title: Systematic investigation of the SERS efficiency and SERS hotspots in gas-phase deposited Ag nanoparticle assemblies.
abstract: 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-2. 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-2and 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.
authors.affiliation: SEU-FEI Nano-Pico Centre, Key Lab of MEMS of Ministry of Education, Southeast University, Nanjing 210096, P. R. China. helongbing@seu.edu.cn slt@seu.edu.cn and National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, P. R. China. sjhanmin@nju.edu.cn.
authors.forename: L B
authors.identifier: 0000-0003-4829-5875
authors.initials: LB
authors.lastname: He
authors.affiliation: SEU-FEI Nano-Pico Centre, Key Lab of MEMS of Ministry of Education, Southeast University, Nanjing 210096, P. R. China. helongbing@seu.edu.cn slt@seu.edu.cn.
authors.forename: Y L
authors.initials: YL
authors.lastname: Wang
authors.affiliation: SEU-FEI Nano-Pico Centre, Key Lab of MEMS of Ministry of Education, Southeast University, Nanjing 210096, P. R. China. helongbing@seu.edu.cn slt@seu.edu.cn.
authors.forename: X
authors.initials: X
authors.lastname: Xie
authors.affiliation: National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, P. R. China. sjhanmin@nju.edu.cn.
authors.forename: M
authors.initials: M
authors.lastname: Han
authors.affiliation: National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, P. R. China. sjhanmin@nju.edu.cn.
authors.forename: F Q
authors.initials: FQ
authors.lastname: Song
authors.affiliation: SEU-FEI Nano-Pico Centre, Key Lab of MEMS of Ministry of Education, Southeast University, Nanjing 210096, P. R. China. helongbing@seu.edu.cn slt@seu.edu.cn.
authors.forename: B J
authors.initials: BJ
authors.lastname: Wang
authors.affiliation: Department of Chemical Engineering, Monash University, Building 36, Clayton, Victoria 3800, Australia.
authors.forename: W L
authors.initials: WL
authors.lastname: Cheng
authors.affiliation: Centre for Nanoscience and Nanotechnology, School of Physics and Technology, and Institute for Advanced Studies, Wuhan University, Wuhan 430072, China.
authors.forename: H X
authors.initials: HX
authors.lastname: Xu
authors.affiliation: SEU-FEI Nano-Pico Centre, Key Lab of MEMS of Ministry of Education, Southeast University, Nanjing 210096, P. R. China. helongbing@seu.edu.cn slt@seu.edu.cn.
authors.forename: L T
authors.identifier: 0000-0001-8848-8845
authors.initials: LT
authors.lastname: Sun