Abstract All-dielectric optical nanoantennas and resonators are attracting an ever increasing interest for enhanced Raman spectroscopy. These systems can take advantage of many factors that concur to determine their Raman response, including the type of material, refractive index contrast between interfaces, size, shape, roughness and geometrical configuration. However, the relative impact of each one of those terms on the Raman enhancement is still unclear. Here we report the Raman characterization of SiO2@TiO2 semishell microspheres obtained by rf-magnetron sputtering deposition of a TiO2 thin layer on SiO2 cores. The samples were able to significantly amplify Raman scattering in comparison to planar counterparts, however the overall enhancement was very limited with reference to that observed in conformal, smooth and compact TiO2 shell layers obtained by atomic layer deposition. These results demonstrated that geometry is a key factor to maximize the Raman response of these systems and, in general, it is more important than other parameters, such as the surface roughness or even refractive index of the shell layer, which are usually considered crucial for achieving Raman enhancement.

中文翻译：

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形态在全介电 SERS 中的作用：保形 (T-rex) 和非保形 TiO2 壳之间的比较

摘要 全介电光学纳米天线和谐振器对增强拉曼光谱越来越感兴趣。这些系统可以利用许多共同确定其拉曼响应的因素，包括材料类型、界面之间的折射率对比度、尺寸、形状、粗糙度和几何配置。然而，这些术语中的每一个对拉曼增强的相对影响仍不清楚。在这里，我们报告了通过 rf-磁控管溅射沉积在 SiO2 核上的 TiO2 薄层获得的 SiO2@TiO2 半壳微球的拉曼表征。与平面对应物相比，这些样品能够显着放大拉曼散射，但是相对于共形观察到的增强，整体增强非常有限，通过原子层沉积获得的光滑致密的 TiO2 壳层。这些结果表明，几何形状是使这些系统的拉曼响应最大化的关键因素，并且一般来说，它比其他参数更重要，例如表面粗糙度甚至壳层的折射率，这通常被认为是至关重要的实现拉曼增强。