氨基苯乙胺（4-ABT）的拉曼峰。然而，当将Ag纳米颗粒附着到4-ABT上时，不仅在632.8 nm处激发，而且在514.5 nm处激发都清楚地观察到拉曼峰，尽管632.8 nm处的峰比514.5 nm处的峰强几十倍。当Au纳米颗粒被附着时，拉曼峰在514.5 nm处的激发下可忽略地观察到，尽管在632.8 nm处的激发下可清楚地观察到。有趣的是，通过将Pt纳米颗粒附着到平坦Ag基底上的4-ABT上以形成Pt@4-ABT/Ag（平坦），甚至在514.5 nm处也可观察到拉曼峰。Pt纳米颗粒越大，在纳米间隙中感生的电磁场越大。对Pt@4-ABT/Au（平坦）体系进行了大致相同的观察。然而，激发波长依赖性是相反的，使得对于Pt@4-ABT/Au（平坦）系统，观察到较高强度的激发顺序为632.8 > 568 > 514.5 > 488 nm，而对于Pt@4-ABT/Ag（平坦）系统，观察到较高强度的激发顺序为488 > 514.5 > 568 > 632.8 nm。尽管如此，Pt@4-ABT/Au（平坦）系统中在632.8 nm激发下的最大增强因子（EF）仅为Pt@4-ABT/Ag（平坦）系统中在632.8 nm激发下可观察到的EF值的约一半，这表明对于借助于覆盖在其上的Pt纳米颗粒的Sers的诱导，平坦Ag基底应当比平坦Au基底有效得多。
Raman peaks are barely detectable for molecules present on macroscopically smooth metal substrates. Raman peaks can be observed, however, by allowing Ag or Au nanoparticles to overlie the adsorbate molecules. For instance, no Raman peaks are detected for 4-aminobenzenethiol (4-ABT) on a flat Au substrate. Upon attaching Ag nanoparticles onto 4-ABT, however, Raman peaks are distinctly observed, not only with excitation at 632.8 nm but also with excitation at 514.5 nm, though the peaks at 632.8 nm are several tens of times more intense than those at 514.5 nm. When Au nanoparticles are attached, Raman peaks are negligibly observable with the excitation at 514.5 nm, though distinctly observed with the excitation at 632.8 nm. Interestingly, Raman peaks are observable even at 514.5 nm by attaching Pt nanoparticles onto 4-ABT on a flat Ag substrate to form Pt@4-ABT/Ag(flat). The larger the Pt nanoparticle is, the greater the electromagnetic field induced in the nanogap. Much the same observation is made for the Pt@4-ABT/Au(flat) system. However, the excitation wavelength dependence is opposite such that the higher intensity is observed in the order of excitations 632.8 > 568 > 514.5 > 488 nm for the Pt@4-ABT/Au (flat) system, while in the order of excitations 488 > 514.5 > 568 > 632.8 nm for the Pt@4-ABT/Ag(flat) system. The maximum enhancement factor (EF) at 632.8 nm excitation in the Pt@4-ABT/Au(flat) system is nonetheless only about one-half of the EF value observable at 632.8 nm excitation in the Pt@4-ABT/Ag(flat) system, suggesting that the planar Ag substrate should be far more effective than the planar Au substrate for the induction of SERS by virtue of Pt nanoparticles overlaid thereon.