Interplay between Near-Field Properties and Au Nanorod Cluster Structure: Extending Hot Spots for Surface-Enhanced Raman Scattering

Materials science has observed a continuous increase in the use of metal nanoparticles in a wide range of studies, from fundamental physics to technological applications such as photocatalysis and optical communication devices. This broad scope has the same fundamental origin, the localized surface plasmons, whose excitation leads to strong light confinement, especially in the vicinity of closely spaced nanoparticles, the hot spots. The field amplification may be used to amplify the Raman scattering of adsorbed molecules, which is known as surface-enhanced Raman scattering (SERS). A crucial and limiting characteristic of SERS hot spots is their very localized nature, that influences the SERS intensity reproducibility as well as the probabilities of observation of single-molecule SERS signals. In this paper we discuss the correlation between SERS performance and gold nanorod cluster structures using transmission electron microscopy, SERS spectra and numerical simulations. The experimental data showed interesting behavior for the combination of end-to-end and side-by-side interactions, revealing the possibility of creating strong hot spots with a more extended spatial distribution. The results give insights into the development of high-performance SERS substrates.

材料科学领域中，金属纳米颗粒（metal nanoparticles）的应用研究持续拓展，覆盖范畴从基础物理研究延伸至光催化、光通信器件等技术应用场景。这类广泛应用的共同本源为局域表面等离子体激元（localized surface plasmons）：其激发可引发强烈的光场束缚效应，在间距紧密的纳米颗粒附近的“热点”（hot spots）区域尤为显著。此种场增强效应可用于放大吸附分子的拉曼散射信号，即表面增强拉曼散射（surface-enhanced Raman scattering, SERS）。SERS热点的一个关键且具有局限性的特征是其极强的局域性，这会影响SERS强度的重现性，以及单分子SERS信号的观测概率。本文探讨了SERS性能与金纳米棒团簇结构（gold nanorod cluster structures）之间的关联，研究采用了透射电子显微镜（transmission electron microscopy）、SERS光谱与数值模拟三种手段。实验数据显示，端对端与肩并肩两种排列方式的组合呈现出有趣的实验现象，表明可构建出空间分布更延展的强热点区域。本研究结果为高性能SERS基底的开发提供了关键参考。