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Polarization-dependent SERS effects of laser-generated sub-100 nm antenna structures

机译：激光产生的100 nm以下天线结构的偏振相关SERS效应

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摘要

Sub-100 nm antenna arrays consisting of a star-like ridge or dome-like structures with needles in their centers are prepared in thin gold films on glass substrates using femtosecond laser pulses. The needles can be bent mechanically to be horizontally aligned to the substrate surface. Controlled variation of the pulse energy allows one to obtain nanostructures of different defined morphologies. These arrays of nanostructures are covered with a thin homogeneous layer of rhodamine molecules. Raman spectra using linearly polarized laser light of 632.8 nm are taken with the laser spot centered on individual nanostructures and at positions on the unstructured film. The average Raman enhancement within the laser spot focused onto a nanostructure is two orders of magnitude higher than on the unstructured film. The nanostructures with bent needles exhibit a polarization dependence of the SERS effect, i.e., typically the enhancement is larger by about a factor of two for excitation light polarized parallel to the needle direction than for the perpendicular case. The enhancement factor of the star-like ridge structures with needles is analyzed by the finite-element method, which agrees with the experiment. We show that the variation of the SERS activity of almost similar structures arises from the inherent randomness of the hot spots created in the fabrication process. Nevertheless, these antenna structures may be useful as elements in novel SERS devices as they can be accurately positioned on a device using a cheap fabrication process compatible with microfabrication technology.
机译：使用飞秒激光脉冲在玻璃基板上的金薄膜中制备100nm以下的天线阵列，该阵列由星形脊或圆顶状结构（其中心为针）组成。可以将针机械弯曲以与基板表面水平对齐。脉冲能量的受控变化允许人们获得具有不同定义形态的纳米结构。这些纳米结构阵列被若丹明分子的均匀薄层覆盖。使用632.8 nm的线性偏振激光获取拉曼光谱，激光点位于单个纳米结构的中心和非结构化膜上的位置。聚焦在纳米结构上的激光点内的平均拉曼增强比非结构化膜上的平均拉曼增强高两个数量级。具有弯曲的针的纳米结构表现出SERS效应的偏振依赖性，即，通常，对于平行于针方向偏振的激发光，其增强比垂直情况下的增强大两倍。采用有限元方法分析了带针星形脊结构的增强因子，与实验结果吻合。我们表明，几乎相似结构的SERS活性变化是由制造过程中产生的热点的固有随机性引起的。然而，这些天线结构可以用作新颖的SERS设备中的元件，因为它们可以使用与微制造技术兼容的廉价制造工艺精确地定位在设备上。

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