单粒子表面增强拉曼光谱的二维成像研究

以单个椭球形Fe₂O₃@Au核壳粒子作为SERS活性基底, 苯硫酚(TP)作为探针分子, 研究了椭球形粒子表面SERS效应的分布, 对比了粒子尖端以及中间SERS效应的差别. 为了得到单个粒子表面不同部分对SERS强度的贡献差别, 通过数学模拟和解析了探针分子SERS的二维成像(2D-mapping)信号, 获得了粒子边缘不同点的SERS效应. 模拟分析结果表明, 当xy平面内粒子在垂直入射(z轴)平面波作用下, 单个椭球形Fe₂O₃@Au核壳粒子表面单位面积上的SERS强度相差极大, 粒子长轴方向端点附近单位面积上的SERS效应最大, 而其它表面部分较弱, 其中与短轴平行方向的表面附近为最弱, 差异可达到约2~3个数量级. 若考虑SERS增强主要为电磁场增强的尖端效应, 则单个椭球形粒子尖端的局域感应电磁场为垂直方向的5倍.

2D-mapping Studies of the SERS Effect on the Single Ellipsoid Fe2O3@Au Particle

The single spindle Fe2O3@Au core/shell particle was employed as surface-enhanced Raman scattering(SERS) substrate and thiophenol(TP) was used as probe molecule to investigate the 2D-mapping and the distribution of SERS effect on the particle surface. The difference in the SERS effect from the tips and the middle part was compared. To obtaining the SERS effect from the different sites of the single particle, we firstly simulated with mathematic model and resolved the SERS 2D-mapping, the SERS effect from the edge of the particle was extracted. The results revealed that the difference in the intensity of SERS signal could reach 2—3 folders while the single core-shell particle was oriented at a certain angle relative to the polarization of excitation laser. Assumed the particle located in xy plane and the incident wave perpendicularly spread through z axis, the intensity of SERS signal exhibited the maximum value near the tip parts of the particle, while the other parts of the particle surface were very weak and the parts near the short axis were in minimum. By considering SERS mainly contributed by lightning rod effect of electromagnetism field enhancement, the local electric field enhancement of the spindle particles near the tip along long axis relative to short axis is about 5 times.