台阶形针尖-活性基底结构的拉曼散射增强特性

Raman Scattering Enhancement Characteristics of a Stepped Tip-Active Substrate Structure

利用基于时域有限差分法的FDTD Solutions软件建立了镀Ag膜台阶形针尖-Ag纳米粒子活性基底结构的表面/针尖增强拉曼光谱(SERS-TERS)仿真模型,并在相同的条件下对其他不同类型的针尖和基底的近场电场分布进行数值计算,验证了所设计的镀Ag膜台阶形针尖和活性基底模型在拉曼散射增强方面的有效性。同时,针对此结构模型系统地分析了台阶形针尖曲率半径、针尖镀Ag膜厚度、针尖镀Ag膜高度、Ag纳米粒子直径、针尖与Ag纳米粒子间距,以及入射光角度对该针尖-基底结构热点位电场强度的影响。结果表明:在针尖曲率半径为5 nm、镀Ag膜厚度为25 nm、镀Ag膜高度为300 nm、Ag纳米粒子直径为55 nm、探针与Ag纳米粒子间距达到1 nm,以及入射光角度为45°时,该结构可产生最大的拉曼增强因子,为10~7量级。仿真结果可为制备高增强效应的针尖和TERS活性基底结构提供重要的理论依据和实验指导。

This study simulates the surface-tip-enhanced Raman scattering （SERS-TERS） model of a stepped tip with a silver film and a silver-nanoparticle-active substrate. The simulation is established by the finite-difference time-domain method. The near-field electric field distributions of different types of needle tips and substrates are numerically calculated under the same conditions, verifying the effectiveness of the designed method in the Raman scattering enhancement. Next, the electric field intensity of the model is systematically analyzed under different influencing factors： the curvature radius of the tip, the thickness and height of the silver film on the tip, the diameter of the silver nanoparticles, the gap between the tip and the silver nanoparticles, and the incident angle. The field enhancement factor is maximized at a tip-curvature radius of 5 nm, a silver-film thickness of 25 nm, a silver-film height of 300 nm, a silver-nanoparticle diameter of 55 nm, a 1 nm gap between the tip and silver nanoparticles, and an incident angle of 45°. The largest enhancement factor is of the order of magnitude of 107. The simulation results provide an important theoretical basis and experimental guidance for preparing high-efficiency tip and TERS active substrate structures.