Taneja Chetna, Elliott Eoin, Kumar G V Pavan, Baumberg Jeremy J, Chikkaraddy Rohit
NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thompson Avenue, Cambridge CB3 0HE, U.K.
Department of Physics, Indian Institute of Science Education and Research, Pune 411008, India.
ACS Photonics. 2024 Dec 10;11(12):5205-5214. doi: 10.1021/acsphotonics.4c01443. eCollection 2024 Dec 18.
Tightly confined plasmons in metal nanogaps are highly sensitive to surface inhomogeneities and defects due to the nanoscale optical confinement, but tracking and monitoring their location is hard. Here, we probe a 1-D extended nanocavity using a plasmonic silver nanowire (AgNW) on mirror geometry. Morphological changes inside the nanocavity are induced locally using optical excitation and probed locally through simultaneous measurements of surface enhanced Raman scattering (SERS) and dark-field spectroscopy. The increasing molecular SERS intensity and corresponding redshift of cavity plasmon modes by up to 60 nm indicate atomic-scale changes inside the nanocavity. We correlate this to diffusion of silver atoms into the nanogap, which reduces the nanogap size and enhances the optical near-field, enhancing the SERS. These induced changes can be locally excited at specific locations along the length of the nanowire and remain stable and nonreversible. Polymer surface coating on the AgNW affects the power threshold for inducing atom migration and shows that strong polyvinylpyrrolidone (PVP)- Ag binding gives rise to higher power thresholds. Such extended nanogap cavities are an ideal system to provide robust SERS while withstanding high laser powers. These results provide insights into the inhomogeneities of NW nanocavities and pave the way toward spatially controlled NW lithography in ambient conditions.
由于纳米尺度的光学限制，金属纳米间隙中紧密受限的等离子体激元对表面不均匀性和缺陷高度敏感，但追踪和监测它们的位置却很困难。在此，我们使用镜面几何结构上的等离子体银纳米线（AgNW）探测一维扩展纳米腔。利用光激发在纳米腔内局部诱导形态变化，并通过同时测量表面增强拉曼散射（SERS）和暗场光谱进行局部探测。分子SERS强度的增加以及腔等离子体激元模式相应的红移（高达60纳米）表明纳米腔内存在原子尺度的变化。我们将此与银原子扩散到纳米间隙中相关联，这会减小纳米间隙尺寸并增强光学近场，从而增强SERS。这些诱导变化可以在沿着纳米线长度的特定位置局部激发，并且保持稳定且不可逆。AgNW上的聚合物表面涂层会影响诱导原子迁移的功率阈值，表明强聚乙烯吡咯烷酮（PVP） - Ag结合会导致更高的功率阈值。这种扩展的纳米间隙腔是一个理想的系统，既能在承受高激光功率的同时提供强大的SERS。这些结果为NW纳米腔的不均匀性提供了见解，并为在环境条件下进行空间控制的NW光刻铺平了道路。
