【摘要】 一直以来,将纳米结构材料用于其表面增强拉曼散射(SERS)时会先测试其吸收光谱,因为一般研究认为,纳米结构材料产生SERS的原因是纳米结构材料对于入射光的吸收产生了局域表面等离子体共振(LSPR),因此我们常把SERS的增强因子随波长变化的曲线等同于吸收光谱曲线。近年来,有学者认为两者之间的联系可能是非常间接的,并且在许多情况下会产生误导。为了能够阐明两个之间的具体关系,考虑到银纳米粒子(AgNPs)以其局域表面等离子体共振而显著提高拉曼散射的能力而闻名,是制备SERS基底的理想纳米材料,我们从实验和理论两个角度研究了三种不同状态的AgNPs中表面增强拉曼散射的增强因子(EF)、吸收光谱以及空间的电场分布。实验上,利用化学还原法制备了银溶胶(Ag-sol),并对Ag-sol做了透射电子显微镜(TEM)、紫外可见分光光度计(UV-Vis)以及拉曼的表征实验,统计和计算了银溶胶的EF和吸收光谱。理论上,利用仿真软件COMSOL Multiphysics建立了不同聚合类型AgNPs的仿真模型,模拟计算了与实验相对应的EF随波长变化的曲线以及吸收光谱。结果表明:表面等离子体共振的空间分布对吸收和最大EF值起着重要的作用;具有固定位置的共振吸收峰(第一个峰位)主要受"单颗粒类型"效应的影响,而最大EF处的吸收峰(第二个峰位)由"耦合间隙类型"效应引起的蓝移谐振峰主导,且最大EF值及第二个吸收峰的峰位会随着粒子的间隙、偏振角度等因素而变化。研究表明,AgNps样品的吸收光谱和最大EF曲线之间是部分相关的。更多还原

【Abstract】 When we use nano-structured materials for surface-enhanced Raman scattering(SERS), we will first test the absorption spectrum because original researchers believe that the reason why nano-structured materials generate SERS is that the absorption of incident light by nano-structured materials causes the localized surface plasmon resonance(LSPR), so we equate the curve of SERS enhancement factor with wavelength to the absorption spectrum curve. In recent years, some scholars believe that the connection between them can be very indirect and can be misleading in many cases. AgNPs are famous for their ability to significantly improve Raman scattering due to their local surface plasmon resonance, so AgNPs are the ideal nanomaterial for the substrate. In order to clarify the specific relationship, we studied the enhancement factor(EF) of surface-enhanced Raman scattering, absorption spectra and spatial electric field distribution of silver nanoparticles(AgNPs) in three different states, experimentally and theoretically. Experimentally, we prepared Ag-sol by chemical reduction method. They were characterized by a transmission electron microscope(TEM), ultraviolet-visible spectrophotometer(UV-Vis) and Raman’s measurements and statistics and calculations of the EF and absorption spectra of silver sols were carried on. Theoretically, we used the simulation software COMSOL Multiphysics to establish different aggregation types of AgNPs models, and simulated the EF curve with wavelength and absorption spectra corresponding to the experiments. The results show that the spatial distribution of surface plasmon resonance plays an important role in absorption and maximum EF value. The resonance absorption peak with a fixed position(first peak position) is mainly affected by the "single particle type" effect, and the absorption peak at the maximum EF(the second peak position) is dominated by the blue-shifted resonance peak caused by the "coupling gap type" effect, the maximum EF value and the position of the second absorption peak will be influenced by the particle gap, polarization angle and other factors. Studies have shown that the absorption spectrum of the AgNps sample is partially related to the maximum EF curve.更多还原