Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India.
Analyst. 2017 Oct 9;142(20):3959-3966. doi: 10.1039/c7an00851a.
Surface enhanced Raman scattering (SERS) has emerged as a promising technique for chemical and biological sensing. "Hot spots" are the areas on noble metal nanostructures where light is highly concentrated into small volumes and enhances the local electromagnetic field near the metal nanostructures. These hot spots have been claimed to provide extraordinary enhancements to the SERS signal. Here, we report the fabrication of nanoporous zig-zag Ag nanostructures with built-in high density hot spots. The zig-zag Ag nanostructures were fabricated by glancing angle deposition of Ag and Al, with Al deposited on the edges of the zig-zag structure during growth. A 2.5 wt% HCl solution was used for etching Al from the Ag-Al zig-zag structure. The etching process produced intra-particle gaps by leaching less stable Al from fully alloyed Al-Ag nanostructures. This step of mild acid etching (2.5% v/v HCl for 45 min) allowed the formation of Raman hot spots on the elbows of zig-zag nanorods while maintaining the zig-zag morphology of highly active Ag nanostructures. A high enhancement factor of ∼10 was observed on nanoporous zig-zag Ag nanostructures obtained by de-alloying, making them very appealing as Raman sensors. The role played by nanogap hot spots in Ag zig-zag nanostructures towards SERS enhancement is modelled by using finite difference time domain (FDTD) simulations.
表面增强拉曼散射（SERS）已成为化学和生物传感的一种很有前途的技术。“热点”是贵金属纳米结构上的区域，光在这些区域高度集中在小体积中，并增强了金属纳米结构附近的局部电磁场。据称，这些热点为 SERS 信号提供了非凡的增强效果。在这里，我们报告了具有内置高密度热点的纳米多孔之字形 Ag 纳米结构的制造。之字形 Ag 纳米结构是通过斜角沉积 Ag 和 Al 制造的，在生长过程中，Al 沉积在之字形结构的边缘上。使用 2.5wt%的 HCl 溶液从 Ag-Al 之字形结构中蚀刻 Al。蚀刻过程通过从完全合金化的 Al-Ag 纳米结构中浸出不稳定的 Al，产生了颗粒内间隙。这一步温和的酸蚀刻（2.5%v/v HCl 蚀刻 45 分钟）允许在之字形纳米棒的肘部分离出 Raman 热点，同时保持高度活性 Ag 纳米结构的之字形形态。通过脱合金化获得的纳米多孔之字形 Ag 纳米结构观察到约 10 的高增强因子，使其成为非常有吸引力的拉曼传感器。通过使用有限差分时域（FDTD）模拟对 Ag 之字形纳米结构中的纳米间隙热点在 SERS 增强中的作用进行建模。
