Chen Wen, Zhang Shunping, Kang Meng, Liu Weikang, Ou Zhenwei, Li Yang, Zhang Yexin, Guan Zhiqiang, Xu Hongxing
1School of Physics and Technology, Center for Nanoscience and Nanotechnology, and Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, Wuhan University, Wuhan, 430072 China.
2The Institute for Advanced Studies, Wuhan University, Wuhan, 430072 China.
Light Sci Appl. 2018 Aug 29;7:56. doi: 10.1038/s41377-018-0056-3. eCollection 2018.
Achieving larger electromagnetic enhancement using a nanogap between neighboring metallic nanostructures has been long pursued for boosting light-matter interactions. However, the quantitative probing of this enhancement is hindered by the lack of a reliable experimental method for measuring the local fields within a subnanometer gap. Here, we use layered MoS as a two-dimensional atomic crystal probe in nanoparticle-on-mirror nanoantennas to measure the plasmonic enhancement in the gap by quantitative surface-enhanced Raman scattering. Our designs ensure that the probe filled in the gap has a well-defined lattice orientation and thickness, enabling independent extraction of the anisotropic field enhancements. We find that the field enhancement can be safely described by pure classical electromagnetic theory when the gap distance is no <1.24 nm. For a 0.62 nm gap, the probable emergence of quantum mechanical effects renders an average electric field enhancement of 114-fold, 38.4% lower than classical predictions.
长期以来，人们一直致力于通过相邻金属纳米结构之间的纳米间隙实现更大的电磁增强，以促进光与物质的相互作用。然而，由于缺乏可靠的实验方法来测量亚纳米间隙内的局部场，这种增强的定量探测受到了阻碍。在这里，我们使用层状二硫化钼作为二维原子晶体探针，置于镜上纳米颗粒纳米天线中，通过定量表面增强拉曼散射来测量间隙中的等离子体增强。我们的设计确保填充在间隙中的探针具有明确的晶格取向和厚度，从而能够独立提取各向异性场增强。我们发现，当间隙距离不小于1.24纳米时，场增强可以用纯经典电磁理论安全地描述。对于0.62纳米的间隙，量子力学效应的可能出现使得平均电场增强为114倍，比经典预测低38.4%。
