Lin Li, Zhang Qiang, Li Xiyao, Qiu Meng, Jiang Xin, Jin Wei, Gu Hongchen, Lei Dang Yuan, Ye Jian
State Key Laboratory of Oncogenes and Related Genes, School of Biomedical Engineering , Shanghai Jiao Tong University , Shanghai 200030 , China.
School of Materials Science and Engineering, Shenzhen Graduate School , Harbin Institute of Technology , Shenzhen 518055 , China.
ACS Nano. 2018 Jul 24;12(7):6492-6503. doi: 10.1021/acsnano.7b08224. Epub 2018 Jun 28.
Charge transport plays an important role in defining both far-field and near-field optical response of a plasmonic nanostructure with an ultrasmall built-in nanogap. As the gap size of a gold core-shell nanomatryoshka approaches the sub-nanometer length scale, charge transport may occur and strongly alter the near-field enhancement within the molecule-filled nanogap. In this work, we utilize ultrasensitive surface-enhanced Raman spectroscopy (SERS) to investigate the plasmonic near-field variation induced by the molecular junction conductance-assisted electron transport in gold nanomatryoshkas, termed gap-enhanced Raman tags (GERTs). The GERTs, with interior gaps from 0.7 to 2 nm, are prepared with a wet chemistry method. Our experimental and theoretical studies suggest that the electron transport through the molecular junction influences both far-field and near-field optical properties of the GERTs. In the far-field extinction response, the low-energy gap mode predicted by a classical electromagnetic model (CEM) is strongly quenched and hence unobservable in the experiment, which can be well explained by a quantum-corrected model (QCM). In the near-field SERS response, the optimal gap size for maximum Raman enhancement at the excitation wavelength of 785 nm (633 nm) is about 1.35 nm (1.8 nm). Similarly, these near-field results do not tally with the CEM calculations but agree well with the QCM results where the molecular junction conductance in the nanogap is fully considered. Our study may improve understanding of charge-transport phenomena in ultrasmall plasmonic molecular nanogaps and promote the further development of molecular electronics-based plasmonic nanodevices.
电荷输运在定义具有超小内置纳米间隙的等离子体纳米结构的远场和近场光学响应中起着重要作用。当金核壳套娃纳米结构的间隙尺寸接近亚纳米长度尺度时，电荷输运可能会发生，并强烈改变填充分子的纳米间隙内的近场增强。在这项工作中，我们利用超灵敏表面增强拉曼光谱（SERS）来研究金纳米套娃中分子结电导辅助电子输运引起的等离子体近场变化，这些金纳米套娃被称为间隙增强拉曼标签（GERTs）。通过湿化学方法制备了内部间隙为0.7至2纳米的GERTs。我们的实验和理论研究表明，通过分子结的电子输运影响了GERTs的远场和近场光学性质。在远场消光响应中，经典电磁模型（CEM）预测的低能间隙模式被强烈淬灭，因此在实验中无法观察到，这可以通过量子校正模型（QCM）得到很好的解释。在近场SERS响应中，在785纳米（633纳米）激发波长下实现最大拉曼增强的最佳间隙尺寸约为1.35纳米（1.8纳米）。同样，这些近场结果与CEM计算结果不一致，但与充分考虑纳米间隙中分子结电导的QCM结果非常吻合。我们的研究可能会增进对超小等离子体分子纳米间隙中电荷输运现象的理解，并促进基于分子电子学的等离子体纳米器件的进一步发展。
