Hossain Mohammad Kamal, Drmosh Qasem Ahmed
Interdisciplinary Research Center for Renewable Energy and Power System (IRC-REPS), Research Institute, King Fahd University of Petroleum & Minerals (KFUPM), Dhahran 31261, Saudi Arabia.
Interdisciplinary Research Center for Hydrogen and Energy Storage (IRC-HES), Research Institute, King Fahd University of Petroleum & Minerals (KFUPM), Dhahran 31261, Saudi Arabia.
Spectrochim Acta A Mol Biomol Spectrosc. 2021 Dec 15;263:120141. doi: 10.1016/j.saa.2021.120141. Epub 2021 Jul 6.
Plasmonic nanostructures, particularly irregular surfaces of ring-like silver (Ag) nanostructures are promising candidates in surface-enhanced Raman scattering (SERS) spectroscopy. In this work, clusters-based Ag nanorings have been fabricated and characterized as SERS-active substrates. The rim of the as-fabricated Ag nanorings was found neither discontinuous nor linear aggregation of nanoparticles. High-resolution field emission scanning electron microscopy (FESEM) revealed that the individual constituent clusters were different from each other, particularly in terms of size and shape in addition to the cases how such clusters were emerged as the edge of the nanoring. Considering the dimensions of the clusters and the arrangement of such clusters as nanorings, it was speculated that the local electromagnetic (EM) near-field distributions would excel and thus enhanced SERS signals would be achieved. Indeed, the inherent features of the nanorings facilitated to achieve SERS enhancement factors as high as 2.1 × 10. SERS-activity of as-fabricated Ag nanorings was confirmed using Rhodamine 6G (R6G) as Raman-active dyes and the enhancement was compared to those obtained from R6G adsorbed on Ag-ZnO/Glass and ZnO/Glass. To the best of our knowledge, this is the first attempt to explore the impact of localized EM near-field within the segments of nanorings through SERS spectroscopy. A model was designed resembling the nanorings under this investigation to simulate EM near-field distributions by finite difference time domain (FDTD) analysis. The dimensions of the model geometry were chosen according to the observations achieved by FESEM. To simplify the simulations, nanoobjects were considered spherical and organized in a periodic fashion, although the constituent clusters of Ag nanorings were found irregular in shape and arrangement. Since EM near-field distribution highly depends on interparticle gaps, three scenarios were implemented, such as, small gap in between two adjacent nanoobjects and adjacent nanoobjects in touch and overlapped. Each configuration was simulated and EM near-field distribution was extracted for s-, p- and 45 of incident polarizations followed by a plausible correlation to SERS enhancements. Such correlated investigations as well as clusters-based Ag nanorings not only inspire the ones to look for cost-effective SERS-active substrate, but also understand the underlying EM mechanism in SERS enhancements.
等离子体纳米结构，特别是环状银（Ag）纳米结构的不规则表面，是表面增强拉曼散射（SERS）光谱中很有前景的候选材料。在这项工作中，基于团簇的银纳米环已被制备并表征为具有SERS活性的基底。所制备的银纳米环的边缘既不是不连续的，也不是纳米颗粒的线性聚集。高分辨率场发射扫描电子显微镜（FESEM）显示，各个组成团簇彼此不同，特别是在尺寸和形状方面，此外还包括这些团簇作为纳米环边缘出现的情况。考虑到团簇的尺寸以及这些团簇作为纳米环的排列方式，推测局部电磁（EM）近场分布会很出色，从而实现增强的SERS信号。实际上，纳米环的固有特性有助于实现高达2.1×10的SERS增强因子。使用罗丹明6G（R6G）作为拉曼活性染料确认了所制备的银纳米环的SERS活性，并将其增强效果与吸附在Ag-ZnO/玻璃和ZnO/玻璃上的R6G所获得的增强效果进行了比较。据我们所知，这是首次尝试通过SERS光谱探索纳米环段内局部EM近场的影响。设计了一个类似于本研究中的纳米环的模型，通过有限时域差分（FDTD）分析来模拟EM近场分布。模型几何结构的尺寸根据FESEM的观察结果选择。为了简化模拟，尽管发现银纳米环的组成团簇形状和排列不规则，但将纳米物体视为球形并以周期性方式排列。由于EM近场分布高度依赖于颗粒间间隙，实施了三种情况，例如两个相邻纳米物体之间的小间隙、相邻纳米物体接触和重叠。对每种配置进行了模拟，并提取了s-、p-和45°入射偏振的EM近场分布，随后与SERS增强进行了合理关联。这种相关研究以及基于团簇的银纳米环不仅激励人们寻找具有成本效益的SERS活性基底，还能理解SERS增强背后的EM机制。
