He L B, Wang Y L, Xie X, Han M, Song F Q, Wang B J, Cheng W L, Xu H X, Sun L T
SEU-FEI Nano-Pico Centre, Key Lab of MEMS of Ministry of Education, Southeast University, Nanjing 210096, P. R. China.
National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, P. R. China.
Phys Chem Chem Phys. 2017 Feb 15;19(7):5091-5101. doi: 10.1039/c6cp08513j.
Gas-phase deposited Ag nanoparticle assemblies are one of the most commonly used plasmonic substrates benefiting from their remarkable advantages such as clean particle surface, tunable particle density, available inter-particle gaps, low-cost and scalable fabrication, and excellent industry compatibility. However, their performance efficiencies are difficult to optimize due to the lack of knowledge of the hotspots inside their structures. We here report a design of delicate rainbow-like Ag nanoparticle assemblies, based on which the hotspots can be revealed through a combinatorial approach. The findings show that the hotspots in gas-phase deposited Ag nanoparticle assemblies are uniquely entangled by the excitation energy and specific inter-particle gaps, differing from the matching conditions in periodic arrays. For Ag nanoparticle assemblies deposited on Formvar-filmed substrates, the mean particle size is maintained around 10 nm, while the particle density can be widely tuned. The one possessing the highest SERS efficiency (under 473 nm excitation) have a particle number density of around 7100 μm. Gaps with an inter-particle spacing of around 3 nm are found to serve as SERS hotspots, and these hotspots contribute to 68% of the overall SERS intensity. For Ag nanoparticle assemblies fabricated on carbon-filmed substrates, the mean particle size can be feasibly tuned. The one possessing the highest SERS efficiency under 473 nm excitation has a particle number density of around 460 μm and a mean particle size of around 42.1 nm. The construction of Ag-analyte-Ag sandwich-like nanoparticle assemblies by a two-step-deposition method slightly improves the SERS efficiency when the particle number density is low, but suppresses the SERS efficiency when the particle number density is high.
气相沉积银纳米颗粒组装体是最常用的等离子体基底之一，因其具有显著优势，如颗粒表面清洁、颗粒密度可调、颗粒间间隙可控、低成本且可扩展制造以及出色的工业兼容性。然而，由于对其结构内部热点缺乏了解，它们的性能效率难以优化。我们在此报告一种精致的彩虹状银纳米颗粒组装体设计，基于此可通过组合方法揭示热点。研究结果表明，气相沉积银纳米颗粒组装体中的热点被激发能和特定颗粒间间隙独特地纠缠，这与周期性阵列中的匹配条件不同。对于沉积在福尔马膜覆盖的基底上的银纳米颗粒组装体，平均粒径保持在10 nm左右，而颗粒密度可广泛调节。具有最高表面增强拉曼散射（SERS）效率（在473 nm激发下）的组装体颗粒数密度约为7100个/μm²。发现颗粒间距约为3 nm的间隙可作为SERS热点，这些热点对整体SERS强度的贡献为68%。对于在碳膜覆盖的基底上制备的银纳米颗粒组装体，平均粒径可进行合理调节。在473 nm激发下具有最高SERS效率的组装体颗粒数密度约为460个/μm²，平均粒径约为42.1 nm。通过两步沉积法构建银 - 分析物 - 银三明治状纳米颗粒组装体，在颗粒数密度较低时会略微提高SERS效率，但在颗粒数密度较高时会抑制SERS效率。
