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.

中文翻译：

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在一维扩展等离子体纳米线镜腔中映射和光学写入纳米间隙不均匀性


由于纳米级光学限制，金属纳米间隙中的紧密限制等离激元对表面不均匀性和缺陷高度敏感，但跟踪和监测它们的位置很困难。在这里，我们使用等离子体银纳米线 （AgNW） 在镜子几何形状上探测一维扩展纳米腔。纳米腔内的形态变化是使用光学激发局部诱导的，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 强度的增加和相应的腔等离子体模式红移高达 60 nm 表明纳米腔内部的原子级变化。我们将其与银原子扩散到纳米间隙相关联，这减小了纳米间隙尺寸并增强了光学近场，从而增强了 SERS。这些诱导的变化可以在纳米线长度的特定位置局部激发，并保持稳定和不可逆。AgNW 上的聚合物表面涂层会影响诱导原子迁移的功率阈值，并表明强聚乙烯吡咯烷酮 （PVP）-Ag 结合会产生更高的功率阈值。这种扩展的纳米间隙腔是提供稳健的 SERS 同时承受高激光功率的理想系统。这些结果提供了对 NW 纳米腔不均匀性的见解，并为在环境条件下进行空间控制的 NW 光刻铺平了道路。